[Chimbote]

Ok here is the question:

You weigh out pure NaH₂PO₄.
Weight of Sodium Dihydrogen phosphate use: 0.4756g

This is dissolved, quantitatively transfered and diluted to 100ml in volumetric flask. 10ml of this is pipetted and again diluted to 100.00ml to make the original phosphate standard.
 Calculate:
                The Phosphate concentration of this solution in mM


I not sure how to start it. Frist i converted 0.4756 g to 475.6mg. What do i do next. DO i divide the MW of sodium dihydrogen phosphate to get the millimoles of solute?

[mike]

Don't use "Help me..." in your subject heading please

I would calculate the concentration in moles first then convert to millimoles at the end.

n = c x v

and

n = m/M

n = number of moles (moles) c = concentration (mol.L-1) v = volume (L) m = mass (g) and M = molecular weight (g.mol-1)