a. If you had 1 mole of CaSO4.2H2O, how many moles of H2O would you have? b. If
ID: 838669 • Letter: A
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