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Community College of Philadelphia Department of Chemistry Laboratory Report Sheet Name: Date: Email: Laboratory Instructor: Course Nbr.: CHEM 101 Distance Section: Experiment Nbr.: 2 Experiment Title: SOLUBILITY Purpose: Concepts related to the textbook: Conclusion: Lab 2 – SOLUBILITY Background Remember the morning when you were so tired that you had trouble waking up to get ready for school? To help get going, you may have staggered into the kitchen to prepare some instant coffee. After putting a teaspoon of coffee granules in the cup, you added hot water and probably added some sugar and milk. As you stirred the coffee, both the granules and the sugar disappeared. However, you knew by the taste, that the coffee and sugar were still there. Obviously, stirring the coffee caused these particles to dissolve in the water until they were too small to see. Whenever a substance completely dissolves in a liquid so that the particles become invisible, a solution has been prepared. Water can dissolve many different substances to form solutions. In the kitchen, you may have used water to dissolve not only coffee and sugar but also salt, powered soft drinks, or packaged soups. The substance that does the dissolving, in this case water, is called the solvent. The substance that is dissolved, the sugar or salt is known as the solute. Since water can dissolve so many different solutes to form solutions, chemists refer to water as a universal solvent. Although water is the most common solvent, other products often found in a kitchen are used to dissolve substances. For example, ammonia is useful for dissolving the grease that may splatter on stove and counter tops from cooking. Another solvent you might find in a kitchen is in the aerosol spray can used to dissolve the adhesive stuck to the skin from a bandage that has been left on for a long time. With either the ammonia or the spray, a solvent is being used to dissolve a solute to make a solution. A solution, however, may consist of several solutes dissolved in more that one solvent. This is the type of solution make in preparing instant coffee. Both the coffee and the sugar are dissolved into the water and milk. In fact, milk itself may be considered as a solution, consisting of a solvent (water) containing several solutes. Whenever the solutes are uniformly spread throughout a solvent, as they are in milk, the solution is said to be homogeneous. Milk is a mix of water, fat, proteins, sugar, and inorganic salts. These constituents are present in the milks of all mammals, but their proportions differ from one species to another and within species, because of diet or other factors. The milk of each species seems to be a complete food for its own young for a considerable time after birth but small quantities of other foods are usually taken early in life. In the stomachs of the young, milk is precipitated as a soft curd that encloses globules of fat. Milk protein is of high nutritional value because it contains all the essential amino acids, that is, those that human infants cannot synthesize in quantities needed. The mineral content includes calcium and phosphorus, adequate for normal skeletal development, but little iron. Milk contains fat-soluble vitamin A and carotene, its precursor, in amounts varying with the food of the lactating animal. Microorganisms contained in raw (unheated) milk eventually make it turn sour and curdle. Cooling to slightly above its freezing point keeps milk palatable for a longer time markedly reducing the multiplication of the bacteria and the chemical changes they induce. Much of the milk sold as a beverage has undergone homogenization, a process in which the milk is forced under high pressure through a small opening to distribute the fat evenly through the milk. Vitamin D in oil solution may be incorporated in milk during homogenization as a nutritional supplement. In addition, milk contains several minerals required for good health. These include calcium, magnesium, and zinc, phosphorous and iron. EXPERIMENT C - SOLUBILITY This experiment deals with the solubility of solids in water. In general, the solubility of a solid is dependent on the nature of the solid and the temperature of the solvent. Polar solids like sugar and salt are soluble in water (up to a point) The point at which the solid ceases to dissolve is called its saturation point and can be easily detected. Usually, the solution will begin to look cloudy while stirring and even after stirring for a length of time. Because not all the solid will be dissolved, some solid will settle to the bottom of the solution. At the point of saturation, you should stop adding solid into your experimental solution. Please note also that sugar and salt have markedly different solubilities in water and markedly different solubility responses to changes in solvent temperature. After you have determined the solubility of your solids at various temperatures, you will report your results graphically. PROCEDURE I - Water is a polar liquid; that has permanent areas of partial charge. Try the following on a thin stream to observe this physical property. 1. Turn on your cold-water tap to thin but continuous/steady stream of water. 2. Rub a plastic comb vigorously through your hair or with a silky piece of cloth (to generate an electrostatic charge). 3. Hold the comb teeth to the side of and parallel to the stream of water (about ½ inch away). 4. Observe and record your observations. [Note: For this experiment to work, you must generate an electrostatic charge on the comb; this may be difficult to do on a humid day.] II - Obtain some table salt (solute –substance to be dissolved) and water (solvent –dissolving medium). Measure out 250 mL of water or use 1 cup if you cannot actually measure in mL. One-cup (1/2 pint) is approximately 250 mL. You will do three sets of data for this solute (6 trials). You will then repeat the entire set of 6 trials using sugar as your solute (substance to be dissolved) and water as your solvent. [Note that the numbers in parentheses in the procedure refer to lines on the data page where the measurements are to be recorded.] 1. The first solubility determination will be done at approximately 0 °C. a. Measure out 250 mL of water and pour into a clear glass. Record the volume of water used on line 1 on the data sheet. b. Place the glass in a larger glass/container that is filled with ice cubes that have been covered with water. This will keep the 250 mL water in the inner glass at the proper temperature; it a few minutes to adjust. If you have a thermometer, record the temperature of the water on the data sheet (2). If you do not have a thermometer, assume and record 0 0 0 C on the data sheet (2). c. Add 1 teaspoon of your solute at a time to the water. Be sure to use level teaspoons each time. After each addition, stir for one minute and be sure that the entire solid has dissolved before adding more. Keep track of how many teaspoons you have added. When you reach the saturation point for your solid, record the total number of teaspoons added (3) for that trial. d. Discard the above solution and repeat (4) with the same solute at the same temperature. This will be Trial II at 0 0 0 C. 2. The second solubility determination will be done at approximately 20 °C. a. Measure out 250 mL of tap water and pour into a clear glass. b. If you have a thermometer, record the temperature of the water on the data sheet (2). If you do not have a thermometer, record the estimate of 20 °C on the data sheet (2). c. Add 1 teaspoon of your same solute at a time to the water. Be sure to use level teaspoons each time. After each addition, stir for one minute and be sure that the entire solid has dissolved before adding more. Keep track of how many teaspoons you have added. When you reach the saturation point for your solid, record the number of teaspoons added (3) for this trial. d. Discard the above solution and repeat (4). This will be Trial II at 20 0 0 C. 3. The third solubility determination will be done at approximately 40 °C a. Measure out 125mL of boiling water and mix with 125 mL of tap water in a clear glass. If you have a thermometer, record the temperature of the water on the data sheet (2). If you do not have a thermometer, record the estimate of 40 °C on the data sheet (2). b. Add 1 teaspoon of your same solute at a time to the water. Be sure to use level teaspoons each time. After each addition, stir for one minute and be sure that the entire solid has dissolved before adding more. Keep track of how many teaspoons you have added. When you reach the saturation point for your solid, record the number of teaspoons added (3). c. Discard the above solution and repeat (4). This will be Trial II at 40 °C. d. Take a teaspoon of this solution and place on a hand mirror. Let the solvent evaporate and examine the salt crystals that remain. Describe them. When you have finished all six trials with salt, repeat using sugar. CALCULATIONS 1. Calculate the average teaspoons of solute for each temperature (5). 2. Calculate and record the solubility of your solute in teaspoons per mL (6) (divide the average teaspoons for each trial by 250 mL) GRAPH Using graph paper, plot the solubility of both the salt and the sugar. Use one color for the salt graph and another color for the sugar graph. Plot the value of tsp./mL on the “x” axis and the temperature in °Celsius on the “y” axis. Draw the best smooth curve possible between the three points for each solute. Be sure to choose the numerical values of the “x” axis so that you use as much of the graph paper as possible. Use equal increments from one number to the next on this axis. Submit your graph with your report. The graph may be handwritten or generated using MS Excel or other graphing tools. DATA SHEET: EXPERIMENT 2 - SOLUBILITY (SUBMIT THE DATA SHEETS WITH YOUR LAB REPORT) I - Observations on a stream of water when adjacent to an electric field: II - Volume of water used in each trial (1) ___________________mL Solute (2) Temp. (0C) (3) Trial I (tsp) (4) Trial II (tsp) (5) Average (tsp) (6) Average (tsp/mL) (Graph) Salt – ice water Salt​​ – room temp Salt – warm water Sugar – ice water Sugar – room temp Sugar – warm water Questions: 1. Describe your salt crystals after evaporation of the solvent. 2. Describe your sugar crystals after evaporation of the solvent. 3. Can you distinguish salt from sugar by their crystals? 4. Describe a homogeneous solution. 5. If you have a solution of coffee sugar and cream, name the solutes and the solvent. 6. What is generally true of the solubility of most solids in liquid solvents as the temperature of the solvent rises? 7. How does this trend compare with the solubility of gases in liquid solvents? (Consult your textbook if necessary.) 8. Using your graph, find the solubility of salt at 300C __________________tsp/mL 9. Using your graph, find the solubility of sugar at 300C _________________tsp/mL 10. Do the following calculation. If 5.72 grams of KNO3 are dissolved in 15.3 mL of water, what is the solubility of KNO3 in grams/mL of water? __________________ g/mL Attach graph lab_2_solubility_v1.doc 1 of 7 _865954423.unknown _865954559.unknown _865954522.unknown _865954378.unknown