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Context for question 3

A student tests two substances: solid A and solution B.

Tests on solid A

Table 3.1 shows the tests and the student’s observations for solid A.

Table 3.1

tests	observations
test 1 Add 10 cm $^{3}$ of water to a boiling tube containing solid A. Place a stopper in the boiling tube and shake the boiling tube to dissolve solid A and form solution A. Divide solution A into two approximately equal portions. To the first portion of solution A, add aqueous sodium hydroxide dropwise and then in excess.	green precipitate the precipitate remains
test 2 To the product from test 1, add about a 4 cm depth of aqueous hydrogen peroxide. Test any gas given off.	brown precipitate and effervescence the gas relights a glowing splint
test 3 To the second portion of solution A, add about a 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate.	white precipitate

Notes for use in qualitative analysis

Tests for anions

anion	test	test result
carbonate, CO $_{3}^{2 -}$	add dilute acid, then test for carbon dioxide gas	effervescence, carbon dioxide produced
chloride, Cl $^{-}$ [in solution]	acidify with dilute nitric acid, then add aqueous silver nitrate	white ppt.
bromide, Br $^{-}$ [in solution]	acidify with dilute nitric acid, then add aqueous silver nitrate	cream ppt.
iodide, I $^{-}$ [in solution]	acidify with dilute nitric acid, then add aqueous silver nitrate	yellow ppt.
nitrate, NO $_{3}^{-}$ [in solution]	add aqueous sodium hydroxide, then aluminium foil; warm carefully	ammonia produced
sulfate, SO $_{4}^{2 -}$ [in solution]	acidify with dilute nitric acid, then add aqueous barium nitrate	white ppt.
sulfite, SO $_{3}^{2 -}$	add a small volume of acidified aqueous potassium manganate(VII)	the acidified aqueous potassium manganate(VII) changes colour from purple to colourless

Tests for aqueous cations

cation	effect of aqueous sodium hydroxide	effect of aqueous ammonia
aluminium, Al $^{3 +}$	white ppt., soluble in excess, giving a colourless solution	white ppt., insoluble in excess
ammonium, NH $_{4}^{+}$	ammonia produced on warming	–
calcium, Ca $^{2 +}$	white ppt., insoluble in excess	no ppt. or very slight white ppt.
chromium(III), Cr $^{3 +}$	green ppt., soluble in excess	green ppt., insoluble in excess
copper(II), Cu $^{2 +}$	light blue ppt., insoluble in excess	light blue ppt., soluble in excess, giving a dark blue solution
iron(II), Fe $^{2 +}$	green ppt., insoluble in excess, ppt. turns brown near surface on standing	green ppt., insoluble in excess, ppt. turns brown near surface on standing
iron(III), Fe $^{3 +}$	red-brown ppt., insoluble in excess	red-brown ppt., insoluble in excess
zinc, Zn $^{2 +}$	white ppt., soluble in excess, giving a colourless solution	white ppt., soluble in excess, giving a colourless solution

Tests for gases

gas	test and test result
ammonia, NH $_{3}$	turns damp red litmus paper blue
carbon dioxide, CO $_{2}$	turns limewater milky
chlorine, Cl $_{2}$	bleaches damp litmus paper
hydrogen, H $_{2}$	‘pops’ with a lighted splint
oxygen, O $_{2}$	relights a glowing splint
sulfur dioxide, SO $_{2}$	turns acidified aqueous potassium manganate(VII) from purple to colourless

Flame tests for metal ions

metal ion	flame colour
lithium, Li $^{+}$	red
sodium, Na $^{+}$	yellow
potassium, K $^{+}$	lilac
calcium, Ca $^{2 +}$	orange-red
barium, Ba $^{2 +}$	light green
copper(II), Cu $^{2 +}$	blue-green

3(a)Easy1 mark

Identify the gas given off in test 2.

3(b)Medium2 marks

Identify solid A.

cation in solid A

anion in solid A

Context for 3(c)

Tests on solution B Solution B is aqueous aluminium nitrate. The student divides solution B into two approximately equal portions. Record the expected observations.

3(c)Easy2 marks

To the first portion of solution B, the student adds aqueous ammonia dropwise until it is in excess.

observations

3(d)(i)Easy2 marks

To the second portion of solution B, the student adds aqueous sodium hydroxide dropwise until it is in excess.

observations

3(d)(ii)Easy1 mark

To the product from 3(d)(i), the student adds a piece of aluminium foil and warms the mixture gently. Any gas given off is tested.

observations

May/June 2026 Paper 61

Questions

Tests on solid A

Notes for use in qualitative analysis