MOLE RATIOS IN CHEMICAL EQUATIONS LEARNING OBJECTIVES This laboratory exercise and its accompanying calculations will reinforce the concept that the coefficients in chemical equations represent the relative number of moles. Practice is obtained in converting from grams to moles DISCUSSION When Fe reacts with CuSO4, either FeSO4 or Fe2(SO4)3 can be formed. The two possible reactions are: (a) Fe + CuSO4 FESO4 Cu (b) 2Fe +3CuSO4 Fe2(SO4)3 3 Cu You will determine the mole ratio experimentally and decide which reaction actually occurred. PROCEDURE Using weighing paper, weigh between 1 and 2 g of steel wool. Record the mass to the accuracy allowed by your balance. Keep the steel wool loose; do not wad it into a tight ball. Transfer the steel wool to a 150-mL or 250-mL beaker. Add 0.35M CuSO4 to the level marked as 100-mL on the beaker. Poke the steel wool below the solution and let it stand for at least ten minutes. Keep the stirring rod in the beaker, and use it occasionally to break up the tuft of steel wool. If your solution turns green or yellow, add more CuSO4. Prepare a piece of filter paper as shown in LABORATORY TECHNIQUES, page ix. Weigh the filter paper after tearing off the corner and after marking it with your initials. Set up your filtering system as shown in LABORATORY TECHNIQUES, pp. ix and x. the Filter the solution, leaving as much solid in the beaker as you can. Wash the residue beaker with 10-mL portions of water, each time allowing the residue to settle before pouring the wash water through the filter. Continue washing until the wash water is clear. Transfer the solid to the filter paper. Wash the solid on the filter paper with a stream of distilled water, again continuing until the water running through the filter is colorless. Your instructor will give you instructions for drying the filter and contents. When it is dry you will weigh it and complete the calculations. 65 1-70 03 Fe (steel wool) 31409 filter paper + Cu 7519 filter paper 2. 3830 Cu CALCULATIONS 1. What is the ratio of moles Cu to moles Fe shown in reaction (a) on p. 65? Divide moles Cu by moles Fe and express this ratio to three significant figures What is the ratio of moles Cu to moles Fe shown in reaction (b) on p. 65? Divide moles Cu by moles Fe and express this ratio to three significant figures. 2. Calculate your experimental moles Fe. How many significant figures should you have? SHOW WORK Calculate your experimental moles Cu. How many significant figures should you have? SHOW WORK. Divide moles Cu by moles Fe and express this ratio to the proper number of significant figures. Did reaction (a) or reaction (b) occur? 67