AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

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AP 7th Class Science 4th Lesson Acids Bases and Salts Questions and Answers

AP Board Solutions Class 7 Science Chapter 4 Acids Bases and Salts

Exercise 

Question 1.
State differences between acids and bases.
Answer:
Differences between acids and bases are :

S.No Acids Bases
1) Acids are sour to taste. Bases are bitter to taste.
2) Acids turns blue litmus to red. Bases turns red litmus to blue.
3) Acids do not give a soapy touch. Bases are soapy in touch.
4) Acid is a substance which contains hydrogen ion (H+). Bases contains hydroxide ions. (OH)

Question 2.
Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature ?
Answer:
Bases turns red litmus paper blue.Ammonia is basic in nature, thus it turns red litmus into blue.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution ?
Answer:
Litmus solution is a natural indicator which is obtained from lichens. It is used as an indicator to distinguish between acids and bases.

Question 4.
Is the distilled water acidic/basic/neutral? How would you verify it ?
Answer:
Distilled water is neutral.We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in distilled water.

Question 5.
Describe the process of neutralisation with the help of an example.
Answer:
The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water (Heat is evolved)
For example, when the solution of sodium hydroxide and hydrochloric acid react with each other, the acidic nature of the acid and the basic nature of base are destroyed. The resulting solution is a neutral solution.
Hydrochloric acid (HCl)+ Sodium hydroxide (NaOH) → Sodium chloride (NaCl)+
In this reaction, the hydrogen ions from the acid reacts with hydroxide ions of the base to from water and salt is formed.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false :
i) Nitric acid turn red litmus blue.
ii) Sodium hydroxide turns blue litmus red.
iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
iv) Indicator is a substance which shows different colours in acidic and basic solutions.
v) Tooth decay is caused by the presence of a base.
Answer:
i) False
ii) False
iii) True
iv) True
v) False

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Answer:
Since the drinks are edible, Dorji can take the decision by testing the drinks. Acidic drinks will be sour to taste whereas basic drinks will be bitter to taste and neutral drinks will have no taste. Dorji will take red and blue litmus paper and one by one dip them in each of the bottle of soft drink.

The drink in which red litmus paper turns blue is the bottle of basic drink. The drink in which blue litmus paper turns into red is the bottle of acidic drink. The drink in which both litmus paper show no changes in colour of is of neutral drink.

Question 8.
Explain why:
a) An antacid tablet is taken when you suffer from acidity.
b) Calamine solution is applied on the skin when an ant bites.
c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
a) We take an antacid such as milk of magnesia to neutralises the excessive acid released in the stomach.

b) When an ant bites, it injects the formic acid into the skin. The effect of acid can be neutralised by applying calamine solution that contains zinc carbonate.

c) Factory wastes contain acids. Therefore, these wastes, when thrown-directly to water bodies it harm aquatic lives. Hence, these wastes are neutralised with basic chemicals before disposing to water bodies.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Answer:
Like the litmus paper, turmeric is also a natural indicator. Turmeric solution turns red, when it comes in contact with bases. It is not affected by acids and neutral substances. Dip the turmeric indicator in each liquid. The liquid which change the colour of turmeric indicator to red is basic in nature, that is, sodium hydroxide.

Since, we already identified as sodium hydroxide. We will pour the sodium hydroxide in other two liquids. The liquid which gets warm after pouring the sodium hydroxide(base) solution in it is of hydrochloric acid as heat gets evolved in the process of neutralisation. The last one which shows no effect is the liquid of sugar solution.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution ? Explain.
Answer:
The solution could be basic or neutral because blue litmus paper does not change its colour in basic as well as neutral solution. The solution can be neutral. A neutral solution has no effect on any indicator.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Question 11.
Consider the following statements :
a) Both acids and bases change colour of all indicators.
b) If an indicator gives a colour change with an acid, it does not give a change with a base.
c) If an indicator changes colour with a base, it does not change colour with an acid.
d) Change of colour in an acid and a base depends on the type of the indicator.
Which of these statements are correct ?
i) All four
ii) a and d
iii) b, c and d
iv) only d
Answer:
iv) only d

Questions given in the lesson

Page No.76

Question 1.
Let us recall tastes of some edible substances listed in Table. If you have not tasted any of these substances taste it now and enter the result in Table.

Substance Taste (sour,/bitter /any other)
Lemon juice
Orange juice
Vinegar
Curd
Tamarind (imli)
Sugar
Common salt
Ami a
Baking soda
Grapes
Unripe mango
Cucumber

Answer:

Substance Taste (sour/bitter /any other)
Lemon juice Sour
Orange juice Sour
Vinegar Sour
Curd Sour
Tamarind (imli) Sour
Sugar Sweet
Common salt Salty
Amla Sour
Baking soda Bitter
Grapes Sour/sweet
Unripe mango Sour
Cucumber Bitter/slightly sweet

Page No. 78

Question 2.
Can I taste all substances to find their taste ?
Answer:
No, we should not taste unknown substances as they could harm us.

Page No. 82

Question 3.
Why a turmeric stain on my white shirt is turned to red when it is washed with the soap?
Answer:
It is because the soap solution is basic in nature.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Page No. 84 

Question 4.
I am not getting the same result when using solid baking soda on dry litmus paper. Why ? Make a solution of baking soda and then try.
Answer:
The solid baking soda does not change colour of dry litmus paper because in solid state, ions are not free to move whereas, solution of baking soda has free ions that change the colour of the litmus paper.

Extended Learning – Activities and Projects

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works.
(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.)
Answer:
Beet root is a natural indicator and changes colour upon reaction with the base i.e., baking soda solution. Hence a message will reappear after sometime.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table.
Answer:
Cut the red cabbage into pieces. Boil the water in a pan. Place the cut pieces of cabbage in a bowl and pour the boiling water in the bowl.Keep the cabbage pieces for thirty minutes until it get soaked. Separate the juice from the leaves by squeezing. Place the glass jars about 2 inches apart.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Pour chemicals, lemon juice, vinegar, detergent soda, etc., in separate jars. test, whether the chemical is a base or an acid,Pour a part of your cabbage into each bar. You may have to swirl your a mixture of bit, if the mixture turns pink, the chemical is an acid and if it turns blue, the chemical is a base.

Indicator Acid Base
Red cabbage Red Bluish-green

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Answer:
Dump a small amount of soil about a teaspoon into a clean container and add distilled water. The mixture should be soggier than mud but without much water, such that all the soil settings to the bottom quickly. Usually, about twice as much water as soil works well. Share,the mixture to evenly distribute the soil.

Dip the end of the litmus paper into the soil and water mixture. Hold it in the mixture for 1 or 2 seconds before pulling it out and then wait for a few seconds until the colour stabilises. If the paper turns red, the soil is acidic. If the paper turns blue, the soil is basic.

Question 4.
Visit a doctor. Find out the medicines, he prescribes to treat acidity. Ask him how acidity can be prevented
Answer:
To prevent acidity which causes indigestion in stomach, doctors give antacids which mainly contain base like magnesium hydroxide present in milk of magnesia. There are many antacids with different compositions which are prescribed by doctors. These medicines neutralises the effects of acids. To avoid acidity, one should eat small meals for the day instead of a few large meals. Also one should healthy and avoid junk food.

Activities

Activity – 4.1  Page No: 80

Question 1.
Mix some water with lemon juice in a plastic cup/tumbler/test tube.
Put a drop of the above solution on a strip of the red litmus paper with the help of a dropper.Is there any change in colour. Repeat the same exercise with the blue litmus paper.Note down if there is any change in colour.
Perform the same activity with the following substances: Tap water, detergent solution, aerated drink, soap solution, shampoo, common salt solution, sugar solution, vinegar, baking soda solution, milk of magnesia, washing soda solution, lime water. If possible make solutions in distilled water. Record your observations as in table.
Answer:

Aim : To test the acidic or basic or neutral nature of the given substances using litmus as the indicator.
Materials required : Water,’test tube, red litmus paper, blue litmus paper, dropper, lemon juice, tap water, detergent solution, aerated drink, soap solution: shampoo, common salt solution, sugar solution, vinegar, baking soda solution, milk of magnesia, washing soda solution, lime water.

Procedure:

  • Take all the given solutions in the labelled test tubes
  • Take one small piece each of the blue and the red litmus papers.
  • Put a drop of the above solutions on a strip of the red litmus paper and the blue litmus paper with the help of a dropper.
  • Observe the change in colour.
  • Note down your observations.
  • Repeat the same for all the observations.

Observations:

S.No. Test solution Effect on red litmus paper Effect on blue litmus paper Inference
1) Lemon juice None Turns red Acidic
2) Tap water None None Neutral
3) Detergent solution Turns blue None Basic
4) Aerated jdrinks None None Basic
5) Soap solution Turns blue None Basic
6) Shampoo Turns blue None Basic
7) Common salt solution None None Neutral
8) Sugar solution None None Neutral
9) Vinegar None Turns red Acidic
10) Baking soda solution Turns blue None Acidic
11) Milk of magnesia Turns blue None Basic
12) Washing soda solution Turns blue None Basic
13) Lime water Turns blue None Basic

Conclusion : From the above activity we can conclude that acidic substances turns blue litmus red and have no effect on red litmus. Basic substances turn red litmus and have no effect on blue litmus. Neutral substances have no effect on both the blue and red litmus paper.

Activity 4.2 Page No : 80

Question 2.
Take a tablespoonful of turmeric powder. Add a little water and make a paste.
Make turmeric paper by depositing turmeric paste on blotting paper/filter paper and drying it. Cut thin strips of the yellow paper obtained. Put a drop of soap solution on the strip of turmeric paper.What do you observe ?
Answer:
Aim : To test the basic or acidic nature of the given substances by using turmeric paper as the indicator.
Materials required: Turmeric powder, water, filter/blotting paper, brush, soap solution, given solutions.

Procedure:

  • Take a tablespoonful of turmeric powder.
  • Make a thick paste of turmeric powder with water.
  • Make turmeric paper by depositing turmeric paste on blotting paper/filter paper and allow it to dry.
  • Cut thin strips of the yellow paper obtained.
  • Put a drop of soap solution on the strip of turmeric paper and notice any change in colour.
  • Note down your observation.
  • Repeat the above steps for all the solutions one by one.
S.No. Test solution Effect on turmeric solution Remarks
1) Soap solution Turns red Base
2) Lemon juice None Acidic or Neutral
3) Orange juice None Acidic or Neutral
4) Vinegar None Acidic or Neutral
5) Milk of magnesia Turns red Base
6) Efaking soda Turns red Base
7) Lime water Turns red Base
8) Sugar None Acidic or Neutral
9) Common salt None Acidic or Neutral

Conclusion: From the above activity we can conclude that acidic and neutral solution remain unchanged when they react with the turmeric. Basic solutions turns yellow colour of turmeric to bright red when they react with turmeric.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Activity 4.3 Page No : 82

Question 3.
Collect some China rose (Gudhal) petals and place them in a beaker. Add some warm water. Keep the mixture for some time till water becomes coloured. Use the coloured water as an indicator. Add five drops of the indicator to each of the solutions given in Table.What is the effect of the indicator on acidic, basic and neutral solutions?
Answer:
Aim : To test the acidic or basic nature of the given solutions by using the China rose extract as the indicator.
Materials required : China rose petals, warm water, beaker, dropper, solutions of different acids and bases.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts 1

Procedure:

  • Collect some China rose (Gudhal) petals and place them in a beaker. Add some warm water.
  • Keep the mixture for some time till water becomes coloured.
  • When water becomes coloured, filter out the petals and use the coloured water as indicator.
  • Take about 2ml of the first solution in a test tube.
  • Add five drops of the indicator to each of the solutions.
  • Observe the changes in colour.
  • Repeat the experiment with other solutions.

Observations: We observe that the colour of the China rose indicator is light pink.

S.No. Test solution Initial colour Final colour
1) Shampoo (dilute solution) Red Green
2) Lemon juice Red Magneta
3) Soda water Red Green
4) Sodium hydrogen carbonate solution Red Green
5) Vinegar Red Magneta
6) Sugar solution Red Red
7) Common salt solution Red Red

Conclusion : FVom the above activity, we can conclude when the pink colour of the China rose’indicator turns magenta then the solution is acidic and when it turns green and then the solution is basic. If there is no change in the colour, then the solution is neutral.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Activity 4.4 Page No : 84

Question 4.
The teacher is requested to get the dilute solution of the following chemicals from his/her school laboratory or from a nearby school: hydrochloric acid, sulphuric acid, nitric acid, acetic acid, sodium hydroxide, ammonium hydroxide, calcium hydroxide (lime water). Demonstrate the effect of the three indicators on each of these solutions. Record your observations in Table.
Answer:
Aim : To test the basic or acidic nature of the given substances by using litmus paper, turmeric paper, china rose solution as the indicators.
Materials required : Litmus paper, turmeric paper, China rose, given solutions.

Observations:

S.No. Name of acid Effect on litmus paper Effect on turmeric paper Effect on china solution
1) Dilute hydrose chloric acid Blue turns red None Magenta
2) Sulphuric acid Blue turns red None Magenta
3) Nitric acid Blue turns red None Magenta
4) Acetic acid Blue turns red None Magenta
5) Sodium hydroxide Red turns blue Turns red Turns green
6) Ammonium hydroxide Red turns blue Turns red Turns green
7) Lime water Red turns blue Turns red Turns green

Conclusion : From the activity we can conclude that

  • The acid substances turn blue litmus red and basic substances turn red litmus blue.
  • Acidic and neutral solution remains unchanged when they react with turmeric and basic solutions turn turmeric into red colour when they react with turmeric.
  • When the pink colour of the China Rose indicator turns magenta then the solution is acidic and when it turns green and then the solution is basic.

Activity 4.5 Page No : 86

Question 5.
Fill one fourth of a test tube with dilute hydrochloric acid. Note down its colour. Note down the colour of phenolphthalein solution also. Add 2-3 drops of the indicator to the acid. Now shake the test tube gently. Do you observe any change in colour of the acid?
Add to the acidic solution a drop of sodium hydroxide solution by a dropper. Stir the tube gently. Is there any change in the colour of the solution? Continue adding the sodium hydroxide solution drop by drop while stirring till the pink colour just appears. Now add one more drop of dilute hydrochloric acid. What do you observe? The solution again becomes colourless. Again add one drop of sodium hydroxide solution. Is there any change in colour?
Answer:
Aim : To show the process of neutralisation.
Materials required : Test tube, phenolphthalein solution, dropper, sodium hydroxide solution.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Procedure:

  • Fill one fourth of a test tube with dilute hydrochloric acid.
  • Note down its colour.
  • Note down the colour of phenolphthalein solution also.
  • Add 2-3 drops of the indicator to the acid.
  • Now shake the test tube gently.
  • Observe any change in colour of the acid.

Observations : We observe that the solution is colourless.

Procedure:

  • Add to the acidic solution a drop of sodium hydroxide solution by a dropper.
  • Stir the tube gently.
  • Continue adding the sodium hydroxide solution drop by drop while stirring till the pink colour just appears.

Observations : We: observe at this point, the solution is just neutral.

Procedure :

  • Now add one more drop of dilute hydrochloric acid.
  • Again record your observations.

Observations : We observe that the pink colour disappears.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts 2

Procedure

  • Again acid one drop of sodium hydroxide solution.
  • Record your observations.

AP 7th Class Science 4th Lesson Questions and Answers Acids Bases and Salts

Observations : ‘M observe that the pink colour reappears.
This happens because phenolphthalein is colourless in acidic medium and pink in basic medium.
Conclusion : From the above activity we can conclude that drop by drop addition of the dilute sodium hydroxide neutralises dilute hydrochloric acid.

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