[alikhan]

Good day Everyone.
I have made a solution which have following components (mmol.dm-3),

(NH4)2HPO4         1.1 mmol/dm3
(NH4)2SO4          1.2 mmol/dm3
CaSO4                2.1 mmol/dm3
MgSO4.7H2O        2.3 mmol/dm3
Sodium lactate     1.4 mmol/dm3
NaCl                   100 mmol/dm3

What will be the ratio of Chloride ions to sum of all other anions in this soltuion (Cl-:all other anions)?

[Arkcon]

Greetings alikhan:, I'd like to welcome you to the Chemical Forums, but I'd like you to re-read the Forum Rules{click}.  We'd like to see some effort from you first.  On some level, this problem is simply a sum,with some chemistry knowledge applied.  Can you begin to do some steps yourself.

[alikhan]

Dear Arkcon, I have tried to do it my self and the answer I am getting is (Cl-: all other anions = 4.1:1). Where as the paper I am reading is showing 5:1. Please confirm which one is correct?

[Arkcon]

Ok, show your work.  Maybe while typing it out, you'll see the problem.

[alikhan]

Here is the workout:

Concentration of anion (HPO4-) in (NH4)2HPO4 is       1.1 mmol/dm3.
Concentartion of anion (SO4-) in (NH4)2SO4 is          1.2 mmol/dm3.
Concentration of anion (SO4-) in CaSO4 is                2.1 mmol/dm3.   
Concentration of anion (SO4-) in MgSO4.7H2O is        2.3 mmol/dm3.   
Concentration of anion (OH-) in MgSO4.7H2O is         16.1 mmol/dm3.   
Concentration of anion (lactate) in sodium lactate is   1.4 mmol/dm3.   
Concentration of anion (Cl-) in NaCl is                      100 mmol/dm3.   

Cl-: Sum of all other anions = 100:24.2 = 4.1:1

Please confirm me that it is correct way to calculate??

[Arkcon]

Concentration of anion (SO4-) in MgSO4.7H2O is        2.3 mmol/dm3.   

Good.

Concentration of anion (OH-) in MgSO4.7H2O is         16.1 mmol/dm3.   

Justify this please.

[alikhan]

There is one SO4- ion and 7 OH- in of MgSO4.7H2O. Therefore, for 2.3 mmol/dm-3 of MgSO4.7H2O we should have

SO4- = 2.3 and OH- = 7 x 2.3 = 16.1

[Arkcon]

7 OH- in of MgSO4.7H2O.

No, that's not correct.  Can you see why?  Consider this.  If that water in the crystal completely ionizes, what's it ionizing in?  The liters of water in solution?  Does the water also ionize completely into H+ and OH-?  Completely?

[alikhan]

I got the point. Water is not ionic compound so it will not ionize like NaCl does.

A part from this, would you confirm the way I am calculating the concentration of anions is correct?

[Arkcon]

Yes.  In each case you used the molecules concentration for the anion concentration, and in no case is there more anions per molecule.