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Flashcards · J248 · Topic 4

Topic C4 – Predicting and Identifying Reactions and Products flashcards

19 cards on Topic 4, subtopics C4.1 to C4.2. Pick a subtopic or study them all.

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C4.1 Predicting Chemical Reactions

Group 1 metals: physical properties and how they are stored
Soft, low density, low melting point (falling down the group). Stored under oil because they react with air and water vapour.
Why does potassium react faster with water than lithium?
Its outer electron is further from the nucleus with more inner shells shielding it, so it is attracted less strongly and lost more easily.
Chlorine, bromine and iodine: state and colour at room temperature
Chlorine: pale green gas. Bromine: red-brown liquid (orange in water). Iodine: grey-black solid (brown in water).
Chlorine water is added to sodium bromide solution. Equation and observation
Cl₂ + 2NaBr → 2NaCl + Br₂. The colourless solution turns orange as bromine forms.
Group 0 (noble gases): properties and the reason for them
Colourless, monatomic, very unreactive gases. Full outer shells (2 for helium, 8 for the rest). Boiling point and density increase down the group.
Transition metals compared with Group 1
Higher melting point and density, much less reactive, ions with different charges (Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺), coloured compounds, and many are catalysts.
Three transition metal catalysts and their reactions
Iron: the Haber process. Nickel: adding hydrogen to alkenes. Manganese(IV) oxide: decomposing hydrogen peroxide.
Metal Q displaces copper from copper(II) sulfate but not iron from iron(II) sulfate. Where is Q?
Between them: iron > Q > copper. A metal displaces only a less reactive metal from its salt.
1.10 g of manganese forms 1.74 g of oxide (Mn = 55, O = 16). Empirical formula?
O = 1.74 − 1.10 = 0.64 g. Mn: 1.10 ÷ 55 = 0.020 mol. O: 0.64 ÷ 16 = 0.040 mol. Ratio 1 : 2, so MnO₂.

C4.2 Identifying the Products of Chemical Reactions

Precipitate
An insoluble solid that forms when two solutions are mixed.
Tests for oxygen, hydrogen and carbon dioxide
Oxygen: glowing splint relights. Hydrogen: lighted splint at the mouth of the tube gives a squeaky pop. Carbon dioxide: bubble through limewater, which turns milky.
Test for chlorine
Damp blue litmus paper (in a fume cupboard) turns red, then is bleached white.
Flame test colours: Li⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺. Why use a blue flame?
Li⁺ crimson, Na⁺ yellow, K⁺ lilac, Ca²⁺ orange-red, Cu²⁺ green. A yellow flame would add its own colour.
Sodium hydroxide test: results for Ca²⁺, Zn²⁺, Cu²⁺, Fe²⁺, Fe³⁺Higher
Ca²⁺ white, stays in excess. Zn²⁺ white, dissolves in excess. Cu²⁺ blue. Fe²⁺ green. Fe³⁺ orange-brown.
Tests for halide ions and their resultsHigher
Acidify with dilute nitric acid, add silver nitrate solution. Cl⁻ white (AgCl), Br⁻ cream (AgBr), I⁻ yellow (AgI).
Tests for sulfate and carbonate ionsHigher
Sulfate: acidify with dilute hydrochloric acid, add barium chloride solution → white BaSO₄. Carbonate: dilute acid → fizzing; the gas turns limewater milky.
The three advantages of instrumental methods named in the specification
Sensitivity (detects very small amounts), accuracy (reliable, correct results) and speed (fast, often automatic).
Molecular ion peak
The peak at the highest m/z in a mass spectrum; its value is the Mr of the compound.
Base peak
The tallest peak in a mass spectrum. It is not always the molecular ion.

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