MTW RF A student is given a sample of red cobalt sulfate hydrate. She weighed th

Question

MTW RF A student is given a sample of red cobalt sulfate hydrate. She weighed the sample in a dry covered crucible and obtained a mass of 26.148 g for the crucible, cover, and sample. Before adding the sample, the crucible and cover weighed 24.322 g. She then heated the crucible to drive off the water of hydration, keeping the crucible at red heat for about 10 minutes with the cover slightly ajar. She then let the crucible cool, and found it had a lower mass; the crucible, cover and contents Show all calculations necessary to answer the following questions 1. What was the mass of the hydrate sample? 2. What is the mass of the anhydrous Coso,? 3. How much water was driven off? weighed 25.329 g. In the process the sample was converted to yellow anhydrous Coso g hydrate Coso 4. What is the percentage of water in the hydrate? mass of water in sample × 100 % water = % H,O - assof hydrate sample 5. How many grams of water would there be in 100.0 g of hydrate? How many moles? g H,O; moles H,O n:

Explanation / Answer

Mass of crucible and cover= 24.322 gm

Mass of crucible, cover and sample= 26.148 gm

Mass of sample = mass of sample, cover and crucible- mass of cover and crucible = 26.148-24.322 =1.826 gm (1)

Mass of crucible, cover and sample after heating= 25.329 gm

Mass of sample after heating = mass of sample,cover and crucible after heating- mass of crucible and cover

Mass of sample after heating= 25.329-24.322 = 1.007 gm (2)

Heating removes water of hydration and hence

Mass of water removed = Eq.2-Eq.1= 1.826-1.007 =0.819 gm

Mass % of water in the hydrate= 100*0.819/1.826= 44.85

Hence in 100 gm, there will be 44.85 gm of water

Moles= mass of water/ molar mass =44.85/18= 2.491 moles

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