Anions and Cations – Common ions and their charges, test to identify cations and anions and observations of test carried out on positive and negative ions

Anions and Cations – Common ions and their charges, test to identify cations and anions and observations of test carried out on positive and negative ions

Anions

Anions are atoms that have gained electrons and since they now have more electrons than protons, anions have a negative charge.

Common Anions and their Charges

Mono-atomic Anions

Names

F

Fluoride

Cl

Chloride

Br

Bromide

I

Iodide

O2

Oxide

S2

Sulphide

Se2-

Selenide

Te2-

Telluride

N3-

Nitride

P3-

Phosphide

A3-

Arsenide

Polyatomic Anions

Name

NH4

Ammonium

NO2

Nitrite

N03

Nitrate

S032-

Sulphite

SO42-

Sulphate

OH

Hydroxide

PO43-

Phosphate

CO32-

Carbonate

ClO3

Chlorate

C2H3O2

Acetate

CH3COO

Ethanoate

MnO4

Manganate (VII)

Cr2O72-

Dichromate (VI)

PO43-

Phosphate

S2O32-

Thiosulphate

Test for the identification of Anions

Anion

Symbol

Test

Results

Bromide

Br

Add silver nitrate to a  solution of  the substance in dilute nitric acid

Cream precipitate, dissolves slightly in ammonia solution

Carbonate

CO32-

  • Add dilute hydrochloric acid to the substance

  • Add a drop of phenolphthalein to a solution of the substance
  • Carbon dioxide gas is given off

  • Turns bright pink

Chloride

Cl

Add silver nitrate to a solution of substance in dilute nitric acid

Thick white precipitate dissolves in ammonia solution

Hydrogen-Carbonate

HCO32-

  • Add dilute hydrochloric acid to the substance

  • Add a drop of phenolphthalein to a solution of the substance.
  • Carbon dioxide gas is given off.

  • Turns light pink

Iodide

I

Add silver nitrate to a solution of the substance in nitric acid

Pale yellow precipitate, does not dissolve in ammonia solution

Nitrate

NO3

Add iron (II) sulphate solution followed by concentrated sulphuric acid to the solution.

Brown rings forms at the junction of the two liquids

Sulphate

SO42-

Add solution of barium chloride to the solution

White precipitate does not dissolve in dilute hydrochloric acid

Sulphite

SO32-

Add solution of barium chloride to the solution

White precipitate dissolves in dilute hydrochloric acid

Sulphide

S2

Add lead (II) ethanoate solution to the solution

Black precipitate.

Cations

Cations are atoms that have lost electrons. Since they now have more protons than electrons, cations have a positive charge.

Common Cations and their Charges

Mono-atomic Cations

Name

H+

Hydrogen

Li+

Lithium

Na+

Sodium

K+

Potassium

Rb+

Rubidium

Cs+

Cesium

Be2+

Beryllium

Mg2+

Magnesium

Sr2+

Calcium

Ba2+

Barium

Al3+

Aluminum

Ga3+

Gallium

Ag+

Silver

Zn2+

Zinc

NH4+

Ammonium

Fe3+

Iron(III)

Fe2+

Iron(II)

Cu2+

Copper(II)

Cu+

Copper(I)

Cr3+

Chromium(III)

Ni2+

Nickel (II)

Pb4+

Lead(IV)

Pb2+

Lead(II)

Hg2+

Mercury (II)

Sn2+

Tin

(Hint: Roman numerals give the positive charge)

Test for the identification of Cations

Cation

Symbol

Test

Results

Aluminum

Al3+

  • Add dilute sodium hydroxide solution to a solution of the substance

  • Add dilute ammonia solution to a solution of the substance
  • White precipitate that dissolves as more sodium hydroxide is added

  • White precipitate that remains insoluble as more ammonia is added

Ammonium

NH4+

Add sodium hydroxide solution to a solution of the substance and gently heat

Ammonia gas is given off

Calcium

Ca2+

Add dilute sulphuric acid to a solution of the substance

White precipitate is formed.

Copper (II)

Cu2+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • Pale blue precipitate that does not dissolve as more sodium hydroxide is added

  • Pale blue precipitate, changing to deep blue as more ammonia is added

Iron (II)

Fe2+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • Pale green precipitate is formed

  • Pale green precipitate is formed

Iron (III)

Fe3+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • Red -Brown precipitate is formed

  • Red-Brown precipitate is formed

Lead (III)

Pb2+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • White precipitate that dissolves as more sodium is added

  • White precipitate that does not dissolve as more ammonia is added

Magnesium

Mg2+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • White precipitate that does not dissolve as more sodium hydroxide is added.

  • White precipitate that does not dissolve as more ammonia is added.

Zinc

Zn2+

  • Add dilute sodium hydroxide solution to a solution of the substance.

  • Add dilute ammonia solution to a solution of the substance

  • White precipitate that dissolves as more sodium hydroxide is added

  • White precipitate that dissolves as more ammonia is added.

Observations of test carried out on Positive and Negative Ions

Positive Ions

Discharge of Positive Ion

Observation

Na+ + e = Na

Grey deposit is formed

Al3+ + 3e = Al

Grey deposit is formed

Pb2+ + 2e = Pb

Grey deposit is formed

Cu2+ + 2e = Cu

Brown deposit is formed

Ag+ + e = Ag

Silver deposit is formed

2H+ + 2e = H2

Gas bubble is formed. a popping sound is produced when a lighted splinter is placed near the mouth of the test-tube

Negative Ion

Discharge of Negative Ion

Observation

2Cl  =  Cl2 + 2e

Bubbles of pungent yellow-green gas are produced. The gas turns moist litmus paper to red and then bleaches it.

2Br =  Br2 + 2e

  • Molten Electrolyte: brown color gas is produced.
  • Aqueous Solution: light brown solution is formed

2I  =  I2 + 2e

  • Molten Electrolyte: brown color gas is produced.
  • Aqueous Solution: light brown solution is formed. the solution turns blue when a few drops of starch solution is added in.

4OH  =  O2 + 2H2O + 4e

Gas bubble is formed. Gas produces light up wooden splinter.

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