[kenny1999]

in my book there are only few examples concerning back titrations and after I do research on web I find it quite difficult to have an explanation that makes me understand.

Sorry, I don't really quite understand when and why to use back titrations.
For example if there is a sample of impure MgO to find its amount or purity, I think we
can directly titrate the sample (after dissolving it in water) with a strong acid HCl in order to find out volume of acid required to react with MgO and thus its amount. Indicator of the end point? Methyl orange, isn't it? Then I think everything is alright.
Really can't think of the reason to use back titrations.

Somebody says MgO is insoluble so back titrations is used. However, I think it is just a matter of chemical equilibrium. Even though I use direct titrations, as MgO continuously reacts with the acid running from the burette, its equilibrium can also be shifted continuously to produce more soluble ions. Isn't it?

Please explain to me, please...and thanks

[Borek]

in my book there are only few examples concerning back titrations and after I do research on web I find it quite difficult to have an explanation that makes me understand.

http://www.titrations.info/back-titration

For example if there is a sample of impure MgO to find its amount or purity, I think we
can directly titrate the sample (after dissolving it in water) with a strong acid HCl in order to find out volume of acid required to react with MgO and thus its amount. Indicator of the end point? Methyl orange, isn't it? Then I think everything is alright.
Really can't think of the reason to use back titrations.

Somebody says MgO is insoluble so back titrations is used. However, I think it is just a matter of chemical equilibrium. Even though I use direct titrations, as MgO continuously reacts with the acid running from the burette, its equilibrium can also be shifted continuously to produce more soluble ions. Isn't it?

Titration will take very long and you have problems detecting end point. In theory direct approach may look well in MgO case, but in reality it would be a nightmare. In back titration you don't have to add acid drop by drop and wait for the equilibrium each time, you add excess acid and wait just once, you can do something in the meantime.

[kenny1999]

in my book there are only few examples concerning back titrations and after I do research on web I find it quite difficult to have an explanation that makes me understand.

http://www.titrations.info/back-titration

For example if there is a sample of impure MgO to find its amount or purity, I think we
can directly titrate the sample (after dissolving it in water) with a strong acid HCl in order to find out volume of acid required to react with MgO and thus its amount. Indicator of the end point? Methyl orange, isn't it? Then I think everything is alright.
Really can't think of the reason to use back titrations.

Somebody says MgO is insoluble so back titrations is used. However, I think it is just a matter of chemical equilibrium. Even though I use direct titrations, as MgO continuously reacts with the acid running from the burette, its equilibrium can also be shifted continuously to produce more soluble ions. Isn't it?

Titration will take very long and you have problems detecting end point. In theory direct approach may look well in MgO case, but in reality it would be a nightmare. In back titration you don't have to add acid drop by drop and wait for the equilibrium each time, you add excess acid and wait just once, you can do something in the meantime.

Thank you I can understand your point that it may take too long time to do so.

However, I remember that some websites also state other reasons for back titration could you suggest them? (I am too tired to rote memorize the point)