RBSE Class 7 Science Important Questions Chapter 5 Acids, Bases and Salts

Rajasthan Board  RBSE Class 7 Science Important Questions Chapter 5 Acids, Bases and Salts Important Questions and Answers.

RBSE Class 7 Science Chapter 5 Important Questions Acids, Bases and Salts

Multiple Choice Questions

Question 1. 
Red litmus turns blue in the presence of
(a) an acid 
(b) a base
(c) a salt 
(d) water
Answer:
(b) a base

Question 2. 
One of these turns pink in basic solution
(a) Blue litmus 
(b) Methyl orange
(c) Phenolphthalein
(d) Red litmus
Answer:
(c) Phenolphthalein

Question 3. 
Litmus, a natural dye, is an extract of 
(a) China rose 
(b) Beetroot
(c) Lichen 
(d) Blueberries
Answer:
(c) Lichen 

Question 4. 
A solution changes the colour of the turmeric indicator from yellow to red, the solution is 
(a) basic 
(b) acidic
(c) neutral
(d) either neutral or acidic
Answer:
(a) basic

Question 5. 
Which of the following set of substances contain ads?
(a) Grapes, lime water
(b) Vinegar, soap
(c) Curd, milk of magnesia
(d) Curd, vinegar
Answer:
(d) Curd, vinegar

Fill in the blanks

Question 1. 
Oxalic add is found in.................. 
Answer:
spinach

Question 2. 
When an ant bites,..................is injected into the skin.
Answer:
formic acid

Question 3. 
Factory wastes are treated with.................. before they are released in water.
Answer:
basic substances

Question 4. 
Citric acid is present in.................. 
Answer:
 lemon

Question 5. 
Acids taste..................
Answer:
sour

State Whether True or False

Question 1. 
Organic acids are generally strong adds.
Answer:
False
 
Question 2. 
Baking soda is an acid.
Answer:
False

Question 3. 
Bases are sour in taste and corrode metals.
Answer:
False

Question 4. 
Water is a neutral substance.
Answer:
True

Question 5. 
Phenolphthalein will turn green in an acidic medium. 
Answer:
False

Match the following

Column I	Column II
1. Citric acid	(a) Lime water
2. Calcium hydroxide	(b) Calcium oxide
3. Antacid	(c) Ant's sting
4. China rose	(d) Lemon, oranges
5. Quick lime	(e) Curd
6. Calcium solution	(f) Grapes
7. Lactic acid	(g) Magnesium hydroxide
8. Tartaric acid	(h) Natural indicator
9. acid rain	(i) Neutralization reaction

Answer:

Column I	Column II
1. Citric acid	(d) Lemon, oranges
2. Calcium hydroxide	(a) Lime water
3. Antacid	(g) Magnesium hydroxide
4. China rose	(h) Natural indicator
5. Quick lime	(b) Calcium oxide
6. Calcium solution	(c) Ant's sting
7. Lactic acid	(e) Curd
8. Tartaric acid	(f) Grapes
9. acid rain	(j) Nitrogen dioxide
10. Add + Base = Salt + Water	(i) Neutralization reaction

Very Short Answer Type Questions

Question 1. 
Name two naturally occurring acids. 
Answer: 
Citric add and tartaric acid.

Question 2. 
Name two natural indicators. 
Answer: 
Litmus paper and China-rose extract. 

Question 3. 
Name two bases.
Answer: 
Sodium hydroxide and calcium hydroxide.

Question 4. 
What is the nature of baking soda?
Answer: 
Baking soda is basic in nature.

Question 5. 
What is the chemical name of baking soda?
Answer: 
The chemical name of baking soda is sodium hydrogen carbonate.

Question 6. 
Name the base which is used as a window cleaner.
Answer: 
Ammonium hydroxide.

Question 7. 
Name two inorganic acids.
Answer: 
Sulphuric add and nitric add.

Question 8. 
What is the most commonly used natural indicator?
Answer: 
The most commonly used natural indicator is litmus.

Question 9. 
What are the generally available forms of litmus?
Answer: 
Litmus is generally available as red and blue litmus paper.

Question 10. 
What is phenolphthalein?
Answer: 
Phenolphthalein is a synthetic indicator. 

Question 11. 
What is salt? What is its nature? Answer: In a neutralisation reaction, a new substance is formed. This is called salt. Salt may be acidic, basic or neutral.

Short Answer Type Questions

Question 1. 
What is the difference between a base and an alkali?
Answer: 
Bases are substances which produce hydroxide ions when added to water. And bases which are soluble in water are called alkalis.
For example - Sodium hydroxide and potassium hydroxide. All alkalis are bases but all bases are not alkalis.

Question 2. 
What are naturally occurring indicators?
Answer: 
The chemical substance which are found naturally and are able to test whether a substance is acidic or basic are called naturally occurring indicators. For example - litmus paper, turmeric solution, china rose extract etc.

Question 3. 
How will you prepare lime water? 
Answer: 
To prepare lime water, dissolve some lime in water in a bottle, stir the solution and keep it for some time. Our lime water solution is ready. It is an aqueous solution of calcium hydroxide.

Question 4. 
How will you prepare a birthday card for your mother on her birthday using turmeric paper?
Answer: 
Prepare a turmeric paste and apply on a sheet of plain white paper and dry it. Draw a beautiful flower with soap solution with the help of a cotton bud, it will turn in red colour flower. We will get a beautiful greeting card.

Question 5. 
How will you obtain China rose extract? 
Answer: 
Collect some China rose petals and. place them in a beaker. Add some warm water. Keep the mixture for some time till water becomes coloured. Filter the extract of China rose to remove the petals. Use the extract as an indicator.

Question 6. 
What is a neutralisation reaction?
Answer: 
The reaction between add 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).
Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water 
HCl + NaOH → NaCl + H₂O

Question 7. 
Book added to dilute sulphuric acid to lime water. Will the reaction mixture become hot or cool?
Answer: 
The reaction mixture becomes hot because a neutralisation reaction takes place between add (dil. H₂SO₄) and lime water (calcium hydroxide) to form salt (calcium sulphate) and water. The evolution of heat is accompanied by the reaction.

Question 8. 
How will you get relief from indigestion?
Answer: 
To get relief from indigestion, we should take an anti-acid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

Question 9. 
What does an ant inject when it bites? How will you treat it?
Answer: 
When an ant bites, it injects the acidic liquid i.e., formic acid into the skin. The effect of the add can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

Question 10. 
Why do we need to treat the soil? 
Answer: 
Most of the plants grow best in neutral soil, but excessive use of fertiliser makes the soil either acidic or basic. This affects the growth of plants by adversely affecting their productivity therefore, we need to treat the soil.

Question 11. 
Why factory wastes need to be treated? How is it done?
Answer: 
The wastes of many factories contain ads. If they are allowed to flow into water bodies, the adds will kill fish and other living organisms. The factory Wastes are thereby neutralized by adding basic substances.

Long Answer Type Questions

Question 1. 
What is acid rain? Why is it called so? List some of the damaging effects of acid rain.
Answer: 
The rain containing an excess of acids is called acid rain. The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in raindrops to form carbonic acid, sulphuric add and nitric acid. Add cause damage to buildings, historical monuments, plants and animals.