Ph wert von 0,48g methansäure in 1 Liter wasser?

Hey, ich brauch ganz dringend hilfe bei einer chemie aufgabe. Und zwar muss ich den ph-wert von 0,48g methansäure in 1 liter wasser ermitteln, habe aber keine Ahnung wie ich das machen soll. Könnte mir wer die Rechenschritte erklären?

dankeschön!!

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indiachinacook
1 year ago

The mass concentration γ=0.48 g/l corresponds to a mass concentration c=γ/M=0.0104 mol/l. The acid constant pKa=3.75 gives a pH of 2.89.

In order to calculate the pH from the concentration, there are a bunch of formulas, of which at least one usually provides the correct or at least one usable solution. The simplest of these, pH=1⁄2(pKa-lg(c)), already yields a good result with 2.87; the more precise formula pH=−lg[√(1⁄4Ka2+Kac)−1⁄2Ka ]=2.89 then also does not bring much. That’s why you don’t need the universal formula

to use which always works in all doubts.

Trojaa
1 year ago

Only calculate the concentration in mol/l, then consider or research whether methane acid (=formic acid) is rather a strong or weaker acid and then use it in the corresponding formula.