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Context for question 3

A student tests two substances: solid C and solution D.

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

Table 3.1

tests	observations
test 1 Carry out a flame test on solid C.	lilac flame
test 2 Place about half of the remaining solid C in a boiling tube. Gently heat solid C in the boiling tube.	condensation forms on the sides of the boiling tube
test 3 Place the remaining solid C in a boiling tube. Add a 10 cm depth of distilled water. Shake the boiling tube to dissolve solid C and form solution C. Divide solution C into two approximately equal portions. To the first portion of solution C, add aqueous sodium hydroxide dropwise until it is in excess.	green precipitate forms which dissolves in excess to form a dark green solution
test 4 To the second portion of solution C, add about 1 cm $^{3}$ of dilute nitric acid followed by a few drops of aqueous barium nitrate.	white precipitate forms

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

3(a)Easy1 mark

State the conclusion that can be made from the observation made in test 2.

3(b)Medium3 marks

Identify the three ions in solid C.

the two metal ions in solid C

the negative ion in solid C

Context for 3(c)

Solution D is aqueous ammonium bromide. The student divides solution D into two approximately equal portions. Record the expected observations.

3(c)Easy1 mark

To the first portion of solution D, the student adds aqueous sodium hydroxide in excess.

observations

3(d)Easy1 mark

The student gently warms the product from 3(c). Any gas given off is tested.

observations

3(e)Easy1 mark

To the second portion of solution D, the student adds about 1 cm

^{3}

of dilute nitric acid followed by a few drops of aqueous silver nitrate.

observations

May/June 2026 Paper 62