Percentage Composition of Hydrates Lab
Hydrates are chemical compounds that have a specific amount of water in the structure
of the compound. This water can be removed from the chemical compound by heating.
The term associated with the leftover solid is anhydrous salt.
We can determine the percentage of water within a hydrate by measuring the mass of the
hydrate and the mass of the anhydrous salt. The amount of water removed from the
hydrate is equal to the difference between the hydrate mass and anhydrous salt mass.
% Water = mass of water
x 100
mass of hydrate
We will be working with manganese (II) sulfate monohydrate (MnSO4H2O). This
hydrate has a slight pink color and as it is converted to the anhydrous salt, the color
should become whiter.
Purpose:
 Experimentally determine a hydrate’s water composition
 Continued practice with Bunsen burner technique
Safety Precautions
 Goggles
 Apron
 Gloves—when handling chemical compound
 Proper Bunsen burner technique—ASK, before acting! **Refer to your technique
sheet**
Procedure:
1) Clean and dry your evaporating dish with distilled water.
2) Prepare a ring-stand set-up as shown in the demonstration at the front of the
classroom.
3) Place the EMPTY evaporating dish on the wire gauze and heat it using the hottest
flame (blue cone) for 3 minutes. This heating ensures complete drying of the
evaporating dish.
 NOTE: light the Bunsen burner AWAY from the ring stand set up
and then place the burner under the wire gauze.
4) Turn the burner OFF and remove the evaporating dish from the ring stand using
crucible tongs. Place the dish on the lab bench to cool for several minutes.
5) Obtain the mass of the evaporating dish once it has cooled using a balance.
Record this mass in the data section.
6) Leave the evaporating dish on the balance and measure out exactly 1.000g of
manganese (II) sulfate monohydrate. Record the mass of both the dish and
compound in the data section.
7) Place the evaporating dish with the hydrate on the wire gauze and heat the dish
gently. Move the burner back and forth under the dish to ensure an even
distribution of heat. GRADUALLY increase the heat.
 NOTE: light the Bunsen burner AWAY from the ring stand set up
and then place the burner under the wire gauze.
8) Heat the dish for 5 minutes or until the color has disappeared.
9) Remove the dish from the wire gauze and allow it to cool for 2 minutes.
10) Immediately obtain the mass of the dish + anhydrous salt. Record this mass in the
data section.
11) Bring the evaporating dish back to your lab area and squirt distilled water on the
anhydrous salt. Note any color change in the data section.
12) Clean your lab area, wash the evaporating dish, and place the anhydrous salt in
the trashcan.
Data Table:
Mass of evaporating dish (g)
Mass of dish + hydrate (g)
Mass of hydrated sample (MnSO4H2O)
(g)
Mass of dish + anhydrous salt (g)
Mass of anhydrous salt (dehydrated
sample) (g)
Calculations and Data Analysis:
1) Calculate the mass of water lost from the hydrate in grams. How many moles?
2) Find the percent of water lost from the hydrate.
3) Calculate the theoretical yield. How well did you perform the lab? Theoretical
yield is the yield/result you SHOULD have if you followed the procedure
perfectly.
 Add up the mass of one water molecule = __________________

Add up the mass for the whole compound = _________________

Theoretical yield = (mass of water/mass of whole compound)x100
4) Percent Error—calculate the your % error using the following formula. Anything
under 10% is good in a high school laboratory setting.
Percent Error = (experimental percent of water/theoretical percent of water) x 100
**In your lab report, your results should include the mass of your dehydrated sample, the
mass of hydrated sample, the mass of water lost from the hydrate, and the percent of
water lost by the hydrate in the experiment. **