Chapter 2– Acids Bases and Salt Solutions
Question - 21 : - 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 - 21 : -
Answer is HCl.
Egg shells contains calcium carbonate, which on reaction with HCl liberates CO2 gas which turn lime water to milky.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl.
Answer - 22 : -
If we take 20 mL of the same solution of NaOH, the amount 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
Since 10 ml of NaOH requires 8 mL of HCL, 20 ml of NaOH require 8 x 2 = 16mL of HCl Hence the answer id option d 16mL.
Question - 23 : - Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic
Answer - 23 : - Indigestion is due to excess production of acid in the stomach. Medicines used to treat indigestion is called as Antacid
Question - 24 : - Write word equations and then balanced equations for the reaction taking place when
Answer - 24 : -
(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 filings.
Answer
(a) dilute sulphuric acid reacts with zinc granules:
=> dilute sulphuric acid + zinc → Zinc Sulphate + Hydrogen Gas
=> H2SO4(aq) + Zn → ZnSO4(aq) + H2(g)
(b) dilute hydrochloric acid reacts with magnesium ribbon.
=> dilute Hydrochloric + Magnesium → Magnesium Chloride + Hydrogen Gas
=> 2HCl(aq) + Mg → MgCl2(aq) + H2(g)
(c) dilute sulphuric acid reacts with aluminium powder.
=> dilute Sulphuric Acid + Aluminium → Aluminium Sulphate + Hydrogen Gas
=> 3H2SO4(aq) + 2Al(s) → Al2(SO4)3(aq) + 3H2(g)
(d) dilute hydrochloric acid reacts with iron filings.
=> dilute Hydrochloric Acid + Iron → Ferrous Chloride + Hydrogen Gas
=> 6HCl(aq) + 3Fe(s) → 3FeCl2(aq) + 3H2(g)
Answer - 25 : - Insert two nails on the wooden or rubber cork and place them on a beaker as shown in figure. Connect iron nail to a bulb, 6 volt battery and a wire connected to switch. Pour some alcohol or glucose so as to dip the nails in glucose or alcohol. Turn the switch on and you the see the bulb not glowing despite of connection to switch. Now empty the beaker and add HCL solution. This time bulb glows. This proves acid can conduct electricity but alcohol and glucose does not conduct electricity.
Question - 26 : - Why does distilled water not conduct electricity, whereas rain water does?
Answer - 26 : -
• Distilled water does not contain any ionic compounds in it.
• Whereas rainwater has a lot, more compounds.
• Rainwater has dissolved acidic gas such as carbon dioxide from the air and that forms carbonic acid. This means that it has hydrogen ions and carbonate ions. Therefore, with the presence of acids, rainwater can conduct electricity.
Question - 27 : - Why do acids not show acidic behaviour in the absence of water?
Answer - 27 : - The acidic behaviour from acids is because of the presence of hydrogen ions. Hydrogen ions can only be produced in the presence of water and therefore water is definitely needed if acids are to show their acidic behaviour.
Question - 28 : - Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
Answer - 28 : -
(a) neutral?
(b) Strongly alkaline?
(c) Strongly acidic?
(d) Weakly acidic?
(e) Weakly alkaline?
Answer
In increasing order of hydrogen ion concentration:
pH 11(B) -> pH 9(E) -> pH 7(A) -> pH 4(D) -> pH 1 (B)
PH11 – Strongly alkaline
pH9 – weakly alkaline
PH7 – Neutral
pH4 – Weakly acidic
pH1 – Strongly acidic
Question - 29 : - Equal lengths of magnesium ribbons are taken in test tubes A and B.
Answer - 29 : - 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 will the fizzing occur more vigorously and why?
Answer
HCl is a strong acidwhereas acetic is a weaker acid. Fizzing occurs because of the production ofthe hydrogen gas obtained due to reaction of the acid on the magnesium ribbon.Since HCl is a very strong acid there is a lot of liberation of hydrogen gasfrom test tube A. therefore, more fizzing take place in test tube A.
Answer - 30 : - Fresh milk is turned to curd due to production of lactic acid. Lactic acid reduces the pH of the milk.