Question

1. While performing the formula of hydrate laboratory experiment, the lid accidently slips over the crucible to completely seal the crucible.

a. What effect this change will cause on your calculated experimental results? Explain.

b. Would your calculated percent water of hydration be high, low or unaffected? Explain your anwer.

2. A student was asked to identify a sample of unknown hydrate. Student was provided with the following experimental data.

[ 3.51g sample of the hydrate when heated loses water completely and the mass of the residue was found to be 2.22g. ]

Student was provided with two reference compounds from which student needs to identify the unknown: Cu(NO3)2 * 3H2O *6 H2O.

Answer the followings.

a. Calculate percent water of hydration in the sample. (show your calculations)

b. Identify the formula of the hydrate.

c. Calculate the percent error in the number of water molecules.(if any)

d. List some possible source of error (if any.)

Answer 1

% water of hydration

= (mass of water/total mass of sample )×100 ............(1)

Mass of water = mass of water evaporated from salt by heating =mass of sample before heating - mass of sample after heating

1a) Since the lid has sealed the crucible so water will not be given off completely. The number of water molecules of hydration calculated will be less.

b) From (1) it is clear that % water of hydration calculated will be less because numerator value is less than the actual value.

2