Question

Please help...........




Suppose we start with unlimited supplies of a 20% h2so4 solution and of a 50% h2so4 solution. We combine x liters of the first with y liters of the second to produce 7 liters of a 40% h2so4 solution. What does x equal?

Answer 1

work in masses of pure sulphuric acid
the mass of acid in 40% solution is 7 * 10 * 40 = 2800g

Answer 2

2.8?

Answer 3

x liters of 20% contains 200x g
y liters of 50% = 500y g

Answer 4

so
200x + 500y = 2800

Answer 5

yea

Answer 6

whats next

Answer 7

now we need to find y in terms of x. Note that the 50% solution i s 5/2 = 2.5 times as strong as the 20% So y liters of 50% = how many liters of 20%?

Answer 8

where did u get the 5/2?

Answer 9

the ratio of 50/20 = 2/2

Answer 10

* 5/2

Answer 11

oh okay

Answer 12

so y liters of 50% = 2.5x liters of 20%

Answer 13

yea

Answer 14

200x + 500*2.5x = 2800
solve for x

Answer 15

1.93?

Answer 16

yes

Answer 17

hmmmm it's supposed to be 2.33333333

Answer 18

oh
yes I've gone wrong somewhere

Answer 19

something wrong in my logic somewhere

Answer 20

set up 2 equations...

x + y = 7
20x + 50y = (40)(7)

Answer 21

yep thats the way

Answer 22

hmmm and then plug it in huh? y=7-x

Answer 23

yes

Answer 24

got it thanx

Answer 25

yea thats an easier way to do it. I still can't see what i did wrong . Worrying !

Answer 26

i see now!

Answer 27

200x + 500y = 2800
was correct
then next step was to replace y with 7 - x

Answer 28

- that is y in tems of x.

Answer 29

I had a mental aberration!