ph question (1 Viewer)

[abbadell]

Can someone please work out and explain the answer to me
Solutions of potassium ethanoate (CH3COOK) are basic. The pH of 0.1 mol potassium ethanoate is 8.5. Solutions of potassium hydroxide are also basic; however the pH of 0.1 mol KOH is not 8.5 it is 13.
By what factor is the concentration of the hydroxide ions greater in the potassium hydroxide solution?

 

[rhia]

Can someone please work out and explain the answer to me
Solutions of potassium ethanoate (CH3COOK) are basic. The pH of 0.1 mol potassium ethanoate is 8.5. Solutions of potassium hydroxide are also basic; however the pH of 0.1 mol KOH is not 8.5 it is 13.
By what factor is the concentration of the hydroxide ions greater in the potassium hydroxide solution?

the factor is that potassium ethanoate is weaker than potassium hydroxide. a greater amount of potassium hydroxide 1- dissociates in solution or 2- removes hydrogen ions/protons from solution than does potassium ethanoate.

 

[Riviet]

Rememeber that the pH + pOH = 14, where pOH is the concentration of hydroxide ions. So if a substance has a pH of 5, then it's pOH or concentration of OH is 14-5=9. Converting the pH's of KOH and and potassium ethanoate, we get:
pOH of KOH = 14-13=1
pOH of potassium ethanoate = 14-8.5=5.5

Remember that an increase/decrease in pH of 1 means an increase/decrease in hydrogen concentration by a factor of 10. This is also true for the concentration of hydroxide.

Since the difference in pOH's of KOH and potassium is 5.5-1=4.5, then the factor that it is greater in hydroxide concentration = 10^4.5=31623.

 

[funking_you]

Can someone please work out and explain the answer to me
Solutions of potassium ethanoate (CH3COOK) are basic. The pH of 0.1 mol potassium ethanoate is 8.5. ...

Do you know why this potassium ethanoate salt is basic?

It is important to know that not all salts have a neutral pH. This is a common misconception since when students here the word 'salt' they think of NaCl(s), which is a neutral salt. However you should recall that a 'salt', in simple terms, is just a common name for ionic solids (i.e. a compound of a cation and an anion)

To answer the question and justify your answer you need to understand:

• Definition of Lowry-Brontead Acid and Base

• Conjugate acid/base pairs

You also need to appreciate that the acid base reaction does not necessarily stop once the salt has formed, the salt may react further with water ... (this is a hint!)

• Lowry-Brontead Acid/Base Theory

Best of Luck to all students completing half-yearly exams. I hope you have all studied an prepared well, if you haven't and your exam is very soon, and you need to get good marks, i suggest you get to it asap or possibly join an organised religion whose god helps students out with school exams, if you cant find one of these, you'd have no other alternative than study.


Cheers,
George