Chemical tests

Question 1

carbonate test

Answer 1

• react with acid (HNO3)
• effervescence

Question 2

sulfate test

Answer 2

• add Ba2+(aq) ions
• form a white precipitate (BaSO4 is insoluble)
  DONT USE BaCl2 (otherwise you will mess up halide results)

Question 3

halide test equation

Answer 3

Ag+(aq) + X-(aq) –> AgX(s)

Question 4

order of tests

Answer 4

Carbonate –> no other ion produces effervescence
Sulfate –> must confirm there is no carbonate (or completely react carbonate ions) as BaSO4 also forms a white precipitate which would give a false result (filter our ppt before doing halide test)
Halide test –> Ag2CO3 and Ag2SO4 both form precipitates

Question 5

carbonyl test

Answer 5

• 2,4-DNPH
• orange precipitate forms

Question 6

aldehyde or ketone test

Answer 6

• mix original sample with Tollens’ reagent
• silver mirror will form if an aldehyde is present

Question 7

Tollens’ reagent formula

Answer 7

[Ag(NH3)2]OH

Question 8

Tollens’ reagent equation

Answer 8

Ag+ (aq) + e- –> Ag (s)
- Ag forms silver mirror

aldehyde + [O] –> carboxylic acid

Question 9

determine a specific carbonyl

Answer 9

• filter, dry and recrystallise the orange precipitate
• find the melting point
• compare value to one in a data book

Question 10

carboxylic acid test

Answer 10

• mix with Na2CO3
• effervescence
• only organic compounds acidic enough to react with carbonates