Mass Percent - Online Tutor, Practice Problems & Exam Prep
Mass Percent is the percentage of a particular element within a compound.
Mass Percent
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Mass Percent Concept
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Here we're going to say that mass percent, also known as weight percent, is a percentage of a given element in a compound. Now we're going to say here it deals with the molar mass in grams of the selected element and 1 mole of the compound. So this translates to say that mass percent equals the mass or grams of an element divided by the grams of the compound and then multiplying that by 100. Using this helps us to determine the percent composition of any particular element within a given compound.
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Mass Percent Example
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Here it says to calculate the mass percent of carbon within sodium carbonate. So sodium carbonate is Na2CO3. We're looking for the mass percent of carbon, so that means we're gonna need the grams of carbon over the grams of the compound itself times 100. Alright. So sodium carbonate has within it 2 sodiums, 1 carbon, and 3 oxygens. We're gonna multiply them each by their atomic masses from the periodic table. So sodium is 22.99 grams, carbon is 12.01 grams and oxygen is 16 grams. So, multiplying them out, we get 45.98 grams, 12.01 grams, and 48 grams. Add them all together, that comes out to 105.99 grams. Take those numbers. So for carbon, its mass is 12.01, and for the compound itself, it's 105.99. So we do 12.01105.99. When we do that we get 11.3% as the mass percent of carbon within sodium carbonate.
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Problem
Problem
Determine the percent composition of nitrogen and oxygen with nitrogen dioxide, NO2.
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Here it says, determine the percent composition of nitrogen and oxygen within nitrogen dioxide. Alright. So what we need to do here is we need to find the mass percent of nitrogen, and then the mass percent of oxygen. Remember, this will be the grams of nitrogen within the grams of the compound times 100. And for oxygen, it'll be grams of oxygen divided by the grams of the compound also times 100. If we look at nitrogen dioxide, it's composed of 1 nitrogen, and it's composed of 2 oxygens. Multiply them by their atomic masses, which you find from the periodic table. Nitrogen weighs 14.01 grams, oxygen weighs 16 grams. Multiply them, and then add up your totals, so the mass of the compound is 46.01 grams. So that's the number that goes here and here. And then all we need to do is plug in what we have for nitrogen, and then when we do that we're going to get here for nitrogen its mass percent as 30.4%. And then for oxygen, you could plug it into this formula. You could also say that we know that 100% of the compound is made up of just nitrogen and oxygen. So you could say 100% minus 30.4% gives us also the percentage of oxygen. So this will come out to 69.6%. So here we have both the mass percent of nitrogen and oxygen. Giving the percentages of all the compounds with all the elements within the compound are classified as the percent composition of the compound. So, the compound is made up of 30.4% nitrogen and 69.6% oxygen.