Ms. Robinson ChemistryStoichiometry Investigation

Stoichiometry: Can You Make 2.00 Grams of a Compound?

You will be assigned one of two reactions A or B:

A. Sodium carbonate + calcium chloride dihydrate

B. Calcium chloride dihydrate + potassium carbonate

Pre-Lab

  1. Read all lab directions (Pre-Lab, Lab, Post-Lab). Prepare a report answering the questions and showing all calculations and data. Put your name, class name and date on top of the first page.
  2. Write a complete word equation listing the names of the reactants, and predicted products. Dihydrate means that there are two molecules of water “frozen” in the ionic crystal for every one unit of compound. Include water in the product from the dihydrate.
  3. Write a balanced formula equation for the double displacement (double replacement) reaction.
  4. Predict which compound will form the precipitate using a solubility rules table (online and in text book ch 9). Complete the equation with (s) and (aq) symbols.
  5. Calculate the molar mass of each reactant and product and write below each formula in the equation.
  6. Calculate the number of moles in 2.00 g of precipitated product.
  7. Use the factor label method to determine the mass of each reactant required to make 2.00 grams of your precipitate (stoichiometry road map). Does the total mass of all reactants equal the total mass of all products? If not, check your work.

Lab

  1. Safety: the compounds selected have low to moderate toxicity, but avoid breathing the dust or getting any in your eyes or on your skin. Sodium carbonate and potassium carbonate may be skin irritants. Calcium chloride is moderately toxic. The solutions can be washed down the drain when done, and solids thrown in the trash. Wear goggles.
  2. Weigh the mass of a piece of filter paper (note it) and prepare your filtration apparatus.
  3. Mass each reactant and place in separate test tubes. Dissolve completely with 25 mL distilled water for each reactant.
  4. Mix together the two solutions to form the precipitate. Wash out the empty test tube with distilled water that you pour out into the mixture.
  5. Recover precipitate by pouring it over filter paper and washing the empty test tube with distilled water and pour this onto the filter paper.
  6. Dry the filter paper in a drying oven set on low.
  7. Mass the solid precipitate and the filter paper.

Post-lab

  1. Complete the data chart below to determine the mass of precipitate formed in the sample experiment:

Mass of dry filter paper + precipitate
Deduct mass of dry filter paper
= mass of precipitate
  1. Calculate your percentage error based on the relationship below:

% error = 1.95g – 2.00gx 100 = 2.5%

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2.00g

  1. Check your work and procedures. Errors can occur in the calculations and lab. Check that you have balanced the formulas and equations, and have the right molar masses. Complete all algebra steps and check. Check you have identified the correct precipitate. Dissolve the reactants completely in distilled water before mixing or there will be reactants mixed up with products when you find the final mass. Completely dry the filter paper before weighing or water will add mass to the product. The slight solubility of the product can reduce the yield to 95-100%.
  2. Extra credit: work out the percentage composition of the water in the calcium chloride dihydride.

2GramsInvestigations.doc Courtesy Flinn Scientific