3.1.4 Qualitative Analysis

Question 1

describe the test for carbonates and give an example equation

Answer 1

• add dilute acid
• observe effervescence
• 2HCl (aq) + Na2CO3(aq) —> 2NaCl + H2O + CO2

Question 2

describe the test for sulphates and give an example equation

Answer 2

•add BaCl2 solution as a reagent
•white precipitate forms
Ba+2(aq) + SO4-2(aq) —> BaSO4(s)

Question 3

why is an acid needed in the test for sulphate ions and why would sulphuric acid not be used

Answer 3

the acid is needed to react with carbonate impurities that would form a ppt and give a false result
sulphuric acid would also form a ppt and give a false result

Question 4

describe the test for halides and give an example equation

Answer 4

•add dilute HNO3 and AgNO3
•AgCl and AgBr dissolve but AgI does not react
AgCl/Br(s) + 2NH3(aq) —> [Ag(NH3)2]+(aq) + Cl/Br-(aq)

Question 5

describe the test for ammonium

Answer 5

• add NaOH(aq) and heat

* NH4(g) would form which turns litmus paper from red to blue