Question

Calculate the percentage of potassium, aluminum, oxygen, and sulfur in KAl(SO4)2 x 12 H2O.

Answer 1

Assume you have one mole of Alum. that means you have:

1 mole K= 39 grams

1 mole Al= 27 grams

2 moles S= 64grams

20 moles O= 320 grams (8 moles from the salt and 12 from the water)

24 moles H= 24 grams


So you have a total of 474 grams, because that is the molar mass of alum.

Figure out each percentage by dividing the mass of that element by the total mass. (remember we are ASSUMING you have 1 moles alum, you have to assume something to do it)

K = 39g/474g= 8.22%

Al= 27g/474g= 5.70%

O= 320g/474g= 67.5%

S=64g/474g= 13.5%

H=24g/474g= 5.06%

those all add up to 99.98%...rounding error