Math Is Fun Forum

Toast

Real Member

Registered: 2006-10-08

Posts: 1,321

Linear Equations - Salt solutions :(

A chemist has 500 mL of a salt solution that contains 2% salt (g/cm³). How much water must be added to reduce the concentration to 0.5%?

Using what a normally do for these types of questions, I went

Yeah, by now I realised it didn't really look too natural, anyways, it solved for -433.3..., so I don't think it was right.

EDITEDITEDIT: Ugggh, that was supposed to be 0.005(500+x), so I guess I got it right... it's just that... adding 0% salt solution (which made x = 0 in the left hand side) felt a bit awkward... ?

Last edited by Toast (2007-02-04 20:50:48)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Linear Equations - Salt solutions :(

You can almost tell just by looking at it what the answer's going to be. You want the solution to be 4 times weaker than it is now, so you need the solution's volume to quadruple.

It's currently 500mL, which means that you want it to become 2L, which means that you need to add 1500mL.

You only really need to resort to algebra if the question gets more complicated. Like if the solution you were adding was still a bit salty, for example.

---

Why did the vector cross the road?
It wanted to be normal.