8.5/15
Chemistry 101
Experiment 2: Empirical Formula and Avogadro’s Number
Pre-lab Assignment
Name: Adam Chebli
Date:23/10/24
Section:B6
•
An analysis shows that 5.85 g of a chromium metal combines with oxygen to form
8.62 g of chromium oxide. What is the empirical formula of the compound?
Cr2O3
(-4 show your work)
•
The formula for rust can be represented by Fe2O3.
• How many moles of Fe2O3 are present in 24.6 g of the compound?
0.154 mol (-0.5 show your work)
•
How many moles of Fe are present in 24.6 g of the compound?
0.308 mol (-0.5 show your work)
•
How many atoms of oxygen are present in 24.6 g of the compound?
2.78*1023 atoms
(-0.5 show your work)
•
Zinc metal has a hexagonal close packed structure. Calculate the volume of a unit cell of
of Zn in cm3.
3.043*10-23 cm3
(-1 show your work)
-1 for significant figures
27/30
Chemistry 101
Experiment 2: Empirical Formula and Avogadro’s Number
Lab Report
Name: Adam Chebli
Part 1
Data:
Date:23/10/24
Mass of 125 mL Erlenmeyer flask = 93.3352 g
Mass of 125 mL Erlenmeyer flask + zinc granules = 94.3574 g
Mass of 125 mL Erlenmeyer flask + zinc granules + iodine= 95.3402 g
Mass of 150 mL beaker = 79.5700 g
Mass of Erlenmeyer flask + unreacted zinc = 94.0866 g
Mass of beaker + zinc iodide = 84.7673 g
Calculations:
Mass of zinc granules = 1.0222 g
Mass of iodine = 0.9828 g
Mass of iodine + zinc (before reaction) = 2.005 g
Mass of unreacted zinc = 0.7514 g
Mass of zinc iodide = 5.1973 g
Mass of reacted zinc = 0.2708 g
Mass of reacted iodine + reacted zinc = 1.2536 g
Mass of unreacted zinc + product = 5.9484 g
Moles of reacted zinc = 0.00414 mol
g/mol)
(Molar mass of Zinc = 65.39
Moles of reacted iodine = 0.00774 mol
(Molar mass of Iodine = 126.9
g/mol)
Ratio of moles of one element to the other = iodine to zinc= 1.90:1.00 = 2.00:1.00
Empirical formula of zinc iodide = ZnI2
Questions
•
Write a balanced chemical equation for the reaction of zinc with iodine.
Zn(s) +I2(s) → ZnI2(s)
•
•
Show by referring to calculations whether mass is conserved in a chemical reaction.
mass of reactants=2.005 g mass of product= 5.1973 g, mass of reactants is not equal to
mass of products, therefore mass is not conserved in this chemical reaction.
Part II
a-Density of distilled water:
Data and calculations:
Trial 1
Trial 2
Mass of empty dry flask
36.6965 g
Omitted
Mass of flask with water
87.5294 g
Volume of water in the
volumetric flask
50.0 ml
Mass of water
50.8329 g
Density of water
1.02 g/mL
b-Density of zinc metal
Data and calculations:
Trial 1
Mass of zinc
1.6039 g
Mass of flask with water
and zinc
88.6030 g
Mass of water and zinc
51.9065 g
Trial 2
Omitted
Mass of water
50.3026 g
Volume of water
49.5 mL
Volume of Zn
0.5 mL
Density of Zn
3.062 g/mL
Volume of unit cell of Zn
3.043x10-23 cm3
Avogadro’s number NA
(experimental)
1.403*10^24
% error on Avogadro’s
number
132.2%
Average of Avogadro’s
number NA (experimental)
------
% error on Avogadro’s
number
Questions
•
How many moles are in 1.5 g of zinc? How many atoms?
0.023 mol
1.4*1022 atoms
(show your work -1)
•
If the displaced water in the volumetric flask is not removed completely to the mark, what
effect will that have on the calculated density of zinc? Explain
The volume of zinc is calculated by subtracting the displacement of volume of water. If the water
level was lower than the mark, then the volume of zinc would be higher and if the water level
was above the mark, then the volume of zinc would be lower leading to incorrect density
readings. (incorrect how? -1)