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Salts and Identification of Ions and Gases

Salts and Identification of Ions and Gases – A salt can be defined as a substance formed when the hydrogen in an acid is replaced by a metal ion.  Salt for human consumption is produced in different forms such as unrefined salt (sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color. You will use some of the reactions of acids to form salts and then isolate them from the reaction mixture.

Basicity

Acid

Salt

Acid salt

1 hydrogen Hydrogen acid (HCl) Calcium chloride CaCl2()Sodium chloride (NaCl)
Nitric acid (HNO3) Magnesium nitrate (Mg(NO3)2)Potassium nitrate (KNO3)
2 hydrogen Sulphuric acid (H2SO4) Copper (II)sulphate (CuSO4)Lead(II)sulphate (PbSO4) Sodium hydrogen sulphate (NaHSO4)
Carbonic acid (H2CO3) Zinc carbonate (ZnCO3)Iron (II) carbonate (FeCO3) Calcium hydrogen carbonate (Ca(HCO3)2)
3 hydrogen Phosphoric acid (H3PO4) Sodium phosphate (Na3PO4)Calcium phosphate (Ca3(PO4)2) Sodium dihydrogen phosphate (NaH2PO4)Disodium hydrogen phosphate (Na2HPO4)

B. Solubility of salt

No.

salt

Solubility in water

soluble (aq state)

(ionised)

Insoluble

(solid state)

1.

acetate (CH3COO-)

all

-

2.

nitrate (NO3-)

all

-

3.

chlorate (ClO3-)

all

-

4.

sulphate (SO42-)

other

Calcium sulphate CaSO4,barium sulphate BaSO4,Lead(II) sulphate PbSO4,Strontium sulphate  SrSO4

5.

chloride (Cl-)

other

Silver chloride AgCl,Lead (II) chloride PbCl2,Mercury (II) chloride Hg2Cl2

6.

bromide (Br-)

other

Silver bromide AgBr,Lead (II) bromide PbBr2,Mercury (II) bromide Hg2Br2

7.

iodide (I-)

other

Silver iodide AgI,Lead (II) iodide PbI2,Mercury (II) iodide Hg2I2

8.

carbonate (CO32-) sodium carbonate Na2CO3,potassium carbonate K2CO3,ammonium carbonate (NH4)2CO3

other

9.

sulfite (SO32-) sodium sulfite Na2SO3,potassium K2SO3,ammonium sulfite (NH4)2SO3

other

10.

silicate (SiO32-) sodium silicate Na2SiO3,potassium silicate K2SiO3,ammonium silicate (NH4)2SiO3

other

11.

phosphate (PO43-) sodium phosphate Na3PO4,potassium phosphate K3PO4,ammonium phosphate (NH4)3PO4

other

12.

arsenate(AsO43-) sodium arsenate Na3AsO4,potassium arsenate K3AsO4,ammonium arsenate (NH4)3AsO4

other

13.

sulfide (S2-) sodium sulfide Na2S,potassium sulfide K2S,ammonium sulfide (NH4)2S,calcium sulfide CaS,strontium sulfide SrS,

barium sulfide BaS,

magnesium sulfide MgS

other

C. Preparation of Soluble Salt

1. Metal and acid

The more reactive metals like Mg, Zn, Fe, Al (not Na, K, and Ca)

metal + acid ? salt +hydrogen

Zn(s) + H2SO4(aq) ? ZnSO4(aq) + H2(g)

2. Metal oxide and acid

For metals which don’t react with dilute acid but react when metal oxides

Metal oxide +acid ? salt + water

CuO(s)  + H2SO4(aq) ? CuSO4(aq) + H2O(l)

3. Metal hydroxide and acid

Especially suitable for soluble metal hydroxides called alkalis. The process is titration.

End react : the end of the titration, is reacted when the colour of the indicator in the alkalis change

Metal hydroxide + acid ? salt + water

KOH(aq)  + HCl(aq)  ? KCl(aq) + H2O(l)

4. Metal carbonate and acid

Metal carbonate + acid ? salt + water + carbon dioxide

ZnCO3 (aq)  + 2HNO3(aq) ? Zn(NO3)2(aq) + H2O(l) + CO2(g)

D. Identification of Ions

As the use of standard chemical procedures to determine the presence and concentration of specific element and compounds within a substance.

Qualitative analysis

Identify elements and compounds present in unknown substances

Quantitative analysis

Measure of the concentration of  elements and compounds present in unknown substances

F. Identification of cations

  • reagent aqueous sodium hydroxide
  • reagent aqueous aqueous ammonia

Cations

Effect of aqueous NaOH

Effect of aqueous NH3

Aluminium, Al3+
  • white precipitate
  • soluble in excess giving a colourless solution
  • white precipitate
  • insoluble in excess

 

Calcium, Ca2+
  • white precipitate
  • insoluble in excess
             no reaction
Copper (II), Cu2+
  • light blue precipitate
  • insoluble in excess
  • light blue precipitate
  • soluble in excess giving a dark blue solution
Iron (II), Fe2+
  • green precipitate
  • insoluble in excess
  • green precipitate
  • insoluble in excess

 

Iron (III), Fe3+
  • red brown precipitate
  • insoluble in excess
  • red brown precipitate
  • insoluble in excess
Lead (II), Pb2+
  • white precipitate
  • soluble in excess giving a colourless solution
  • white precipitate
  • insoluble in excess

 

Ammonium, NH4+ ammonia produced on warming, smell
Zinc, Zn2+
  • white precipitate
  • soluble in excess giving a colourless solution
  • white precipitate
  • soluble in excess giving a colourless solution

G. Identification of anions

Anion

Test

Observation

Carbonate, CO32+ add dilute hydrochloride acid
  • effervescence occurs
  • CO2 liberated (can be identified as it turn limewater milky)
Chlorine, Cl- add dilute nitric acid, followed by aqueous silver nitrate or lead (II) nitrate white precipitate
Iodide, I- add dilute nitric acid, followed by aqueous silver nitrate or lead (II) nitrate yellow precipitate (PbI2)
Sulphate, SO42- add dilute nitric acid, followed by aqueous barium nitrate or lead (II) nitrate white precipitate
Nitrate, NO3- add dilute sodium hydroxide, followed by aluminium foil/ powder. Warm gently
  • effervescence
  • NH3 gas liberated

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