Question

You choose to investigate some of the solubility guidelines for two ions not listed in Table 4.1, the chromate ion \(\left(\mathrm{CrO}_{4}{ }^{2-}\right)\) and the oxalate ion \(\left(\mathrm{C}_{2} \mathrm{O}_{4}{ }^{2-}\right)\). You are given \(0.01 \mathrm{M}\) solutions (A, B, C, D) of four water-soluble salts: $$ \begin{array}{lll} \hline \text { Solution } & \text { Solute } & \text { Color of Solution } \\ \hline \mathrm{A} & \mathrm{Na}_{2} \mathrm{CrO}_{4} & \text { Yellow } \\ \mathrm{B} & \left(\mathrm{NH}_{4}\right)_{2} \mathrm{C}_{2} \mathrm{O}_{4} & \text { Colorless } \\ \mathrm{C} & \mathrm{AgNO}_{3} & \text { Colorless } \\ \mathrm{D} & \mathrm{CaCl}_{2} & \text { Colorless } \\ \hline \end{array} $$ When these solutions are mixed, the following observations are made: $$ \begin{array}{lll} \hline \text { Expt } & \text { Solutions } & \\ \text { Number } & \text { Mixed } & \text { Result } \\ \hline 1 & \mathrm{~A}+\mathrm{B} & \text { No precipitate, yellow solution } \\\ 2 & \mathrm{~A}+\mathrm{C} & \text { Red precipitate forms } \\ 3 & \mathrm{~A}+\mathrm{D} & \text { No precipitate, yellow solution } \\ 4 & \mathrm{~B}+\mathrm{C} & \text { White precipitate forms } \\ 5 & \mathrm{~B}+\mathrm{D} & \text { White precipitate forms } \\ 6 & \mathrm{C}+\mathrm{D} & \text { White precipitate forms } \\ \hline \end{array} $$ (a) Write a net ionic equation for the reaction that occurs in each of the experiments. (b) Identify the precipitate formed, if any, in each of the experiments. (c) Based on these limited observations, which ion tends to form the more soluble salts, chromate or oxalate?

Short answer

The net ionic equations for the reactions that produce precipitates are: - Expt 2: $$\mathrm{CrO}_4^{2-} + 2\mathrm{Ag}^+ \rightarrow \mathrm{Ag}_2\mathrm{CrO}_4$$ - Expt 4: $$\mathrm{C}_2 \mathrm{O}_4^{2-} + 2\mathrm{Ag}^+ \rightarrow 2\mathrm{Ag}\mathrm{C}_2\mathrm{O}_4$$ - Expt 5: $$\mathrm{C}_2 \mathrm{O}_4^{2-} + \mathrm{Ca}^{2+} \rightarrow \mathrm{Ca}\mathrm{C}_2\mathrm{O}_4$$ - Expt 6: $$2\mathrm{Cl}^- + \mathrm{Ag}^+ \rightarrow \mathrm{AgCl}$$ The identified precipitates are: - Expt 2: Red precipitate of \(\mathrm{Ag}_2\mathrm{CrO}_4\) - Expt 4: White precipitate of \(\mathrm{Ag}\mathrm{C}_2\mathrm{O}_4\) - Expt 5: White precipitate of \(\mathrm{Ca}\mathrm{C}_2\mathrm{O}_4\) - Expt 6: White precipitate of \(\mathrm{AgCl}\) and \(\mathrm{CaCl}_2\) From these observations, chromate ions tend to form more soluble salts compared to oxalate ions, based on the limited data.

Step-by-step solution

Identify possible reactions

We have six experiments mixing two solutions each. For each experiment, we should identify the possible reactions that might occur, then check which ones produce precipitates by referring to the solubility rules and observations.

Write net ionic equations for the reactions

For each experiment, write the net ionic equation for the possible reactions that produce precipitates. The net ionic equation focuses on the ions that react and produce the precipitate.

Identify the precipitates formed

Based on the net ionic equations and the provided observations, identify the precipitates formed in each experiment.

Compare chromate and oxalate ions' solubility

Determine whether chromate or oxalate ions tend to form more soluble salts by comparing their reactions and precipitates formed.

Identify possible reactions

For each experiment, we will list the possible reactions that might occur: - Expt 1: A + B, \(\mathrm{Na}_2 \mathrm{CrO}_4\) and \((\mathrm{NH}_4)_2 \mathrm{C}_2 \mathrm{O}_4\) - Expt 2: A + C, \(\mathrm{Na}_2 \mathrm{CrO}_4\) and \(\mathrm{AgNO}_3\) - Expt 3: A + D, \(\mathrm{Na}_2 \mathrm{CrO}_4\) and \(\mathrm{CaCl}_2\) - Expt 4: B + C, \((\mathrm{NH}_4)_2 \mathrm{C}_2 \mathrm{O}_4\) and \(\mathrm{AgNO}_3\) - Expt 5: B + D, \((\mathrm{NH}_4)_2 \mathrm{C}_2 \mathrm{O}_4\) and \(\mathrm{CaCl}_2\) - Expt 6: C + D, \(\mathrm{AgNO}_3\) and \(\mathrm{CaCl}_2\)

Write net ionic equations for the reactions

- Expt 1: No precipitate is formed, so no net ionic equation is needed. - Expt 2: $$\mathrm{CrO}_4^{2-} + 2\mathrm{Ag}^+ \rightarrow \mathrm{Ag}_2\mathrm{CrO}_4$$ - Expt 3: No precipitate is formed, so no net ionic equation is needed. - Expt 4: $$\mathrm{C}_2 \mathrm{O}_4^{2-} + 2\mathrm{Ag}^+ \rightarrow 2\mathrm{Ag}\mathrm{C}_2\mathrm{O}_4$$ - Expt 5: $$\mathrm{C}_2 \mathrm{O}_4^{2-} + \mathrm{Ca}^{2+} \rightarrow \mathrm{Ca}\mathrm{C}_2\mathrm{O}_4$$ - Expt 6: $$2\mathrm{Cl}^- + \mathrm{Ag}^+ \rightarrow \mathrm{AgCl}$$ and $$2\mathrm{Cl}^- + \mathrm{Ca}^{2+} \rightarrow \mathrm{CaCl}_2$$

Identify the precipitates formed

Based on the net ionic equations and the observations, the precipitates formed are: - Expt 1: None - Expt 2: Red precipitate of \(\mathrm{Ag}_2\mathrm{CrO}_4\) - Expt 3: None - Expt 4: White precipitate of \(\mathrm{Ag}\mathrm{C}_2\mathrm{O}_4\) - Expt 5: White precipitate of \(\mathrm{Ca}\mathrm{C}_2\mathrm{O}_4\) - Expt 6: White precipitate of \(\mathrm{AgCl}\) and \(\mathrm{CaCl}_2\)

Compare chromate and oxalate ions' solubility

Based on the above experiments, we can see that the chromate ion forms a precipitate only when mixed with \(\mathrm{Ag^+}\) ions (Expt 2), while oxalate ion forms precipitates when mixed with both \(\mathrm{Ag^+}\) and \(\mathrm{Ca^{2+}}\) ions (Expt 4 and 5). As a general trend, it seems that chromate ions might form more soluble salts compared to oxalate ions, based on these limited observations.