Chemistry Past Questions and Answers

Elements \(P\) has an atomic number of 12 while element \(Q\) has an atomic number 15. Combination of \(P\) and \(Q\) gave a compound \(P _{m} Q _{n}\). the respective values of \(m\) and \(n\) are ____________

\(C _{4} H _{2}+90_{2} \rightarrow 6 CO _{2}+6 H _{2} O\).<br/>The hydrocarbon, \(C _{x} H _{2}\), in the reaction above is most likely ____________

A \(512 cm ^{3}\) sample of a gas weighed \(1.236 g\) at \(20^{\circ} C\) and a pressure of one atmosphere. The relative molecular mass of the gas is \(\left[R=8.314 K ^{-1} mol ^{-1} ; 1 atm =101,325 Jm ^{-3}\right]\).

The amount of methane molecules, \(CH _{4}\), in \(8.0\) grams of methane is ____________

The concentration of a solution obtained by dissolving \(0.53 g\) of pure anhydrous \(Na _{2} CO _{3}\) in water to make \(250 cm ^{3}\) of solution is ____________