Guide
1
Mass fraction - a ratio of weight substance to the weight of the solution or mixture: w = m (in) / m (p-pa), where w - mass fraction, m (c) - a substance weight , m (p-pa) - weight of the solution, or w = m (to) / m (cm), where m (cm) - weight of the blend.It is expressed as a decimal or percentage.
additional formulas which may be needed to meet the challenges in the mass fraction of substance :
1) m = V * p, where m - mass, V - volume, p - density.
2) m = n * M, where m - mass, n - the number of substances , M - molar mass.
2
mole fraction - the ratio of moles substance to moles of all substances: q = n (a) / n (tot), where q - mole fraction, n (a) - amount of the particular substance , n (total) - the total number of subs
tances.Additional
formula:
1) n = V / Vm, where n - the number substance , V - volume, Vm - molar volume (under normal conditions is 22.4 liters / mole).
2) n = N / Na, where n is the number of substances , N - number of molecules, Na - Avogadro constant (a constant and is equal to 6.02 * 10 23 degrees 1 / mol).
3
volume fraction - is the ratio of substance by volume mixture: q = V (c) / V (cm), where q - volume fraction, V (c) - the volume substance ,V (cm) - the volume of the mixture.
4
Molar concentration - the ratio of this substance by volume mixture: Cm = n (a) / V (cm) where Cm - molar concentration (mol / l), n - the number substance (mol), V (cm) - the amount of the mixture (L).We will solve the problem in the molar concentration .The molar concentration solution obtained by dissolving sodium sulfate weight of 42.6 g in water of 300 g when the specific gravity of the resulting solution is 1.12 g / ml.Writing a formula to calculate the molar concentration: Cm = n (Na2SO4) / V (cm).We see that the need to find a number of substances sodium and volume of the solution.
expect: n (Na2SO4) = m (Na2SO4) / M (Na2SO4).
M (Na2SO4) = 23 * 2 + 32 + 16 * 4 = 142 g / mol.
n (Na2SO4) = 42,6 / 142 = 0.3 mol.Looking
solution volume: V = m / p
m = m (Na2SO4) + m (H2O) = 42,6 + 300 = 342.6 g = 342.6
V / 1,12 = 306 ml = 0,306 l.
substitute to the general formula: Cm = 0,3 / 0,306 = 0,98 mol / l.The problem is solved.