Chemistry: calculate mass fraction? As in this task? Amount of substance, mass u. Density are given?


I come for days at a task no further! It is:

To 25ml vinegar (CH3COOH) are added a few drops of phenolphthalein. Until the first permanent red coloration of the solution 20ml sodium hydroxide solution of concentration c (NaOH) = 1 mol / l required. Calculate the amount of material, the mass and the mass fraction of dissolved in the vinegar of acetic acid and the molar concentration of acetic acid. Go out in the calculation of the mass fraction of a density p (vinegar) = 1 g / ml.

Until now I could only charge the amount of substance and the mass. If these bills because even right up to now ?:

n = c V n = 1 mol / l n = 0.02l 0,02mol

m = n M M = 60 g / mol m = 0,02mol 60g / mol m = 1.2g

So. Now I need to calculate the mass fraction yes aloud task. But how?? Which formula? And can one explain this also again to me? I have looked to the Internet. But at Wikipedia as I understand simply nothing. Not even the formula.

Thanks in advance!

The best answer

In your sample (25 ml acetic acid solution) put 20 mmol = 1.2 g of pure acetic acid, balance water. Consequently, the Stoffmengenkonzentation 20 mmol / 25 ml = 0.8 mole / l and the mass concentration of 1.2g / 25 ml = 48 g / l.

Since Thou shalt accept the density ρ = 1 g / mol, weigh your 25 ml sample and 25 g. The mass fraction is therefore 1.2 g / 25 g = 4.8%.

The Massenateil (w) is defined as m (fabric) / m (solution).

Most of this is given in percent.

Date: 2019-01-20 Views: 1

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