Amount of substances

Hi, I'm new to chemistry and I have problem in answering the questions below. Hope anyone can help, thanks. :smile:

Find the number of moles
g)of hydroxide ions in 29.6 g of calcium hydroxide
i)of water molecules in 5.16 gof calcium sulphate-2-water, CaSO4.2H20.

Find the empirical formula for each of the following compounds.
d)an oxide of phosphorus, 0.89 g of which are formed from 0.39 g of phosporus

Find the molecular formula for each of the following compounds:
e)0.02moles of a substances has a mass of 0.94 g and this mass contains 0.80 g of mercury, the rest being chlorine.

1.8
a)Silver suphate has the formula Ag2SO4. What mass of silver sulphate contains one mole of silver ions?
b)Aluminium hydroxide has the formula Al(OH)3. Find the mass of aluminium hydroxide which contains0.02 mol of hydroxide ions.
c)Sodium carbonate-10-water has the formula Na2CO3.10H20. Find the mass of it which contains 2 mol of water of crystallization.

Reply 1

NathanM

g)Start off by writing your equation Ca(OH)₂ or ionically; Ca²⁺+2OH^-

1 mole calcium hydroxide = 57g
29.6g = 0.519 moles

therefore, there are 2*0.519 moles OH = 1.038 moles

i)1mole = 154.1g
5.16g = 0.033 moles therefore there are 2*0.033 moles water = 0.066moles

d&e) It's been a while since I last did empirical formula, and can't remember how it's done...sorry :redface:

a) since you have 2 moles of silver in each mole of silver sulphate, then 0.5 mole of silver sulphate contains 1 mole of silver ions
1 mole silver sulphate = 204g; 0.5M=102g

am too tired to try the other two...am so sorry...will try the other ones in the morning :wink:

Reply 2

Civ-217

Thank you. :smile:

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