CBSE Class 7 Science Acids Bases And Salts Worksheet Set 06

Question. Given below are the pH values of different liquids.7.0, 14.0, 4.0, and 2.0. Which of these could be that of-
a) lemon juice
b) distilled water
c) sodium hydroxide solution
d) tomato juice.
Ans: a) lemon juice- 2.0
b) distilled water-7.0
c) sodium hydroxide solution `14.0
d) tomato juice- 4.0 18

Question. Write the name of the products formed by heating gypsum at 373K.Write one use of it.
Ans: Plaster of Paris and water. It is used for plastering fractured bone.

Question. The acid having highest hydrogen ion concentration is one with
a) pH=2.5
b) pH = 1.8
c) pH=7
d) pH=10
Ans: B

Question. Which of the following gives the correct increasing order of acidic strength?
a) Water< Acetic acid < Water < Hydrochloric acid
b) Hydrochloric acid < water < Acetic acid 19
Ans: A

Question. a) Crystals of a substance changed their color on heating in a closed test tube but regained it after some time when they were allowed to cool down. Name the substance and write its formula. Explain the phenomenon.
b) How is sodium carbonate prepared? Give two uses of the compound
Ans: a) Copper sulphate, CuSO₄.5H₂O. It is blue. It becomes white on heating due to loss of water molecule. CuSO4.5H₂O —Heat–> CuSO₄+5 H₂O It regains its colour by absorbing water from atmosphere CuSO₄+ 5 H₂O –→ CuSO₄.5H₂O
b) Sodium carbonate is prepared by passing CO₂ through ammoniac brine. Used for production of washing powder & manufacture of glas

Question. Write the chemical name of Plaster of Paris. Write a chemical equation to show the reaction between Plaster of Paris and water. Name the compound produced in this reaction.
Ans: Calcium Sulphate hemihydrates.
        CaSO₄. 1 /2H₂O +1 /2H₂O–→ CaSO₄.2H₂O
        The compound produced is Gypsum.

Case Study Based Questions

Question. Ritesh was asked to determine the melting point of a given organic solid. For this, he used a bath containing cone. H₂SO₄. When he was looking at the thermometer, he lost his concentration and became a little casual. The beaker containing boiling Sulphuric acid fell on his clothes. His clothes were burnt and he got severe burns on hands.

1. Why did Ritesh meet with an accident?
2. Why did he get severe burns on the hands?
3. What lessons can a student learn from the above episode?
Ans: 1. The bath or the beaker containing cone. H₂SO₄ was not properly placed on the tripod stand. It lost balance and the acid fell over him.
2. Sulphuric acid is a very powerful dehydrating agent. It removed water contents from the skin which got charred and burns appeared on hands.
3. While working in the chemistry laboratory, a student must observe the following precautions:
1. Must always wear an appron in the laboratory.
2. Must always keep some distance from the table where the experiment is performed.
3. Must always remain alert in the laboratory and must not lose concentration.

Question. Ram was suffering from a stomach pain for a number of days. He consulted a doctor who advised him to take two antacid tablets after each meal for about a week and avoid spicy food. Ram followed the advice strictly and was cured.
1. What was the problem faced by Ram?
2. How did doctor help him?
3. Write the chemical equation if any
4. What is the value associated with this?
Ans: 1. Ram had developed acidity in the stomach resulting in the formation of small ulcers which caused pain.
2. The antacid tablets contain base like NaHCO₃ or Mg (OH)₂ which neutralize the effect of HCl released in the stomach.
3. NaHCO₃ + HCl ———–> NaCl + H₂O + CO₂ (Antacid)
4. As far as possible, one should always avoid spicy and fried food stuff. They create acidity in the stomach. This leads in the formation of small ulcers which give pain. Apart from that one must always keep some antacid tablets or liquid gels.

Question. Kamla was playing in the garden. She was stung by a wasp and started crying. Her mother immediately applied a coating of tooth paste on the affected area and then took her to the doctor.
1. Why did Kamla cry?
2. What does wasp sting contain?
3. Why did her mother apply tooth paste on the affected area?
4. What values are displayed by this episode?
Ans:
1. Kamla cried because the sting by the wasp is very painful.
2. Wasp sting contains in its formic acid (HCOOH)
3. Tooth paste contains in it some basic ingredients which neutralize the effect of formic acid (HCOOH) and give relief.
4. Kamla’s mother had knowledge of chemistry. Tooth paste is readily available and she gave a first aid to her daughter.

Acids, Bases and salts

Question 1. Classify the following substances as acids and bases : Tomato juice, tamarind juice, curd, toothpaste, soap solution, raw mangoes.
Answer: - Acids: Tomato juice, tamarind juice, curd, raw mangoes.
- Bases: Toothpaste, soap solution.
In simple words: Sour substances containing natural acids are classified as acids, while bitter or soapy substances that feel slippery are bases.

Exam Tip: Remember that edible items containing organic acids are generally acidic, whereas cleaning agents and personal care products like soaps are basic.

Question 2. Some acids, bases and salts are commonly used in our daily life. Find out the names of such substances, specify whether they are acids, bases or salts and write their uses.
Answer: 1. Vinegar (Acetic Acid) - Acid - Used for food preservation and cooking flavor.
2. Baking Soda (Sodium Hydrogen Carbonate) - Base - Used in baking cakes and as an antacid.
3. Common Salt (Sodium Chloride) - Salt - Used for cooking and food seasoning.
In simple words: Common household items have different chemical natures and serve various purposes in food and health.

Exam Tip: Always categorize substances clearly by name, chemical nature, and specific utility when asked about daily applications.

Question 3. what are mineral acids.? Give two examples.
Answer: Mineral acids (also known as inorganic acids) are acids derived from one or more inorganic compounds. They are generally strong and corrosive. Examples: Hydrochloric acid (\(\text{HCl}\)) and Sulphuric acid (\(\text{H}_2\text{SO}_4\)).
In simple words: Mineral acids are laboratory-made acids obtained from minerals found in the earth.

Exam Tip: Always give chemical formulas along with names when asked for examples of mineral acids.

Question 4. complete the table given below :
Answer:

Exam Tip: Natural acids are organic acids found in plants and animals, whereas mineral acids are prepared from minerals.

Question 5. write any two general properties of acidic substances.
Answer: 1. Acidic substances taste sour.
2. They turn blue litmus paper to red.
In simple words: Acids are sour to taste and change blue litmus to red.

Exam Tip: Mention taste and indicator color change as the standard diagnostic properties of acids.

Question 6. Name any three mineral acids.
Answer: 1. Hydrochloric acid (\(\text{HCl}\))
2. Sulphuric acid (\(\text{H}_2\text{SO}_4\))
3. Nitric acid (\(\text{HNO}_3\))
In simple words: These are powerful inorganic acids commonly used in science laboratories and industries.

Question 7. What happens when :
i. Magnesium is burnt in the presence of Oxygen and the product obtained is added to water
ii. An acid and a base is reacted.
iii. Blue litmus is added to vinegar.
iv. Lemon juice is added to baking soda
Answer: i. Magnesium burns to form magnesium oxide (\(\text{MgO}\)), which is basic in nature. When added to water, it forms magnesium hydroxide (\(\text{Mg(OH)}_2\)), which turns red litmus blue.
ii. A neutralization reaction takes place, producing salt and water along with the evolution of heat.
iii. Blue litmus turns red because vinegar is acidic in nature.
iv. Effervescence (bubbling) occurs due to the release of carbon dioxide gas as a result of the neutralization reaction between the acid (lemon juice) and base (baking soda).
In simple words: Chemical reactions between acids and bases neutralize each other, while metal oxides dissolve in water to form bases.

Exam Tip: Always state the final observation (color change, gas evolution, or salt formation) clearly for each reaction sub-part.

Question 8. Complete the given table :
Answer:

Exam Tip: Practice indicator color tables thoroughly as they form the core of practical-based questions in chemistry.

Question 8 (re-numbered in source). What are indicators? Give examples. Why do we use indicators?
Answer: Indicators are special substances used to test whether a substance is acidic or basic. They change their color when added to a solution containing an acidic or basic substance. Examples: Litmus, turmeric, and China rose extract. We use indicators to safely identify the acidic or basic nature of various substances without tasting them.
In simple words: Indicators act as chemical test papers or liquids that change color to show if a substance is an acid or a base.

Exam Tip: Definition, examples, and purpose must all be explicitly covered to secure full marks in this question.

Question 9. What are neutral substances?
Answer: Substances that are neither acidic nor basic are called neutral substances. They do not change the color of any indicator (such as litmus). Example: Pure water and common salt solution.
In simple words: Neutral substances are harmless items that show no acidic or basic properties.

Exam Tip: Always mention that neutral substances have no effect on indicators.

Question 10. Ammonia is used in many household products like window cleaners. It turns red litmus to blue. What is the nature of ammonia?
Answer: Ammonia is basic in nature because it turns red litmus paper to blue.
In simple words: Since it turns red litmus blue, ammonia is a base.

Exam Tip: Link the color change directly to the chemical property (turning red litmus blue indicates a base).

Question 11. What causes acidity in stomach? Why does a doctor recommend an antacid to a person suffering from acidity.
Answer: Our stomach produces hydrochloric acid to help digest food. When the stomach produces excess acid, it causes indigestion and acidity/pain. A doctor recommends an antacid (which is a mild base, such as milk of magnesia containing magnesium hydroxide) because it neutralizes the excess acid in the stomach and provides relief.
In simple words: Too much stomach acid causes pain, and an antacid base neutralizes it to make you feel better.

Exam Tip: Use the keyword neutralization to explain how antacids cure stomach acidity.