Chemical Calculations and Measurement

Stoichiometry

Measurement is one of the hallmarks of every science. Of all the measurements made in chemistry, those made when substances react are the most important.

In this experiment, you will use a balanced chemical equation and known amounts of reactants to predict the masses of the products. You will then experimentally check your prediction by measuring the actual mass of the products. In this way, you will obtain a working, practical understanding of molar relationships and appreciation of the importance of chemical equations.

Purpose

1) To balance the equation for a given reaction and predict the mass of each product

2) To measure the actual masses of the product and compare with the predicted masses

Materials

Apparatus

Balance

Stirring rods

Ring stand

Ring clamp or funnel holder

Filter paper

Funnel

Wash bottle

Mass boats

Assorted beakers

Marking pencil

Reagents

Strontium chloride hexahydrate, SrCl2x 6H2O

Sodium Carbonate monohydrate Na2CO3X H2O

Deionized water

Procedure

Part 1

  1. A strontium chloride solution(aq) mixed with sodium carbonate solution(aq) yields strontium carbonate(s) and sodium chloride(aq). Write and balance the equation for this reaction.
  2. Calculate the masses of 0.010 mol of SrCl2 x 6H2O and 0.010 mol Na2CO3 x H2O.
  3. Using the balanced equation and assuming the complete conversion of 0.010 mol of reactants to products, calculate the mass predictions for SrCO3(s) and NaCl(s) and record these values in Table 1 under “Calculated mass”.

Part 2

  1. Put on lab apron and safety goggles.
  2. Using clean, dry massing boats, separately mass 0.010 mol of SrCl2 x 6H2O and 0.010 mol of Na2CO3 x H2O.
  3. Add about 50mL deionized water to a 150mL beaker. Transfer the SrCl2 x 6H2O solid from step 5 into the beaker. Stir with a stirring rod until the solid dissolves.
  4. Add the Na2CO3 x H2O solid to another 150 ml beaker containing about 50 ml deionized water and stir until the solid dissolves.
  5. Determine the mass of a dry piece of filter paper and record in Table 1.
  1. Pour the SrCl2 solution into the beaker containing the Na2CO3 solution. Stir. Place the massed filter paper into a funnel on a ring stand. Under the funnel, place a clean, dry, massed (to the nearest 0.01 g) 400mL beaker that has been marked with your name and “NaCl.” Record this mass in Table 1.
  2. Filter the mixture of SrCO3 and NaCl being careful not to overflow the filter.
  3. Wash the SrCO3 three times with deionized water from a wash bottle.
  4. Place the marked 400mL beaker with the NaCl in the drying oven until the next day when you will record the mass of the beaker and the solid sodium chloride.
  5. Carefully transfer the filter paper and the solid SrCO3 into a clean, dry, massed (to the nearest 0.01 g)50 ml beaker that has been marked with your name and SrCO3.
  6. Place the 50 ml beaker with the filter paper and strontium carbonate in the drying oven until the next daywhen you will record the mass of the beaker and the solid strontium carbonate.

Data Presentation

TABLE 1. Data Table

Object / Mass (g) / Calculated mass (g) / Percent Error
Dry piece of filter paper / SrCO3(s) / SrCO3(s)
Clean, dry 400mL beaker / NaCl(s) / NaCl(s)
Dried 400mL beaker and solid NaCl / Actual mass (g) / Overall
Clean, dry 50 ml beaker / SrCO3(s)
Dried 50 ml beaker, filter paper, SrCO3 / NaCl(s)

Data Analysis

  1. Type in, using subscripts, the balanced equation for this reaction.
  2. From your data, calculate the actual mass of SrCO3(s) produced. Record this mass on the data table under “actual mass”. Show your calculations.
  3. From your data, calculate the actual mass of NaCl(s) produced. Record this mass on the data table under “actual mass”. Show your calculations.
  4. Determine the percentage error of SrCO3(s) and NaCl(s). To do this, take the

absolute value of the difference between each of your predicted (calculated) masses and the actual mass of that substance produced. Divide by the predicted mass and multiply by 100. Show your calculations.

% error = /calculated mass – actual mass / X 100

calculated mass

  1. Determine the overall percent error

Overall % error = /sum of calculated masses – sum of actual masses / X 100

sum of calculated mass

Conclusions

  1. Based on the percent error calculations, explain if the experimental (actual) data support thecalculatedpredictions?
  2. How can the differences between the calculated results and the actual results be explained?
  3. If this experiment were to be repeated, what might be done differently to reduce the percent error?