Question

How many grams of HCI are there in 100.0 mL of concentrated HCl which is approximately 12.1M and 37% HCl by weight and the density of 1.191 g/mL?

Answer 1

`"44 g"`

Explanation:

The first thing to take note of here is that the problem provides you information you don't actually need.

The molarity of the solution is not important in determining how many grams of hydrochloric acid you have in that `"100.0-mL"` sample volume.

So, you know that the solution has a density of `"1.191 g/mL"`, which means that every mililiter of this solution has a mass of `"1.191 g"`.

The mass of the sample you have here will thus be

`100.0color(red)(cancel(color(black)("mL"))) * "1.191 g"/(1color(red)(cancel(color(black)("mL")))) = "119.1 g"`

Now, you know that the solution has a `37%` concentration by mass, which means that every `"100 g"` of solution will contain `"37 g"` of hydrochloric acid.

This means that your sample will contain

`119.1color(red)(cancel(color(black)("g solution"))) * "37 g HCl"/(100color(red)(cancel(color(black)("g solution")))) = "44.067 g HCl"`

Rounded to two sig figs, the number of sig figs you have for the percent concentration by mass, the answer will be

`m_"HCl" = color(green)("44 g HCl")`