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Flashcards in C3 Analysis Deck (19)
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1

What are the distinctive colours in the flame tests of lithium, sodium, potassium, calcium and barium compounds?

lithium compounds result in a crimson flame

sodium compounds result in a yellow flame

potassium compounds result in a lilac flame

calcium compounds result in a red flame

barium compounds result in a green flame.

2

What happens when you add sodium hydroxide solution to solutions containing aluminium, calcium and magnesium ions?

Aluminium, calcium and magnesium ions form white precipitates of the metal hydroxide solids

3

Write ionic equations for the reactions when you add sodium hydroxide solution to solutions containing aluminium, calcium and magnesium ions

Al3+(aq) + 3OH-(aq) → Al(OH)3(s)

Ca2+(aq) + 2OH-(aq) → Ca(OH)2(s)

Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s)

4

Which of the ions  when you add sodium hydroxide solution to solutions containing aluminium, calcium and magnesium ions reacts further with excess sodium hydroxide solution?

Only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution

Al(OH)3(s) + OH-(aq) → [Al(OH) 4]- (aq)

5

What happens when you add sodium hydroxide solution to Copper(II), iron(II) and iron(III) ions?

They form coloured precipitates with sodium hydroxide solution. Copper forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate.

6

Write ionic equations for the reactions when you add sodium hydroxide solution to Copper(II), iron(II) and iron(III) ions

Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)  (blue)

Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s) (green)

Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s) (brown)

7

What happens when dilute acids are added to metal carbonate powders or solutions?

Carbonates react with dilute acids to form bubbles of carbon dioxide.

8

How would you prove the identity of the compoundwhen dilute acids are added to metal carbonate powders or solutions

Carbon dioxide produces a white precipitate with limewater. This turns limewater milky.

9

How would you test for the presence of halide ions in solution?

Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid.

10

How would you identify which halide you had?

Silver chloride is a white precipitate, silver bromide is cream and silver iodide is yellow.

11

Write ionic equations for the reactions you test for the presence of halide ions in solution

Ag+(aq) + Cl-(aq) → AgCl(s)  (white)

Ag+(aq) + Br-(aq) → AgBr(s) (cream)

Ag+(aq) + I-(aq) → AgI(s) (yellow)

12

Why is dilute nitric acid added to the solution before the silver nitrate solution in a test for a halide?

The acid reacts with any carbonate present. Silver carbonate is a white solid and it would give a false positive in the test.

13

How would you test for the presence of sulphate ions in solution?

Sulphate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.

14

Write an ionic equation for the reaction to test for the presence of sulphate ions in solution

Ba2+(aq) + SO42-(aq) → BaSO4(s)  (white)

15

How would you measure the volumes of a strong acid and alkali reacting together?

By titration. The alkali is pipetted into a conical flask. A suitable indicator is added. The acid is added carefully from a burette until the indicator shows that the solution is just neutralised.

16

What equation could you use to find the number of moles of a substance in solution?

Moles = concentration x volume in dm-3

17

If you know the concentration of the alkali, how would you find the concentration of the other reactant?

the results of a titration can be used to find the concentration of the other reactant.

18

When 25cm3 of 0.1mol dm-3 NaOH were titrated with 20cm3 of HCl. Find the concentration of the HCl.

HCl + NaOH → NaCl + H2O

Number of moles= 0.1x0.025 = 0.0025 moles of NaOH.

So 1:1 ratio of HCl:NaOH

So 0.0025 moles of HCl used

Concentration=0.0025/0.02

= 0.125 mol dm-3

19

If you had no indicator, what device could you use to measure the pH?

A pH meter or a pH sensor on a data-logger.