Ok, this is a section from my lab report. Skim through it briefly:
First off, set up a Bunsen burner to be able to hold an evaporating dish. Find the mass of the evaporating dish, and record that mass. With the evaporating dish on the balance, measure 1.00 g of copper sulfate hydrate. Record the mass. Place the evaporating dish and hydrate over the heat source. Heat the sample slowly at first, then increase the heat as time progresses. Avoid any splattering and popping. Heat strongly for 5 minutes or until the blue color has disappeared. During heating, a stirring rod may be used to spread the solid and break up any caked portions of the hydrate. Be careful not to pick up any of the solid on the stirring rod. If the edges of the solid appear to be turning brown, remove the substance from the heat momentarily and resume heater at a gentler rate. Allow the evaporating dish to cool. Find the mass of the dish and anhydrous salt. Record the mass. Reheat the sample. Allow it to cool. Find the mass of the dish and anhydrous salt. Record the mass. Continue to reheat until the mass of the anhydrous salt remains constant.
Data and Calculations:
Mass of hydrate: 1.05g
Mass of anhydrous salt: 0.70g
Mass of water lost: 0.35g
Moles of anhydrous salt: 4.39x10-3 mol
Moles of water lost: 1.94x10-2 mol
% water in hydrate (by mass): 48.57% water
% water in hydrate (by moles): 81.58% water
Ok, now, I must find the empirical formula of the hydrate. Can someone walk me through this step by step? (Our teacher sucks)
First off, set up a Bunsen burner to be able to hold an evaporating dish. Find the mass of the evaporating dish, and record that mass. With the evaporating dish on the balance, measure 1.00 g of copper sulfate hydrate. Record the mass. Place the evaporating dish and hydrate over the heat source. Heat the sample slowly at first, then increase the heat as time progresses. Avoid any splattering and popping. Heat strongly for 5 minutes or until the blue color has disappeared. During heating, a stirring rod may be used to spread the solid and break up any caked portions of the hydrate. Be careful not to pick up any of the solid on the stirring rod. If the edges of the solid appear to be turning brown, remove the substance from the heat momentarily and resume heater at a gentler rate. Allow the evaporating dish to cool. Find the mass of the dish and anhydrous salt. Record the mass. Reheat the sample. Allow it to cool. Find the mass of the dish and anhydrous salt. Record the mass. Continue to reheat until the mass of the anhydrous salt remains constant.
Data and Calculations:
Mass of hydrate: 1.05g
Mass of anhydrous salt: 0.70g
Mass of water lost: 0.35g
Moles of anhydrous salt: 4.39x10-3 mol
Moles of water lost: 1.94x10-2 mol
% water in hydrate (by mass): 48.57% water
% water in hydrate (by moles): 81.58% water
Ok, now, I must find the empirical formula of the hydrate. Can someone walk me through this step by step? (Our teacher sucks)
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all you need to do is reduce the mole ratio of CuSO4 to H2O to the smallest whole number ratio
4.39E-3 CuSO4 : 1.94E-2 H2O
divide through by the smaller
1.00 CuSO4 : 4.42 H2O
now comes the problem
ordinarily you would round the numbers to the closest fraction
1/1 CuSO4 : 22/5
then multiply by LCD (5)
5CuSO4:22H2O
but
it should be CuSO4:5H2O
I would guess that not all of the water was driven off in the experiment
4.39E-3 CuSO4 : 1.94E-2 H2O
divide through by the smaller
1.00 CuSO4 : 4.42 H2O
now comes the problem
ordinarily you would round the numbers to the closest fraction
1/1 CuSO4 : 22/5
then multiply by LCD (5)
5CuSO4:22H2O
but
it should be CuSO4:5H2O
I would guess that not all of the water was driven off in the experiment
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You want to find the mole ratio of CuSO4 to H2O. From the experiment you have found the weight ratio.
From mass and the formula weights you calculate moles!
mole CuSO4 = 0.70 g CuSO4 x 1 mol CuSO4/160 g CuSO4 = 0.0044 mol CuSO4
mole H2O = 0.35 g H2O x 1 mol H2O/ 18 g H2O = 0.019 mol H2O
Now divide each by the smallest number of mole to set the ratio of the smallest to 1
0.019 mol H2O / 0.0044 mol CuSO4 = 4.3
0.0044 mol CuSO4 / 0.0044 mol CuSO4 = 1
From your data the mole ratio is 4.3 to 1 or in simplest whole numbers 4:1 So the empirical formula from your data is CuSO4*4H2O.
The actual formula is CuSO4*5H2O so I suspect a little more heating was needed to vaporize off more water.
From mass and the formula weights you calculate moles!
mole CuSO4 = 0.70 g CuSO4 x 1 mol CuSO4/160 g CuSO4 = 0.0044 mol CuSO4
mole H2O = 0.35 g H2O x 1 mol H2O/ 18 g H2O = 0.019 mol H2O
Now divide each by the smallest number of mole to set the ratio of the smallest to 1
0.019 mol H2O / 0.0044 mol CuSO4 = 4.3
0.0044 mol CuSO4 / 0.0044 mol CuSO4 = 1
From your data the mole ratio is 4.3 to 1 or in simplest whole numbers 4:1 So the empirical formula from your data is CuSO4*4H2O.
The actual formula is CuSO4*5H2O so I suspect a little more heating was needed to vaporize off more water.