I have the same question as Chopsticks
determine the emperical formula of the compound
25.3%copper, 12.9%sulphur, 25.7% oxygen, 36.1% water
Can the answer be CuSO4(H2O)5?
or does it have to be CuSO4 x 5H2O
thanks in advance.
Assume you have 100 g of the stuff.
25.3gCu=.398 mol Cu
12.9gS=.401 mol S
25.7gO=1.61 mol O
36.1gwater=2.01mol water.
Normalize, by dividing by the lowest number of moles
Cu 1
S 1
O 4
water 5
Yes, you are right.
You may right the formula as
CuSO4(H2O)5 or CuSO4.5H2O or CuSO4*5H2O.
Most texts write it as CuSO4.5H2O BUT these boards don't let us put the decimal point in the middle of the line so we write a period (.) or an asterisk (*). Neither means TIMES. CuSO4*5H2O is read as copper II sulfate with 5 molecules of water of crystallization or as copper II sulfate pentahydrate.
To determine the empirical formula of a compound, you need to calculate the ratio of each element present in the compound.
Let's start by assuming that we have 100 grams of the compound.
Given the percentages:
- 25.3% copper means we have 25.3 grams of copper
- 12.9% sulphur means we have 12.9 grams of sulphur
- 25.7% oxygen means we have 25.7 grams of oxygen
- 36.1% water means we have 36.1 grams of water
Next, we need to convert these masses into moles. To do this, we divide the mass by the molar mass of each element.
The molar mass of copper (Cu) is 63.55 g/mol, sulphur (S) is 32.07 g/mol, oxygen (O) is 16.00 g/mol, and water (H2O) is 18.02 g/mol.
- Copper: 25.3 g / 63.55 g/mol = 0.398 mol
- Sulphur: 12.9 g / 32.07 g/mol = 0.402 mol
- Oxygen: 25.7 g / 16.00 g/mol = 1.605 mol
- Water: 36.1 g / 18.02 g/mol = 2.00 mol
Now, to determine the ratio of each element, divide each mole value by the smallest mole value (which is 0.398 in this case).
- Copper: 0.398 mol / 0.398 mol = 1
- Sulphur: 0.402 mol / 0.398 mol = 1.01
- Oxygen: 1.605 mol / 0.398 mol = 4.04
- Water: 2.00 mol / 0.398 mol = 5.03
Based on these ratios, the empirical formula can be written as CuSO4 x 5H2O because the ratio of water molecules to the rest of the compound is close to 5.
So the answer is CuSO4 x 5H2O.