Wednesday, May 22, 2013

CBSE Chemistry 7th Acids bases and Salts [Solved]

Read Full Post: 7th Acids bases and Salts [Solved]

Q1. What are acids?

Ans. Acids are the substances which are sour in taste.

Q2. What are bases?

Ans. Bases are the substances which are bitter in taste & soapy to touch.

Q3.Give examples of acids and bases.

Ans. Acids- hydrochloric acid, acetic acid, citric acid, lactic acid etc

Bases- baking soda, sodium hydroxide, soap etc

Q 4. Name the acids present in the following substances.

acetic acid
lactic acid                                
oxalic acid
citric acid                                  
citric acid
tartaric acid

Q5. What are indicators? Give examples.

Ans. Indicators are the special type of substances which are used to distinguish between acids & bases by showing colour changes.

Example: litmus, turmeric, beetroot, China rose extract, phenolphthalein etc.

Q6.Name the source from which litmus is obtained.

Ans. Litmus is obtained from a plant lichens.

Q7. in what forms is litmus available?

Ans. Litmus is available in the form of solution or in the form of strip of paper.

It is available as red & blue litmus.

Q8. Why do we use indicators?

Ans. We use indicators to find out whether a substance is acidic, basic or neutral, as all the substances can’t be tasted. Some of the substances are highly corrosive and hence can be harmful to us if tasted.

Q9.What happens when phenolphthalein is added to  (a) Acidic solution (b) basic solution (c) Neutral solution

(a) in acidic solution, the colour of phenolphthalein remains colourless.

b) When phenolphthalein is added to basic solution, the colour changes to pink (magenta).

c) In neutral solution, it remains colourless.

Q10.What are neutral substances?

Ans. The substances which are neither acidic nor neutral are known as neutral solutions.

Q11. What happens when a base is put on turmeric paste? What will happen when acid is added to the same?

Ans. When base is added to turmeric paste, then its colour changes to red. If we put an acid on the same then changes to yellow again.

Q12. How will you identify weather a substance is acidic or basic using red & blue litmus?

Ans. Acids & bases can be distinguished using litmus solutions as follows:

- if the colour of red litmus changes to blue, then the substance is basic in nature.

- if the colour of blue litmus changes to red, then the substance is acidic in nature.

Q13. Ammonia is used in many household products like window cleaners. It turns red litmus to blue. What is the nature of ammonia?

Ans. As ammonia turns red litmus to blue that shows it is basic in nature.

Q14. What is the effect of China rose indicator on acidic & basic solutions?

Ans. China rose indicator turns acidic solutions to dark pink and basic solutions to green.

Q15.What is neutralization reactions?

Ans. The reaction in which an acid & a base react to form salt and water, with the evolution of heat is known as neutralization reaction.

Acid + base ------> salt + water.

Hydrochloric acid + sodium hydroxide --> sodium chloride + water

Q16. What are salts? Are they acidic, basic or neutral?

Ans. Salts are substances formed by the reaction of an acid and base. Salts can be acidic, basic or neutral.

Q17. What are antacids?

Ans. antacids are the medicines that arte use to relieve from acidity in stomach. Example: milk of magnesia, eno etc.

Q18 what causes acidity in stomach?

Ans. Our stomach contains hydrochloric acid which helps us to digest food. When the amount of acid present in stomach increases, it leads to acidity.

Q19 How is antacids helpful in relieving indigestion?

Ans. Antacids are basic in nature, hence they neutralize the effect of excess of acid and relieve us from indigestion.

Q20. Why is calamine solution put on the ant sting?

Ans. When an ant bites, it injects formic acid into the skin. The effect of acid can be neutralized by applying calamine solution which is basic in nature.

Q21.Sometimes we treat the soil with bases. Give reasons why?

Ans. Excessive use of fertilizers makes the soil acidic, which is not suitable for the growth of the plants .Hence we treat the soil with bases like calcium oxide to neutralize of acid.

Q22.The factory waste is treated with basic substances before disposing it?

Ans. The wastes of factories contain acids. If they are allowed to flow into the water bodies, then they are harmful to the aquatic life. Therefore, factory waste are treated with basic solutions.

Q23.What is the chemical name of the following:

Common name
Chemical name
Quick lime
Calcium oxide
Slaked lime
calcium hydroxide
Baking soda
sodium hydrogen carbonate

Q24. What is the chemical composition of milk of magnesia?

Ans. The chemical composition of milk of magnesia is magnesium hydroxide.

Q25. What is the chemical composition of calamine solution?

Ans. The chemical composition of calamine solution is zinc carbonate.

Related study materials
MCQ:Acid base and salt: For Olympiads-1 
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MCQ:Acid base and salt: For Olympiads-2
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