Q7. Dr Entropy has a water sample containing both phosphate and sulfate, and the five solutions

shown here:

• sodium chloride, NaCl  
• iron(III) nitrate, Fe(NO3)3
• calcium nitrate,
• potassium hydroxide, KOH
• ammonium fluoride, NH4F

(i)  Explain how the two anions (phosphate and sulfate) could be separated making use of the solutions above and an equipment like a Büchner funnel that can collect precipitated solids on a filter while allowing the remaining solution to pass through into a flask.

(Hint: Refer to the solubility table at the end of this document to determine what could be added to precipitate only one of the two anions.)

(ii) In your answer show balanced chemical reaction equation for any relevant precipitation reaction, including the states of all chemical species.

ANSWER:

Solubility tableIONIC COMPOUNDSOLUBLE SALTSINSOLUBLE SALTSNitrates (NO3)With all cationsSodium (Na+)With all anionsPotassium (K+)With all anionsAmmonium (NH4+)With all anionsChlorides, lodides andBromides (CI-, I-, Br)With most cations, except…Ag+, Pb2+, Hg+Chlorate CIO4With all cationsAcetate (CH=COO-)With almost all cations except…CH,COOAg (sparingly)Nat, K+ NH4+Hydroxide (OH-)With all other cationsCa2+, Ba2+, Sr2+, Mg2+ (sparingly)Nat, K* NH4+Sulfide ($2-)Ca2+, Ba2+, Sr2+, Mg2+With all other cationsCarbonates (CO32-)Nat, K* NH4+With all other cationsPhosphates (PO43-)Nat, K+ NH4+With all other cationsSulfate (SO42-)With most cations except…Ag+, Cal+, Ba?+, Sr2+, Hg*, Pb2+