6: Lab Water of Hydration
Name: Smrithi Prem Partner: Michael? Objective: The objective of this lab is to determine the number of moles of water in the hydrated compound. Material and Equipment: 1. 2. 3. 4. 5. 6. Two beakers Scale Hot plate Desiccator Magnesium sulfate.nH2O Nickel Sulfate. nH2O Date: March 9th 2005 Lab Section : 9-5 class sect: 9-4
Procedure: First, weigh the beaker and then take about 1.0-1.5 grams of the compound in the beaker. Place the beaker with the compound on the scale and record the weight. Then place the beaker with the compound on the hot plate and heat for about 10 minutes or until water is thoroughly removed. Take the beaker and place it in the desiccator to allow it to cool. Once the sample is cooled, take the weight and record it. Repeat the same procedure for the second sample. Data and Observation Data: 1. Mass of beaker = 51.59 g 2. Mass of beaker + MgSO4.nH2O = 52.70 g 3. Mass of MgSO4 + beaker = 52.15 g 4. Mass of MgSO4.nH2O = 1.11 g 5. Mass of MgSO4 = 0.55 g Observation: On heating the MgSO4.nH2O, the compound starts wiggling and jumping. When water is added to the already dried magnesium sulfate, it absorbs water. Calculations:
Mass of hydrated compound (MgSO4.nH2O) = 1.11g Mass of MgSO4 = 0.55 g Molar mass of MgSO4 = 24.31+ 32.06+64.0 = 120.37 Moles MgSO4 of = 0.55 g x 1 mole 120.37 g = 0.00456 moles MgSO4.nH2O = 1.11g MgSO4 = 0.55 g Therefore, mass of water, n.H2O = 1.11 - 0.55 = 0.56 g Molar mass of water = 2.02 + 16 = 18.02 g Moles of water, H2O = 0.56 g x 1 mole 18.02 g = 0.0311 moles Moles of water of hydration = 0.0311/0.00456 = 6.81 ~ 7.0 Therefore n = 7 Conclusion: The number of moles of water of hydration can be determined by knowing the weight of hydrated compound and the weight of the dry compound. The dry compound is obtained by heating the hydrated compound. Questions: 1. Explain how the calculated value of n would be affected if all of the water wasnt heated off. (ie would the calculated be higher or lower than the actual value and why?) Ans: The calculated value of n will be lower than the actual value because the mass of water will be lower if it is not heated off well. When the mass is lower, the moles of water of hydration will be lower. 2. What experimental evidence (observations) do you have that the water molecules are weakly bonded to the ionic compound although they may not be a part of it? Ans: On heating the compound, the water molecules are easily liberated from the compound indicating that they are weakly bonded to the compound. Also, the dry compound absorbs water easily by simply exposing to moisture.