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Scientists analyze a 140-gram sample of contaminated river water.
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They find that the sample contains 105 grams of water.
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What is the impurity percentage for this sample?
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(A) 7.5 percent, (B) 75 percent, (C) 10 percent, (D) 2.5 percent, or (E) 25 percent.
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We are told in the question that a 140-gram sample of contaminated river water contains 105 grams of water.
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So what makes up the remaining 35 grams of this sample?
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As we are told that the sample is contaminated, the remaining 35 grams must be contaminants or impurities.
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Impurities are any undesired material mixed in with the desired substance.
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To answer the question, we need to represent the amount of impurities in the sample with the impurity percentage.
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To calculate a standard percentage, we divide the part in question by the whole then multiply by 100 percent.
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When we calculate an impurity percentage, we want to know what part of the sample is made up of impurities.
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So the equation to calculate the impurity percentage is impurity percentage equals the mass of the impurities divided by the mass of the sample times 100 percent.
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The mass of the impurities is 35 grams.
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The total mass of the river water sample is 140 grams.
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Performing the calculation, we find that the impurity percentage is 25 percent.
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So a 140-gram sample of river water that contains 105 grams of water has an impurity percentage of 25 percent, answer choice (E).