Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

(a)[1]

Write $K_w$ in mathematical form by completing the statement. $K_w =$

(b(i))[2]

Two solutions, V and W, are given. V is $\text{HCl}(aq)$. W is $\text{NaOH}(aq)$. The concentration of HCl in V is the same as the concentration of NaOH in W. At $298\,\text{K}$, the pH values of V and W differ by exactly $11.00$. Calculate the concentration of HCl in V. concentration of HCl in V $=$ $\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots$ $\text{mol dm}^{-3}$

(b(ii))[1]

Equal volumes of solutions V and W are combined to make solution X. Name solution X and give its pH. solution X $\ldots\ldots\ldots\ldots\ldots$ \quad pH $\ldots\ldots\ldots\ldots\ldots$

(b(iii))[1]

A $1\,\text{cm}^3$ sample of $1.0\,\text{mol dm}^{-3}\,\text{HNO}_3$ is added to $100\,\text{cm}^3$ of solution X, forming mixture Y. A $1\,\text{cm}^3$ sample of $1.0\,\text{mol dm}^{-3}\,\text{KOH}$ is added to $100\,\text{cm}^3$ of solution X, forming mixture Z. Estimate the pH of mixtures Y and Z. No calculations are required. mixture Y $\ldots\ldots\ldots\ldots\ldots$ \quad mixture Z $\ldots\ldots\ldots\ldots\ldots$

(c(i))[3]

All three, $\text{CH}_3\text{CH}_2\text{COOH}$, $\text{CH}_3\text{CCl}_2\text{COOH}$ and $\text{H}_2\text{SO}_4$, are acidic. Suggest how their relative acid strengths compare. Explain your answer. strongest acid $\ldots\ldots\ldots\ldots\ldots$ \quad weakest acid $\ldots\ldots\ldots\ldots\ldots$

(b)

Two solutions, $V$ and $W$, are given. • $V$ is $\text{HCl(aq)}$. • $W$ is $\text{NaOH(aq)}$. • The concentration of $\text{HCl}$ in $V$ matches the concentration of $\text{NaOH}$ in $W$. • The pH values of $V$ and $W$ differ by exactly $11.00$ at $298\,\text{K}$.

(c(ii))[2]

When concentrated $\text{H}_2\text{SO}_4$ is added to water, a sequence of acid-base reactions takes place. Three conjugate acid-base pairs can be identified in this sequence. Write the formulae of these three conjugate acid-base pairs. conjugate acid 1 $\ldots$ conjugate base 1 $\ldots$ conjugate acid 2 $\ldots$ conjugate base 2 $\ldots$ conjugate acid 3 $\ldots$ conjugate base 3 $\ldots$

(d(i))[1]

The partition coefficient, $K_{pc}$, of a substance $Q$, between hexane and water is $7.84$ at $298\,\text{K}$. $Q$ is more soluble in hexane than it is in water. Define partition coefficient, $K_{pc}$.

(d(ii))[1]

A sample of $5.00\,\text{g}$ of $Q$ is shaken with $100.0\,\text{cm}^3$ of water and $100.0\,\text{cm}^3$ of hexane at $298\,\text{K}$, then left until the concentrations stop changing. Calculate the mass of $Q$ dissolved in the water. mass of $Q$ = $\ldots\ldots\ldots\ldots$ g

(d(iii))[1]

A sample of $Q$ is shaken with a different water-hexane mixture and left until the concentrations no longer change. It is found that the mass of $Q$ dissolved in each solvent is equal. Use the value of $K_{pc}$ to suggest possible values for the volume of water used and the volume of hexane used. volume of water = $\ldots\ldots\ldots\ldots\ldots$ $\text{cm}^3$ volume of hexane = $\ldots\ldots\ldots\ldots\ldots$ $\text{cm}^3$

(d(iv))[1]

$Q$ is more soluble in hexane than it is in water. It is suggested that $Q$ is one of $\text{KCl}$, $\text{CH}_3(\text{CH}_2)_4\text{OH}$ or $\text{HCOOH}$. Identify $Q$. Explain your answer.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Correct ionic product of water expression: $K_w=[H^+][OH^-]$ or $[H_3O^+][OH^-]$

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI