10th Class PS 2nd Lesson Acid Bases and Salts Textbook Questions and Answers
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Question 1.
A solution turns red litmus blue, its pH is likely to be
a) 1
b) 4
c) 5
d) 10
Answer: d) 10
Question 2.
A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
a) NaCl
b) HCl
c) LiCl
d) KCl
Answer: b) HCl
Question 3.
10 ml of a solution of NaOH is found to be completely neutralised by 8 ml of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be
a) 4 ml
b) 8 ml
c) 12 ml
d) 16 ml
Answer: d) 16 ml10 ml of NaOH will neutralise = 8 ml of HCl
10 ml of NaOH will neutralise = 8/10 × 20 = 16 ml of HCl.
Question 4.
Which one of the following types of medicines is used for treating indigestion ?a) Antibiotic
b) Analgesic
c) Antacid
d) Antiseptic
Answer :: c) Antacid
Question 5.
Write word equation and then balanced equations for the reaction taking place when –
a) dilute sulphuric acid reacts with zinc granules.
b) dilute hydrochloric acid reacts with magnesium ribbon.
c) dilute sulphuric acid reacts with aluminium powder.
d) dilute hydrochloric acid reacts with iron fillings.
Answer:
Question 6
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it. (Activity 2.8) (TP No. 48)
Answer:
Aim : To prove that alcohols and glucose do not conduct electricity in their solution form.Procedure :
Fix two iron nails on a cork and place this cork in a beaker.
Connect the nails to the two terminals of a 6 volt battery through a switch and bulb a as shown in Figure.
Now add some dilute hydrochloricacid in the beaker and switch on the current. Take the observation. Acid solution in water conducts electricity
Repeat the experiment separately with alcohol and glucose solution.
Observation : You will observe that in case of dilute hydrochloric acid bulb glows but when glucose or alcohol solution is taken in beaker, the bulb does not glow.
Conclusion:
Alcohol and glucose do not conduct electricity suggesting that they do not form ions.
Dilute hydrochloric acid solution conducts electricity suggesting that it forms ion and the electric current is carried through the solution by ions.
Question 7.
Why does distilled water not conduct electricity, whereas rain water does ?
Answer: Distilled water does not contain any ionic compounds like acids, bases or salts. Therefore, it does not dissociate into ions as it is a.weak electrolyte. Salts are present in rain water which help in dissociation of rain water into ions which help in conduction of electricity.
Question 8.
Why do acids not show acidic behaviour in the absence of water ?
Answer:It is because adds do not dissociate into ions in absence of water. But when an acid is dissolved in water, it forms hydrogen ions and hence, show acidic behaviour,
Question 9.
Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4, 1, 11,7 and 9, Which solution is
a) neutral ?
b) strongly alkaline ?
c) strongly acidic ?
d) weakly acidic ?
e) weakly alkaline ?
Arrange the pH increasing order of hydrogen-ion concentration.
Answer:
a) ‘D’ with pH = 7 is neutral
b) ‘C’ with pH = 1 1 is strongly alkaline
c) ‘B’ with pH = 1 is strongly acidic
d) ‘A’ with pH = 4 is weakly acidic
e) ‘E’ with pH = 9 is weakly alkaline
C, E, D, A, B is increasing order of H+ ion concentration.
Question 10.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube v will the fizzing occur more vigorously and why?
Answer:
Fizzing occurs more vigorously in hydrochloric acid (A) than in acetic acid (B) because HCl is stronger acid than acetic acid. HCf dissociates into H+ and Cl– ions completely whereas acetic acid partially dissociates into its ions.
Question 11.
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd?
Explain your answer.
Answer:
pH will decrease form 6
Reason : Curd is more acidic than milk. When milk changes into curd, lactose (organic sugar) present in milk gets converted into lactic acid due to the fermentation process.
Question 12.
A milkman adds a very small amount of baking soda to fresh milk.
a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline ?
b) Why does this milk take a long time to set as curd ?
Answer:
a) It is done to increase the shelf life of milk.
b) The alkaline milk takes a longer time to set into curd because lactic acid being formed has to neutralise the alkali present in it.
Question 13.
Plaster of Paris should be stored in a moisture-proof container. Explain why ?
Answer:
Plaster of Paris changes into a hard solid mass on mixing with water. This solid mass is of gypsum
Due to this reason, Plaster of Paris is always stored in a moisture – proof container.
Question 14.
What is a neutralisation reaction ? Give two examples.
Answer:
The reaction in which a base reacts with an acid is called neutralisation reaction.Examples : NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
HCl(aq) + NHOH(aq) → NH4Cl(aq) + H2O (l)
Question 15.
Give two important uses of washing soda and baking soda.
Answer:
Uses of washing soda:
It is used in glass, soap and paper industries.
It is used in the manufacture of sodium compounds.
It is used as a cleaning agent for domestic purposes.
It is used for removing permanent hardness of water.
Uses of Baking soda:
It is used in soda – acid fire extinguishers.
It is used as an ingredient in antacids, as it neutralises excess acid in the stomach
