Section A: Identify 'X', 'Y', 'Z' Puzzles
Solve these identification problems:
- A white powder X is used for baking cakes to make them soft and spongy. It is also
an ingredient in antacids.
(a) Name X.
(b) Write the chemical formula of X.
(c) Write the reaction that takes place when it is heated during cooking.
- A compound X of sodium forms a white powder. It is a constituent of baking powder
and is used in soda-acid fire extinguishers. When heated, it gives a compound Y
which is used for removing permanent hardness of water. Identify X and
Y.
- A white powder A is a mild non-corrosive base. When mixed with water, it is used as
an antacid. On heating A, it produces a compound B, water vapor
and a gas C. The gas C turns lime water milky. Identify
A, B and C.
- A student dropped few pieces of marble in dilute Hydrochloric acid contained in a test tube. The
evolved gas was passed through lime water.
(a) What change would be observed in lime water?
(b) Write balanced chemical equation for both the changes.
- A sulphate salt of Group 2 element 'M' is a white soft substance, which can be moulded into
different shapes by making its dough with water. When this compound is left in open for some time,
it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why
does it behave so? Write the reaction.
- A compound X is prepared from Gypsum ($CaSO_4 \cdot 2H_2O$). It has a property of
hardening when mixed with proper quantity of water.
(a) Identify X.
(b) Write the chemical equation for its preparation.
Section B: Short Answer Competency
- 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:
(a) Neutral?
(b) Strongly Alkaline?
(c) Strongly Acidic?
(d) Weakly Acidic?
(e) Weakly Alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
- Explain why an aqueous solution of sodium chloride is neutral but an aqueous solution of sodium
carbonate is basic?
- (a) What happens when copper oxide reacts with Hydrochloric acid? Write the equation.
(b) What is the colour change observed?
(c) What does this tell us about the nature of metallic oxides?
- Write the name and formula of 'Plaster of Paris'. How is it prepared? Write the chemical equation.
Why should it be stored in a moisture-proof container?
- What is 'Water of Crystallisation'? Name and write the formula of two salts which contain water of
crystallisation. (Hint: Blue Vitriol, Washing Soda).
Section C: Diagram & Application Based
- Chlor-Alkali Process: Brine is electrolyzed.
(a) Name the gas evolved at Anode. Mention one use.
(b) Name the gas evolved at Cathode. Mention one use.
(c) Name the product formed near the cathode.
- A student adds a few drops of universal indicator to a solution of dilute HCl. What will be the
color change? If he adds NaOH drop by drop to this mixture, how will the color change proceed?
- (a) Why does acidic solution conduct electricity?
(b) Can dry HCl gas turn blue litmus red? Why?
- Fresh milk has a pH of 6. When it turns into curd, will its pH increase or decrease? Why?
- How is the concentration of hydronium ions ($H_3O^+$) affected when a solution of an acid is
diluted?
- How is the concentration of hydroxide ions ($OH^-$) affected when excess base is dissolved in a
solution of sodium hydroxide?
