Acids Bases and Salts Important Question and Answers

Q1.Why alkalis like sodium hydroxide and potassium hyd roxide should not be left exposed to air?

Ans.Alkalis should not be left exposed to air be cause they are hygroscopic in nature and absorb moisture from atmosphere in which they g et dissolved.

Q2.Dry ammonia has no action on litmus paper but a sol ution of ammonia in water turns red litmus paper blue. Why is it so?


Ans.n dry state Ammonia contains no hydroxyl io ns. On dissolving in water, it forms NH 4 OH which dissociates to give NH 4 + and OH - ions. Thus solution becomes basic and turns red litmus paper blue.

Q3.Bleaching powder forms a milky solution in water. E xplain.

Ans.When bleaching powder gets dissolved in wate r, the solution turns milky due to the formation of Calcium Hydroxide Ca[OH]₂

Q4.A first aid manual suggests that vinegar should be used to treat wasp sting and balking soda for bee stings.

(a) What does this information tell you about the c hemical name of the wasp sting?

Ans.he chemical present in the sting must be base because vinegar (acetic acid) is used to heal or neutralize the effect of w asp stings.

(b) If there were no baking soda in the house, what other house hold substances would you use to treat as stings?

Ans.Since bee stings are treated by backing soda which is a base it means they must contain some acid. If baking soda is not avail able in the house, solution of ammonium hydroxide NH 4 OH can be used for the same purpose.

Q5.Does Tartaric acid helps in making cake or bread fl uffy. Justify.

Ans.o, tartaric acid does not evolve any carbon dioxide during baking. Its role is to react with Na 2 CO 3 formed when NaHCO 3 decomposes.

Q6.Explain why?

(a) Common salt becomes sticky during the rainy sea son.

Ans.Common salt contains impurity of magnes ium chloride (MgCl ₂ ) which is of deliquescent nature. When exposed to atmosphere, it becomes moist. Therefore common salt becomes sticky during the rai ny season.

(b) Blue vittriol change to white upon heating.

Ans.during heating it changes to a anhydrous copper sulphate (CuSo ₄ ) which is white in colour.

Q7.A compound X of sodium is commonly used in kitchen for making crispy pakoras. It is also used for curing acidity in the stomach. Identify ‘X’. What is its chemical formula? State the reaction that takes pla ces when it is heated during cooking?

Ans.ompound X is a constitute of baking powder. It is also called as baking soda. Chemically, the compound is sodium hydrogen carbona te with formula NaHCO ₃ . Upon heating the compound X releases CO ₂ gas

NaHCO₃---------> Na₂CO₃ + CO₂ + H₂O

Q8.(a) Why does an aqueous solution of acid conduct el ectricity?

Ans.n aqueous solution of an acid conducts electricity because in water an acid (HCl) dissociates to give ions. Since the current i s carried out by the movement of ions, an aqueous solution of acid condu cts electricity.

(b) How does the concentration of hydrogen ions [ H3 O +] changes when the solution of an acid is diluted with water? Ans.During dilution, more of acid dissociates int o ions. Thus concentration of [ H3O +] ions will increase on dilution

(c) Which has higher pH. A concentrated or dilute s olution of HCL?

Ans.Concentrated solution (d) What would you observe on adding dil HCL acid t o (i) Sodium bicarbonate placed in a test tub e. Ans.Evolution of Carbon dioxide along with brisk effervescenc e (ii) Zinc metal in a test tube.

Ans.Hydrogen gas will evolve with brisk efferevescence

Q9.Why does not an acid show any acidic behavior is th e absence of w ater?

Ans.An acid gets ionized only in aqueous solut ion which means in the presence of water. Also it releases H + ions and show acidic behavior in the presence of w ater

Q10.Fresh milk has a pH of 6. What will be the PH value if milk changes into a curd Justify.

Ans.When milk changes into a curd, its PH value decreases i.e. lactose gets converted into lactic acid. As more of acid is formed, its PH value decreases.

Q11.If bottle full of concentrated sulphuric acid is left open in the atmosphere by accident, the acid starts flowing out the bottle of its own.

Ans.Concentrated sulphuric acid is highly hygrosc opic it absorbs moisture from air and gets diluted. Since the volume increases, t he acid starts flowing out of the bottle.

Q12.How is pl aster of Paris chemically different from gypsum? Ho w ma y these b e inter converted? Write one use of plaster of Paris?

Ans.laster of Paris is different from Gypsum as it is prepared from heating gypsum. Plaster of Pairs is a major constituent of surgical bandages used for setting fractured bones. Before applying on fractured bone, it is made wet with water and as a result of hydration it changes into gypsum whi ch keeps the bones in position. These may be interconverted by the reaction.

he use of plaster of Paris are- (i) It is used for making moulds or casts for toys pott ery, ceramics etc.

(ii) In surgical bandages for setting fractured bones.

Q13.A road t anker carrying an acid was in v o l ved in an accident and its contents spilled on the road. At the side of the road iron d rain cover began melting and fizzing as the acid ran over them. A specialist was called to see if the acid actually leaked into the nearby river.

(a) Explain why specialist could carry out sample t est to see of the river water contains some acid or not

Ans.t can be done by adding a strip of blu e litmus paper into a tube containing a small amount of sample water if the colour changes int o red, this means that some acid has gone into the river.

(b) Suggest a better report name for the word ‘melt ing’

Ans. The acid has reacted chemically with the drain cover which is usually made of iron. The correct word is corrosion. (c) Explain why the drain covers began fizzing as t he acid ran over them.

Ans.Iron reacts with an acid to evolve hydrogen gas. Since the gas is released immediately accompanied by large number of bub bles Fizzing of detain covers is expected.

Q14.

Q14. For making cake, baking powder is taken. If at ho me your mother uses baking soda instead of baking powder in cake,

(a) how will it affect the taste of the cake and why?
Ans. Use of baking soda; instead of baking powder; will mak e the taste of cake bitter. This happens because of formation of sodium carbonate.

(b) how can baking soda be converted into baking powder? Ans. Baking soda can be converted into baking powder by mi xing edible acid; like tartaric acid.

(c) what is the role of tartaric acid added to baking soda ?

Ans. When tartaric acid is dissolved in water, it gives h ydrogen ions. Hydrogen ions react with sodium carbonate to produce carbon dioxide. Carbon di oxide makes the cake soft and spongy

Q15. dry pellet of a common base B, when kept in open abs orbs moisture and turns sticky. The compound is also a by–product of chloralk ali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

Ans. Sodium hydroxide is a byproduct of chloralkali process. When it is kept in open, it absorbs moisture and turns sticky. When sodium hydroxide is treated with carbon dioxide, it gives sodium carbonate. It is important to remember that carbon dioxide is acidic oxid e.

Since this reaction is between a basic compound and a n acidic compound, hence it is a neutralization reaction. B is sodium hydroxide.

Q16.What happens when nitric acid is added to egg shel l?

Ans. When nitric acid is added to egg shell, it dissolves egg shell. Egg shell is composed of calcium carbonate which dissolves in nitric acid. The reaction between nitric acid and calcium carbonate yields calcium nitrate and carbon d ioxide gas.