Question

According to a magazine, a cleaning solution of 5% bleach will remove mildew from a shower or tub.

Answer 1

Percent concentration, %, is [mass of solute / mass of solution]  * 100

Then, if you know the percent and the mass of solution you can find mass of solute as:

mass of solute = % * mass of solution / 100

In this case the solute is bleach.

You have the volume of solution but you need the mass of solution.

The only way to find the mass of solution knowing its volumen is using the density, because density = mass / volume => mass = volume * density.

Then you need the density of the solution, which is not a data.

Then you can find it either experimentally or serching in tables.

I found in Internet that a common density is 1.11 g /ml

Now, we must convert quarts unit to ml, using the conversion factor : 1 quart = 946.35 ml

1 quart * 946.35 ml / quart * 1.11 g/ml = 1050.45 grams of solution

=> grams of solute = 5 * 1050.45 grams / 100 = 52.7 grams of solute

Now use a conversion factor to pass grams to ounes:

1 ounce = 28.35 g

52.7 grams * 1 ounce / 28.35 grams = 1.86 ounces

Answer: 1.86 ounces and I have explainded the method using complete senteces.