C3 Analysis Flashcards

1
Q

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

A

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.

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2
Q

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

A

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

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3
Q

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

A

Al3+(aq) + 3OH-(aq) → Al(OH)3(s)

Ca2+(aq) + 2OH-(aq) → Ca(OH)2(s)

Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s)

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4
Q

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?

A

Only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution

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

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5
Q

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

A

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

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6
Q

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

A

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)

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

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

A

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

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10
Q

How would you identify which halide you had?

A

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

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11
Q

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

A

Ag+(aq) + Cl-(aq) → AgCl(s) (white)

Ag+(aq) + Br-(aq) → AgBr(s) (cream)

Ag+(aq) + I-(aq) → AgI(s) (yellow)

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12
Q

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

A

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

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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

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

A

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.

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16
Q

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

A

Moles = concentration x volume in dm-3

17
Q

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

A

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

18
Q

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

A

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
Q

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

A

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