F4Chem acid&base 40pts!!!

1)
10.0 g of a sample of zinc carbonate powder were contaminated with zinc oxide. Excess dilute hydrochloric acid was added to the sample. After effervescence stopped, there was a total loss of 3.2g of the reaction mixture.
*Write equation(s) for the reaction(s) that caused effervescence.
*Calculate the percentage by mass of zinc carbonate in the sample.

ZnCO3(s) + 2HCl(aq) → ZnCl2(aq) + H2O + CO2(g)
(The reaction between ZnO and HCl gives no effervescence.)

Mole ratio ZnCO3 : CO2 = 1 : 1
Mass of CO2 formed = Loss of mass = 3.2 g
Molar mass of CO2¬ = 12 + 16x2 = 44 g/mol
No. of moles of CO2 formed = 3.2/44 mol
No. of moles of ZnCO3 in the sample = 3.2/44 mol
Molar mass of ZnCO3 = 65.4 + 12 + 16x3 = 125.4 g/mol
Mass of ZnCO3 in the sample = (3.2/44) x 125.4 = 9.12 g
% by mass of ZnCO3 in the sample = (9.12/10) x 100% = 91.2% …… (answer)


2) ascorbic : m.p. = 192 oC
*Explain the fact that the b.p. of the ascorbic acid cannot be determined.

This is because ascorbic acid is heated to decompose at a temperature lower than its melting point.


3) Harpic is a common toilet cleaner.
It's a powder with sodium hydrogensulphate (NaHSO4) as the active ingredient.
*When NaHSO4 is dissolved in water, the solution has a pH of 0-1.
Write equation for the reaction which causes the low pH of the solution.

NaHSO4(s) + aq → Na⁺(aq) + H⁺(aq) + SO¬₄²⁻(aq)


4)
Calcium carbonates were present in eggshell.
Experiment : Heating eggshell
Results: A colourless gas was formed which turned limewater milky.
* With the help of an equation, explain the formation of the colourless gas in the experiment.

Colourless gas of carbon dioxide is formed in the reaction of heating calcium carbonate.
CaCO3(s) → CaO(s) + CO2(g)