1. Complete the following table. For each of the hydrates: 1) write the chemical

Question

1. Complete the following table. For each of the hydrates: 1) write the chemical formula; 2) calculate the formula mass; and 3) calculate the mass percentage of water. Chemical Formula Fomula | Mass % Water Hydrate Mass Nickel(lI)chloride hexahydrate Cobalt(I)chloride hexahydrate Copper(I)sulfate pentahydrate 2. A student dehydrated an unknown hydrate. The mass of the compound was initially 4.13 g. After heating, the mass was 3.52 g. a. Calculate the mass percentage of water in the hydrate. b. The table below lists the possible hydrates that could be your unknown. Complete the table. c. Compare the mass% values to determine the identity of your unknown. d. Unknown Identity Hydrate CuSO4·5H20 BaCl2 2H20 Mass Salt (g) | Mass water (g) Mass Percent (%) “ Previous Page Page 50 of 73 Next Page»

Explanation / Answer

Q1) percentage of water by mass = mass of water in the formula/ formula mass

S.No. chemical formula formula mass % of water by mass

1. NiCL2.6H2O 237.69 45.09%

2. CoCl2.6H2O 237.93 45.39%

3. CuSO4.5H2O 249.72 36.09%

Q2)

The mass of sample = 4.13 g

mass of anhydrous sample after heating = 3.52 g

Thus mass of water = 4.13 -3.52 =0.61 g

therefore % mass of water = (0.61g/ 4.13) x100

= 14.76%

b)

S.No. chemical formula formula mass % of water by mass

1. CuSO4.5H2O 249.72 36.09%

2. BaCl2.2H2O 244.27 14.73%

3. MgSO4.7H2O 246.5 51.11%

c) Comparing these values with the unkown BaCL2.2H2O has the same % of water as that of unknown.

d) unknown identity = BaCl2.2H2O

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