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. methane, $\mathrm{CH}_{4}$ b. sodium nitrate, $\mathrm{NaNO}_{3}$ c. carbon monoxide, $\mathrm{CO}$ d. nitrogen dioxide, $\mathrm{NO}_{2}$ e. 1 -octanol, $\mathrm{C}_{8} \mathrm{H}_{18} \mathrm{O}$ f. calcium phosphate, $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ g. 3 -phenylphenol, $\mathrm{C}_{12} \mathrm{H}_{10} \mathrm{O}$ h. aluminum acetate, $\mathrm{Al}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{3}$

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.
a. methane, $\mathrm{CH}_{4}$
b. sodium nitrate, $\mathrm{NaNO}_{3}$
c. carbon monoxide, $\mathrm{CO}$
d. nitrogen dioxide, $\mathrm{NO}_{2}$
e. 1 -octanol, $\mathrm{C}_{8} \mathrm{H}_{18} \mathrm{O}$
f. calcium phosphate, $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$
g. 3 -phenylphenol, $\mathrm{C}_{12} \mathrm{H}_{10} \mathrm{O}$
h. aluminum acetate, $\mathrm{Al}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{3}$

Key Concepts

Molar Mass

Molar mass is the combined mass of all the atoms in a molecule, calculated by adding together the atomic masses of each element in the chemical formula in proportion to the number of atoms present. It is fundamental in converting between the mass of a substance and the number of moles, and it underpins all quantitative chemical calculations.

Atomic Mass

Atomic mass is a measure of the mass of a single atom, expressed in atomic mass units (amu) or grams per mole. It is essential for determining the mass contribution of each element in a compound and is used in the calculation of the compound's overall molar mass.

Percent Composition

Percent composition refers to the fraction of the total mass of a compound that is contributed by a particular element, expressed as a percentage. This is calculated by dividing the total mass of the element in one mole of the compound by the molar mass of the compound, and then multiplying by 100. This concept is key for understanding the relative abundance of each element within a compound.

Chemical Formula Interpretation

Interpreting a chemical formula involves identifying the types and numbers of atoms present in a compound. This step is crucial for setting up mole ratios, calculating molar mass, and eventually determining the percent composition of each element in the compound.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the amounts of reactants and products in chemical reactions, based on the law of conservation of mass. In the context of percent composition, stoichiometric principles guide the correct calculation of each component's contribution to the overall mass of the compound.

Transcript

00:01 We have to find the percent by mass of each one of the first elements in their own compounds.

00:07 The first one is carbon in methane.

00:10 Well, let's figure out first what the formula is for percent by mass.

00:15 So what percent by mass is, you take the mass of something, so in this case we'll say element one, you divide it by the total mass of the compound, and then you take that entire fraction and you multiply it by 100 percent.

00:43 Now if you notice, we don't have the masses of either carbon or the mass of methane or any of our other elements or compounds, so we're going to have to use a different formula.

00:56 In this case, we're going to make one giant assumption.

01:00 We're going to assume that we have one mole of each compound.

01:11 So when we have one mole of each compound, that means we can use the molar mass.

01:19 So this means we take the molar mass of element one, and then we divide it by the total molar mass of the compound.

01:35 I'm just going to shorten that to mm of the compound, and then we're going to multiply this by 100 percent.

01:45 So that is the formula we're actually going to be using.

01:49 So let's take a look at the first one.

01:51 So the first one is carbon in methane.

01:54 The molar mass for carbon is 12 .01.

01:59 The total molar mass for methane is going to be 16 .042.

02:06 So we take that fraction and multiply it by 100 percent, and we will end up with 74 .80 percent.

02:19 So carbon is 74 .80 percent of the mass of methane.

02:27 Now we have to figure out the mass of sodium and sodium nitrate.

02:31 The molar mass of sodium is 22 .99.

02:37 The total mass of sodium nitrate is going to be 85.

02:42 And note the units for all of these are going to be grams per mole, and since we're dividing grams per mole by grams per mole, they actually cancel each other out.

02:54 So when we multiply by a percentage, that's how come we end up with our percent.

02:59 So the mass of sodium and sodium nitrate ends up coming 27 .05 percent.

03:10 Now let's consider carbon and carbon monoxide.

03:14 Carbon is again 12 .01.

03:18 The total mass of carbon monoxide is 28 .01.

03:24 And there's a train going off in the background.

03:26 I apologize for that.

03:28 I live near train tracks...