Additional Questions With Solutions
Question 1: Name two natural detectors.
answer :
(i) litmus paper
(ii) Turmeric
Question 2: Name two synthetic detectors.
answer :
(i) Methyl Orange
(ii) phenolphthalein
Question 3: Some substances whose smell changes in acidic or basic medium. What are they called?
Answer: Aromatic indicator.
Question 4: The metal reacts with acid residues to form a compound and release hydrogen gas. What is this compound called?
Answer: Salt.
Question 5: Name the different forms of calcium carbonate.
Answer: Chosen stone, quarry, marble.
Question 6: On passing carbon dioxide gas through lime water, a white precipitate of calcium carbonate and water is obtained.
(i) Write the overall equation of this reaction.
(ii) What is this white precipitate called?
(iii) What is obtained when a large amount of carbon dioxide gas is passed through?
answer:
(i) Overall equation of this reaction :
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O (l)
(ii) Calcium Carbonate (CaCO3)
(iii) Ca(HCO3)2 (aq) soluble in water is obtained.
Question 7: The reaction between an acid and a base, in which salt and water are obtained, what is this reaction called?
Answer: Neutralization reaction.
Question 8: What is a neutralization reaction called?
Answer: The reaction between an acid and a base in which salt and water are obtained and they neutralize each other's effect, this reaction is called neutralization reaction.
base + acid → salt + water
Question 9: What is the nature of metallic oxides?
Answer: Metallic oxides are basic in nature.
Question 10: What is the nature of non-metallic oxides?
Answer: Metallic oxides are acidic in nature.
Question 11: Why curd and sour substances should not be kept in brass and copper utensils?
Answer: Curd and sour substances are acidic in nature, the acid present in it reacts immediately with brass and copper and destroys the vessel. And the substances kept in it also get spoiled.
Question 12: Which gas is usually released when an acid reacts with a metal? Explain with an example. How will you check the presence of this gas?
Answer – Normally hydrogen gas is evolved when an acid reacts with a metal. like-
2HCl + Mg → MgCl2 + H2 (g)
To check the presence of this gas, when we take a burning candle near this gas, the combustion of hydrogen gas occurs with the sound of burst.
Question 13: What is a base soluble in water called?
Answer: alkali.
Question 14: Tooth enamel is one of the hardest substances in our body. How does this decay happen by eating chocolates and sweets? What should be done to prevent it? What is enamel made of? What is the pH value of the mouth?
Answer – Bacteria present in the mouth after the meal degrade the waste sugar and food items in the mouth to produce acid. This acid becomes less than the pH value of the mouth, due to which tooth decay starts. To prevent this, the mouth should be cleaned after meals. Enamel is made up of calcium phosphate. The pH value of the mouth is 5.5.
Question 15: Why do muscles have cramps?
Ans- Cramps occur due to excess of lactic acid in the muscles.
Question 16: A substance A is obtained by the action of washing soda with vinegar. What is substance A?
Answer: Substance A is sodium acetate, the reaction of this reaction is as follows.
Question 17: To stabilize a broken bone, doctors use a paste made of white powder in water.
1. Name this substance.
2. Write its chemical formula.
3. State one special property of this substance.
4. Why should this substance be kept in a damp proof container?
answer :
1. The name of this substance is plaster of paris.
2. Its chemical formula is CaSO4. 1/2 H2O.
3. A special property of this substance is that as soon as water is mixed, it becomes hard immediately. Therefore it is used in making toys.
4. This material is kept in a moisture proof vessel because it reacts with moist air to form gypsum.
Question 18: What is dilution?
Answer: On adding acid or base to water, the concentration of ion (H3O/OH) per unit volume decreases, this process is called dilution.
Question 19: Write the importance of pH in daily life.
answer :
1. Our body works in the pH range of 7.0 to 7.8.
2. If the pH of the soil is acidic in nature then it is not favorable for the crop.
3. Our stomach contains hydrochloric acid which helps in digestion without harming the stomach.
4. If the face value of the mouth is less than 5.5, then the teeth are destroyed.
Question 20: Write three uses of how bleaching powder is prepared.
Answer: Bleaching powder is formed by the action of chlorine on dry slaked lime [Ca(OH)2].
Answer : Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses of bleaching powder:
(i) For bleaching cotton and linen in the textile industry, wood marrow in the paper factory and for bleaching clean clothes in the laundry.
(ii) As an auxiliaries in chemical industries.
(iii) As a disinfectant to make drinking water free from bacteria.
Question 21: Where do we get litmus paper?
Answer: It is obtained from lichen plant of Thallophyta group.
Question 22: Name three natural substances which indicate the presence of acids and bases.
answer:
1. Turmeric
2. litmus paper
3. Red Cabbage
Question 23: Write two chemical properties of acid and base.
Answer: Chemical properties of acids:-
(i) It provides H+ ions with water.
(ii) Acid reacts with metal to give salt and hydrogen gas.
Chemical properties of bases:-
(i) It provides (OH)- ion with water.
(ii) Base reacts with acid to give salt and hydrogen gas.
Question 24: Why is distilled water not a conductor of electricity while rain water is?
Answer: Distilled water is not a conductor of electricity because it does not contain H+ ions, distilled water is neutral. Whereas rain water is weakly acidic in nature. It contains H+ ions which conduct electricity.
Question 25: Why curd and sour substances are not kept in brass and copper utensils?
Answer: Do not keep curd and sour substances in brass and copper utensils because the acid present in curd and sour substances reacts with brass and copper and destroys the vessel and the taste of the substance changes.
Question 26: Effervescence is produced when a metal compound 'A' reacts with dilute hydrochloric acid. The gas produced by this extinguishes the burning candle. If one of the compounds produced is calcium chloride, then write the balanced chemical equation for this reaction.
Answer: Ca + 2HCl → CaCl2 + H2
Question 27: Tooth enamel is one of the hardest substances in our body. How does this decay happen by eating chocolates and sweets? What should be done to prevent it? What is enamel made of? What is the pH value of the mouth?
Answer: (i) This can be prevented by rinsing the mouth after meals. Using an alkaline toothpaste to clean the mouth can neutralize the excess acid that results in tooth decay.
(ii) Tooth enamel is made up of calcium phosphate.
(iii) The pH value of the mouth is 5.5.
