Mass & Mole Relationships in a Chemical Reaction



E-21 Mass & Mole Relationships LAB

In this experiment, you will measure the mass of the solid reactant, NaHCO3, and that of the solid product, NaCl. Using these masses, you will determine the mole ratio of these two compounds. As you learned in the E-19 “Single Replacement” Lab the mole ratio is the ratio of the coefficients in a balanced chemical equation. In this experiment, you will be adding sodium bicarbonate (baking soda) with hydrochloric acid to produce sodium chloride, carbon dioxide, and water.

Purpose:

1. To calculate the number of moles of reactant and product in a simple chemical equation.

2. To experimentally determine the mole ratio between a reactant and product and compare the resulting ratio to the coefficients in a balanced chemical equation for the reaction.

3. To list two possible sources of error in the E-21 lab and explain how they would affect the results of the lab.

Safety: Goggles, tie back hair, close fitting sleeves, long pants, apron, closed toed shoes / heat, vapors, eye and skin irritants (strong acid), glass

Prelab: 1. Write up the lab & copy the data tables into your lab notebook.

2. Look up the chemical formulas for the following compounds: sodium bicarbonate, hydrochloric acid, sodium chloride, carbon dioxide, and water.

3. Write a balanced equation for the reaction of sodium bicarbonate with hydrochloric acid.

Materials:

Chemicals: 3 M hydrochloric acid in dropper bottle sodium bicarbonate

Apparatus: evaporating dish watch glass balance

spatula or spoon 10 mL graduated cylinder stirring rod

crucible tongs or hot mitts drying oven

Procedure: Day One

1. Place an evaporating dish on top of a watch glass. Measure and record the mass of the evaporating dish and watch glass together.

2. Add about 2-3 grams of NaHCO3 to the evaporating dish. Measure and record the mass of dish, watch glass, and NaHCO3.

3. Carefully pour about 10 mL of 3M hydrochloric acid into a graduated cylinder. (If only 6M acid is available, pour 5 mL of distilled water and 5 mL of the acid into the cylinder.) Slowly add the acid to the evaporating dish while stirring.

4. If your dish is still bubbling after adding 10 mL of HCl and stirring well, use the medicine dropper in the HCl to add more acid dropwise to the evaporating dish until there is no more bubbling.

5. When your experiment has finished bubbling, place the watch glass curved side down on top of the dish.

6. Write your name on a small piece of paper and use masking tape it attach it to the watch glass.

7. Place the apparatus into the drying oven overnight (Make sure the oven is turned on!!).

Day Two:

1. Remove your apparatus from the drying oven and allow it to cool for 10 minutes.

2. Remove your nametag from the watch glass, then measure and record the mass of dish, glass, and product.

3. Record the name of the product and the formula of the product in the data table.

E-21 Data Table:

|#1 |Mass of dish and watch glass | |

|#2 |Mass of dish, glass, and NaHCO3 | |

|#3 |Mass of dish, glass, and product | |

|#4 |Name of product | |

|#5 |Formula of product | |

Calculations: Be sure to show your work, and use significant figures. Then record your data in the calculation table.

1. Calculate the mass of the reactant, NaHCO3. (#2- #1)

2. Calculate the number of moles of reactant, NaHCO3.

3. Calculate the mass of the product in the dish. (#3-#1)

4. Calculate the number of moles of product.

5. Calculate the experimental mole ratio of the reactant to the product.

6. Using the reaction you wrote in pre-lab #3, determine the theoretical mole ratio of the reactant to the product.

7. Determine your percent error for your experimental mole ratio. See the E-9 Lab for the formula.

Questions:

1. In this experiment, three products were formed, but only one of them was in the evaporating dish on day 2. Explain what happened to the other two products.

2. Why do you need to add the acid dropwise in step #4? What would happen to your results if you added too much acid?

3. When sodium bicarbonate is added to vinegar (acetic acid), the mixture bubbles and a similar reaction occurs.

a. Write a balanced equation for this reaction.

b. If an experiment with 5.00 g of sodium bicarbonate produces 4.65 g of the solid product, what is the percent error of the experiment? (Hint: Use stoichiometry to determine the theoretical yield for the product.

4. When hydrogen gas (H2) reacts with oxygen gas (O2), gaseous water is formed.

a. Write a balanced chemical equation for this reaction.

b. Fill in the correct values in the following chart with the correct stoichiometric quantities.

|H2 (g) |O2 (g) |H2O (g) |

|2 moles | | |

| |2 molecules | |

|2.24 L | | |

| | |18 grams |

Conclusion: Remember to refer to the purpose.

Mind Prober:

Baking powder consists of a mixture of baking soda and a substance called cream of tartar. Baking soda and baking powder react differently when used in cooking situations. When water is added to baking soda, it just dissolves. But when water is added to baking powder, carbon dioxide is produced. What is the purpose of the cream of tartar? If you were baking bread or cake, would you use baking soda or baking powder?

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