### Video Transcript

A bottle of a tile cleanser contains 135 grams of HCl and 775 grams of water. What is the percent by mass of HCl in this cleanser?

A percent can be calculated by dividing the part in question by the whole and multiplying by 100 percent. For example, if we wanted to know what percentage of the dots in the box are pink, we would divide the number of pink dots, the part, by the total number of dots, the whole, then multiply by 100 percent. So 40 percent of the dots are pink.

In the question, we’re told to calculate a percent by mass. This just tells us that instead of counting up the number of each species in the sample, we’ll instead use their masses. So percent by mass can be calculated by dividing the mass of the part by the mass of the whole and multiplying by 100 percent.

In the question, we are told that a bottle of a tile cleanser contains 135 grams of HCl and 775 grams of water. Using this information, we need to calculate the percent by mass of HCl in the cleanser. This tells us that HCl is the part in question. So, in the equation, we can place 135 grams in the numerator. The whole is the entire bottle of cleanser, which should have a mass of 910 grams.

We are now ready to solve the problem. The unit grams will cancel. And after performing the calculation, we’ll find the percent by mass of HCl to be 14.835 percent, which we can round to one decimal place. Therefore, the percent by mass of HCl in this bottle of cleanser is 14.8 percent.