a. If you had 1 mole of CaSO4.2H2O, how many moles of H2O would you have? b. If

Question

a. If you had 1 mole of CaSO4.2H2O, how many moles of H2O would you have?

b. If you had 0.681 moles of CaSO4.2H2O, how many moles of H2O would you have?

2. You have a 1.00 g sample of a hydrate of Na2CO3. By heating the compound, you drive off the water and are left with 0.3704 g of the anhydrous compound.

a. What mass of water has been driven off?

b. What is the % by mass of Na2CO3 in the hydrate?

c. What is the % by mass of water in the hydrate?

d. If you had started with 1.623 g of the hydrate, what mass of water would you expect to lose upon heating?

3. Borax (a laundry additive you can buy in the grocery store) is a hydrated sodium tetraborate compound and contains 47.24% water by mass. If you have 15.00 g of borax, how many grams of water are present in the sample?

4. Name the following hydrates

a. Ba(OH)2.8H2O
b. LiClO4.3H2O
c. SnCl4.4H2O
d. Cu2SO3.H2O

Explanation / Answer

1a) Look at the formula: CaSO4, 2H2O. So 1 mole of CaSO4, 2H2O contains 2 moles of water.

1b) So 0.681 moles of CaSO4, 2H2O will contain 0.681 x 2 = 1.362 moles of water

2a) Mass of water diven off = 1 - 0.3704 = 0.6296 g

2b) % mass of Na2CO3 in hydrate = (0.3704 /1) x 100 = 37.04 %

2c) % mass of water in hydrate = (0.6296 /1) x 100 = 62.96 %

2d) Water expelled = 62.96 % of 1.623 g = 1.623 x (62.96 / 100) = 1.02 g

3) Water present = 47.24 % of 15 g = 15 x (47.24/100) = 7.086 g

4a) Barium Hydroxide Octahydrate

4b) Lithium perchlorate trihydrate

4c) Tin (IV) Chloride Pentahydrate or Stannic Chloride Pentahydrate

4d) Copper (I) sulphite monohydrate or Cuprous sulphite monohydrate

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