Thanks for your help.

I have a problem to solve et don't know how to do part of it.

We have a solution of XNO3 (X = monovalent cation
We add a solution of K2SO4.
We obtain an insoluble sulfate which precipitate and KNO3

The precipitate = 3.900 g

The analyses shows that the precipitate contains 10,263% of S and that its molar mass = 312 g/mol

1) Find the equation

My equation is: 2XNO3 + K2SO4 = X2SO4 + 2KNO3

2) What's the mass of SO4?

3) What's the molar mass of Cation X?

my answer is: (312-32-16X4)/2 =108

I can't find the answer of the second question

Thank you for your help

find moles of S.

molesS=totalmass*.10263/32=.39/32= .0122
molesO=4*.0122=.0488
massO=.0488*16=.788 grams
massX=(3.9-.788-.39)=2.72
molesX=2*.0122=.0244
molemassX=mass/moles=2.72/.0244=111.5
check that, most of it was in my head.

Thank you. It is all right. I've understood.

Have a nice day

To answer the second question about the mass of SO4, we need to use stoichiometry and the molar mass of the precipitate.

1) From the balanced equation you provided:
2XNO3 + K2SO4 = X2SO4 + 2KNO3

We can see that the ratio of K2SO4 to X2SO4 is 1:1. This means that for every 1 mole of K2SO4, we will get 1 mole of X2SO4.

2) Given that the molar mass of the precipitate, X2SO4, is 312 g/mol, we need to find the mass of SO4 in that compound.

From the periodic table, we know that sulfur (S) has a molar mass of 32 g/mol, and oxygen (O) has a molar mass of 16 g/mol. Since there are 4 oxygen atoms in the sulfate ion (SO4), the molar mass of the sulfate ion is:
32 g/mol + (16 g/mol x 4) = 96 g/mol.

Therefore, the mass of SO4 in X2SO4 is 96 g/mol.

In the chemical equation, we see that 1 mole of X2SO4 corresponds to 1 mole of SO4. So, to find the mass of SO4, we need to multiply the molar mass of SO4 by the ratio of the molar mass of X2SO4 to the molar mass of SO4:

Mass of SO4 = (Mass of X2SO4 / Molar mass of X2SO4) x Molar mass of SO4

Plugging in the known values:

Mass of SO4 = (312 g/mol / 312 g/mol) x 96 g/mol
Mass of SO4 = 96 g/mol

Therefore, the mass of SO4 in the precipitate is 96 g.

Please let me know if you need further assistance or if you have any other questions!