Stoichiometry Lab Report Essay

Aim: To determine what solid product is produced in the decomposition of NaHCO3, based on the pre-calculated mass of the solid products versus the mass found in the experiment.

Hypothesis: I think that the solid product produced from the decomposition of baking soda will be Na2CO3 because out of the three possible products it weighs the most. The two bi-products H2O and CO2 weigh almost nothing and therefore subtract almost nothing from the weight of the reactant.

Theory: In this experiment, two branches in chemistry are involved: chemical decomposition as well as stoichiometry. Decomposition is the separation of a chemical compound into two or more elements or other compounds. It can be defined as the opposite of chemical synthesis. In this experiment we are using thermal decomposition because we are using extreme environmental conditions like heat to limit the stability that the chemical compound ordinarily has. The reaction is usually endothermic because it is absorbing heat because heat is required to break the chemical bonds in the compound in order to undergo decomposition. In decomposition of carbonates it is knows that carbon dioxide and water is almost always one of the products. However with others it is metal oxide and carbon dioxide. You can see this from the balanced equations because carbon dioxide is a bi-product in all three cases.

The second branch that this experiment explores is stoichiometry. It deals with the quantitative relationships between the reactants and the products in chemical reactions. The quantitative relationships primarily cover the ratio of moles between the different reactants and products in a reaction. This is reaction stoichiometry. With this ratio, composition stoichiometry can be used to calculate the amount or the weight of the products with any given mass or number of moles of the reactant.

1. NaHCO3 –> NaOH + CO2

2. 2NaHCO3 –> Na2O + 2CO2 + H2O

3. 2NaHCO3 –> Na2CO3 + CO2 + H2O

Variables:

Controlled:

Independent:

Dependent:

– Time (10 min)

– Mass of Baking soda (2.0 g)

– Crucible

– Temperature (Celsius) of the baking soda

– Mass of the solid product

How to Control the Variables:

* You can keep the time controlled by either looking at the clock every couple of minutes or putting a timer to 10 minutes.

* To keep the mass of the baking soda at 2.0 grams exactly, you have to weigh it very carefully each trial. Using the more precise scale will also help.

* You have to keep the crucible controlled because they often have impurities left behind in the crucible. If you have that for one trial, you have to keep it the same for the second trial.

Materials:

– tripod

– Bunsen burner

– clay triangle

– crucible with lid

– 2.0 grams of baking soda for each trial

– stopwatch or timer

Diagram:

Procedure:

1. Set up a tripod and a Bunsen burner. Place a clay triangle on the tripod.

2. Clean the empty crucible and then measure the mass of it and record the mass in the data table.

3. Measure the 2.0 grams of baking soda in the crucible and record this in the data table.

4. Measure the total mass of the crucible and the baking soda. Record this measurement in the data table.

5. Heat the crucible for 10 minutes. During the heating process, break up the clumps that form with a stirring rod.

6. Once the crucible has cooled to room temperature, measure the mass of the crucible and the remaining solid material. Record this measurement in the data table.

Data Table (+/- .001 g)

Mass of crucible

Mass of baking soda

Mass of crucible and baking soda

Mass of crucible and solid product

Mass of solid product

9.615 g

2.000 g

11.615 g

10. 335 g

1.28 g

9.555 g

2.000 g

11.555 g

10.325 g

1.23 g

Average mass of solid product produced: 1.255 g = 1.26 g Na2CO3

Data Processing:

1. NaHCO3= 84 g => moles= mass/ molecular mass => 2/84 = .0238 g NaHCO3

.0238 mol NaOH (because the ratio is 1:1) x 40 g (molecular mass) = .952 g NaOH

2. .0238 mol NaHCO3 x 1 mol Na2O/ 2 mol NaHCO3 = .0199 mol Na2O

.0199 mol Na2O x 61.98 (molecular mass) = .738 g Na2O

3. .0238 mol NaHCO3 x 1 mol Na2CO3/ 2 mol NaHCO3 = .0199 mol Na2CO3

.0199 mol Na2CO3 x 105.99 (molecular mass) = 1.26 g Na2CO3

Conclusion:

Based on the results we can conclude that the solid product produced in the decomposition of NaHCO3 is Na2CO3. The pre-calculations showed that the mass of Na2CO3 that should form in the decomposition reaction is 1.26 grams. The solid product that formed when we did the experiment averaged at 1.255 grams which rounds to 1.26 grams. This is almost exactly equal to the calculated mass and therefore we can conclude that it is correct.

Evaluation:

As you can see from the results, the second trial was less precise than the first. I have come to the conclusion that this is because the procedure was not followed 100 percent correctly. First of all, a different crucible was used the second trial because it was done on a different day. Because we were in a hurry we did not clean the crucible as properly as in the first trial. This may have caused the reaction to change due to impurities interfering with the decomposition. Second of all, we didn’t stir throughout the 10 minutes. This means that any clumps in the baking soda would not have reacted completely. Also if it is less hot towards the outer layer of the baking soda, the chemical bonds may not have been broken down as well as the baking soda towards the bottom of the crucible. Third of all, we did not measure the weight of the crucible with the final product when it was completely cooled off. The reaction may not have been fully done until all the heat was used; however because we didn’t wait, the results may have been affected.

Improvement:

Based on the evaluation you can see that it is imperative to follow the procedure exactly as it is. If not, you are risking faulty data. If I were to repeat this experiment again for a third time, I’d make sure I clean the crucible to the best of my ability. I’d also make sure to stir throughout the ten minutes as well as measure the final weight after it cooled off.