Chemie pH-Wert?

Kann mir jemand bei der Berechnung des pH-Wertes helfen?

a) Ameisensäure (0,01mol/l) ; pKS= 3,65

b) Bromwasserstoffsäure (0,02mol/l) ( starke säure glaube ich?)

c)Natriumacetat (0,1mol/l)

d) Kaliumfluorid (0,25mol/l) ; pKB= 11

e)Natriumhydrogensulfat (0,5mol/l)

bei b) Bromwasserstoffsäure habe ich -log (0,02) = 1,698

den rest weiss ich nicht wie ich das berechnen soll.. Bei schwachen und starken Säuren gibt es nämlich verschiedene Rechenwege

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Phleppse
1 year ago

There are a total of two relevant formulas for pH calculation, once in the case of strong acids which virtually completely dissociate, and once in the case of weak acids in which there is hardly any dissociation. We skip the pH formula for medium-strong acids.

With strong acids, the pH is calculated by

because you can start from a complete dissociation.

With weak acids, you expect

It should be noted that in the case of corresponding bases, you must first calculate the pOH value to weak acids (e.g. in the case of acetate) above the pKB value before you are then using the relationship

pH + pOH = 14

to pH.

Phleppse
1 year ago

The pKS value is sufficient for the pH calculation. But if you want to determine the Ks value from the pKs, you expect

KS = 10^-pK