Mercurochrome dissolved in water is a reddish liquid...

Mercurochrome dissolved in water is a reddish liquid formerly used as an antiseptic. Calculate the percent composition of mercurochrome, $\mathrm{HgNa}_{2} \mathrm{C}_{20} \mathrm{H}_{8} \mathrm{Br}_{2} \mathrm{O}_{6}$.

Key Concepts

Percent Composition

Percent composition is the measure of the percentage by mass of each element in a chemical compound. It is calculated by dividing the mass contribution of each element by the total molar mass of the compound and then multiplying by 100. This concept is fundamental in analytical chemistry for determining the ratio of elements in unknown substances and for confirming empirical formulas.

Molar Mass Calculation

The molar mass of a compound is obtained by summing the atomic masses of all the atoms present in its formula, each multiplied by the number of times the element occurs in the molecule. This calculation is crucial because it provides the total mass of one mole of the compound, which is then used in various stoichiometric calculations, including percent composition.

Stoichiometry

Stoichiometry refers to the quantitative relationships among reactants and products in chemical reactions, as well as the relationships between the elements within a compound. In the context of percent composition, stoichiometry helps in understanding how individual atomic masses contribute to the overall molecular mass, enabling precise calculations of mass percentages.

Transcript

00:01 When calculating the percent composition of a compound, we need to know what is meant by percent composition.

00:11 Some students assume that the percent composition is the atom composition.

00:19 So if a compound contains five atoms of carbon and there's a total of ten atoms in the compound, that the percent composition would be 50 percent, five divided by ten times a hundred.

00:32 But percent composition almost exclusively refers to mass percent composition.

00:40 So to answer this question, you need to calculate the mass of each element and the total mass of the compound.

00:48 It's helpful when calculating these masses to assume that you have one mole of the compound.

00:55 If you have one mole of the compound, then the mass of the entire compound is simply its molar mass.

01:01 And you can calculate the mass of each element in a mole of the compound.

01:05 Compound by using the subscripts in the chemical formula.

01:12 This compound has the chemical formula shown.

01:17 Mercura chrome is a reddish liquid that is used as an aniseptic, and it contains 1 mole mercury, 2 mole sodium, 20 moles carbon, 8 moles hydrogen, 2 moles bromine, and 6 moles of oxygen.

01:36 So if i have 1 mole of this compound, i have 1 mole of mercury.

01:40 Well, what is the mass of one mole of mercury? i go to the periodic table.

01:46 I look it up.

01:46 It's 20 .59 grams.

01:50 If i have one mole of this compound, i have 2 moles of sodium.

01:53 So i go to the periodic table, multiply 2 by the molar mass of sodium, and i'll get the mass of sodium in 1 mole of this compound, 45 .98 grams.

02:07 If i have one mole of the compound, i have 20 moles of carbon.

02:10 So the mass of carbon in the compound will be 20 times the molar mass of carbon, 12 .011, and i get 240 .22 grams of carbon...

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