Calculate the percent by mass of the element listed first in...

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds. a. adipic acid, $\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{4}$ b. ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$ c. caffeine, $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2}$ d. chlorine dioxide, $\mathrm{ClO}_{2}$ e. cyclohexanol, $\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{OH}$ f. dextrose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$ g. eicosane, $\mathrm{C}_{20} \mathrm{H}_{42}$ h. ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.
a. adipic acid, $\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{4}$
b. ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$
c. caffeine, $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2}$
d. chlorine dioxide, $\mathrm{ClO}_{2}$
e. cyclohexanol, $\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{OH}$
f. dextrose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$
g. eicosane, $\mathrm{C}_{20} \mathrm{H}_{42}$
h. ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$

Key Concepts

Percent Composition

Percent composition refers to the percentage by mass of an element in a compound. It is calculated by taking the mass of the element in one mole of the compound, dividing it by the molar mass of the compound, and then multiplying by 100%. This concept is fundamental in determining the proportion of each constituent in a chemical compound.

Molar Mass Calculation

Molar mass calculation involves summing the atomic masses of all atoms present in a compound's molecular formula, accounting for the number of each type of atom. This calculation is critical, as the molar mass serves as the denominator in percent composition calculations and is essential for converting between mass and moles.

Atomic Weight

Atomic weight, expressed in grams per mole, is the weighted average mass of the atoms of an element from a mixture of isotopes found in nature. It is a key factor in determining the mass contributions of individual elements when calculating both the molar mass of a compound and the corresponding percent composition.

Chemical Formula Interpretation

Chemical formula interpretation involves reading and understanding the molecular formula of a compound to determine the number and type of atoms present. This skill is important for applying stoichiometric coefficients correctly during computations, such as calculating the mass contributions of elements for percent composition.

Transcript

00:11 In this question, we're asked to find the percent by mass of the element listed first in each of the following compounds.

00:16 So the first thing we want to do with each of these questions is find the total molar mass of the compound.

00:23 So we know carbon has a molar mass of 12 grams per mole, hydrogen is 1 gram per mole, and oxygen is 16 grams per mole.

00:33 So our molar mass is going to be 12 times 6 plus 10 times 1 plus 16 times 4, which comes out to be, 146.

01:01 Now the first element listed here is carbon.

01:04 So to find the percent of carbon, we're going to want to find the total mass of carbon in this compound.

01:12 So we take 6 times 12, and we divided by the molar mass of the entire compound, 146.

01:20 So this is going to equal 72 over 146.

01:28 We're going to want to multiply this by 100 to get 49 .31%.

01:45 Okay, so let's go ahead and do the next one.

01:48 Nitrogen has a molar mass of 14, hydrogen is 1, another nitrogen we know is 14, and oxygen is 16.

01:57 So, molar mass is going to be 14 times 2, plus 1 times 4, plus 16 times 3, which is equal to 80 grams per mole.

02:17 Now we want to find the percent of nitrogen, but we have to remember there are two nitrogen in this.

02:23 So it's going to be 14 times 2 over 80, which is equal to 35%.

02:35 All right.

02:49 Next we have c8h10 and 4 .02.

02:52 Again, carbon has a molar mass of 12 grams per mole, hydrogen 1 gram per mole, nitrogen 1 gram per mole, nitrogen 14 grams per mole, and oxygen 16 grams per mole.

03:02 So the molar mass is going to be 8 times 12 plus 10 times 1, plus 14 times 4 plus 16 times 2, which is equal to 194 grams from more.

03:25 We're going to find the percent of carbon.

03:29 So again, 12 times 8 over 194, which is equal to 96 over 194 times 100 again.

03:46 And we get 49 .48%...

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