3.2 Ion Tests

Question 1

What is the test for Cl- ions?

Answer 1

Add a few drops of AgNO3 followed by HNO3 and a white ppt of AgCl forms which dissolves in dilute ammonia.
Ag+ + Cl- → AgCl
AgCl + 2NH3 → Ag(NH3)2+ + Cl-

Question 2

What is the test for Br- ions?

Answer 2

Add a few drops of AgNO3 followed by HNO3 and a cream ppt of AgBr forms which partiallty dissolves in dilute ammonia and fully in concentrated ammonia.
Ag+ + Br- → AgBr
AgBr + 2NH3 → Ag(NH3)2+ + Br-

Question 3

What is the test for I- ions?

Answer 3

Add a few drops of AgNO3 followed by HNO3 and a yellow ppt of AgI forms which is insoluble in concentrated ammonia.
Ag+ + I- → AgI

Question 4

What is the test for CO32- ions?

Answer 4

Add dilute HCl to the sample. bubbles of CO2 are given off.

Na2CO3 +2HCl → 2NaCl + CO2 + H2O

Question 5

What is the test for SO42- ions?

Answer 5

Add a few drops of dilute nitrc acid followed by a few drops of BaCl2 solution. A white ppt of BaSO4 forms.
Ba2+ SO42- → BaSO4

Question 6

What is the test for Ba2+ ions?

Answer 6

Add sulphuric acid to the sample. A white ppt of BaSO4 forms.
Ba2+ SO42- → BaSO4

Question 7

What is the test for OH- ions?

Answer 7

Add MgCl2 to the sampl. A white ppt of Mg(OH)2 forms which turns universal indicator blue.
Mg2+ + 2OH- → Mg(OH)2
MgCl2 + 2NaOH- → Mg(OH)2 + NaCl

Question 8

What is the test for Mg2+ ions?

Answer 8

Add NaOH to the sample. A white ppt of Mg(OH)2 forms.

Mg2+ + 2OH- → Mg(OH)2

Question 9

What is the test for NH4+ ions?

Answer 9

Warm the sample carefully. Ammonium is given off which turns damp litmus paper blue.