How do you compute a molarity of a solution when you add 29.8 mL of 1.30 M HCl to 12.5 mL of 6.40 M HCl?

Question

okay what happens when you add water to a hydrocloric acid solution in terms of molarity?

Answer 1

The way to calculate this is very logical.
The molarity of a solution is defined as the number of moles of a particular component in 1 litre of solution. In this case, it is important to note that both solutions contain the same dissolved material, HCl.

The total volume after adding the two different solutions together will be 29.8 + 12.5 = 42.3mL

Now we need to know the TOTAL number of moles of HCl in the solution after they have been combined.
In the first we have
1.30 moles/litre X 0.0298 litre = 0.03874 moles
and in the second we have
6.40 moles/litre X 0.0125 litre = 0.08 moles

So after adding the two different solutions together we end up with a single solution that has a total of 0.11874 moles of HCl in a total volume of 42.3 mL, or 0.0423 litre

The concentration is therefore
0.08 moles / 0.0423 litre = 1.89 moles / litre, or 1.891M

Note that the actual calculation produces a much longer fractional component, but in practice we can not know the total answer any more accurately than the numbers we started with.

Answer 2

Molarity is moles/Liter. So your total volume is going to be 29.8+12.5 which is 32.3mL. Which is .0323L. The number of moles of HCl is 6.4*12.5+1.3*29.8. Then divide and presto.