Water containing more than 3.0 grains of dissolved solids per gallon is considered to be hard [1 grain (gr) = 64.8 mg]. So, if a
kettle contains 18 gal of tap water, which is allowed to evaporate. The solid material left behind has a mass of 1.7 g. Is such tap water considered to be hard?
<em><u>Yes, such tap water is considered to be hard.</u></em>
Explanation:
The <em>solid material left behind</em>, after the <em>18 gal of tap water</em> was <em>evaporated,</em> is the amount of dissolved solids in that quantity of water.
You must convert the amount in grams (1.7g) into grains:
17.g × 1,000mg/g × 1 gr/64.8mg = 262.34 gr
That is in 18 gallons. Then, divide by 18 gal to obtain the number of grains dissolved per gallon:
262.34gr / 18 gal ≈ 15 gr per gallon.
That is much greater than 3.0 grains per gallon; thus,<em> such tap water is considered to be hard.</em>
