6: Solubility Product
- Page ID
- 516591
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PURPOSE
- To prepare a saturated solution of calcium iodate.
- To determine the concentration of a saturated solution of calcium iodate using a redox titration.
- To determine the solubility product for calcium iodate and compare it to the known value.
INTRODUCTION
In chemistry, the solubility of a compound refers to the maximum amount of solute that can dissolve in a given solvent at equilibrium, forming a saturated solution. For slightly soluble ionic compounds, this equilibrium is described by the solubility product constant (\( K_{\text{sp}} \)), a fundamental equilibrium constant that quantifies the extent to which a solid dissolves in solution.
For calcium iodate, \( \text {Ca}(\text {IO}_3)_2 \), the equilibrium in a saturated solution is represented as:
\[
\text {Ca}(\text {IO}_3)_2 (s) \rightleftharpoons \text {Ca}^{2+} (aq) + 2\, \text {IO}_3^- (aq)
\]
The solubility product expression is given by:
\[
K_{\text{sp}} = [\text{Ca}^{2+}][\text{IO}_3^-]^2
\]
where \( [\text{Ca}^{2+}] \) and \( [ \text{IO}_3^-] \) are the molar concentrations of the dissociated ions in equilibrium.
To determine the solubility of calcium iodate experimentally, we need to measure the concentration of iodate ions in a saturated solution. This is achieved through a redox titration using a standardized sodium thiosulfate (\( \text{Na}_2 \text{S}_2 \text{O}_3 \)) solution in the presence of potassium iodide (KI) and starch indicator.
The reaction between iodate ions and potassium iodide in acidic solution generates molecular iodine:
\[
\text{IO}_3^- + 5\,\text{I}^- + 6\,\text{H}^+ \rightarrow 3\,\text{I}_2 + 3\,\text{H}_2\text{O}
\]
The molecular iodine (\( \text{I}_2 \)) is then titrated with sodium thiosulfate, which reduces it back to iodide:
\[
\text{I}_2 + 2\,\text{S}_2\text{O}_3^{2-} \rightarrow 2\,\text{I}^- + \text{S}_4\text{O}_6^{2-}
\]
where \( \text{S}_4\text{O}_6^{2-} \) is the tetrathionate ion.
Since the amount of thiosulfate used directly correlates with the amount of iodate originally present in solution, this titration allows us to calculate the molarity of iodate ions, determine the solubility of calcium iodate, and compute its solubility product constant (\( K_{\text{sp}} \)).
Additionally, this experiment explores the concept that the solubility of a slightly soluble salt is independent of the volume of water used to dissolve it, meaning that different volumes of solvent should yield the same solubility value when equilibrium is reached.
- 6.1: Solubility Product - Experiment
- This page provides safety precautions for hydrochloric acid and chemical waste disposal in a lab setting. It details required equipment and chemicals for preparing saturated solutions of calcium iodate. The experimental procedure is divided into two parts: Part A describes the preparation and filtration of the solutions, while Part B outlines the titration analysis process, including reagent addition and measurement recording.
- 6.2: Solubility Product - Pre-lab
- This page covers the titration process, focusing on the importance of potassium iodide and hydrochloric acid for accuracy. It explains the use of starch as an indicator for identifying the endpoint through color changes. The page also emphasizes the need for dry filter paper and a funnel when filtering saturated solutions, noting that wet filter paper can negatively impact the clarity and concentration of the results.
- 6.3: Solubility Product - Data and Report
- This page outlines a titration experiment using sodium thiosulfate and iodate ions, featuring data collection tables for titration volumes and calculations of moles and molarity. It also addresses the solubility of calcium iodate and its Ksp. Post-lab questions prompt students to conduct calculations, evaluate precision and accuracy, compare findings to standard values, and reflect on possible experimental errors.