What is the molecular formula of ..?

Question

A sample of NiCl*H2O is found experimentally to contain 0.0116 moles of H2O, 0.0055 moles of Ni, and 0.00121 moles of Cl. What is the molecular formula of NiCl*H2O? How can I calculate it?

In the actual question, it says Ni(subscript x)Cl(subscript y) * zH2O, but i dont really think those are important. And does anyone know why they are there or why the z is infront of the water molecule and not a subscript?

Answer 1

The good news is that everything is already given in moles and you don't need to convert from grams to moles first.

Select the smallest number of moles given (0.00121 mol Cl) This has to be the lowest subscript. To find the other subscripts you will determine the lowest whole-number ratio of the moles. This sounds hard, but all you do is divide each number of moles given by the lowest number of moles (0.00121 mol Cl)

0.0116 mol / 0.00121 mol = 9.56
0.0055 mol / 0.00121 mol = 4.55
0.00121 mol / 0.00121 mol = 1

Since you cannot have a subscript with a decimal, multiply each answer by 2 to remove the fractional denominator (0.5 = 1/2)

9.56 x 2 = 19
4.55 x 2 = 9
1 x 2 = 2

Ni9Cl2*19 H2O

Answer 2

to answer the second part, the x and y are there to show you that the formula given (NixCly) is not complete, you need to find out what the x and y are. The z in front of the H2O means how many moles of water there are per mole of NiCl. It's not a subscript because the formula for H2O is correct, and doesn't need to change. You just need to find out how many H2O are present.

Here is how you do it:
get the simplest whole number ratio of the moles of each part, divide each one by the smallest number
0.0116 mol H2O / 0.00121 = 9.6
0.0055 mol Ni / 0.00121 = 4.5
0.00121 mol Cl / 0.00121 = 1

then multiply to get whole numbers, that will give you the numbers to put into your formula

side note: are you sure this problem is written correctly? The ratios don't make sense at all. The most likely formula is NiCl2•6H2O, but your numbers don't match that.

Answer 3

The z is a coefficient and will count the number of the hydrate.

The smallest mol will be sub scripted as 1. then just divide all the others by that to get their whole integers. ( May be a fraction, which you will have to multiply to get whole integer )

X and Y are place holding variables.

Answer 4

Well i do know that NiCl and H20 = salt water..