Here is a AP chemistry problem I need help with!!?

Question

1.00 mL of a 3.50 x 10^–4 M solution of oleic acid is diluted with 9.00 mL of petroleum ether, forming solution A. 2.00 mL of solution A is diluted with 8.00 mL of petroleum ether, forming solution B. How many grams of oleic acid are 5.00 mL of solution B? (molar mass for oleic acid = 282 g/mol)

Answer 1

Use conservation of moles in this problem.
Apply formula:
M1*V1 = M2*V2 = milimoles (since volume is in millilitres)


Consider solution A
3.5 * 10^–4 * 1 = M2 * (9+1)
M2 = 3.50x10^(–5) M
conc of A = 3.50x10^(–5)M

Consider solution B
2 * 3.50x10^(–5) = M2 * (8+2)
M2 = 7*10^(-6) M
conc of B = 7*10^(-6) M

In 5.00 mL of solution B millimoles of oleic acid = 5*7*10^(-6)
= 3.5*10^(-5) millimoles
= 3.5*10^(-8) moles
grams of oleic acid = 282 * 3.5*10^(-8) = 9.87*10(-6) grams
weight of oleic acid = 9.87 microgram