Stoichiometry

Laboratory: Stoichiometry & % Yield

Purpose: To predict a theoretical yield for a chemical reaction using stoichiometry, then to calculate the % yield after measuring the actual yield of the reaction.

Background: By using the coefficients of a balanced equation, it is possible to predict the ratios in which reactants and products are consumed and/or are made. The principal tool for such calculations is the mole ratio, which is a conversion factor has the format X moles A/Y moles B, assuming the chemical reaction xA + yB  zAB. As an example, the mole ratio between hydrogen and oxygen in the reaction

2 H2 + O2  2 H2O would be 2 mol H2/1 mol O2.

In this lab, you will be studying the reaction between calcium chloride (Here found in the form CaCl2•2H2O) and sodium carbonate (Na2CO3). One of the products of this reaction is a precipitate: By filtering and drying out this precipitate, we will be able to compare the theoretical and actual masses.

Materials:

CaCl2•2H2O powder Na2CO3 powder 250 mL beakers (2)

Filter paper Funnel Electronic balance

Squeeze bottle of DI water

Safety: Wear safety goggles and aprons during the performance of this lab. Avoid inhalation of the solid chemicals.

Procedure:

Place a 250-mL beaker on the balance and press “zero” (or “tare”) to turn the mass to zero. Slowly add solid CaCl2•2H2O until you have between 1.00 and 2.25 g. Record this in the appropriate place in your data table. Repeat, using your other beaker and the Na2CO3.

Obtain a piece of filter paper and record its mass in your data table. Prepare your filtering apparatus as was demonstrated in class (fold filter paper in ¼, put 3 sheets one way, 1 the other). Place the cone of paper in the filter and spray it with a bit of deionized water to make it stay in the filter.

Add about 20 mL of deionized water to each beaker, and carefully swirl until all solid has dissolved. If some solid remains, add a bit more water to dissolve it. Mix the...