A2 chemistry - buffer solutions

I will first type out a question and from there explain what a buffer solution is and if anything i have missed, feel free for someone to add in so i can fully understand this.

".....when dissolved in water, Ca(H2PO4)2 dissociates forming H2PO4- ions which are easily......

A solution of of calcium dihydrogenphosphate, Ca(H2PO4)2, in water acts as a buffer solution.

Suggest, with aid of equations, how this buffering action takes place."

So from the first information we are given i knew that Ca(H2PO4)2 would dissociate to -----> H2PO4- + CaH2PO4+

A buffer solution is a chemical that resists changes to pH in a environment. So, always describe when H+ is added and OH- is added

So when H+ is added: H2PO4- + H+----> H3PO4
When OH- is added: H2PO4- + OH- -----> H2O + HPO42-

Is that correct because for the OH- hence the minus part i always thought was reserved for an hydroxide so can i use H2PO4- for this or should i be using CaH2PO4- instead?

Thanks in advance. Please quote with help.

I will first type out a question and from there explain what a buffer solution is and if anything i have missed, feel free for someone to add in so i can fully understand this.

".....when dissolved in water, Ca(H2PO4)2 dissociates forming H2PO4- ions which are easily......

A solution of of calcium dihydrogenphosphate, Ca(H2PO4)2, in water acts as a buffer solution.

Suggest, with aid of equations, how this buffering action takes place."

So from the first information we are given i knew that Ca(H2PO4)2 would dissociate to -----> H2PO4- + CaH2PO4+

A buffer solution is a chemical that resists changes to pH in a environment. So, always describe when H+ is added and OH- is added

So when H+ is added: H2PO4- + H+----> H3PO4
When OH- is added: H2PO4- + OH- -----> H2O + HPO42-

Is that correct because for the OH- hence the minus part i always thought was reserved for an hydroxide so can i use H2PO4- for this or should i be using CaH2PO4- instead?

Thanks in advance. Please quote with help.

edit - from an earlier question we are told that the H2PO4- ion can act as an acid or a base.

Oh hold on, we are also told that the H2PO4- ion can act as an ACID AND BASE. So, that's why we can use it.

First of all you have to lose the calcium, as it's ionic.

Ca(H₂PO₄)₂ --> Ca2+(aq) + 2H₂PO₄(-)

The you just consider the dihydrogen phosphate ions.

These can act as an acid by reacting with base:

H₂PO₄(-) + OH- --> HPO₄(2-) + H₂O

or they can react as a base:

H₂PO₄(-) + H+ --> H₃PO₄

As the ions can absorb either acid or base then they are behaving as a buffer.

Thanks for your reply and answer!!! I have one question... as i mentioned in my OP, the question said when dissolved in water it forms H2PO4- ions meaning one and not 2H2PO4- because you use H2PO4- and not 2H2PO4- ????

Large numbers in front of species are called coefficients and are only used to balance the equation.

There is no such thing as 2H2PO4-, it simply means two lots of H2PO4-.

First of all you have to lose the calcium, as it's ionic.

Ca(H₂PO₄)₂ --> Ca2+(aq) + 2H₂PO₄(-)

The you just consider the dihydrogen phosphate ions.

These can act as an acid by reacting with base:

H₂PO₄(-) + OH- --> HPO₄(2-) + H₂O

or they can react as a base:

H₂PO₄(-) + H+ --> H₃PO₄

As the ions can absorb either acid or base then they are behaving as a buffer.