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Guide
1
Mass fraction - a ratio of the weight of the solute to 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).Any
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 share substances in the solution, which is denoted by the letter w (omega).
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Example 1. Weight 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%
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Example 2. The mass of water 100 grams, the weight of salt '20 Find 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%