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og 156

Expert replies
by mepinoargote » Wed Jun 16, 2010 2:59 pm
Hi, english is not my first language, so i´m having trouble understanding the question 156 of the official guide (12th).

A tank contains 10,000 gallons of a solution that is 5% sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

10,000 (0.05) = 500 gallons of sodium chloride
10,000-2500 = 7,500
500/7,500=6.67%

What exactly does "by volume" means? By looking at the answer i can deduce that even if 2500 gallons of the solution evaporate, the percent of the sodium remains 5 %, So every time a question gives a value "by volume" should i assume that the value given won´t change?. Please explain, thanks.
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Source: — Problem Solving |

by amising6 » Wed Jun 16, 2010 4:56 pm
volume means gallon of solution:

now let solve the problem:
10,000 gallon of solution
5% sodium chloride
sodium chloride=5%10,000=500 gallon
so remaining is water
water=10,000 -500=9,500 gallon os water
now 2500 gallon of water evaporates so
now water in solution:9500-2500=7500
sodium chloride =500 gallon

so total solution=water+sodium chloride=7500+500=8000 gallon
sodium chloride in %=(500/8000)*100=6.25%
hope this helps
Ideation without execution is delusion
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by mepinoargote » Wed Jun 16, 2010 6:57 pm
Thanks amising6, understood.
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