Statement: A gas pipe contains 2 mol of carbon dioxide, 10 mol of oxygen, 52 mol of nitrogen, and 1.3 mol of methane. Thus, the mass percentage of oxygen and nitrogen is 23 % and 77 %. Let w O 2 and w N 2 be the mass fraction of oxygen and nitrogen respectively. So, 100 mol of air contains 21 mol of oxygen and 79 mol of nitrogen. Solution: The above percentages are not in mass but in the mole. The molar mass of oxygen and nitrogen is 15.999 g mol −1 and 14.007 g mol −1. Statement: Air contains 21 % of oxygen and 79 % of nitrogen. In short, the mass fraction and the percentage composition are the same when it comes to elements of a compound. When the mass fraction of an element is calculated, it is called the percentage composition of that element. Percentage CompositionĪ compound consists of different elements. The mole of a substance is the mass divided by the molar mass. The volume of solution is typically expressed in decimetre cube (dm 3). The molarity or molar concentration ( C i) is the mole of the solute ( n i) per unit volume of the solution ( V). The mass concentration of a solute ( ρ i) is the ratio of the mass of a solute ( m i) to the volume of the solution ( V).įrom the above equation, the mass concentration of a solute is the mass fraction of the solute times the density of the solution. The volume fraction ( v i) is the volume of a component ( V i) to the total volume of the mixture ( V mix). Thus, we have established the relationship between the mole fraction and the mass fraction. Here, is the average molar mass of the mixture. We also know, the mole of a substance is a ratio of the mass ( m i) to the molar mass ( M i). The mole fraction of the i th component is x i. Let n i be the mole of the i th component of a mixture. It is also a dimensionless quantity and is the ratio of the mole of a component to the total mole of the mixture. The mole fraction is widely used quantity in chemistry and engineering. Now, we can express w 1 and w 2 in terms of r m. Let m 1 be the mass of pure substance 1 and m 2, of pure substance 2. The mixing ratio of a component is the abundance of that component of a mixture relative to other components. But there are also other quantities like mole fraction, molarity, mass concentration, among others. The mass fraction is one of a quantity used for expressing the composition of a mixture. The weight percentage of MnSO 4 and H 2O are calculated as follows: Relationship with Other Quantities Solution: The mass of the manganese sulphate is 86 g and the water, 74 g. Statement: A flask of manganese (II) sulphate solution contains 86 g of MnSO 4 and the rest is H 2O. The total mass of a mixture is the sum of the mass of each component. Here, w i is the mass fraction of the i th component, m i is the mass of the i th component, and m T is the total mass of the mixture. Since the mass fraction is a ratio of mass to mass, it is a dimensionless quantity. It is also known as mass per cent or percentage by mass when expressing in percentage. The mass fraction of a substance in a mixture is the ratio of the mass of the substance to the total mass of the mixture. But the below definition of the mass fraction is also applicable to the other types. In chemistry, most mixtures are solutions, homogeneous mixture of a solute and a solvent. Figure 1: Types of Mixtures: Solutions (salt and water), Suspensions (soil and water), and Colloids (milk) (from left to right)
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