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. copper(II) bromide, $\mathrm{CuBr}_{2}$ b. copper(I) bromide, CuBr c. iron(II) chloride, $\mathrm{FeCl}_{2}$ d. iron(III) chloride, $\mathrm{FeCl}_{3}$ e. cobalt(II) iodide, $\mathrm{Col}_{2}$ f. cobalt(III) iodide, $\mathrm{CoI}_{3}$ g. tin(II) oxide, $\operatorname{SnO}$ h. tin(IV) oxide, $\operatorname{SnO}_{2}$

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.
a. copper(II) bromide, $\mathrm{CuBr}_{2}$
b. copper(I) bromide, CuBr
c. iron(II) chloride, $\mathrm{FeCl}_{2}$
d. iron(III) chloride, $\mathrm{FeCl}_{3}$
e. cobalt(II) iodide, $\mathrm{Col}_{2}$
f. cobalt(III) iodide, $\mathrm{CoI}_{3}$
g. tin(II) oxide, $\operatorname{SnO}$
h. tin(IV) oxide, $\operatorname{SnO}_{2}$

Key Concepts

Percent Composition

Percent composition is a way to express the concentration of an element in a compound by mass. It is calculated by taking the mass of the particular element (obtained by multiplying its atomic mass by the number of times it appears in the compound) and dividing it by the total molar mass of the compound, then multiplying the result by 100 to get a percentage.

Molar Mass Calculation

Molar mass calculation involves summing the atomic masses of all the atoms in a chemical formula. This process requires identifying the number of each type of atom contained in the compound, using the periodic table to obtain their atomic masses, and then performing the necessary arithmetic to find the total mass per mole of the compound.

Chemical Formula Interpretation

Chemical formula interpretation is the practice of reading formulas to determine the types and numbers of atoms present in a chemical compound. This skill is crucial for calculations involving molar mass and percent composition, as it provides the necessary information on stoichiometry—that is, the ratios in which the elements combine in the compound.

Transcript

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

00:17 So the first thing we're going to want to do is we're going to want to find the total molar mass of each of these compounds.

00:22 So let's go ahead and do that.

00:24 Copper has a molar mass of 65, or i'm sorry, 63 .5 grams per mole, and bromine has a molar mass of 79 .9 grams per mole.

00:41 So our molar mass for this compound is going to be 63 .55 plus 79 .9 times 2, which comes out to be 223 .35 grams per mole.

01:01 Since copper is listed first, we're going to want to find the amount of copper in this compound.

01:07 So we take 63 .55 and divided by the total molar mass, which is 223 .35, which comes out to be .285.

01:23 So there's 28 .5 % copper by mass in this compound.

01:31 So we're going to do this.

01:32 We're going to follow the same method for every question we have.

01:36 So again, we have cubr.

01:39 Copper has a molar mass of 63 .55.

01:42 Bromene has a molar mass of 79 .9.

01:46 So if we add these two together, we get our molar mass, which is 143.

01:58 0 .45 grams per mole.

02:03 Now the percent we want is for copper, excuse me, since that's the first one listed.

02:08 So we take 63 .55 divided by 143 .45 and multiply that by 100 to get our percent, which comes out to be 44 .3 percent copper by mass.

02:27 Next we have iron two chloride, fecl2.

02:31 So we take a look at our periodic table and we see that iron, has a molar mass of 55 .85 and chlorine has a molar mass of 35 .45.

02:55 So the total molar mass of this compound is going to be 55 .85 plus 35 .45 times 2 for each of the chlorines to be 126 .75 grams per mole.

03:08 Now we're going to want to find the percent of iron since that is the first element listed in this formula.

03:14 So we take the molar mass of iron, divided by the total molar mass, and we get 44 .1%.

03:36 Now we have fecl3, again, 55 .85, 35 .45.

03:47 Molar mass is going to be 55 .85 plus 35 .45 times 3, which is going to be 162 .2 grams from mole...

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