Percentage Composition for JEE

Percentage composition is the ratio of the amount of each element to the total amount of individual elements of the compound, multiplied by 100. Take H₂O, or water, as an example. There are two molecules of hydrogen in water, 18.0152 grams in one mole of water and 1.008 grams in one mole of hydrogen atoms. The weight of 2 moles of hydrogen is 2.016 grams. Therefore, 1 mole of water contains 2.016 grams of hydrogen. Therefore, the percentage composition of hydrogen is 2.016 / 18.0152 = 11.19%.

Percentage Composition Formula

• The following formula can be used to express the composition percentage of a particular element.

• The percentage composition of a solution can be expressed as $Percentage{C}_E={\displaystyle \frac{g^E}{g^T}}\times 100$ (where $Percentage{C}_E$ is the percentage composition of element E,  $g^E$ is total amount of E present in the compound and $g^T$ is the total amount of all element present in the compound. 

• This is the value to calculate. The counter on the right shows the total amount of element E present in the compound. The denominator, on the other hand, is the sum of all the elements present in a compound.

• Multiply this ratio by 100 to get the percentage of the composition.

• Next, let's take a closer look at the mass percent composition. 

Mass Percentage Composition

The concept of mass percent composition is used to indicate the concentration of an element or component in a compound. The term is used to indicate the total mass percent of each element present in a compound. It is important to note that the mass percent composition can be calculated by dividing the mass of one component by the total mass of the mixture. Then multiply this ratio by 100. This is also called mass percent (w / w)%.

$Masspercentage={\displaystyle \frac{M_{solute}\left(g\right)}{M_{solution}\left(g\right)}}\times 100$

Volume Percentage

The volume fraction of a solution is defined as the ratio of the volume of solute present in the solution to the total volume of the solution. This type of concentration, usually calculated for liquid and gas phase solutions, is also expressed as a percentage, so this ratio should be multiplied by 100, as shown below.

$Volumepercentage={\displaystyle \frac{V_{solute}\left(mL\right)}{V_{solution}\left(mL\right)}}\times 100$

As a solution is composed of both a solute and a solvent, the total volume of the solution is equal to the total volume of the solute and the solvent contained therein. Therefore, the volume fraction of a solution can also be calculated using the following equation:

$Volumepercentage={\displaystyle \frac{V_{solute}\left(mL\right)}{V_{solute}\left(mL\right)+V_{solvent}\left(mL\right)}}\times 100$

Importance of Mass Percentage

For many scientific and practical reasons, it is necessary to know the number of elements contained in a particular compound.  This is essential for chemists to obtain the molecular formulas of many compounds. This formula is useful for showing the minimum integer and relative atomic number of each element of a compound. With the help of mass percentage, chemists can also calculate the actual molecular formula. The formula shows the exact number of atoms in the compound.

Determining Mass Percentages from Chemical Formula

The basics of calculating mass percent are clarified. Let's take a look at glucose. 

• The formula for glucose is C₆H₁₂O₆. Let's calculate the mass percentage of each element of glucose.

• You can check the number of moles of each element from the formula.

• Glucose has 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.

• Next, let's multiply each atom by its molar mass. 

• This will give you the mass of each element of glucose.

• Here, divide each mass by the mass of 1 mol of glucose to obtain the mass fraction of each element. 

• Multiply this value by 100 to get the mass fraction of the element.

What is a Mole?

Atoms and molecules are known to be very small. Therefore, it is very difficult to count with an accurate number. Now, this problem is solved by using Avogadro's number. This number is expressed as NA = 6.023x10²³. Mole is defined as a number equal to Avogadro’s number. In other words, mole is the unit used to represent 6.023x10²³ particles of the same substance. More specifically, a mole is the total amount of a substance that contains the same number of atoms, molecules, ions, electrons, or other basic entities as 12 grams of carbon atoms.

Equivalent Weight

The equivalent weight of a substance is the mass (in grams) of the substance that is combined with 8 grams of oxygen or 1 gram of hydrogen or is chemically equivalent. In other words, it is equal to the mass (in grams) of the substance that reacts with or replaces 1 gram of hydrogen. Equivalent weight is expressed as the ratio of molecular weight to valence (combining power).

Some Basic Concepts of Chemistry Class Formulas

Here we will discuss some basic concepts of chemistry five percentage composition

• Molality(m) $={\displaystyle \frac{\text{Number of moles of solute}}{\text{Mass of solvent in Kg}}}$

• Molarity(M) $={\displaystyle \frac{\text{Number of moles of solute}}{\text{Volume of solution in mL}}}$

• Mole fraction(xA) $={\displaystyle \frac{\text{Number of moles of solute(A)}}{\text{Total number of moles in solution}}}$

Summary

The percentage composition of a particular compound is the ratio of each element present in the compound to the total amount of individual elements present in the compound, multiplied by 100. Here, we measure the amount of existing elements in grams. Percent composition of a compound is a representation of its composition for all elements present. The importance of this composition calculation is found in chemical analysis.