HSC 2007 multiple Choice Q (1 Viewer)

[mtsmahia]

Hi guys,

can someone explain how to determine the answer for this Q.

Which of the following aqueous solutions has a pH greater than 7?

Sodium Citrate

Sodium Chloride

Ammonium Nitrate

Ammonium Chloride

The answer is Sodium Citrate, but can anyone please support it with a equation or theory?

Thanks

 

[x jiim]

with these, you want to think about the reaction that formed the salts [or their reaction with water, but the first one's usually easier]. pH>7 means you're looking for a basic salt, formed when a strong base and weak acid react.

Sodium Chloride- NaOH [strong base] + HCl [strong acid] --> neutral salt
Ammonium Nitrate- NH4 [weak base] + HNO3 [strong acid] --> acidic salt
Ammonium Chloride- NH4 [weak base] + HCl [strong acid] --> acidic salt
Sodium Citrate- NaOH [strong base] + citric acid [weak acid] --> basic salt

does that make sense?

 

[mtsmahia]

with these, you want to think about the reaction that formed the salts [or their reaction with water, but the first one's usually easier]. pH>7 means you're looking for a basic salt, formed when a strong base and weak acid react.

Sodium Chloride- NaOH [strong base] + HCl [strong acid] --> neutral salt
Ammonium Nitrate- NH4 [weak base] + HNO3 [strong acid] --> acidic salt
Ammonium Chloride- NH4 [weak base] + HCl [strong acid] --> acidic salt
Sodium Citrate- NaOH [strong base] + citric acid [weak acid] --> basic salt

does that make sense?

Oh ok... Thanks heaps