The Nature and Properties of Solutions
The experiment aimed to describe the various ways of expressing the concentration of solutions; prepare solutions of definite concentrations from standard substances by dilution and solve problems involving preparation of solutions and their concentrations. BACKGROUND INFORMATION
A solution is any homogenous mixture of two or more substances, the relative properties of which may vary within certain limits. The two components of solutions are the solute (substance being dissolved) and the solvent (substance that does the dissolving). The maximum amount of solute which can be dissolved in 100 g of a given amount of solvent at a specified temperature is called solubility. There are ways of increasing the solubility of solutes: pulverizing (reducing the size of solid solutes), heating (increasing the temperature), and agitation (stirring). The concentration of a substance in a solution is the quantity of the substance in a given quantity of the solution or solvent. There are qualitative ways of expressing concentration such as: diluted, concentrated, saturated, unsaturated and supersaturated. While the quantitative ways could be express as: Percentage by weight = mass of solute X 100
Total mass of sol’n
Percentage by volume = volume of solute X 100
Total volume of sol’n
Molarity (M) of the solution is defined as the number of moles of solute present in a liter of the solution. Molarity = mol of solute
L of sol’n
The Normality (N) of the solution is defined as the number of equivalent weights of the solute in 1 L of solution.
Normality = equivalent of solute
The molality (m) of solute is the number of moles solute per 1000g solvent or 1kg solvent.
Molality = mol of solute
The composition of a mixture is often expressed as the mole fraction (X) of each of the components.
Mole fraction = mole solute
Total mol sol’n
Dilution is the process in which more solvent is added to reduce the concentration of solute in the original solution.
A. Factors Affecting the Rate of Solution
A pinch of blue vitriol (CuSO4•5H2O) was dropped in each of the two test tubes half filled with water. The contents of the first test tube were shaken. The observations were written down. The data were then presented to the instructor for comments. Two small crystals of cupric sulfate were taken. One of the crystals was pulverized in a mortar. The unpulverized crystal was placed in one test tube and the pulverized crystal in a second test tube. 5 mL of water was added to each and were shaken. The time it took to dissolve the cupric sulfate was noted. The data were then presented to the instructor for comments. B. Factors Affecting the Solubility of a Substance
Nature of Solute. 0.5 g of common table salts, sodium sulfate and benzoic acid were weighed. The substances were placed into different test tubes and an exact 5 mL of water was added in each test tubes. Each mixture was shaken and allowed to stand for sometime. The order of solubility of the compounds was determined from the amount of undissolved substance in each test tube. The observations were then recorded. For the nature of solvent, the procedure above was repeated but ether was used instead of water. The observations were recorded.
Effect of Temperature and Pressure
A few drops of HCl were added to 1 mL lead acetate solution in a test tube. 10 mL of water was added and heated nearly to boiling. The tube was cooled by running tap water over the outside of the tube. A bottle of carbonated softdrink was opened. The effervescence was allowed to subside. About 30 mL of the softdrink was transferred into a clean Erlenmeyer flask. A rubber stopper was inserted which is fitted with a bent glass tubing that leads into a solution of...