Module 2 · Answers
Answers & explanations
Brief reasoning included where the answer needs more than a fact.
Section A — Easy
01
An element is made of one type of atom only. A compound contains atoms of two or more elements chemically bonded together.
02
Any three: shiny, good conductor of heat, good conductor of electricity, malleable, ductile, high density, high melting point.
03
Group 1.
04
They have a full outer electron shell, so they don't need to gain or lose electrons.
05
(a) Filtration (b) Evaporation (c) Distillation (d) Chromatography
06
Solute = the substance that dissolves. Solvent = the liquid it dissolves in. Solution = the mixture formed when the solute dissolves in the solvent.
Section B — Medium
07
Potassium reacts more violently than sodium — it fizzes vigorously, melts into a ball, may ignite with a lilac flame. Reactivity increases down Group 1 because the outer electron is further from the nucleus and lost more easily.
08
Chlorine is more reactive than bromine, so it displaces it. The colourless solution turns orange-brown as bromine is released.
chlorine + potassium bromide → potassium chloride + bromine
chlorine + potassium bromide → potassium chloride + bromine
09
A mixture. A pure substance melts at one fixed temperature; a range of temperatures shows it isn't pure.
10
Rf = 6 ÷ 8 = 0.75
11
Distillation collects the water vapour and condenses it back to pure water. Evaporation just lets the water escape, so you only keep the salt — not the water.
Section C — Hard
12
Group 1 atoms react by losing their single outer electron. Down the group the outer electron is in a higher shell, further from the nucleus, so it's lost more easily — reactivity rises.
Group 7 atoms react by gaining one electron. Down the group the outer shell is further from the nucleus, so an extra electron is attracted less strongly — reactivity falls.
Group 7 atoms react by gaining one electron. Down the group the outer shell is further from the nucleus, so an extra electron is attracted less strongly — reactivity falls.
13
At 20°C only 25 g out of a possible 36 g is dissolved (unsaturated). When heated to 70°C, solubility increases — even more salt could now dissolve. The solution stays unsaturated unless more salt is added. (Most solid solubilities increase with temperature because particles move faster and the solvent can break the solute apart more easily.)
14
Argon is inert (full outer shell), so it won't react with the hot filament. Air contains oxygen, which would react with the filament and cause it to burn out quickly.
15
Two of the three Rf values match (0.2 and 0.5) but one doesn't (suspect 0.8 vs note 0.7). The two pens share some inks but are not identical, so the note was probably not written with the suspect's pen — or the note's pen had at least one different ingredient.