Salt Analysis flash cards

1. 1.What is the aim of qualitative salt analysis?

   To identify the acidic radical (anion) and the basic radical (cation) present in an unknown inorganic salt through systematic dry and wet tests.

   Hint: One anion + one cation.

2. 2.In systematic salt analysis, why are dry (preliminary) tests performed before wet tests?

   They give quick clues (colour, smell, flame colour, gas on heating) that narrow down which ions are likely present, guiding the confirmatory wet tests.

   Hint: Screening step.

3. 3.A salt is coloured. Which cations are commonly indicated by blue, green, pink, and brown/yellow colours?

   Blue $\to$ $Cu^{2+}$; green $\to$ $Ni^{2+}$/$Fe^{2+}$/$Cu^{2+}$; pink $\to$ $Co^{2+}$/$Mn^{2+}$; brown/yellow $\to$ $Fe^{3+}$.

   Hint: Transition metal ions.

4. 4.What does a white colour of a salt generally suggest about the cation?

   Absence of coloured transition metal ions; likely a cation like $Pb^{2+}$, $Al^{3+}$, $Zn^{2+}$, $Ca^{2+}$, $Ba^{2+}$, $Mg^{2+}$ or $NH_4^{+}$.

   Hint: No d-d colour.

5. 5.Which salt gives a pink/light red colour due to $Mn^{2+}$ and which gives violet due to $MnO_4^{-}$?

   $Mn^{2+}$ salts (e.g. $MnCl_2$) are pale pink; $MnO_4^{-}$ (permanganate) is intensely violet/purple.

   Hint: Oxidation state difference.

6. 6.Which anions can be detected by smell of the dry salt or its gas?

   Rotten-egg smell $\to$ $S^{2-}$ ($H_2S$); pungent choking $\to$ $SO_3^{2-}$ ($SO_2$) or $NH_4^{+}$ ($NH_3$); vinegar smell $\to$ $CH_3COO^{-}$; pungent brown $\to$ nitrite/nitrate.

   Hint: Gas odour clues.

7. 7.What is the purpose of heating the dry salt in a test tube (dry heating test)?

   To observe evolution of gases, colour changes, sublimation, and decrepitation which indicate specific ions.

   Hint: Watch gas + colour.

8. 8.During dry heating, evolution of a colourless gas that turns lime water milky indicates which anion?

   $CO_3^{2-}$ (carbonate) or $HCO_3^{-}$, evolving $CO_2$.

   Hint: Lime water test.

9. 9.During dry heating, a reddish-brown gas is evolved. What does it indicate?

   $NO_3^{-}$ (nitrate) evolving $NO_2$; also nitrites give brown fumes.

   Hint: $NO_2$ colour.

10. 10.On heating, a salt gives a gas that smells like rotten eggs. Which radical is present?

    Sulphide, $S^{2-}$, evolving $H_2S$.

    Hint: $H_2S$.

11. 11.On heating, a salt sublimes leaving a white sublimate and gives pungent gas turning moist red litmus blue. Identify.

    Ammonium salt ($NH_4^{+}$); $NH_3$ turns red litmus blue.

    Hint: $NH_3$ basic gas.

12. 12.What colour change on heating indicates $Zn^{2+}$ salts (ZnO behaviour)?

    $ZnO$ is yellow when hot, white when cold.

    Hint: Reversible colour.

13. 13.What colour change on heating indicates $Pb^{2+}$ / $PbO$?

    Residue is yellow (or brown-yellow) when hot and turns yellowish on cooling; PbO (litharge) is yellow.

    Hint: Litharge.

14. 14.Explain the principle of the flame test.

    Volatile chlorides of certain metals, when heated in a Bunsen flame, get thermally excited; electrons fall back emitting characteristic visible-wavelength light, giving a coloured flame.

    Hint: Electronic excitation/emission.

15. 15.Why is conc. HCl used with the platinum wire in the flame test?

    It converts the metal salt to the more volatile metal chloride, which vaporises easily and gives a sharper flame colour; it also cleans the wire.

    Hint: Make volatile chloride.

16. 16.Give the flame test colours for $Na^{+}$, $K^{+}$, $Ca^{2+}$, $Ba^{2+}$, $Cu^{2+}$.

    $Na^{+}$ golden yellow; $K^{+}$ lilac/violet; $Ca^{2+}$ brick red; $Ba^{2+}$ apple/grassy green; $Cu^{2+}$ blue-green (bluish green).

    Hint: Na yellow, K lilac.

17. 17.Which flame colour is given by $Sr^{2+}$ and by $Pb^{2+}$?

    $Sr^{2+}$ crimson red; $Pb^{2+}$ dull bluish/greyish (bluish-white, faint).

    Hint: Sr crimson.

18. 18.Why is $K^{+}$ flame (lilac) often viewed through blue cobalt glass?

    To mask the intense yellow $Na^{+}$ flame (a common impurity) so the faint lilac potassium colour becomes visible (appears crimson/pink through the glass).

    Hint: Filter out Na yellow.

19. 19.State the principle of the borax bead test.

    Borax on heating forms a glassy bead of $NaBO_2 + B_2O_3$; this reacts with coloured metal oxides to form metaborates of characteristic colour in oxidising/reducing flame.

    Hint: Metaborate colours.

20. 20.Write what happens chemically when borax is heated for the bead test.

    $Na_2B_4O_7\cdot 10H_2O \to Na_2B_4O_7 \to 2NaBO_2 + B_2O_3$ (transparent glassy bead).

    Hint: Sodium metaborate + boric anhydride.

21. 21.Give borax bead colours of Cu in oxidising (hot/cold) and reducing flame.

    $Cu$: oxidising flame — green (hot), blue (cold); reducing flame — colourless/red (opaque red $Cu_2O$ or Cu).

    Hint: Blue $\to$ red on reduction.

22. 22.Give borax bead colour of Fe and Cr in oxidising flame.

    $Fe^{3+}$: yellow/brown (hot) to yellow (cold); $Cr^{3+}$: green (both hot and cold).

    Hint: Fe yellow, Cr green.

23. 23.Give borax bead colours of Co and Mn.

    $Co$: deep blue (both hot and cold); $Mn$: violet/amethyst (oxidising), colourless (reducing).

    Hint: Co blue, Mn violet.

24. 24.Give borax bead colour of Ni.

    $Ni$: brown (oxidising, hot reddish-brown / cold yellow-brown); grey/colourless in reducing flame.

    Hint: Brown bead.

25. 25.State the principle of the charcoal cavity test.

    The salt mixed with $Na_2CO_3$ is heated in a cavity on charcoal; the metal oxide is reduced to metal (bead) by carbon, and the residue colour + bead identify the metal.

    Hint: Carbon reduces oxide to metal.

26. 26.Charcoal cavity: a yellow residue (hot) turning white (cold) with no metallic bead indicates which cation?

    $Zn^{2+}$ — residue is ZnO (yellow hot, white cold), no fusible bead.

    Hint: ZnO colour play.

27. 27.Charcoal cavity: a yellow residue (hot) and yellow (cold) with a soft malleable grey bead indicates?

    $Pb^{2+}$ — grey malleable lead bead with yellow PbO incrustation.

    Hint: Soft lead bead.

28. 28.Charcoal cavity: a brown residue (hot and cold), no bead, indicates which cation?

    $Cd^{2+}$ (brown CdO); also compare — $Zn$ turns white on cooling whereas Cd stays brown.

    Hint: Brown, stays brown.

29. 29.In the cobalt nitrate (Rinmann's) test on charcoal, a green mass indicates which cation?

    $Zn^{2+}$ — forms green $CoZnO_2$ (Rinmann's green / cobalt zincate).

    Hint: Rinmann's green = Zn.

30. 30.In the cobalt nitrate test, a blue mass and a pink/flesh mass indicate which cations?

    Blue $Co(AlO_2)_2$ (Thenard's blue) $\to$ $Al^{3+}$; pink/flesh $CoMgO_2$ $\to$ $Mg^{2+}$.

    Hint: Al blue, Mg pink.

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