# Video 703 Solutions and Answers

### Video Lab Solutions

Mass of empty pipet

2.84 g

Mass of hydrate and pipet

3.27 g

Mass after 1st heating

3.11 g

Mass after 2nd heating

2.84 g

Calculations:

1. Using the data, calculate the mass of the water driven off.

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.

? 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.

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.

? 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.

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.

water

2. Define “anhydrous.”

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.

ZnSO4 • 7H2O

Which of the following would be considered an empirical formula?

C3H8

Which of the following correctly represents the compound formed from the ions Sr2+ and Se2-?

SrSe

Which of the following represents the actual number of atoms of each element in a compound?

molecular formula

A compound has a molar mass of 52.0 g/mol and an empirical formula of CH. What is the molecular formula?

C4H4

The molecular formula for a given compound is always different from the empirical formula.

False

A compound with water molecules attached is called ______?