mixture problems

Question

1- How many milliliters of water must be added to 145 ml of 45% salt solution to produce a 30% solution?

 

2-How many ml of 50 percent acid should be added to pure acid to make 70 ml of 55 percent acid?

 

3-How many ml of 50 percent acid should be added to pure acid to make 80 ml of 85 percent acid?

 

4-How many ounces of pure salt must be added to 8oz of 30% salt solution to produce a 60% solution? (Pure salt is 100%Round your answer to the nearest hundredth of an oz

Answer 1

For concentration problems remember that when C1 = concentration1, V1 = Volume1 C2, V2, C3,V3 etc.

 

C1V1 + C2V2 +...+CnVn = CtotalVtotal

and

V1 + V2 +...+Vn = Vtotal

So for the first case: C1 = 45% or .45 V1 = 145 C2(of water) = 0, V2 = x

 

.45 * 145 + 0 * x = CtotalVtotal

145 + x = Vtotal

therefore

.45*145 = .30 *(145+x)

65.25 = 43.5 + .3x
Solve for x:

65.25 - 43.5 = .3x

21.75 = .3x

x = 21.75/.3 = 72.5

 

For the rest, just change C2 to the actual concentration of the acid(1 for pure acid)