Calculate the final concentration of 2.0 L of a 2.50 M HNO3 solution is added to water so that the final volume is 6.0 L.

Question

Express your answer to two significant figures and include the appropriate units.

Answer 1

Just pretend this is really happening. Let's follow the moles.

Remember M, molar, literally means moles per liter - or the number of moles we have in ONE liter.

If we have 2.0L of a 2.50M HNO₃ solution - we have

(2.0L)(2.5 moles/L) = 5.0 moles.(2 sig figs because the lowest # of sig figs in the multiplication is 2)

I don't care about the volume, I am only interested in the moles.

I put this is a new container. There are 5 moles in my new container. I make the final volume in my new container 5.0L. Concentration is often defined in MOLARLITY, or moles/liter.

So I have 5.0 moles / 6.0 L = .8333333... M - which I have to put in the correct amount of sig figs. I need 2 sig figs accoring to the sig figs in the calculation. So the answer is 0.83M.

Hope that helps.