you need

- pen, paper and calculator

Guide

1

Mass fraction - a ratio of the weight of the solute to the mass

solution consists of a solvent (water - the most common solvent) and solute.For example, any solution of a salt solvent
is water, and as the solute will be the salt itself.

The calculations need to know at least two options - a lot of water and a lot of salt.This will enable to calculate the mass

**solution**.Moreover, it can be measured or percentage, then this result is multiplied by 100% or weight parts (in this case, does not have units).Anysolution consists of a solvent (water - the most common solvent) and solute.For example, any solution of a salt solvent

The calculations need to know at least two options - a lot of water and a lot of salt.This will enable to calculate the mass

**share**substances in the solution, which is denoted by the letter w (omega). 2

Example 1. Weight

m (KOH) = 20 g

m (KOH) = 100 g

w (KOH) -? There is a formula that can determine a mass fraction

w (KOH) = m (KOH) / m (

w (KOH) = 20 g / 120 g x 100%= 16,6%

**solution of potassium hydroxide (KOH) 150 g, the weight of the solute (KOH) '20 Find the mass****share**alkali (KOH) in the resulting solution.m (KOH) = 20 g

m (KOH) = 100 g

w (KOH) -? There is a formula that can determine a mass fraction

**substance.**w (KOH) = m (KOH) / m (

**solution**(KOH) × 100% Then, calculate the mass**share**solute potassium hydroxide (KOH):w (KOH) = 20 g / 120 g x 100%= 16,6%

3

Example 2. The mass of water 100 grams, the weight of salt '20 Find

m (NaCl) = 20 g

m (water) = 100 g

w (NaCl) -? There is a formula that can determine a mass

w (NaCl) = m (NaCl) / m (

m (

w (NaCl) = 20 g / 120 g x 100% = 16,7%

**share**mass of sodium chloride in solution.m (NaCl) = 20 g

m (water) = 100 g

w (NaCl) -? There is a formula that can determine a mass

**share**substance.w (NaCl) = m (NaCl) / m (

**solution**NaCl) x 100% Before use this formula, get the weight**solution**, which consists of the mass of solute and water mass. Therefore: m (**solution**NaCl) = m (solute NaCl) + m (water) Substitute specific values m (

**solution**NaCl) =100 g ± 20 g = 120 gTeper**calculate the mass fraction of solute**:w (NaCl) = 20 g / 120 g x 100% = 16,7%

Helpful Hint When

calculation does not confuse concepts such as the mass of the solute and the mass fraction of solute