Percentage by Weight

[piraterach]

I have been given 3 concentrations of Ti. (200, 500 and 720 micromolL-1) How do i find the percentage by weight of these 3 samples?

RMM Ti = 47.88
(started as 50mg, added to 10ml nitric acid, 2ml of solution taken and diluted to 50ml)

Thanks

[Teddio]

1 mole per litre of Titanium ions will have a mass of 47.88 grams. 200 micromoles of Titanium ions will have a mass of 47.88/1000000 X 200 = 0.00958 grams

As a percentage by mass, assuming 1 litre of solution has a mass of 1000g, % = 0.00958/1000 X 100% = 0.000958%

For your solutions: 50 mg = 0.050g = 0.050/47.88 = 0.00104 moles of Titanium ions.
This is dissolved in 50ml = 0.050 litres so the concentration = 0.00104/0.050 = 0.0209 moles per litre.
You took 2ml of solution so the number of moles present is
2/50 X 0.0209 = 0.000835 moles.
Mass of Ti (3+) present in 2 ml = 2/50 X 0.000835 = 0.0000334g (sorry about the lack of standard form)