$1 \mathrm{g}$ of a sample containing $\mathrm{NaCl}$, $\mathrm{NaBr}$and an inert material with excess of ${\mathrm{AgNO}}_3$ produces $0.526 \mathrm{g}$ of precipitate of $\mathrm{AgCl}$ and $\mathrm{AgBr}$. By heating this precipitate in a current of chlorine, $\mathrm{AgBr}$ is converted into $\mathrm{AgCl}$ and the precipitate then weighed $0.426 \mathrm{g}$. Find the percentage of $\mathrm{NaCl}$ and $\mathrm{NaBr}$ in the sample.

[Hint: Only $\mathrm{Al}$ produces ${\mathrm{H}}_2$]

One litre of an acidified solution of ${\mathrm{KMnO}}_4$ containing $15.8 \mathrm{g}$ of ${\mathrm{KMnO}}_4$ is decolourised by passing a sufficient amount of ${\mathrm{SO}}_2$. If ${\mathrm{SO}}_2$ is produced by roasting of iron pyrites $\left({\mathrm{FeS}}_2\right)$, what will be the amount of pyrites (in grams) required to produce the necessary amount of ${\mathrm{SO}}_2$?

(Atomic mass of $\mathrm{K}=39, \mathrm{Mn}=55, \mathrm{S}=32, \mathrm{O}=16, \mathrm{Fe}=56, \mathrm{H}=1$)

Round off your answer to the nearest integer.

When a mixture of $\mathrm{NaBr}$ and $\mathrm{NaCl}$ is repeatedly digested with sulphuric acid, all the halogens are expelled and ${\mathrm{Na}}_2{\mathrm{SO}}_4$ is formed quantitatively. With a particular mixture, it was found that the weight of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ obtained was precisely the same as the weight of $\mathrm{NaBr}-\mathrm{NaCl}$ mixture taken. Calculate the ratio of the weights of $\mathrm{NaCl}$ and $\mathrm{NaBr}$ in the mixture.

Give the final answer up to two places of decimal.

An alloy of aluminium and copper was treated with aqueous $\mathrm{HCl}$. The aluminium dissolved according to the reaction $\mathrm{Al}+3{\mathrm{H}}^{+}\to {\mathrm{Al}}^{3+}+\frac{3}{2}{\mathrm{H}}_2$, but the copper remained as a pure metal. A $0.350 \mathrm{g}$ sample of the alloy gave $415 \mathrm{cc}$ of ${\mathrm{H}}_2$ measured at $273 \mathrm{K}$ and $1 \mathrm{atm}$ pressure. What is the weight percentage of $\mathrm{Al}$ in the alloy?

Give the final answer up to first place of decimal after rounding off.

$1 \mathrm{g}$ of dry green algae absorbs $4.7\times {10}^{-3}$ moles of ${\mathrm{CO}}_2$ per hour by photosynthesis. If the fixed carbon atoms were all stored after photosynthesis as starch, ${\left({\mathrm{C}}_6{\mathrm{H}}_{10}{\mathrm{O}}_5\right)}_{\mathrm{n}}$, how long (in hours) would it take for the algae to double their own weight assuming photosynthesis takes place at a constant rate?

Round-off your answer to two places of decimal.

Crude calcium carbide is made in an electric furnace by the following reaction:

$\mathrm{CaO}+3\mathrm{C}\to {\mathrm{CaC}}_2+\mathrm{CO}$

The product contains $85\%$ of ${\mathrm{CaC}}_2$ and $15\%$ of unreacted $\mathrm{CaO}$.

How much $\mathrm{CaO}$ is to be added to the furnace charge for each $1000 \mathrm{kg}$ of ${\mathrm{CaC}}_2$ (pure) produced?