What Is the Original Concentration of the Solution?

[DB]

Having a little trouble tackling this one.
"What is the concentration of a 500 ml solution if, when diluted to a volume of 2 Liters, its new concentration becomes 20 g/L?"

Here what I did, all in ml.

$$\frac{x}{500+1500}$$

$$\frac{x}{2000}=\frac{20}{1000}$$

$$\frac{20*2000}{1000}=40=x$$

$$\frac{40}{2000}=\frac{10}{500}$$

Obviously the anwser can't be 10g/500ml, can someone help me out?
Thanks

 

[Doc Al]

$$\frac{x}{500+1500}$$

$$\frac{x}{2000}=\frac{20}{1000}$$

$$\frac{20*2000}{1000}=40=x$$

Right. "x" is the quantity of "stuff" in the mix, in g. That stuff doesn't change when you dilute it, so 40g of stuff must have been in the original 500ml. Now can you calculate the original concentration?

 

[DB]

O so do you mean that solute is 40g for 2000ml and as well for 500ml? Making the answer 40g/500ml?

 

[Doc Al]

Yes. That's what I would say.

 

[DB]

Thanks for all your help