need help on a 2012 STAV practice exam question!

[laura4]

For those of you who may have the paper,it's question 3d,II)

basically we've been given a table with the concentrations and absorptions of 5 standard solutions of 'fluorescent brightener 101' and then the absorbance of 'supa white' solution (which the question states earlier that fluorescent brightener 101 is used in the commercial product 'supa white' )

we are then asked to graph the data given in the table and then find the concentration of Supa White(for which we were given the absorbance of 0.68) now i found the concentration-which is 5.7 mg/L-1
and then the second part of q.d states;
the fluorescent brightener 101 has the chemical formula C16H1203. calculate the mass of the fluorescent brightener 101 in the 500.0 mL volumetric flask.

In the answers they took the concentration of 'supa white' which is 5.7,then divided it by 2 to find the mass of fluorescent brightener 101,which is said to be 2.9 mg.
but i have no idea why they have divided it by 2??

N.b,earlier the question stated; A 0.986g sample of 'Supa White' was dissolved in 100ml of distilled water. this was transferred to a 500.0ml volumetric flask with three rinsings and the solution made up to the calibration line with distilled water...

please help,i have no idea why they've divided it by 2,or really why they're used the concentration of the supa white to find the fluorescent brightener 101:/

[asiandee]

This is because the 500.0ml volumetric flask has the exact same concentration as the 10.0ml sample. Thus by using simple ratios you will get 2.9mg
i.e.
5.7mg/l =>2.85mg in 500.0ml=2.9mg in 500.0ml

[laura4]

This is because the 500.0ml volumetric flask has the exact same concentration as the 10.0ml sample. Thus by using simple ratios you will get 2.9mg
i.e.
5.7mg/l =>2.85mg in 500.0ml=2.9mg in 500.0ml

thankyou!:)