# Quantitative chemistry

#### rahmatkat

I have an assignment that i have to do this weekend and i was wondering if anyone can help me with it, here's the only question that I don't understand;

1)calculate the mass of the water that will react completely with 4.0g of pure calcium metal according to the following equation:

Ca(s) + 2H2O ------ Ca(OH)2(s) + H2(g)

Ar(H) = 1, Ar(O) = 16, Ar(Ca) = 40

I don't know how to convert mole ratio to mass ratio.

Last edited:
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#### symbolipoint

Homework Helper
Education Advisor
Gold Member
You simply need to convert the mole ratio to mass ratio. Once done, use it.

What is the formula weight for Calcium? What is the formula weight for water, H2O ?

#### rahmatkat

I have add the formula weight of water and calcium, and I don't know how to convert mole ratio to mass ratio cause i forgot how.

#### Borek

Mentor
Consult your textbook please. "I forgot" is rather weak reason to ask for help.

#### rahmatkat

sorry but I don't have a text book, that why I was asking for your help guys. I know that it sounds funny but in our school we weren't given any text books, we just have to rely on our teachers notes, the reason is that we don't have much, and another problem is that i left my form five chemistry text book in Kiribati, I'm in fiji right now, so I wish you guys can help me with this problem, i'll be clad to received your help.

#### Borek

Mentor
It boils down to the conversion between numer of moles of mass of the substance.

n=m/M

where
n - number of moles
m - mass of the substance
M - molar mass

So, you are from Kiribati? Rather remote place.

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