titration of ammonia (1 Viewer)

[Jaydels]

Does anyone know why hydrated oxalic acid is a suitable primary standard for the titration of ammonia?

 

[funking_you]

For something to be a suitable primary standard it must fulfill the following conditions.

• 
  the compounds molecular formula must be known

• 
  it must be a STABLE (relatively inert) solid compound

• 
  it must be pure
  (is its relatively inert as a solid...it wont react with moisture and other elements...hence it will remain sufficiently pure)

Oxalic acid it used to standardise ammonia, since ammonia is basic.


does that answer your question?



george

 

[Jaydels]

yeah, but why oxalic acid over acids like hydrochloric acid, sulfuric acid, or nitric acid (I was told these were not suitable)?

 

[jamesy_1988]

Commercially produced solutions of acids like hydrochloric, sulfuric and nitric are not made up to any certain standard. Thus the concentration of these solutions can vary. That is why oxalic acid is used as a standard solution because the *exact* concentration of the acid can be calculated easily.

If you need to use a hydrochloric acid, sulfuric acid or nitric acid as a standard solution you must first standardise them against a standard basic solution such as sodium carbonate.

hope that this answers your question

Jamesy

 

[Jaydels]

actually i do remember hearing something about HCl becoming diluted as it reacts with H20 in the air

that does answer my question, thanks

 

[Arvin Sloane]

I don't know about all of you, but this topic is titillating!

 

[Templar]

actually i do remember hearing something about HCl becoming diluted as it reacts with H20 in the air

To some extend, although it is more evident in higher concentrations or in NaOH (which need to be standardised every day if it is to be used accurately)

 

[funking_you]

yeah, but why oxalic acid over acids like hydrochloric acid, sulfuric acid, or nitric acid (I was told these were not suitable)?

You have to go through the list i gave you to justify a choice as a primary standard.

Firstly, hydrochloric acid does not exsist as a solid at lab conditions, its HCl is normally a gas, and when dissolved in water, forms an acid.
i'm sure solids of Sulfuric and nitric can be made, but i STRONGLY doubt these solids will be stable...they will react with moisture and react with the contain they are kept it....a primary standard such as oxalic acid will not...cause its a stable (inert) solid.



George

 

[Jaydels]

oh ok, thankyou
that makes sense