If combustion of $4 \ g$ of $CH_4$ liberates $2.5 \ kcal$ of heat,the heat of combustion of $CH_4$ is ..... $kcal/mol$.

$P_4O_6$ reacts with water according to the equation $P_4O_6 + 6H_2O \to 4H_3PO_3$. Calculate the volume of $0.1 \ M$ $NaOH$ solution required to neutralize the acid formed by dissolving $1.1 \ g$ of $P_4O_6$ in $H_2O$. (in $mL$)

To neutralize $25 \, mL$ of $0.25 \, M$ $Na_2CO_3$ solution,how much volume of $0.5 \, M$ $HCl$ is required? (Note: The reaction is $Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$)

What is meant by stoichiometry?

Magnetite can be reduced with $CO$ to yield iron metal and carbon dioxide. Calculate the mass of magnetite (in $kg$) needed to obtain $4 \ kg$ of iron if the process is $80 \%$ efficient. [Atomic weight of $Fe$ and $O$ are $56 \ g$ and $16 \ g$, respectively]

$A$ sample of $CaCO_3$ and $MgCO_3$ weighing $2.21 \ g$ is ignited to a constant weight of $1.152 \ g$. The composition of the mixture is:
(Given molar mass in $g \ mol^{-1}: CaCO_3 = 100, MgCO_3 = 84$)