Chem1025C Lab Solubility

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Solubility INTRODUCTION Many materials we encounter every day are mixtures. In a mixture, more than one substance is found together in a system. Mixtures can have different characteristics. For example, a mixture that is uniform throughout is called a homogeneous mixture or solution. Any part of that system would have the same components in the same proportion throughout the entire sample. An example of a homogeneous mixture is sweet tea. The most familiar homogeneous mixture is a liquid solution. In this case, a solute (a liquid or solid) is completely mixed in a solvent (a liquid). Another characteristic of a solution is that even upon standing the solute will not separate from the solvent. Liquids dissolved in liquids may also form homogeneous mixtures. Some liquids have a limited solubility, whereas some liquids can mix in all proportions. The word miscible is used when describing two liquids that mix with one another. Solubility depends on several factors. An important generalization is that “like dissolves like.” This means the more similar the solute is to the polarity of the solvent, the more likely the two will form a homogeneous mixture, or solution. Polar solvents will dissolve other polar compounds, and nonpolar solvents will dissolve nonpolar solutes. Ionic substances tend to dissolve more readily in polar solvents. Another factor in solubility is the temperature. In general, solids and liquids will have a higher solubility when the temperature is increased. Therefore, temperature is given when referring to the solubility limit. Prepare your notebook. When the lab is complete your lab notebook should include the following:

1. Include Solubility Lab in the Table of Contents 2. Write the title of the lab on the top of the page. 3. Date/number the page (if you work on it over a few days, date each time you are

working). Sign in your lab notebook each time you stop working. 4. Record the Purpose of Experiment in your own words. Remember the purpose is the

overall question that will be answered by collecting the data and doing any requested calculations.

5. Indicate PPE (personal protection equipment) required while performing the lab: goggles, gloves, lab apron, and closed-toed shoes.

6. Prepare your notebook to record observations for each reaction by writing tables. 7. Complete the post-lab question.

Solubility Activity: In this lab you will mix several solids and liquids to determine how the nature of the solute and the solvent affects solubility. Keep in mind the generalization that “like dissolves like.”

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Before you begin: You will be using table salt, sugar, and oil from your household. It is important not to contaminate these household products. To make sure the lab kit materials do not come in contact with the household supplies pour the salt, sugar and oil out of the container into their own weigh boats. Use the chemicals from the weighing boat. Do NOT pour any material back into the original containers. Do NOT place a pipette directly into the original bottle. This will avoid contamination of your supplies. Materials/Equipment needed: 1 teaspoon table salt in a weighing boat 1 teaspoon sugar in a weighing boat 1 teaspoon oil (olive, vegetable, etc.) in a weighing boat 1 teaspoon water 2 pipettes from lab kit (one for water and one for oil)

4 weighing boats from lab kit 5 test tubes from lab kit

Goggles should be worn while performing this experiment. As standard procedure, always wash your hands and your work space when you are finished with the lab. PROCEDURE Directions - Study of the Solubility of Solids Words to use when describing how the components of a mixture mix.

soluble – solid mixes completely in the liquid insoluble – solid does not mix in the liquid miscible – two liquids mix completely immiscible – two liquids do not mix

1. Place a small amount of salt (1-2 pinches) into a test tube. Fill a pipette with water

and add it to the salt. Carefully swirl to mix completely. Did the salt dissolve? Record your observations in the data table 1. Pour the salt and water down the sink. Rinse and dry the test tube.

2. Place a small amount of sugar (1-2 pinches) into a test tube. Fill a pipette with

water and add it to the sugar. Carefully swirl to mix completely. Did the sugar dissolve? Record your observations in the data table 1. Pour the sugar and water down the sink. Rinse and dry the test tube.

3. Place a small amount of salt (1-2 pinches) into a test tube. Fill a pipette with oil and

add it to the salt. Carefully swirl to mix completely. Did the salt dissolve? Record your observations in the data table 1. Pour the salt and oil down the sink or place it in the trash. Rinse and dry the test tube.

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4. Place a small amount of sugar into a test tube. Fill a pipette with oil and add it to the sugar. Carefully swirl to mix completely. Did the sugar dissolve? Pour the sugar and oil down the sink or place it in the trash. Record your observations in data table 1. Rinse and dry the test tube.

5. Place a pipette full of water into a test tube. Fill a pipette with oil and add it to the

water. Carefully swirl to mix completely. Did the two liquids mix? Did the liquids form layers? Which liquid is the top layer? Record your observations in the data table 2. Pour the oil and water down the sink or place it in the trash. Rinse and dry the test tube.

6. Remember to return all dry test tubes to your kit. Throw any remaining salt, sugar, and oil in the trash. Pipets can be thrown away.

DATA Table 1: Solubility of Solids in Liquid Solvents Solvents

Solutes Water Oil

Salt

Sugar

Table 2: Miscibility of Liquids in Liquids Mixture Observations Miscibility

Water + Oil

Post-Lab Questions Be sure to give complete answers.

1. Classify the salt, sugar, water, and oil as nonpolar, polar, or ionic. Use your observations to discuss the generalization of “like dissolves like?” Be specific.

2. Using “like dissolves like” explain why sugar, C6H12O6, dissolves in water but would not dissolve in hexane, C6H12.

3. Did oil and water mix? How could you tell which liquid has a greater density? Explain your reasoning.