Video Lab Solutions
After you have viewed the video and recorded your data, check your answers below.
Mass of empty pipet
ANSWER
2.84 g
Mass of hydrate and pipet
ANSWER
3.27 g
Mass after 1st heating
ANSWER
3.11 g
Mass after 2nd heating
ANSWER
3.10 g
Calculations:
Check your solutions by hovering over the word Answer.
1. Using the data, calculate the mass of the water driven off.
ANSWER
3.27 g – 3.10 g = 0.17 g
2. Using your answer to number 1, calculate the number of moles of water driven off.
ANSWER
? mol H2O = 0.17 g H2O (1 mol H2O / 18.0 g H2O) = 0.0094 mol H2O
3. Using the data, calculate the mass of the “anhydrous” salt.
ANSWER
3.10 g – 2.84 g = 0.26 g CuSO4
4. Using your answer to number 3 and the fact that your “anhydrous” salt is copper (II) sulfate, calculate the number of moles of “anhydrous” salt.
ANSWER
? mol CuSO4 = 0.26 g CuSO4 (1 mol CuSO4 / 159.6 g CuSO4) = 0.0016 mol CuSO4
5. Using your answers to numbers 2 and 4, determine the formula of the hydrate.
ANSWER
0.0094/0.0016 = 6 CuSO4 x 6 H2O
(Note: The formula actually has 5 molecules of water. Remember that experimental error is possible.)
Conclusions:
1. A hydrate is a crystal with _____________ molecules adhering to the ions or molecules.
ANSWER
water
2. Define “anhydrous.”
ANSWER
the dry salt remaining after the water is driven off from the hydrated salr
3. Write the formula for hydrated zinc sulfate with 7 molecules of water adhering to each formula unit of zinc sulfate.
ANSWER
ZnSO4 • 7H2O
Video Quiz Answers:
Which of the following would be considered an empirical formula?
ANSWER
C3H8
Which of the following correctly represents the compound formed from the ions Sr2+ and Se2-?
ANSWER
SrSe
Which of the following represents the actual number of atoms of each element in a compound?
ANSWER
molecular formula
A compound has a molar mass of 52.0 g/mol and an empirical formula of CH. What is the molecular formula?
ANSWER
C4H4
The molecular formula for a given compound is always different from the empirical formula.
ANSWER
False
A compound with water molecules attached is called ______?
ANSWER
a hydrate
A hydrated compound has a mass of 1.73 g before it is heated. After it is heated completely and then allowed to cool, the compound has a mass of 1.68 g. What is the mass of the water driven off?
ANSWER
0.05 g