Question

A particular type of hops contains 15.4 % m/m acids. If 25 mL of methanol contains 1.00 g of hops, what is the percent by mass of acids in the solution?

The density of methanol is 0.792 g/mL.

Answer 1

The concentration of the acids in the methanol is 0.921 % by mass.

Explanation:

The hops contain 18.4 % of acids.

`"Mass of acids" = 1.00 color(red)(cancel(color(black)("g hops"))) × "18.4 g acids"/(100 color(red)(cancel(color(black)("g hops")))) = "0.184 g acids"`

`"Mass of methanol" = 25 color(red)(cancel(color(black)("mL"))) × "0.792 g"/(1color(red)(cancel(color(black)("mL")))) = "19.8 g"`

`"Mass of acids + methanol" = "0.184 g + 19.8 g" = "19.984 g"`

The formula for mass percent is

`color(blue)(bar(ul(|color(white)(a/a) "Mass %" = "Mass of component"/"Total mass" × 100 %color(white)(a/a)|)))" "`

∴ `"Mass % of acids" = (0.184 color(red)(cancel(color(black)("g"))))/(19.984 color(red)(cancel(color(black)("g")))) × 100 % = 0.921 %`