Lab: Solubility Curve of Potassium Nitrate in Water, Lecture notes of Chemistry

Download Lab: Solubility Curve of Potassium Nitrate in Water and more Lecture notes Chemistry in PDF only on Docsity! Lab: Solubility Curve of Potassium Nitrate in Water Introduction: Solutions are homogeneous mixtures of solvents (the larger volume of the mixture) and solutes (the smaller volume of the mixture). For example, a hot chocolate is a solution, in which the solute (the chocolate powder) is dissolved in the solvent (the milk or water). The solute and solvent can be a solid, liquid, or a gas. A solution forms when the attractive forces between the solute and the solvent are similar. For example, the ionic or polar solute, NaCl, dissolves in water, a polar solvent. The phrase “like dissolves like” has often been used to explain this. As the water molecules collide with the ionic compound (NaCl), the charged ends of the water molecule become attracted to the positive sodium ions (Na+) and negative chloride ions (Cl-). The water molecules surround the ions and the ions move into solution. This process of attraction between the water molecules (the solvent) and the ionic compound (NaCl), the solute) is called solvation. Solvation continues until the entire crystal has dissolved and all ions are distributed throughout the solvent. Solvation Process of NaCl http://homepages.ius.edu/GKIRCHNE/Water.htm Some solutions form quickly and others form slowly. The rate depends upon several factors, such as, the size of solute, stirring, or heating. When making hot chocolate, we stir chocolate powder into hot milk or water. When a solution holds a maximum amount of solute at a certain temperature, it is said to be saturated. If we add too much chocolate powder to the hot milk, the excess solute will settle on the bottom of the container. Generally, the chocolate powder dissolves better in hot milk than cold milk. Thus, heating the solution can increase the amount of solute that dissolves. Most solids are more soluble in water (solvents) at higher temperatures. Solubility is the quantity of solute that dissolves in a given amount of solvent. The solubility of a solute depends on the nature of the solute and solvent, the amount of solute, the temperature and pressure (for a gas) of the solvent. Solubility is expressed as the quantity of solute per 100 g of solvent at a specific temperature. Objectives: In this experiment, you will be:  Measuring the solubility of different quantities of potassium nitrate (KNO3) at various temperatures of crystallization. The start of crystallization indicates that the solution has become saturated at this temperature.  Constructing a solubility curve for (KNO3) in water.  Able to identify and understand the key terms: solubility, solute, solvent, solvation, saturated, unsaturated, and supersaturated solutions.  Able to use the solubility curve graph to solve various problems and determine trends in the curve. Materials List: Balance Thermometer Hot plate 10 mL graduated cylinder Spatula Stirring rod Test tubes Ring stand Test tube holder and rack 400 mL Beaker Utility clamp Potassium Nitrate, KNO3 Distilled water Marking pencil Procedure: 1. Divide the lab up so that one lab partner completes steps 2-3, while the other partner begins on Step 4. 2. Using a marking pencil, number four test tubes (1-4) and place them into a test tube rack. 3. Using a balance to measure the KNO3 prepare the test tubes as indicated below: Test Tube # Mass of KNO3 (g) Volume of distilled H2O (mL) 1 2.0 5 2 4.0 5 3 6.0 5 4 8.0 5 4. Fill a 400 mL beaker about ¾ full of tap water. This will be used as a hot water bath. Place the water bath on the hot plate (set to medium temperature). Place test tube #1 in the utility clamp and attach the clamp to the ring stand. Lower the test tube into the hot water bath. Continue heating the water bath until the temperature reaches 90°C and adjust the heat to maintain this temperature.