2020 Oct Nov Paper 12 Q5
A white powder is known to be a mixture of magnesium oxide and aluminium oxide.
100 cm3 of 2 mol dm-3 NaOH (aq) is just enough to dissolve the aluminium oxide in \(x\) grams of the mixture.
The reaction is shown.
\[
Al _{2} O _{3}+2 OH ^{-}+3 H _{2} O \rightarrow 2 Al ( OH )_{4}^{-}
\]
800 cm3 of 2 mol dm-3 HCl (aq) is just enough to dissolve all of the oxide in \(x\) grams of the mixture.
The reactions are shown.
\[
\begin{aligned}
Al _{2} O _{3}+6 H ^{+} & \rightarrow 2 Al ^{3+}+3 H _{2} O \\
MgO +2 H ^{+} & \rightarrow Mg ^{2+}+ H _{2} O
\end{aligned}
\]
How many moles of each oxide are present in \(x\) grams of the mixture?
2009 May June Paper 11 Q2
A household bleach contains sodium chlorate(I), \(NaClO\), as its active ingredient. The concentration of \(NaClO\) in the bleach can be determined by reacting a known amount with aqueous hydrogen peroxide, \(H _{2} O _{2}\).
\[
NaClO ( aq )+ H _{2} O _{2}( aq ) \rightarrow NaCl ( aq )+ O _{2}( g )+ H _{2} O ( I )
\]
When \(25.0 cm ^{3}\) of bleach is treated with an excess of aqueous \(H _{2} O _{2}, 0.0350 mol\) of oxygen gas is given off.
What is the concentration of \(NaClO\) in the bleach?