# What is the concentration of diluted acid if 10cm3 of concentrated HCl are diluted to 100cm3 and 10cm3 diluted acid reacts with 40cm3 0.05M NaOH?﻿I've got that there are 2x10^-3 moles of HCl and...

What is the concentration of diluted acid if 10cm3 of concentrated HCl are diluted to 100cm3 and 10cm3 diluted acid reacts with 40cm3 0.05M NaOH?﻿

I've got that there are 2x10^-3 moles of HCl and the molar ratio is 1:1. But I'm not sure how to work out the last step, which is the concentration of the undilued acid.

william1941 | College Teacher | (Level 3) Valedictorian

Posted on

According to the information given first 10 cm^3 of HCl was diluted to 100 cm^3 of HCl. The diluted acid reacted with 40 cm^3 of NaOH with a concentration of 0.05 M.

Now we need to find the concentration of the undiluted acid.

Now the concentration of the diluted acid is 0.05 M as one molecule of HCl reacts with one molecule of NaOH, so the dilute HCl has the same concentration as the NaOH or 0.05.

Let the concentration of the undiluted acid be C. 90 cm^3 of water is added to it to make 100 cm^3 of diluted acid. If there were M molecules of HCl initially per cm^3, now there are M/10 molecules of HCl.

So as the diluted acid is 0.05 M, the concentrated acid has a molarity of 0.05*10 = 0.5M

The molarity of the undiluted acid is 0.5M