Definitions of acid and base (1 Viewer)

[Pace_T]

Hello everybody
Can someone please help me with this point?
Identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature
I dont really understand it.
So a salt (produced from strong acid + weak base) forms has an acidic nature in solution?
I really don't understand this point at all..
Thanks in advance.

 

[Dreamerish*~]

Hello everybody
Can someone please help me with this point?
Identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature
I dont really understand it.
So a salt (produced from strong acid + weak base) forms has an acidic nature in solution?
I really don't understand this point at all..
Thanks in advance.

The question is somewhat badly phrased. It means:

Explain why after neutralisation, some salt solutions are neutral, while others are acidic or basic.

Basically, this is asking you to talk about how weak acid + strong base = basic salt, etc.

Strong acid + Strong base = Salt solution of pH=7.

Strong acid + Weak base = Salt solution of pH<7.

Weak acid + Weak base = Salt solution of pH=7.

Weak acid + Strong base = Salt solution of pH>7.

(Strong acids: HCl, HNO₃, H₂PO₄.Weak acids: CH₃COOH, HNO₂, C₆H₈O₇. Strong bases: NaOH, KOH. Weak bases: NH₃.)

Hope that helped.

 

[Pace_T]

Thank you very much.

 

[LaCe]

Does anyone know why this happens?

eg. in a strong acid + weak base, the anion of the conjugate acid (of the weak base) acts as an acid and therefore the salt is acidic. Follow? Is this true?

 

[Dreamerish*~]

Does anyone know why this happens?

eg. in a strong acid + weak base, the anion of the conjugate acid (of the weak base) acts as an acid and therefore the salt is acidic. Follow? Is this true?

A strong acid forms a weak conjugate base, and a strong base forms a weak conjugate acid.

When a strong acid reacts with a strong base, both conjugate acid and base are weak, therefore the salt solution is neutral.

When a weak acid reacts with a weak base, both conjugate acid and base are strong, therefore the salt solution is neutral.

When a strong acid reacts with a weak base, the conjugate base is weak, therefore the pH of the salt solution leans to the left of 7.

When a weak acid reacts with a strong base, the conjugate acid is weak, therefore the pH of the salt solution leans to the right of 7.

I'm quite sure I'm not wrong, hope that wasn't too confusing.

 

[nit]

Originally posted by Dreamerish*~
A strong acid forms a weak conjugate base, and a strong base forms a weak conjugate acid.

When a strong acid reacts with a strong base, both conjugate acid and base are weak, therefore the salt solution is neutral.

When a weak acid reacts with a weak base, both conjugate acid and base are strong, therefore the salt solution is neutral.

When a strong acid reacts with a weak base, the conjugate base is weak, therefore the pH of the salt solution leans to the left of 7.

When a weak acid reacts with a strong base, the conjugate acid is weak, therefore the pH of the salt solution leans to the right of 7.

I'm quite sure I'm not wrong, hope that wasn't too confusing.

Just to fix up your terminology, the conjugate base of a strong acid is a negligible base and similarly for a base. The conjugate base of a weak acid is a weak base. Negligible acids and bases mean that the respective equilibria lie completely (well barring a very, very, small fraction of molecules) to the left. Weak acids and bases can cause pH shifts from neutral conditions in whatever medium.

 

[xiao1985]

further, weak + weak should be ambiguous... not necessarily 7...

usually u won't be titrating weak base vs weak acid any way...

 

[Dreamerish*~]

further, weak + weak should be ambiguous... not necessarily 7...

usually u won't be titrating weak base vs weak acid any way...

Oh yes, I rememer the weak + weak curve. You can't really pinpoint the end point. :uhhuh: