Percentage Composition – EP – 2
5 Minutes
Percentage composition for students teaches how to calculate molar mass and element percentages in water and salt. An English science lesson.
- Calculating the molar mass of water and its element percentages
- How explosive sodium and toxic chlorine combine to make salt
- Calculating the percentage of sodium and chlorine in salt
What this lesson teaches
Percentage composition is the measure of how much of a compound's total mass comes from each individual element. It is calculated by dividing the total molar mass of a specific element in the compound by the total molar mass of the compound and multiplying the result by one hundred.
Molar mass of elements and compounds
Every chemical element has a specific mass listed below its symbol on the periodic table. When this value is taken in grams, it represents the molar mass, which is the mass of one mole of that element. To find the molar mass of an entire molecule, the molar masses of all the individual atoms inside that molecule must be added together.
Percentage calculation for water
A single water molecule consists of two hydrogen atoms and one oxygen atom. The molar mass of two hydrogens is calculated by adding 1.008 grams and 1.008 grams to get 2.016 grams, while oxygen has a molar mass of 15.99 grams. Adding these values together gives water a total molar mass of 18.015 grams. Dividing 2.016 by 18.015 and multiplying by one hundred shows that hydrogen makes up 11.19 percent of water, while dividing 15.99 by 18.015 gives an oxygen percentage of 88.8 percent.
Properties of sodium and chlorine
Common table salt is sodium chloride, which splits into the two elements sodium and chlorine. On their own, these two elements are dangerous, as metallic sodium explodes when placed in water, and chlorine gas becomes poisonous when it exceeds a certain level. Despite these hazardous traits, combining explosive sodium with toxic chlorine gas produces ordinary salt, which is safe and essential for human diet.
Percentage calculation for salt
The molar mass of sodium is 22.989 grams, and the molar mass of chlorine is 35.453 grams. Adding these two values together gives a total molar mass of 58.442 grams for sodium chloride. To calculate the percentage of sodium, 22.989 is divided by 58.442 and multiplied by one hundred, which gives 39.33 percent. Performing the same calculation for chlorine results in 60.66 percent, showing that atom count does not determine the percentage mass of a substance.