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# need serious help with as chem Watch

1. got these questions i need help and advice

recomended daily allowance of zinc is 15.2mg (0.0152g)

1)calculate the relative molecular mass of hydrated zinc sulphate crystals
ZnSO4.7H2O
(assume 1 mole of hydrated zinc sulphate contains 1 mole of zinc)

2) this is normally taken via 5cm3 dose of an aqueous solution of hydrated zinc sulphate calculate the concentration of this solution in g dm-3

2. (Original post by woodsy344)
got these questions i need help and advice

recomended daily allowance of zinc is 15.2mg (0.0152g)

1)calculate the relative molecular mass of hydrated zinc sulphate crystals
ZnSO4.7H2O
(assume 1 mole of hydrated zinc sulphate contains 1 mole of zinc)

2) this is normally taken via 5cm3 dose of an aqueous solution of hydrated zinc sulphate calculate the concentration of this solution in g dm-3

Presumably you can do part 1.

For part 2 you are gonna need 5cm3 to contain 15.2mg, so calculate this mass in moles ( = mass(g)/Mr) and then use:

concentration = moles/vol(litres)

to work out the concentration.
3. 1) Add up the masses of the individual elements from the periodic table.

2) You need 15.2mg of zinc in your 5ml solution. Work out how many moles of zinc this is (ballpark figure: 0.0002 moles) so using the mass you found in 1) you should be able to calculate the mass of hyd. zinc sulphate in 5ml of solution (ballpark figure: 0.06g). Extrapolate up to how many grams you need in 1dm3 and you have your answer (ballpark figure: 13g/dm3)

N.B. The balpark figures are not correct but give you an idea if you are along the right lines in terms of decimal places!
4. sorry i had the questions mixed up thanks for your help but i still dont get it

the questions were
question 1 the realative molecular mass

question 2 calculate the mass of hydrated zinc which would be needed to be taken to obtain the rda for zinc (15.2g)

question 3 normally this mass is taken via 5cm3 dose of aqueous solution of hydrated zinc sulphate calculate the concentration of this solution in g dm-3

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