Activity Two: Determining relative atomic mass by experimentation
In this experiment you will synthesize a compound, zinc chloride, and determine the mass ratio of
zinc to chlorine. Using the experimental data, the relative mass for each element and the chemical formula
of zinc chloride will be determined. The reaction in words:
zinc
+
hydrochloric acid
----->
zinc chloride
+
hydrogen gas
Construct a data table which should include:
First Day:
mass of beaker
mass of beaker + zinc
mass of zinc
mass of beaker + solid (zinc chloride)
mass of zinc chloride
mass of chlorine that combined with the zinc
Second Day:
A. First Day:
1. Weigh a clean, dry 100 ml beaker and label it with your lab group’s name.
2. Add 0.65 g of granular zinc to the beaker and record the exact mass.
3. Add 15 mL of dilute hydrochloric acid and record your observations.
4. Set the beaker aside to react completely overnight.
Begin Activity Three – This is an extreme thinking activity. Put your brains and algebra to work!
B. Second Day:
1. Evaporate the solution to dryness over a burner. Heat gently, as strong heating may result in
splattering your product.
2. Extended heating will melt the solid. When the solid melts stop heating.
3. When the beaker has cooled, weigh the beaker and solid.
4. Wash the beaker with water to remove the solid.
Findings
1. Calculate the mass ratio of chlorine to zinc in your sample. Compare your ratio with other lab groups
and compute an average ratio for chlorine to zinc.
2. You started with 1/100 the relative mass of zinc, 0.65g. If each atom of zinc combined with one atom of
chlorine, the formula of zinc chloride would be ZnCl. The mass of zinc chloride would be
zinc
chlorine
zinc chloride
0.65 g
0.35 g +
1.00 g
If each atom of zinc combined with two atoms of chlorine, the formula of zinc chloride would be ZnCl2.
How much zinc chloride would be formed?
3 From separate experiments it is determined that oxygen has a relative mass of 16.00 and in the
compound ZnO the zinc to oxygen mass ratio was 4.086 to 1. What is the relative mass of zinc?
4.Assume that you had one zinc atom for each chlorine atom in your sample. Using your average ratio
from number 1, calculate the relative mass of chlorine.
5. If you had two chlorine atoms for each zinc atom in your sample what would be the relative mass of
chlorine?
6.In another experiment a chlorine to oxygen ratio of 2.219 to 1.00 was found (O = 16.000 amu).
Calculate the relative mass of chlorine in this experiment. Based upon the data from this experiment and
your experiment, does zinc chloride have one atom of zinc to one atom of chlorine or does it have one atom
of zinc to two atoms of chlorine? Write a valid formula for the compound zinc chloride (ex. CuCl ) and
2
explain your selection. Use Data from this lab to substantiate your formula.
Further Extension: The mole concept
1. A mole is the SI unit of amount. One mole is equivalent to 6.02 x 10^23 particles. The mass of 6.02 x
10^23 particles varies with the type of particle. One mole or 6.02 x 10^23atoms of carbon has a mass of
12.0 grams. Since titanium atoms are 3.99 times as massive as carbon atoms, then what is the mass of one
mole of titanium atoms?
2. The mass of one mole is also called the molar mass. If lithium atoms are 0.578 as massive as carbon
atoms, what is the molar mass of lithium if the molar mass of carbon is 12.0 grams?
3. If 6.02 x 10^23 atoms of Mg are 2.025 times as massive as carbon atoms what is the mass of one mole if
carbon having a molar mass of 12.0 grams?