This is the offset fourth dimension learners are introduced to acids and bases. The approach is to start from the known and innovate the topic through learner'due south experiences with everyday acids and bases. Nosotros will also start await at how nosotros experience acids and bases in foods. This links to Life and Living and the senses. We will so look at acids and bases in the laboratory and the bones properties of acids, bases and neutrals. They will await at acids and bases once more in Gr. ix in more item, too covering the pH scale, and the reactions of acids and bases.
3.1 Tastes of substances (i hr)
Tasks
Skills
Recommendation
Activity: Have a look at your own natural language
Observing, comparing
Suggested
3.two Properties of acids, base and neutrals (2 hours)
Tasks
Skills
Recommendation
Activeness: True or faux?
Accessing and recalling information
Suggested
Activity: Acids and bases in our homes
Accessing and recalling information, observing, comparison, sorting and classifying
CAPS suggested
three.3 Acid-base indicators (iii hours)
Tasks
Skills
Recommendation
Activity: Preparing and testing cerise cabbage juice with acid and base
Following instructions, practical skills, observing, comparing
Suggested
Activity: Making red cabbage indicator newspaper
Post-obit instructions, practical skills
Optional
Investigation: How does litmus answer to acids and bases?
Hypothesising, doing investigation, recording information, comparing, interpreting information
CAPS suggested
Investigation: Is red cabbage paper suitable equally acid-base indicator?
Doing investigation, recording information, interpreting information
Optional
Which tastes can we sense with our tongues?
How does our sense of gustatory modality ensure our survival?
What are the unique properties of:
acids;
bases;
neutral substances?
Which household substances are (or contain):
acids;
bases;
neutral substances?
How can we tell if something is an acid, a base or a neutral substance?
What do you know well-nigh acids? Would you affect an acrid? Take you ever tasted an acrid? Do you call up information technology is possible to taste an acid without burning your natural language? What practice you think it would feel similar when an acrid burned your tongue?
Before nosotros talk more well-nigh acids, allow united states first examine the homo tongue. It is a near fascinating organ, and plays an important office in our sense of sense of taste.
Tastes of substances
flavour
sense
sense of taste buds
chemoreceptor
savoury
instinct
natural language map
What is your favourite food? What do you similar most about your favourite food? You volition probably say that you but Beloved the gustation of it! The taste of our favourite foods make us feel good. How do we gustatory modality our food?
We taste nutrient with tiny structures on our tongues!
Look in the mirror, and stick out your tongue. Look for small, round bumps. These are chosen papillae. Near of them contain gustatory modality buds. The taste buds are very small structures which accept sensitive hairs. The chemicals in the food that you lot swallow dissolve into your saliva in solution. The chemicals then stimulate the tiny hairs within the tastebuds and turn these signals into impulses. These impulses travel to the brain allowing us to experience the awareness of taste.
Insects accept the about highly developed sense of taste. They have gustatory modality organs on their feet, antennae, and mouthparts.
Learners will study the nervous system in more detail in Gr. 9 Life and Living, equally well as in Life Sciences if they carry on with the bailiwick in Gr. ten. For now, this is just interesting information about how we sense of taste foods and distinguish between different tastes.
We have more 10 000 taste buds in our mouth. You even have taste buds on the roof of your oral cavity.
Have a wait at your ain tongue
As a homework exercise, learners can do the following activity. Otherwise, if yous accept some mirrors available in the classroom, learners can have a wait at their tongues. If you practice this in form, try bringing some lemons to class for learners to taste so describe their experiences.
MATERIALS:
mirror
pencil
sugar water
lemon juice
INSTRUCTIONS:
Await in the mirror at your natural language.
Stick it out equally far you lot tin can and try to meet the papillae. Are they larger in some areas?
Take yous tasted a lemon before?
Close your optics and imagine biting into a slice of lemon. Tin can yous describe the feel? What does the lemon taste like? Sweetness, sour, salty or biting?
Sour
If you have carbohydrate solution and lemon juice available in the class, taste these different substances. See if you tin can identify where on your tongue you taste the ii different tastes.
Your tongue can only sense iv flavours
You can only sense four unlike tastes with your tongue. Tin you name them?
Sweet, sour, bitter and salt.
The tongue map.
The four primary tastes that are most mutual, are sweetness, sour, salt and biting. These tastes combine to brand up the dissimilar flavours of our foods.
A season is a combination of tastes and smells.
How would you classify the gustation of apples? Sweet or sour? Bitter? Mayhap a combination?Many people really enjoy the sour-salty taste of salt and vinegar chips!
There is a good reason for why nosotros like certain tastes, simply not others.
Our sense of gustation protects united states of america
But as nosotros like and seek out foods that taste skilful, our bodies have also been programmed to avoid food with stiff bitter or sour tastes. This helps to protect usa confronting poisons, which often take a strong bitter taste. 'Bitter' is also the basic taste that our tongues are most sensitive to. Spoiled food often tastes sour and it may also take a bad smell. Our instinct will be to avert it, which will protect u.s. from condign ill from ingesting the organisms that take spoiled the food.
Almond basics tin can be sweet or bitter, depending on the blazon of tree they come from. The sweetness almonds (which we eat) do non contain poisonous chemicals. Bitter almonds from another tree species contain chemicals which are toxic to humans.
Sweetness almonds, such as these, are edible as they do non contain toxic chemicals, dissimilar the wild bitter almonds.Cocoa beans come from cocoa pods. Chocolate is made from cocoa, but cocoa is very bitter. Lots of sugar is added to chocolate to get in sugariness. http://www.flickr.com/photos/michaelsgalpert/3681442211/in/photostream/
Shortly the link between the tongue and chemical substances volition become articulate.
Properties of acids, bases and neutral substances
corrosive
acrid
chemic formula
essential
immune system
When we want to say something has the properties of an acid, we use the adjective acidic. When we want to say something has the properties of a base of operations, nosotros use the adjective basic.
In the previous section you had to imagine what it would feel like if an acid burned your tongue. In the next section we are going to learn more nearly acids. We will learn that they taste sour (and also why it is not a good thought to taste them!).
We will also acquire about other substances that take a special relationship with acids. They are called bases. Finally, nosotros will too learn nearly substances that are neither acids or bases, but neutral substances.
Acids
ascorbic acid
citric acid
formic acid
Practice you know the names of any acids? Think about this as a grade and make a list of all the acrid names yous have heard.
Y'all can do this on the board and ask learners for their answers to write down. Some examples might be vinegar (which contains acetic acrid), citric acid (found in citrus fruits such as lemons, oranges and grapefruit), ascorbic acid (besides known equally Vitamin C, which comes in tablets, capsules or chewable sweets, and information technology occurs naturally in citrus fruit, tomatoes, strawberries), tartaric acid, etc).
There are many different acids. You might have already tasted an acid in class. Was it the sugar water or the lemon juice?
Enquire your learners these questions. The answers are: The lemon juice contains an acid. The lemon juice was sour. Encourage learners to write in their workbooks and make notes in the margins and empty spaces! They should non be afraid of scribbling and taking notes during grade whilst you are talking or explaining a concept. Taking notes is a very important skill to learn.
Do you like sour sweets, such as sour worms? The sour taste comes from fumaric acid. Fumaric acid is a natural acid with a sour sense of taste, that is oftentimes added to foods.The juice of lemons is rich in ascorbic acid (vitamin C) and citric acrid, which makes information technology sense of taste sour.
All acids sense of taste sour. Does this hateful that all acids are prophylactic to taste? Definitely NOT! Side by side, we will acquire which acids should non be tasted nether whatever circumstances.
The discussion acid comes from the Latin word acidus, meaning 'sour'.
Laboratory acids
Concentrated hydrochloric acid is very corrosive and dangerous. http://www.flickr.com/photos/maticulous/2552655853/
Some acids are very dangerous and must be handled carefully. These acids are corrosive. They tin can cause serious burns on your peel. Scientists always wear protective clothing when handling these acids. It would be very dangerous to taste them. These acids are most often constitute and used in laboratories and sure industrial processes. We will refer to them as laboratory acids.
This scientist is handling an acid. Can yous come across he is wearing protective habiliment, gloves and safe spectacles? http://world wide web.flickr.com/photos/rdecom/4968163345/ Look out for this label on bottles which contain corrosive substances, such as strong acids.
The following tabular array contains the names and chemic formulae of the iii almost common laboratory acids. Even though you lot have non learnt how to write chemical formulae notwithstanding, we accept included them hither. You should handle containers with these formulae printed on them with care.
Learners will only study chemical formulae in particular in Gr. ix Matter and Materials, however, this is a good opportunity to introduce them to the concept especially so that learners are able to recognise dangerous chemical substances.
The chemical formula of a substance tells usa which elements information technology contains.
Name of the acid
Formula of the acid
hydrochloric acid
HCl
nitric acid
HNO3
sulfuric acid
H2SOiv
There are many other laboratory acids that we have not listed. These are only the about mutual ones.
You have a laboratory acid inside your body?! Your breadbasket contains hydrochloric acid (HCl). HCl helps break downwardly the food for digestion. Your stomach has a very mucous lining which helps protect information technology from the potent acid.
Other acids in the foods we eat are non unsafe. In fact, some are even vital for our health and well-existence. Let'due south now have a await at acids that are safe to handle.
Natural and household acids
Not all acids are dangerous. I such acid is chosen ascorbic acid, or vitamin C. Vitamin C helps our immune arrangement. Which foods contain vitamin C? Accept a look at the pictures.
Most people associate oranges with a loftier vitamin C content, but in that location are other foods which are much higher in vitamin C. These include chillies, guavas, strawberries, bong peppers, broccoli, kiwi fruits and papaya.
Kiwi fruit. http://www.flickr.com/photos/dan4th/5317566258/ Strawberries.Broccoli. http://commons.wikimedia.org/wiki/File:Brocolli_%284700583979%29.jpg Bell peppers.
If you lot do non accept enough vitamin C in your diet you may develop a number of symptoms: you may get tired easily, bruise easily, develop bleeding gums, dry out skin and pilus, become moody and lose weight. These are all symptoms of a weakened allowed arrangement.
We will call the acids that nosotros find in food natural acids. Many of these natural acids are plant in the kitchen. For this reason they are likewise sometimes called household acids.
One very well-known household acid is acetic acid. Vinegar is a mixture of a small corporeality of acetic acid dissolved in water. So vinegar is a solution of acetic acrid in water.
Spirit vinegar and balsamic vinegar.
This is a good place to briefly revise some of the concepts learnt in Gr. 6 near solutions and mixtures, and to refer back to Chapter 2 well-nigh separating mixtures.
Formic acid is what gives ants their sting when they seize with teeth. 'Formic' comes from the Latin word for pismire 'formica'.
True or false?
INSTRUCTIONS:
Let's briefly revise some of the concepts we have learnt and then far.
Below are some statements. You need to state whether they are truthful or faux. If they are fake, explain why.
True or false?
We tin can sense three tastes with our tongues.
Imitation, we can sense four tastes, namely salty, sweet, sour and biting.
If nosotros want to know if something is an acid, we tin merely taste information technology.
Simulated, not all acids are safe to sense of taste, such as laboratory acids.
False, there are many household acids which are not dangerous, such as acetic acid and acids in foods.
Vinegar is a mixture of a small amount of acetic acid dissolved in water.
Laboratory acids must be handled with intendance and using protective clothing.
The following symbol means y'all can launder your hands using this substance.
False. This symbol ways that the substance is corrosive, it is a warning.
Formic acid is commonly referred to as Vitamin C.
False, ascorbic acrid is commonly referred to as Vitamin C.
Oranges are the food which contain the highest amount of ascorbic acrid.
False, there are many other foods with college ascorbic acrid (Vitamin C), such equally strawberries and chillies.
Many of the fizzy drinks that nosotros drink contain carbonic acid.
Do y'all recall that it would exist possible for acids to lose their force? There is one form of compounds that can brand acids lose their strength. These compounds are chosen bases.
Bases
base of operations
neutral substance
neutralise
alkali
Bases tin neutralise acids and vice versa. What does it mean to neutralise something?
At this level, learners can think of neutralisation as a process in which something potent (and potentially harmful) is inverse into something harmless (or at to the lowest degree less harmful). Afterward on (in Gr. ix) they will learn the proper scientific definition of neutralisation: "the process in which an acid reacts with a base of operations to grade a salt and water". It is important to note that a neutralisation reaction does not necessarily result in a neutral solution.
When an acid and a base are mixed together in thecorrect ratio, they will neutralise each other. This means that the solution made upwardly of the acid and the base becomes something that is neither an acid nor a base, but neutral. In the procedure, both the acid and the base volition lose their unique characteristics.
Bases and acids have chemical properties that are the opposite of each other. Nosotros can think of bases as the chemical opposite of acids.
Every bit with acids, there are some bases that are extremely dangerous. The same gamble symbol that is used to warn people of the dangers of acids, is besides used for these bases. Potent bases react corrosively with other materials and can burn your skin. They must be handled advisedly and ever while wearing appropriate protective clothing, such as lab coats, gloves and safety spectacles.
Sodium hydroxide is a strong base used in laboratories. Practise yous run across the yellow corrosive warning symbol? http://commons.wikimedia.org/wiki/File:Sodium_hydroxide_solution.jpg
Other bases are mild enough to be used as cleaning materials in and around the home. This does not hateful that they are completely harmless. Information technology merely means that they have been mixed with other substances so that they are non then corrosive.
Acids and bases in our homes
For this action, learners must first identify the products in the photograph provided. All of these household products contain bases. The side by side role of the activeness is a demonstration which you can prepare beforehand in the forepart of your classroom. Instructions and materials for the sit-in are supplied here:
MATERIALS:
v bowls
water
washing powder
handy andy
bicarbonate of soda or baking pulverisation
lemon juice
vinegar
labels for each basin showing the production that is in them
a towel for drying hands
INSTRUCTIONS:
Place the bowls in a row on a desk in the front end.
Mix each of the bases (washing pulverisation, handy andy, blistering pulverisation) in dissever bowls with some h2o.
Cascade some lemon juice into another basin and some vinegar into the final bowl.
Arrange the bowls in a row, alternating between a base and an acid.
Once the learners have filled in the table to identify the products, become them to come up up to the forepart in groups to put their fingers in the bowls to feel the different substances.
They must take note of what they are feeling and should dry their hands between each substance.
Later feeling the difference between the acids and bases, the learners can get back to their desk to complete the activity.
Every bit an extension, yous can besides permit learners take note of the deviation between the dry out powder for washing powder and and so how it feels when it is mixed with h2o. Bases which dissolve in h2o are called alkalis.
All of the products in the picture below contain bases. Which of the products exercise you recognise? Write their names and what they are used for in the table.
Some household products which are bases.
Many household products (such as certain apple tree-scented shampoos and dishwashing liquids) comprise apple or lemon scents or essences as additives. It has been noted that some of these products may be more acidic than bones. Brand certain to test all the products you volition be using in the form beforehand, to make certain the bases all react equally expected.
Ingredient in broiled goods, also a mild disinfectant
Bleach
Disinfecting and removing stains
Sunlight liquid
Cleaning dishes, cutlery and crockery
Adjacent, your instructor volition let you come to feel different substances which are either bases or acids. All of these substances are safe to touch. Take note of how they experience between your fingers and then come back to fill in the table.
Substance
How did it experience between the fingers?
Is it an acid or a base of operations?
Substance
How did it feel between the fingers?
Is it an acid or a base?
Washing pulverization
Glace
Base of operations
Lemon juice
Feels slightly crude between the fingers
Acid
Handy andy/lather
Slippery
Base
Vinegar
Leaves a rough feeling on the skin
Acrid
Baking powder
Slippery
Base
The bases will exist easy to describe every bit they by and large experience quite slippery between the fingers. Acids more often than not get out a "rough" feeling on the skin and are not slippery like bases.
QUESTIONS:
What can you conclude about how bases feel?
What can you conclude about how acids feel?
By and large, acids feel rough on the skin.
What did your instructor have to do to the dry washing powder before you could feel it in the bowl? Practice you know what we call the solution which forms? If then, write information technology down, otherwise your teacher will help you.
She/he had to add together water to get in slippery. A solution of a base of operations and water is called an alkali metal solution.
Although we have spoken about acids and bases as beingness chemical opposites, what property do many of them have in common?
Many acids and bases are dangerous to affect or taste - they are corrosive.
Bases that can dissolve in water are calledalkalis. For this reason, the terms base and alkali are sometimes considered to have the aforementioned meaning. (Words that accept the same meaning are chosen synonyms.)
Finally, at that place is a grade of substances that are neither acids nor bases. They are called neutral substances. We will explore them side by side.
Neutral substances
We accept learnt that when an acrid and a base of operations are mixed (in the correct amounts), they will neutralise each other. That ways that, together, they volition change into something that is neither an acid nor a base of operations. So the acid will lose its properties and so will the base. And the new substance that forms from the two substances will be neither an acid nor a base of operations. We call it a neutral substance.
Some neutral substances are formed when an acid is mixed with a base and a neutralisation reaction occurs. Other substances are neutral to brainstorm with. They are not the product of a neutralisation reaction. The neutral substances that are the almost well known are: water, table table salt, sugar solution and cooking oil.
Cooking oil is a neutral substance.
We have learnt about three classes of substances: acids, bases and neutral substances. Merely, we cannot tell whether a substance is an acid, base, or a neutral substance, merely past looking at information technology. We know that acids taste sour, but we take also learnt that information technology is never a good thought to taste chemicals.
Let'south imagine we take an unknown substance. It is colourless and looks merely like h2o. Information technology is as well odourless (that means it has no smell). There are no physical signs to evidence whether it is acidic, bones, or neutral. How tin can nosotros tell what it is?
Acrid-base indicators
indicator
litmus
What do the indicators on a automobile do?
Inquire your learners this question to highlight the significant of the word "indicate", which is to show. When the indicators on a automobile low-cal upwards, they show other motorists that the commuter of the automobile intends to turn left or right.
To indicate ways to prove.
Acids and bases can alter the colour of some substances. In the next activity, we are going to investigate a substance that changes colour when we mix it with an acid or a base.
It has been noted that some household indicators that appear on the list in a higher place are not very effective, such as tea and beetroot. Some are more sensitive, including curry powder and turmeric. If yous explore other indicators with the class, make sure to test a few to determine which ones produce the best results. Here is a table of other naturally occurring indicators which y'all could utilise in class:
Take you ever eaten red cabbage? Information technology is not merely tasty, but also very salubrious. We are going to see how blood-red cabbage juice changes when we mix it with different substances.
Video on red cabbage and black tea equally indicators
Preparing and testing red cabbage juice with acid and base
Y'all will demand to buy a cerise cabbage prior to this activity. Red cabbages are available during winter and spring. One cabbage should make enough excerpt for an entire class of learners. You can prepare the extract in the class, or you could make it ahead of time and merely demonstrate the method (cutting the cabbage, humid and straining it) to the learners without boiling the cabbage in course.
If you are not able to become carmine cabbage, you can try using some of the other foods listed in the previous table which are also natural indicators. Another case which is easy to utilise and obtain is black tea.
MATERIALS:
one large, red cabbage
pot with water for boiling
hot plate (or stove)
strainer
sharp knife
container for red cabbage juice (ice cream tub or big yoghurt tub will work well)
white plate
vinegar
baking soda solution
INSTRUCTIONS:
Prepare the cabbage juice:
Cut the cabbage into sparse slices and identify information technology in the pot.
Add just enough water to encompass the cabbage slices.
Boil information technology over low oestrus for approximately 30 minutes, calculation h2o to keep the cabbage covered if necessary.
Remove the pot from the heat and let information technology cool completely.
Strain the juice off the cabbage slices into the ice cream tub. The boiled cabbage slices tin can be eaten (or placed in the compost).
If kept in the refrigerator the red cabbage juice will last about iii days.
Test the cabbage juice indicator
Carefully place three big drops of the cabbage juice on a smooth, white surface (a white plate or tile will work well).
Cascade a few drops of vinegar into ane of the drops of cabbage juice. What practice yous see?
Pour a few drops of baking soda solution into ane of the remaining drops of cabbage juice. What practise you lot come across?
Red cabbage juice mixed with blistering soda (left) and with vinegar (correct). The bluish drop at the top is the unmixed juice.
These two videos are both demonstrations of the cabbage juice indicator experiment yous just completed
These demonstration videos extract the ruby cabbage juice by blending it with some h2o in a blender instead of humid it. Both methods are every bit effective in extracting the juice from the cabbage leaves.
In the next activity we are going to preserve the blood-red cabbage juice by absorbing it on some filter paper, and drying it, then that we tin apply it later.
Making red cabbage indicator paper
If time permits, you tin make these indicator strips in class with your learners using the cabbage juice from the previous experiment. If you do not take time, exercise this yourself outside of class and then merely get through the steps below explaining to your learners what you did. If you lot exercise not accept fourth dimension to practice it in class, yous tin also encourage learners to do information technology at habitation with their parents if they take capacity and resources.
MATERIALS:
pieces of absorbent paper
reddish cabbage juice from the previous activity in a container
scissors
container
Filter paper is best, or paper used for painting with watercolours (available from jotter or fine art supply shops); java filters or fifty-fifty newspaper towel would as well work. The cabbage juice should not be too dilute; you tin can concentrate information technology past heating it over low rut for xx minutes and allowing it to absurd.
INSTRUCTIONS:
Identify the absorbent paper in the cabbage juice.
After 30 minutes, remove the newspaper and leave it in a warm place to dry out.
You can likewise dry the paper with a hair dryer, only do non leave it in directly sunlight.
When the paper has completely dried, cut it into strips (approximately 1 cm wide). You tin keep the strips for a long time if y'all store them in a dry out place.
We volition use the scarlet cabbage paper strips later, equally office of an investigation.
Some other substances besides change color when an acid or a base is added to them. By changing their color, they show that they accept reacted with an acid or a base. That is why we call them acid-base indicators.
The nigh well-known acrid-base indicator is a substance called litmus.
Blue and crimson litmus newspaper.
Litmus is a coloured substance that comes from the pigments of a living organism called lichen. Pigments are coloured substances found in nature.
Litmus comes from pigments in the lichen which are found growing in many different places, generally on rocks.
Litmus solution is about commonly soaked into newspaper, the paper is then stale and cut into strips nosotros then call "litmus paper". Information technology is but like the cherry cabbage paper we made earlier. Litmus paper is available in two colours: blue and red.
How does litmus paper indicate whether a substance is an acid or a base of operations? In the side by side action, nosotros will investigate how litmus responds to some household acids and bases.
Colourful chemistry with acids and bases using household products (video)
How does litmus reply to acids and bases?
CAPS suggests that you lot as well test various beverages to run across whether they are acids, bases or neutrals. A proffer is to do this investigation presented here first where learners offset determine how litmus responds to acids and bases, and then if y'all take fourth dimension as an extension, get learners to test various drinks, such as water, Ceylon tea, rooibos tea, orange juice, milk, coffee and any fizzy drink to see whether they are acids, bases or neutrals.
AIM: To decide how litmus responds to some household acids and bases.
HYPOTHESIS: What is your hypothesis for this investigation?
Learners may non yet know how litmus reacts to acids and bases, and then they may have to come back to propose a new hypothesis when they are writing their conclusions. They should non be encouraged to come back to this infinite, cantankerous out the hypothesis and write a new one which they know to be true. This is an important concept in scientific discipline investigations - a hypothesis is a proposed explanation, which needs to be tested further using the scientific method. One can then verify whether the hypothesis was true (and it is accepted) or it is fake (and it is rejected) and you come upward with a new proposed hypothesis.
MATERIALS AND APPARATUS:
It would exist advisable to label the containers to prevent learners from disruptive the substances.
pocket-sized containers (test tubes or yoghurt tubs) filled with the post-obit substances:
water
soda water
vinegar
lemon juice
sugar h2o (one tablespoon dissolved in a cup of water)
baking soda (ane tablespoon dissolved in a cup of water)
Handy Andy (ane tablespoon dissolved in a cup of h2o)
aspirin (Disprin) (1 tablet in 2 tablespoons of water)
dishwashing liquid (1 teaspoon dissolved in a cup of water)
whatsoever other substances ordinarily used at home that are not dangerous
litmus paper (blue and crimson)
glass or plastic rods (plastic teaspoons will also work well).
METHOD:
Cutting a small piece (1 cm long) of blueish and ruby litmus for each substance that you lot will be testing.
Apply the plastic teaspoon or rod to place just 1 drop of water on the blue litmus. Practice the same with a piece of crimson litmus.
Did the blue litmus change colour? Did the red litmus change colour? Write the new colours in your table, in the appropriate place.
Repeat the procedure to exam all the substances you have been given. Y'all must rinse the teaspoon or rod with water in between substances.
Relieve all your test substances, because y'all will demand them for another investigation afterward.
RESULTS AND OBSERVATIONS:
Record your observations in the table. If you did not utilize some of these substances, cross them out and write headings for your substances in the empty rows.
Substance
Colour with blue litmus
Colour with blood-red litmus
Water
Soda water
Vinegar
Lemon juice
Sugar water
Blistering soda
Handy Andy
Aspirin
Dishwashing liquid
ANALYSIS:
Let us now accept a look at our observations to see what nosotros can conclude.
How does the litmus newspaper indicate when a substance is an acid?
In an acid, the blue litmus inverse to cherry-red and the ruddy litmus remained cherry-red.
Which of the substances y'all tested are acids?
Depending on the substances you use, but according to those listed here, the acids are: soda water, vinegar, lemon juice and aspirin.
How does the litmus paper signal when a substance is a base?
In a base of operations, blueish litmus remains bluish and red litmus changes blue.
Which of the substances you tested are bases?
Depending on the substances you use, merely according to those listed here, the bases are: baking soda, handy andy, dishwashing liquid.
How would you lot draw a neutral substance?
Learner-dependent answer.
How does the litmus paper signal when a substance is neutral?
Neither the red or the bluish litmus paper volition modify color when a substance is neutral.
Which of the substances you tested were neutral?
Water and sugar solution.
Why do you think yous had to rinse the glass rod or teaspoon in between testing each substance?
Y'all demand to do this to avoid contamination and mixing of the substances otherwise, for example, there might be some acid left over when testing a base which would change the litmus paper resulting in an incorrect result for the base.
CONCLUSION:
Write a conclusion based on your results in response to the initial aim for this investigation.
A conclusion must respond to the aim and hypothesis for the investigation. In this case the aim was to determine how litmus newspaper responds to some household bases and acids. Therefore a determination is: In response to some household acids and bases, reddish litmus paper turns blue in bases and remains red in acids, and blue litmus paper turns red in acids and remains blue in bases. Both cherry-red and blue litmus paper will remain red or blue, respectively, in the presence of neutral substances. Learners can run into whether they refuse or take their hypotheses.
Extension: If you have time in class with your teacher, use your knowledge of how litmus responds to acids and bases to test some of the beverages that you drink every mean solar day. Y'all can use litmus newspaper to indicate whether beverages such as ceylon tea, rooibos tea, orange juice, milk, coffee and fizzy drinks are acids, bases or neutrals. If yous do so, record your findings here:
The first 5 minutes of this video (
We tin say the following about litmus:
Blue litmus is used to test for acids:
acids turn blueish litmus red.
Bases and neutral substances practise non change the colour of blueish litmus.
Red litmus is used to exam for bases
bases turn red litmus blue.
Acids and neutral substances do not alter the color of red litmus.
What most the crimson cabbage paper that we fabricated earlier? Can these paper strips be used to tell if something is an acid or a base of operations? Allow's find out.
Is crimson cabbage newspaper suitable as acid-base indicator?
This is an optional, extension activity.
AIM: To make up one's mind whether red cabbage is a suitable acid-base indicator.
MATERIALS AND APPARATUS:
Learners tin use the saved substances from the litmus investigation they did earlier. Top up the solutions if necessary.
pocket-sized containers with the same substances as in the previous investigation
carmine cabbage newspaper strips
glass or plastic rods
METHOD:
Employ a small strip (2 cm long) of red cabbage newspaper for each substance that you volition be testing.
Dip a fresh piece of paper into each of the exam solutions. Does the paper change colour? Write the colour of the paper with each substance in your table in the appropriate place.
RESULTS AND OBSERVATIONS:
Record your observations in the tabular array.
Substance
Colour with red cabbage newspaper
H2o
Soda water
Vinegar
Lemon juice
Sugar water
Blistering soda
Handy Andy
Aspirin
Dishwashing liquid
QUESTIONS:
Which of the examination substances are acids? (Bank check the results from the litmus investigation that you lot did earlier.)
Learner-dependent answer.
What colour did the red cabbage paper turn in the test substances that were acids?
The red cabbage paper should plough a blood-red-pinkish colour in an acid.
Which of the test substances are bases? (Check the results from the litmus investigation that you did earlier.)
Learner-dependent respond.
What colour did the red cabbage newspaper turn in the exam substances that were bases?
The red cabbage paper should plough a blue-green color in a base.
Did the crimson cabbage paper change colour with all the substances? If in that location were some substances that did not change the colour of the paper, write their names beneath.
Learner-dependent respond.
Are these substances acidic, basic or neutral (also check your litmus test results)?
Learner-dependent answer.
Do you think reddish cabbage paper makes a good acrid-base of operations indicator? Why do you lot say so?
Learner-dependent answer. They should note that a good indicator is something which can tell you if information technology is an acrid or a base, in that the aforementioned paper turns different colours whether in an acid or a base.
Summary
Our tongues can sense 4 dissimilar flavours namely, sweetness, salty, sour and bitter.
Our sense of taste protects usa from eating foods that are harmful and stimulates us to eat foods that are nutritious and energy-rich.
Acids and bases are chemical opposites of each other.
Though it is non a practiced idea to gustation chemicals, acids have a sour gustation and bases gustatory modality biting.
When they are in solution with h2o, acids feel crude and bases feel slippery.
Some acids and bases are nowadays in foods and in household items. These are relatively safe to handle. Others are often very corrosive and should only be handled when you are wearing protective article of clothing.
Substances which are neither acidic nor basic, are called neutral substances.
When an acrid is mixed with a base in the right quantities, they neutralise each other. That means they lose their ability.
Some substances change colour when they react with an acid or a base. These substances are called acid-base indicators. One household case of an acid-base indicator is ruddy cabbage juice.
Litmus is the best known of all acid-base indicators. Information technology does not alter color in the presence of a neutral substance, merely responds to acids and bases in the following way:
litmus is crimson in the presence of an acrid; and
litmus is blue in the presence of base.
Concept map
The man natural language can taste 4 main unlike tastes. What are these? Make full them in the spaces below. You also need to complete the section of the concept map about indicators. Can you work out how to do this? You demand to fill in the colour that litmus turns (or remains) in each either an acid or a base (or neutral).
Teacher's version.
Revision Questions
The box below is filled with ideas relating to acids and bases.
Yous must sort the ideas into 2 columns in the table. One column is labelled 'Acids' and the other is labelled 'Bases'. Write each idea inside the correct column. If an thought fits into both columns, y'all must write information technology in both. [16 marks]
Ideas
Sour sense of taste
Bitter gustation
Tartaric acid
Bicarbonate of soda
Feels slippery
Feels rough
Vinegar
Soaps
Lemon Juice
Citric acrid
Formic acid
Bleach
Turns scarlet litmus blue
Turns blue litmus red
Corrosive
Acids
Bases
Sour taste
Tartaric acid
Feels rough
Vinegar
Lemon juice
Citric acid
Formic acid
Turns blue litmus red
Corrosive
Bitter gustation
Bicarbonate of soda
Soaps
Feels glace
Bleach
Turns scarlet litmus blue
Corrosive
To mark this question, the beginning 9 items in the acids column should be marked, and the get-go 7 in the bases column. This is to discourage learners simply putting the whole listing into both columns.
Here is some other box; this one is filled with words. You must use the words to consummate the sentences that follow. Write out the sentences in total. Each discussion can exist used but once. [xi marks]
Words
Indicator
Sour
Red cabbage
Bitter
Poisonous
Corrosive
Neutralise
Sweet
Neutral
Litmus
Salty
The most well-known of all acid-base indicators is called _____ .
The most well-known of all acid-base indicators is chosen litmus.
A substance that can consume away at other substances is called _____
A substance that tin can consume away at other substances is chosen corrosive.
Foods that are _____ often taste biting.
Foods that are poisonous often taste bitter.
Some scientists believe the human tongue can taste four flavours. These flavours are: _____, _____ ,_____, and_____.
Some scientists believe the human tongue tin can taste iv basic flavours. These flavours are: salty, sweet, biting and sour (in any order).
An acid-base _____ is a substance that changes colour when it reacts with an acid or a base.
An acrid-base of operations indicator is a substance that changes colour when it reacts with an acid or a base of operations.
_____ substances are neither acids nor bases.
Neutral substances are neither acids nor bases.
An acid volition _____ a base (and vice versa).
An acid will neutralise a base of operations (and vice versa).
The juice of the _____ makes a very good acid-base indicator.
The juice of the red cabbage makes a very proficient acid-base indicator.
Give an example of a strong acid and a strong base, commonly used in the laboratory. [ii marks]
Strong acids include muriatic acid, sulfuric acid, and a strong base is sodium hydroxide.
Write 1 or two sentences to explain what is meant past the term neutralise. [two marks]
Learner's answer should incorporate at to the lowest degree 2 of the following ideas:
When an acrid reacts with a base, the acid and the base will neutralise each other.
That means they will both lose their forcefulness/say-so.
The acid volition not exist an acid anymore, and the base will not exist a base anymore.
They will combine to form a neutral substance.
Write a curt paragraph to explain how laboratory acids should exist handled. Your paragraph should contain the post-obit words: corrosive; gustatory modality; clothes. [3 marks]
Learner's respond should contain at to the lowest degree the following ideas:
Laboratory acids should exist handled very carefully because they are corrosive.
Laboratory acids should never be tasted.
You should protect yourself by wearing protective wearing apparel, safety goggles and gloves when handling these acids.
Would all acids burn down your tongue or is information technology OK to taste some acids? Explicate your answer. [ii marks]
Some household acids can be tasted. Some household acids are in our nutrient. Laboratory acids should never exist tasted. (optional)
Requite 2 examples of acids that are safe to taste. [i mark]
Examples of acids that are condom to taste are: vinegar, lemon juice, ascorbic acid (vitamin C), citric acrid (any other acceptable examples; learner should proper name 2).
How you would exist able to recognise an acrid when yous gustation it? [1 mark]
We recognise them as acids past their taste; acids have a sour taste.
How does our gustatory modality warn the states when nutrient is not good to eat? [two marks]
Learner'southward answer should contain at least 2 of the following ideas:
Most people don't similar bitter food; that is because poisonous substances often have a bitter gustation.
When nutrient tastes sour, it may exist a sign that the food has spoiled.
When food tastes strange (different from the manner we remember it to taste) information technology may be a alert that the food has spoiled.
Have you lot heard of acrid rain before? Read the following information and written report the diagram. So respond the questions that follow.
Which two gases are mentioned in the text and on the diagram which contribute to forming acid rain? [2 marks]
They are sulfur dioxide and carbon dioxide.
Where do these gases come from? [2 mark]
They come from factories, power stations and auto exhausts.
The gases then combine with water aerosol in the atmosphere to make acids. What are some of the environmental impacts of acrid rain? Written report the diagram for some clues. [three marks]
The impacts include:
damage of plant life, both wilderness areas and too crops, depending on where the pelting falls
the rain goes into soil, polluting it and making it more acidic
the rain tin can fall into various water sources and pollutes information technology.
Acid pelting can as well impairment buildings every bit information technology 'eats away' the stone. What property of acids allow it to do this? [one mark]
Acids are corrosive and and then they can corrode surfaces over time.
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