After 0.6523 g of CoCl2 • 6 H2O is heated, the residue has a mass of 0.3423 g. Calculate the percent H2O in the hydrate. What is the formula of the hydrate?

Question

Can someone help me with this?

Answer 1

The mass lost is the mass of water that was removed during heating:

0.6523 g -0.3423 g = 0.31 g water in the hydrate

 

If water made up 0.31g of the total 0.6523 grams of hydrated compound, then we can find the percent water by dividing their masses and multiplying by 100%:

 

% water in the hydrate = (0.31g water/0.6523 g hydrate) x 100 = 47.53%

 

So water makes up 47.53% of the hydrate, and we know so because that percent of the mass was removed during heating. 

 

It looks like that formula of the hydrate was already given: CoCl2 • 6 H2O 

This matches what we've found, because the total molar mass of the hydrate is about 238g, and water makes up 47.53% of that, as well:

[(6x18g)/238] = 47.53%