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# need help revision isnt relating to questions Watch

1. got these questions i dont understand

minerals containing zinc are important to the human body,since zn2+ ion os important in many enzymes. zinc sulphate can be used as a dietary supplement in cases of zinc deficiency. the compound crystalises as a hydrated salt, ZnSO4.7H20
and is soluble in water.
the recomended daily allowance (rdA) of zinc if 15.2mg (0.0152g)

1)calculate the relative molecular mass of hydrated zinc sulphate crystals ZnS04.7H20

2)calculate the mass of hydrated zinc sulphate crystals which would be needed to be taken to obtain the rda for zinc

3)normally this is taken via a 5cm3 dose of an aqueous soloution of hydrated zinc sulphate ZnSO4.7H2O. Calculate the concentration of this solution

please help i have no idea how to do these questions ive revised moles and it just isnt relating to it
2. a) relative molecular mass is the sum of the atomic masses so: ZnSO4.7H2O = 65 + 32 + (16*4) + 14 + (16*7) = 287?

b) moles of Zinc = mass of zinc (the rdA value ) / mr of Zinc
= 0.0152/65 = 2.3384 * 10^-4

mass of hydrated zinc sulphate = moles * mr
= 2.3384 * 10^-4 * 287
= 0.067g

c) concentration = moles / volume
= 2.3384 * 10^-4 / 5
=4.677*10^-5 cm3

I think thats how you would do them, I did chemistry A level last year but am on a gap year since and haven't really kept my knowledge up to date!
3. *10^-4 mean
4. multiply by ten to the power of minus four, otherwise known as 0.0001

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