[AdiDex]

I recently prepared Manganese Phosphate in thelab , but My teacher didn't explained everything so i have some doubts I've tried to figure out them but not getting clue.

Q.1 she didn't mentioned that It will be Hydrate ,
"The hydrate is prepared by Oxidation of manganese(II) acetate with KMnO4 in glacial acetic acid"
- Inorganic Chemistry, N.N Greenwood
So It must be MnPO4.xH2O , Isn't it ??

Q.2 I prepared it from dissolving MnSO4 and (NH₄)₂HPO₄ , adding pure acetic acid ..!! After boiling , Oxidizing it using KMnO₄ .
Why we can't use HNO3 , or HCl or H2SO4 ??

My reasoning
I've read that Mn³⁺ is not so stable ,but It is stable in Acidic medium so we need acid.

HCl - Since we are using KMnO4 , Cl^- also can get oxidized . So can't use HCl , it we reduce the Yield .

H2SO4 - not aboe to figure out ..Any hint ??

HNO3 - May be it will oxidise Mn³⁺ further , as KMnO4 and HNO3 both will be combined .

Any idea plzz ... Guide me

[AdiDex]

Inshort my Q.2 is What is the role of acetic acid .!!!

[AWK]

Compare strength of acetic acid, H₃PO₄, and HCl or HNO₃ or H₂SO₄.
MnPO₄ is formed even without strong oxidizer - oxygen from air is sufficent but you need mixing about 2 weeks. In this case you need manganese acetate and phosphoric acid.
There is also method that use nitric acid as oxidizer.
There are 2 hydrates of MnPO₄: mineral serrabrancaite - monohydrate (serrabrancaite (was synthesized by oxidizing Mn(H2PO4)2 with NaClO solution in 2010) and synthetic sesquihydrate.

You quote from Greenwood concern manganese acetate complex, not phospate. There is also information that Mn(III) is stabilized by O-donors.

[AdiDex]

Acidic strength of H2SO4 > HCl > HNO3 >  H3PO4 > Acetic Acid

In some literature I've Found that HCl is better acid. Than H2SO4..!!!

Bdw Meanwhile I've found that Mn⁺³ is get stablized by Hard bases.... Acetate is also an Hard base so as PO4^3- .
But I've not read about Soft-Hard Acid Base concept in detail , I know about it in nutshell , High charge density = Hard Base..
Since in Phosphate and Nitrate and Sulphate ion the unit charge is dispersed on More than one atom they are slightly softer base... ??
Acetic acid is harder than these ...!!
It can be the reason why we only acetic acid ??

And In strong acidic medium the KMnO4 will become very strong Oxidizing agent , may be it will oxidise Mn+3 further to +4 or +5??

According to you we need mild Oxidizing agent since without it , reaction will be slow.....so we used KMnO4 , but I didn't get hy we used Acetic acid ??

Moreover I've quoted for acetate complex , I thought it is relevant  because in solution when Mn+3 ions was forming intially they were getting stablized by Acetate then when they come in contact of Phosphate ion they get precipitate out from solution.  Is there any problem in my thought ??

[AWK]

HCl cannot be used with KMnO₄ but you may use stoichiometric amount of HCl with hypochlorite as oxidizer of Mn(II) acetate.
Mn(H₂PO₄)₂ is the best reagent for oxidation. For this purpose acetic acid is used (look at pKas of H₃PO₄). Strenght of oxidizer is not important when relatively stable in acidic medium Mn(III) is precipitaded as MnPO₄. Dissolution of this compound in strong acid allows further oxidation of Mn(III).
In oxidation with oxygen an additional equilibrium gas-liquid is involved, hence much more time is needed.
Trivalent metal phosphates show rather small solubility products. This cause that they are insoluble in very diluted HNO₃. So, theoretically, you can also use nitric acid as oxidizer with substantial loss of yield.

[AdiDex]

pKa of H3PO4 is 7.2 x 10^-3 and pKa of acetic acid is 1.76x10^-5 .

So main point is we need to stop the dissolution of Manganese Phosphate in water , if we use strong acid it will get dissloved and get further oxidized .
Thats why we are using Acetic acid ?? 
Let suppose if we use KMO4 with HCl in non stoichiometric amount then what will happen ??
Our KMnO4 will get wasted ?? As it will oxidise Cl^- first to Cl2 ??
And Hypochlorite will prevent this wastage ?? Even Hypochlorite can oxidise the Chloride .!!

Nd I didn't get Why Mn(H2PO4)2 is the best reagent ??

Sorry for asking such questions....I am very bad in inorganic 

[AWK]

pKa of H3PO4 is 7.2 x 10^-3 and pKa of acetic acid is 1.76x10^-5 .

pK_a2 ?

So main point is we need to stop the dissolution of Manganese Phosphate in water , if we use strong acid it will get dissloved and get further oxidized . Thats why we are using Acetic acid ??

Manganese phosphate does not dissolve in water and acetic acid.

Let suppose if we use KMO4 with HCl in non stoichiometric amount then what will happen ??
Our KMnO4 will get wasted ?? As it will oxidise Cl^- first to Cl2 ??

Do you prefer danger (Cl₂) and difficulties in isolation?

Even Hypochlorite can oxidise the Chloride .!!

for chloride and hypochlorite ??

Nd I didn't get Why Mn(H2PO4)2 is the best reagent ??

This is the experience of chemists showed in publications that you should read.
Your procedure also use it.

Q.2 I prepared it from dissolving MnSO4 and (NH4)2HPO4 , adding pure acetic acid

Acetic acid converts hydrogen phosphate anion into dihydrogen phosphate anion. Coordinated Mn(II) is oxidized to Mn(III) and  the manganese(III) phosphate is formed. This pH (acetic acid) prevents precipitation of Mn₃(PO₄)₂.

[AdiDex]

From where can i  get those Journals or articles ??

I got that why we need acetic acid  it s k_a just in between k_a2  and k_a1 of phosphoric acid . And its the experimental fact that we need H₂PO₄^- for smooth Oxidation .

Its all about pH , that means we can use  propanoic acd or  formic acid .??

[AWK]

Searching carefully internet you can find at least three methods of synthesis. Then you should find journals in your library, or find them through library access to journals from your library.
Below you find an abstract from Elsevier Journal (hypochlorite oxidation)
http://www.sciencedirect.com/science/article/pii/S129325581000066X
This abstract is in public domain and for wise chemist is sufficient for repeating this synthesis.