MOLE RELATIONSHIP IN A CHEMICAL REACTION
Chemists can determine the equation for a chemical reaction by identifying the type and amount
of the substances involved. The coefficients for the balanced equation can be determined by converting
mass values to moles and expressing the mole values in terms of small whole number ratios.
It is not always practical to determine mass values for all of the substances involved in the
reaction, particularly if gases are produced. Therefore, chemists will often use only the mass values for
one of the reactants and one of the products. By incorporating knowledge of the law of conservation
of mass—energy, the balanced equation can be determined. For example, if aluminum reacts with
hydrochloric add, aluminum chloride and hydrogen gas are produced. Let us assume that 54.8 g, or
1.5 mol HCI is reacted and 66.8 g, or 0.5 mol AlCl3 is produced.
Doubling these values yields a 3:1 ratio, which can be used to begin balancing the equation.
AI + 3HCI -----> (1)AlCl3 + H2
These coefficients balance the number of aluminum and chlorine atoms, but hydrogen is still not
balanced. Therefore, the coefficients for HCl and AlCl3 must be doubled, a coefficient of two added
to aluminum, and a three to H2.
2AI + 6HCI -----> 2AlCl3 + 3H2
These coefficients conserve all three types of atoms in the reaction and maintain the 3:1 ratio between
HCI and AlCl3.
In this experiment you will react sodium hydrogen carbonate, NaHCO3 with HCI to form NaCI
and two other products. You will determine the mole relationship between NaHCO3 and NaCI, and
use this data along with the law of conservation of mass-energy to predict a balanced equation for
the reaction.
Objectives
In this experiment, you will
• react a known mass of NaHCO3 with excess HCl,
• calculate the mole relationship between NaHCO3 and NaCl,
• predict a balanced equation for the reaction, and
• determine whether your results support the law of conservation of mass-energy.
Procedure
1. Clean and dry an evaporating dish and watch glass. Measure and record their mass to the nearest 0.01g
2. Weigh out approximately 2 grams of Sodium hydrogen carbonate (NaHCO3) on weigh paper. Transfer this
compound to the evaporating dish and record the mass of the compound, dish, and watch glass.
3. Obtain about 6mL of 6M HCl in a clean graduated cylinder. Gradually add the acid to the baking soda in the
evaporating dish with a small pipet. Allow the drops to enter the lip of the dish so that they gradually flow
down the side. **BE CAREFUL NOT TO SPLASH ACID ON YOUR HANDS**
4. Continue adding the acid slowly until the reaction has stopped (no more gas bubbles produced). You will
have to swirl the dish gently to keep the acid reacting with the NaHCO3.
5. Once all of the baking soda, the limiting reactant, has been consumed, examine the underside of the watch
glass for any particles of baking soda. If any particles are attached to the underside of the watch glass, rinse
them into the evaporating dish with a SMALL amount of distilled water.
6. Heat the liquid in the evaporating dish GENTLY on a wire gauze/ring stand. Continue to heat gently until all
of the water has evaporated.
7. Wait at least 5 minutes to allow the dish to cool. DO NOT TRY TO MOVE THE DISH UNTIL IT IS COOL!
Measure and record the mass of the evaporating dish, watch glass, and solid product (sodium chloride).
Record in the data table.
8. Clean all glassware and return all lab equipment.
Name: _________________________________ Period: _________ Date: _______________________
Mole Relationship in a Chemical Reaction – Data Sheet
Mass of evaporating dish and watch glass
Mass of evaporating dish, watch glass, and
NaHCO3
Mass of NaHCO3
Mass of evaporating dish, watch glass, and
NaCl
Mass of NaCl
Calculations: Show all work, units, and SigDigs!
1. Calculate moles of NaHCO3:
2. Calculate moles of NaCl:
3. Calculate whole number mole ratio between NaHCO3 and NaCl:
______ moles NaHCO3 : ______ moles NaCl
4. Write a balanced chemical equation for the reaction of NaHCO3 and HCl:
5. Using stoichiometry, calculate the theoretical yield of NaCl that you would expect to produce based on your
starting quantity of NaHCO3:
6. What is the % yield of NaCl (based on the quantity actually produced):
7. Use your knowledge of mole ratios, oxidation numbers, and chemical formulas to solve the following
problem:
1.46 grams of HCl was used to completely react with 3.27 grams of an unknown carbonate compound
(molar mass = 327 g/mol). Determine the mole ratio between the carbonate compound and the HCl, then
fill-in all of the blanks below.
____ X(CO3)_____
+
____ HCl
--------> ____ XCl_____
+
____ H2O
+
2 CO2