Question

A quantitative definition of solubility is the number of grams of a solute that will dissolve in a given volume of water at a particular temperature. Describe an experiment that would enable you to determine the solubility of a soluble compound.

Short answer

Dissolve solute in water at a set temperature, filter excess, and calculate dissolved amount.

Step-by-step solution

Gather Materials

To conduct the experiment, you'll need the soluble compound, a balance, water, a beaker, a stirring rod, a thermometer, and a hot plate to maintain the temperature.

Prepare a Saturated Solution

Add a known volume of water to the beaker and heat it to the desired temperature using the hot plate. Gradually add the soluble compound while stirring until no more can dissolve, indicating a saturated solution.

Measure the Undissolved Solute

Allow the solution to cool if necessary (or maintain it at the target temperature), then filter the solution to separate any undissolved solute. Dry and weigh the undissolved solute to determine how much excess was added.

Calculate Solubility

Subtract the mass of the undissolved solute from the total solute added to find how much dissolved in the given volume of water. Divide this mass by the volume of water to obtain the solubility, expressed in grams per 100 mL.

Key concepts

Quantitative Definition of Solubility

Solubility is a term that describes how much of a solute (like salt or sugar) can dissolve in a solvent (usually water). To quantitatively define solubility, we use the measurement of how many grams of a solute can dissolve in 100 mL of water at a specified temperature. This definition is crucial for experiments as it provides a clear framework to determine and compare the solubilities of various substances under different conditions. When planning an experiment on solubility, it is important to consider both the amount of solute and the exact volume of solvent used, as these factors are instrumental in accurately calculating solubility.

Saturated Solution

A saturated solution occurs when no more solute can dissolve in the solvent at a given temperature. As you conduct a solubility experiment, you will aim to reach this point. When you see the solute stop dissolving, any additional solute remains undissolved, settling at the bottom of the container. This visual cue indicates that the maximum solubility at that temperature has been reached. It is crucial to reach saturation to correctly assess the solute's solubility, as continuing beyond this point can lead to inaccurate measurements.

Experimental Procedure

Conducting a solubility experiment involves a structured process to ensure accurate results. Begin by gathering the necessary materials like the solute, water, a beaker, and precision measurement tools. Heat the water to the chosen temperature using a hot plate, ensuring even temperature distribution for consistency. Gradually add the solute while stirring, which helps it dissolve properly. Once you've added enough and no more can dissolve, you've achieved a saturated solution. Carefully handle instruments and always measure accurately to maintain the integrity of your experiment.

Solute Measurement

In solubility experiments, measuring the solute accurately is key. Initially, precisely weigh the solute using a balance before adding it to the water. During the experiment, determine how much solute actually dissolved by subtracting the mass of any undissolved solute from the initial mass of the solute added. This step is critical for calculating solubility, as you need to know how much solute is in the solution rather than added to it. Always dry any undissolved solute thoroughly before weighing to avoid errors from extra moisture.

Temperature Control in Experiments

Temperature plays a significant role in solubility experiments as it affects the dissolving ability of solutes. Different temperatures can significantly change the solubility of a substance, making careful temperature control vital. Use a thermometer to monitor the temperature continually, ensuring it remains consistent throughout the experiment. If the temperature fluctuates, it can lead to inaccurate solubility results, potentially causing solutes to dissolve more or less than they would under constant conditions. Using a hot plate can help maintain the desired temperature, providing stability for the experiment's duration.