Chemistry ICSE Class 7 Important Questions Chapter 5 Acids, Bases and Salts

Question 1.
Define salts.
Answer:
Salts are products of neutralization reactions between acids and bases. A salt is a compound which, when dissolved in
water, yields a positive ion other than hydronium ion and a negative ion other than hydroxyl ion.
Examples : NaCl (sodium chloride/common or table salt), baking soda (sodium hydrogencarbonate, NaHCO3)

Question 2.
What are dilute acids and concentrated acids ?
Answer:
Dilute acids are those acid solutions that contain a low percentage of acid in die aqueous solution. Concentrated acids are those solutions that contain a high percentage of acid in die aqueous solution.

Question 3.
What are organic and inorganic acids ?
Answer:
Acids that are present in fruits and naturally occurring substances are called organic acids or naturally occurring acids. They are found in animal and plant products. Examples : acetic acid in vinegar; citric acid in oranges, lactic acid in sour milk and curd. Acids that are obtained from minerals are called inorganic or mineral acids. Examples : hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3).

Question 4.
Why a danger mark is put on containers containing concentrated acids ?
Answer:
Strong acids and concentrated acids are highly corrosive and cause painful blisters if they fall the skin. Therefore, a danger marie is put on their container

Question 5.
Name the acid used :

  1. for flavouring food and as food preservative.
  2. in medicine (source of vitamin C), in soft drinks and as preservative.
  3. as constituent of baking powder.
  4. as an eyewash and for preservation of grains.
  5. to lend fizz of aerated drinks.

Answer:

  1. Acetic acid
  2. Citric acid
  3. Tartaric acid
  4. Boric acid
  5. Carbonic acid

Question 6.
Mention two practical applications of neutralization reaction.
Answer:
1. Indigestion – During indigestion, the stom ach produces too much acid, which causes pain and irritation. 1 he excessive acid is neutralized with the help of antacids hike mlik of magnesia (magnesium hydroxide) which is a base.
2. Soil treatment – The acidic effect of the so.ji can be neutralized by adding basic substances like calcium hydroxide, calcium oxide or powdered chalk (calcium carbonate)’. If the soil is too alkaline, then it is neutralized by adding decaying organic matter (manure or compost) which contains acidic materials.

Question 7.
Name few natural indicators.
Answer:
(i) Litmus
(ii) Turmeric
(iii) Red-cabbage extract

Question 8.
Why does a yellow stain of curry on a white cloth turns reddish-brown when soap is scrubbed on it ?
Answer:
Soap solution is basic in nature, which changes the colour of turmeric (In basics medium, turmeric changes its colour from yellow to reddish-brown.)

Question 9.
Classify the following as acidic or basic substances : Lime juice, vinegar, vitamin C tablet, milk of magnesia, slaked lime soap solution.
Answer:
Acidic substances – lime juice, vinegar and vitamin C tablets. Basic substances – milk of magnesia, slaked lime, soap solution.

Question 10.
Write pH value of the following :

  1. pure water
  2. blood
  3. milk
  4. lemon juice

Answer:

  1. Pure water – 7.0 (neutral)
  2. Blood – 7.4 (slightly alkaline)
  3. Milk – 6.5 (slightly acidic)
  4. Lemon juice – 2.5 (acidic)

Question 11.
Fill in the blanks
1. Milk of magnesia, slaked lime, whitewash and soap solution are …………. in nature.
Answer:
Milk of magnesia, slaked lime, whitewash and soap solution are; basic in nature.

2. A …………. ion is actually hydrated hydrogen ion.
Answer:
A hydronium ion is actually hydrated hydrogen ion.

3. …………… hydroxide is a base but is not a metallic hydroxide.
Answer:
Ammonium hydroxide is a base but is not a metallic hydroxide.

4. Bases react with some metals to form ………….. gas.
Answer:
Bases react with some metals to form hydrogen gas.

5. …………. is used as a foaming agent in fire extinguishers.
Answer:
Aluminium hydroxide [Al(OH)3] is used as a foaming agent in fire extinguishers.

6. ………….. is made from a plant pigment that is sensitive to changes in hydrogen ion concentration.
Answer:
Litmus is made from a plant pigment that is sensitive to changes in hydrogen ion concentration.

7. Red-cabbage extract remains ……………. in acidic medium but turns …………… in basic medium.
Answer:
Red-cabbage extract remains red in acidic medium but turns green in basic medium.

8. The basic strength of basic solution increases with ……………. in pH number.
Answer:
The basic strength of basic solution increase’s with an increase in pH number.

9. A ……………. indicator is a mixture of different indicators (or dyes) which gives different colours at different pH values.
Answer:
A universal indicator is a mixture of different indicators (or dyes) which gives different colours at different pH values.

10. …………… are sour in taste and corrosive in nature.
Answer:
Acids are sour in taste and corrosive in nature.

11. …………… are bitter in taste and soapy to touch.
Answer:
Bases are bitter in taste and soapy to touch.

Question 12.
Balance the following neutralization reactions :
1. H2SO4 + NaOH →Na2SO4 + H2O
2. HCl + Mg(OH)2 → MgCl2 + H2O
Answer:
1. H2SO4 + 2NaOH → Na2SO4+ 2H2O
2. 2HCl + Mg(OH)2 → MgCl2 + 2H2O

Concept Map :

ICSE Class 7 Chemistry Important Questions

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