20. What will be the concentration, in mol dm, of the resulting solution when 200 cm' of 0.200 mol dmhydrochloric acid, HCl(aq) are mixed with 300 cm of 0.100
mol dm HCl(aq)?

0.140mol/dm^3.

Explanation:

200cm3 = 0.2dm^3.

0.2dm^3 * 0.200mol/dm^3 = 0.040mol

300cm^3 = 0.3dm^3

0.3dm^3 * 0.100mol/dm^3 = 0.030mol

The number of moles is 0.070mol of HCl (aq).

The volume of the solution is 0.5dm^3.

Hence the concentration is 0.140mol/dm^3.

i think the answer is terrae but not 100 percent sure. ▓▬▬ §