Section A: High Order Thinking Skills (HOTS)
- A metal compound 'X' reacts with dilute hydrochloric acid to produce effervescence. The gas evolved
extinguishes a burning candle.
(a) Identify the gas evolved.
(b) If one of the compounds formed is calcium chloride, write a balanced chemical equation for
the reaction.
(c) What is the nature of 'X'? (Acidic/Basic)
- (a) What is the chemical name of Bleaching Powder?
(b) Why does bleaching powder smell strongly of chlorine?
(c) What happens when bleaching powder is exposed to air for a long time? Write the equation.
- Salt Families: Classify the following salts as Acidic, Basic or Neutral:
(a) Sodium chloride ($NaCl$)
(b) Ammonium chloride ($NH_4Cl$)
(c) Sodium carbonate ($Na_2CO_3$)
Hint: Think about the strength of parent Acid and Base.
- Equal lengths of magnesium ribbon are taken in test tubes A and B. Hydrochloric acid (HCl) is added
to test tube A, while Acetic acid ($CH_3COOH$) is added to test tube B. In which test tube will the
fizzing occur more vigorously and why?
- A gas X goes out with a pop sound when a burning candle is brought near it. Another gas Y turns lime
water milky.
(a) Identify X and Y.
(b) What happens when we pass gas X over heated copper oxide?
Section B: Case Based Competency Questions
Case I: pH in Digestive System
Our stomach produces hydrochloric acid which helps in the digestion of food without harming the stomach.
During indigestion the stomach produces too much acid and this causes pain and irritation. To get relief
from this pain, people use bases called antacids.
- What is the approximate pH of the acid produced in our stomach?
- Name a common mild base used as an antacid.
- How does the antacid work? Write the type of reaction involved.
- Can we use Sodium Hydroxide (NaOH) as an antacid? Why or why not?
Case II: Tooth Decay. Tooth enamel, made of Calcium phosphate is the hardest substance
in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5.
- What is the chemical formula of tooth enamel? ($Ca_3(PO_4)_2$ or Hydroxyapatite).
- How do bacteria present in the mouth produce acid?
- Why is using toothpaste recommended to prevent tooth decay?
- If a toothpaste has pH 8.0, is it suitable? Why?
Section C: Miscellaneous & Olympiad Level
- Blue vitriol is heated in a test tube.
(a) What visual change is observed?
(b) Is this a physical or chemical change?
(c) On adding water to the residue, what happens?
- Assertion (A): Sodium Carbonate is a basic salt.
Reason (R): It is a salt of a strong base (NaOH) and a weak acid ($H_2CO_3$).
Comment on the validity.
- Explain why copper sulphate crystals which seem to be dry contain water of crystallisation.
- Give two strong acids and two weak acids from the following list: Hydrochloric acid, citric acid,
acetic acid, nitric acid, formic acid, sulphuric acid.
- While eating food, you spill some curry on your white shirt. You immediately scrub it with soap.
What happens to its yellow colour? Why? What happens when you wash it with plenty of water?
- How is the concentration of Hydroxide ions ($OH^-$) affected when excess base is dissolved in a
solution of Sodium Hydroxide?
- Write the equations involved in the preparation of Sodium Carbonate from Sodium Chloride. (Solvay
Process steps - Advanced).
1. $NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$
2. $2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2$
