Originally Posted by

**earboth** to a) I assume that the "2,5 saltsolution" is actually 2.5% saltsolution. If so:

Calculate the total amount of salt:

50 g + 2.5% * 500 g = 50 g + 12.5 g = 62.5 g

Calculate the total mass:

800 g + 50 g + 500 g = 1350 g

Therefore you have the ratio $\displaystyle \frac{salt}{total\ mass} = \frac{62.5}{1350} = 0.046296.. \approx 4.63\%$

to b) For convenience I use grams:

Calculate the total amount of detergent in 3 g of the 20%-solution:

$\displaystyle \frac{20}{100} \cdot 3 = 0.6\ g$ of detergent.

The total mass of the thinned solution is 53 g (You added 50 g to the original 3 g of concentrated detergent)

Therefore you have the ratio $\displaystyle \frac{detergent}{total\ mass} = \frac{0.6}{53} = 0.01132.. \approx 1.13\%$

to c) Let V denote the unknown volume of the 45%-acid.

Calculate the total amount of acid:

$\displaystyle 0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot (500+V)$

$\displaystyle 0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot 500+0.3 \cdot V$ . Collect all terms with V at the LHS, all constants at the RHS:

$\displaystyle V(0.45 - 0.3) = 150 - 60~\iff~ V = 600$