Equilibria

Complete the expression for $K_{\text{sp}}$ of $\text{Cr(OH)}_3$. Include the units.

Calculate the solubility, in $\text{g dm}^{-3}$, of $\text{Cr(OH)}_3$ in pure water at 298 K.

Show your working.

$\text{Cr(OH)}_3$ is less soluble in $0.100 \text{ mol dm}^{-3} \text{ NaOH}$ than it is in pure water.

Explain this observation.

Calculate the pH of $0.100 \text{ mol dm}^{-3} \text{ CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ at 298 K.

Show your working.

Calculate the pH of $0.100 \text{ mol dm}^{-3} \text{ NaOH}$ at 298 K.

$5.00 \text{ cm}^3$ of $0.100 \text{ mol dm}^{-3} \text{ NaOH}$ is added to $10.00 \text{ cm}^3$ of $0.100 \text{ mol dm}^{-3} \text{ CH}_3\text{CH}_2\text{CH}_2\text{COOH}$.

Calculate the pH of the resulting solution.

Show your working.

$80.0 \text{ cm}^3$ of an aqueous solution containing $0.704 \text{ g}$ of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ is shaken with $100 \text{ cm}^3$ of benzene, $\text{C}_6\text{H}_6$.

There is $0.556 \text{ g}$ of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ in the $100 \text{ cm}^3$ of $\text{C}_6\text{H}_6$ at equilibrium.

Calculate the partition coefficient, $K_{\text{pc}}$, of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ between $\text{C}_6\text{H}_6$ and water.

Show your working.

Complete the expression for $K_{\text{sp}}$ of $\text{Cr(OH)}_3$. Include the units.

units = ..............................

Calculate the solubility, in $\text{g dm}^{-3}$, of $\text{Cr(OH)}_3$ in pure water at 298 K.

Show your working.

solubility = .............................. $\text{g dm}^{-3}$

$\text{Cr(OH)}_3$ is less soluble in $0.100\text{ mol dm}^{-3}$ $\text{NaOH}$ than it is in pure water.

Explain this observation.

Calculate the pH of $0.100\text{ mol dm}^{-3}$ $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ at 298 K.

Show your working.

pH = ..............................

Calculate the pH of $0.100\text{ mol dm}^{-3}$ $\text{NaOH}$ at 298 K.

pH = ..............................

$5.00\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ $\text{NaOH}$ is added to $10.00\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$.

Calculate the pH of the resulting solution.

Show your working.

pH = ..............................

$80.0\text{ cm}^3$ of an aqueous solution containing 0.704 g of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ is shaken with $100\text{ cm}^3$ of benzene, $\text{C}_6\text{H}_6$.

There is 0.556 g of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ in the $100\text{ cm}^3$ of $\text{C}_6\text{H}_6$ at equilibrium.

Calculate the partition coefficient, $K_{\text{pc}}$, of $\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$ between $\text{C}_6\text{H}_6$ and water.

Show your working.

$K_{\text{pc}}$ = ..............................

Define buffer solution.

dilute aqueous sodium hydroxide

dilute aqueous nitric acid.

Calculate the $\text{H}^+$ concentration and the $\text{C}_6\text{H}_5\text{COOH}$ concentration in the buffer solution described. Use the expression for the $K_a$ of $\text{C}_6\text{H}_5\text{COOH}$ to calculate the concentration of $\text{C}_6\text{H}_5\text{COO}^-\text{Na}^+$ in the buffer solution.

Show your working and give each answer to a minimum of three significant figures.

A $10.0\text{ cm}^3$ sample of the buffer solution is mixed with $10.0\text{ cm}^3$ of $1.00\text{ mol}\text{ dm}^{-3}\text{ KOH}$. Both solutions are at $298\text{ K}$. A reaction is allowed to occur without stirring.

Two observations are recorded:

• the temperature, after the reaction is complete, is fractionally above $298\text{ K}$
• the $\text{pH}$, after the reaction, is greater than 13.

Explain these two observations.

Calculate the solubility of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ in water at $298\text{ K}$. Give your answer in $\text{g}\text{ dm}^{-3}$.

Show your working.

[$M_r$: $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$, 266.3]

An excess of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ is added to a sample of $0.50\text{ mol}\text{ dm}^{-3}\text{ MgSO}_4$ at $298\text{ K}$.

State whether the equilibrium concentration of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ is higher than, the same as, or lower than your answer to (i). Explain your answer.

The concentration is ..................................................................... the concentration in (i).

explanation ........................................................................................................................

Define $K_w$ mathematically by completing the expression.

Calculate the concentration of $\text{HCl}$ in V.

Equal volumes of the two solutions V and W are mixed, giving solution X.

Name solution X and state its pH.

solution X .............................. pH ..............................

A $1\,\text{cm}^3$ sample of $1.0\,\text{mol}\,\text{dm}^{-3}\,\text{HNO}_3$ is added to $100\,\text{cm}^3$ of solution X, forming mixture Y.

A $1\,\text{cm}^3$ sample of $1.0\,\text{mol}\,\text{dm}^{-3}\,\text{KOH}$ 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 .............................. mixture Z ..............................

$\text{CH}_3\text{CH}_2\text{COOH}$, $\text{CH}_3\text{CCl}_2\text{COOH}$ and $\text{H}_2\text{SO}_4$ are all acidic.

Suggest the trend in the relative acid strength of these three compounds.

Explain your answer.

....................................... ....................................... .......................................
strongest acid                   weakest acid

explanation ........................................................................................................................

When concentrated $\text{H}_2\text{SO}_4$ is added to water a series of acid-base reactions occurs.

There are three conjugate acid-base pairs that can be identified during this series of reactions.

Write the formulae of these three conjugate acid-base pairs.

conjugate acid 1 ......................................... conjugate base 1 .........................................

conjugate acid 2 ......................................... conjugate base 2 .........................................

conjugate acid 3 ......................................... conjugate base 3 .........................................

Define partition coefficient, $K_{\text{pc}}$.

$5.00\,\text{g}$ of Q is shaken with a mixture of $100.0\,\text{cm}^3$ of water and $100.0\,\text{cm}^3$ of hexane at $298\,\text{K}$ and left until there is no further change in concentrations.

Calculate the mass of Q dissolved in the water.

A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations.

It is found that the mass of Q dissolved in each solvent is the same.

Use the $K_{\text{pc}}$ value to suggest possible values for the volume of water used and the volume of hexane used.

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.

State what is meant by partition coefficient.

The partition coefficient, $K_{\text{pc}}$, for butanoic acid between ethoxyethane and water is 3.50.

A solution of $2.00\ \text{g}$ of butanoic acid in $100\ \text{cm}^3$ ethoxyethane is added to water. This mixture is left until there is no further change in the concentration of butanoic acid in either solvent. The mass of butanoic acid dissolved in the ethoxyethane layer is now $1.62\ \text{g}$.

Calculate the volume of water used.

Define buffer solution.

Suggest one organic compound, and one inorganic compound, that can be added to two different samples of aqueous butanoic acid to produce buffer solutions.

organic compound:

inorganic compound:

Give the expression for the solubility product, $K_{\text{sp}}$, of aluminium hydroxide.

Calculate the numerical value of the $K_{\text{sp}}$ of aluminium hydroxide. Include the units of $K_{\text{sp}}$ in your answer.

Calculate the solubility of $\text{Fe}(\text{OH})_3$ in water.

$\text{solubility} = \text{.............................. } \text{mol dm}^{-3}$

Calculate the solubility of $\text{Fe}(\text{OH})_3$ in $0.010 \text{ mol dm}^{-3}$ barium hydroxide, $\text{Ba}(\text{OH})_2(\text{aq})$.

$\text{solubility} = \text{.............................. } \text{mol dm}^{-3}$

$\text{Fe}(\text{OH})_3$ is less soluble in $\text{Ba}(\text{OH})_2(\text{aq})$ than it is in pure water.

Name this effect.

Define conjugate acid-base pair.

Identify the two conjugate acid-base pairs shown in the equation above.

$\begin{aligned} &\text{pair one: } \text{.............................. (acid)} \quad \text{.............................. (base)} \\ &\text{pair two: } \text{.............................. (acid)} \quad \text{.............................. (base)} \end{aligned}$

Calculate the pH of solution $\mathbf{X}$. Show all your working.

$\text{pH} = \text{..............................}$

A solution containing $2.00 \times 10^{-3} \text{ mol}$ of $\text{NaOH}$ is added to solution $\mathbf{X}$. A buffer solution is formed.

Calculate the pH of this buffer solution.

$\text{pH} = \text{..............................}$

State what is meant by partition coefficient.

The partition coefficient, $K_{\text{pc}}$, for butanoic acid between ethoxyethane and water is $3.50$.

A solution of $2.00\,\text{g}$ of butanoic acid in $100\,\text{cm}^3$ ethoxyethane is added to water. This mixture is left until there is no further change in the concentration of butanoic acid in either solvent. The mass of butanoic acid dissolved in the ethoxyethane layer is now $1.62\,\text{g}$.

Calculate the volume of water used.

Define buffer solution.

Suggest one organic compound, and one inorganic compound, that can be added to two different samples of aqueous butanoic acid to produce buffer solutions.

organic compound ..............................................................................................................

inorganic compound ...........................................................................................................

Give the expression for the solubility product, $K_{\text{sp}}$, of aluminium hydroxide.

Calculate the numerical value of the $K_{\text{sp}}$ of aluminium hydroxide. Include the units of $K_{\text{sp}}$ in your answer.

Write an expression for the $K_a$ of $\text{Cl(CH}_2)_3\text{CO}_2\text{H(aq)}$.

Write a mathematical expression to describe the relationship between $K_a$ and $\text{p}K_a$.

Calculate $[\text{H}^+]$ in solutions Y and Z.

Calculate the ratio $\frac{[\text{HCl}]\text{ dissolved in solution Y}}{[\text{Cl(CH}_2)_3\text{CO}_2\text{H}]\text{ dissolved in solution Z}}$.

A buffer solution of pH 5.00 is produced by adding sodium propanoate to $5.00\text{ g}$ of propanoic acid in $100\text{ cm}^3$ of distilled water.

Calculate the mass of sodium propanoate that must be used to produce this buffer solution.
The $K_a$ of propanoic acid is $1.35 \times 10^{-5}\text{ mol dm}^{-3}$.

[$M_r$: propanoic acid, 74.0; sodium propanoate, 96.0]

Some dilute sulfuric acid is mixed with a small sample of the buffer solution described in (b).
The final pH of the mixture is close to 1.

Explain this observation.

In an experiment, octan-1-ol at $20\,^{\circ}\text{C}$ is added to a solution of ethoxyethane in water at $20\,^{\circ}\text{C}$. The mixture is analysed immediately and a value of $K_{\text{pc}}$ is calculated.

The calculation is performed correctly; the value calculated is 5.625.

Explain why the value calculated is less than 6.760.

Calculate the concentration, in $\text{g dm}^{-3}$, of ethoxyethane in the aqueous layer.

$100\text{ cm}^3$ of the octan-1-ol layer is taken and shaken with $100\text{ cm}^3$ of water.

Calculate the maximum amount, in mol, of ethoxyethane that can be extracted into the water.

Use these data to calculate a value for the solubility product, $K_{\text{sp}}$, of lead(II) iodide.

State the units of $K_{\text{sp}}$.

Potassium iodide is very soluble in water.

Describe and explain what is seen if a few drops of saturated potassium iodide solution are added to a portion of solution X.

Write an expression for the $K_a$ of $\text{Cl(CH}_2\text{)}_3\text{CO}_2\text{H(aq)}$.

Write a mathematical expression to describe the relationship between $K_a$ and $\text{p}K_a$.

Calculate $[\text{H}^+]$ in solutions Y and Z.

Calculate the ratio

A buffer solution of pH 5.00 is produced by adding sodium propanoate to $5.00\text{ g}$ of propanoic acid in $100\text{ cm}^3$ of distilled water.

Calculate the mass of sodium propanoate that must be used to produce this buffer solution.
The $K_a$ of propanoic acid is $1.35 \times 10^{-5}\text{ mol dm}^{-3}$.

[$M_r$: propanoic acid, 74.0; sodium propanoate, 96.0]

Some dilute sulfuric acid is mixed with a small sample of the buffer solution described in (b). The final pH of the mixture is close to 1.

Explain this observation.