A uniform metre rule is pivoted at its 50 cm mark. A 2.0 N weight hangs at the 20 cm mark. A 3.0 N weight is hung on the other side to balance the rule. Calculate the position of the 3.0 N weight.
The salt is dissolved, so it is not removed by filtering
Slow evaporation, then cooling, gives crystals
Ask what state the wanted substance is in. Dissolved means filtration cannot help, whatever the apparatus looks like.
Zinc reacts with hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂. 6.5 g of zinc reacts completely. The relative atomic mass of zinc is 65 and the molar volume of a gas at room temperature is 24 dm³. Calculate the volume of hydrogen produced.
"Energy is made" is not acceptable — energy is released, not manufactured. Small wording, real mark.
A student has two lamps and one battery. Describe what happens when the lamps are connected in series, then compare that with connecting them in parallel, referring to current, p.d. and brightness in each case.
Answer: Series: one path, same current through both lamps, p.d. shared, both dimmer. Parallel: two paths, same p.d. across each lamp, larger total current from the battery, each lamp at normal brightness.
Series: a single path, so the current through both lamps is the same (1 mark)
Series: the battery p.d. is shared between the lamps, so each lamp is dimmer (1 mark)
Parallel: each lamp is connected across the battery, so each has the full p.d. and normal brightness (1 mark)
Parallel: the total current from the battery is the sum of the branch currents, so it is larger and the battery drains faster (1 mark)
Write comparisons as pairs — one sentence with "whereas" in the middle scores two marks that two separate paragraphs do not.
Figure 2 describes four features of a root hair cell: a long, thin extension of the cell surface; a large permanent vacuole filling much of the cell; no chloroplasts; and many mitochondria.
Answer: Root hair (extension) — increases surface area for water uptake. Large permanent vacuole — stores cell sap and keeps the cell rigid. No chloroplasts — the cell is underground, in darkness, so photosynthesis cannot occur. Many mitochondria — release energy for active transport of mineral ions.
Names the root hair extension and gives its function: surface area for absorption (1 mark)
Names the permanent vacuole and gives its function: stores sap, helps keep the cell firm (1 mark)
States that chloroplasts are absent and links it to the absence of light underground (1 mark)
Names the mitochondria and links the number to active transport and energy release (1 mark)
Label questions are the cheapest marks on the paper and the most commonly rushed. Draw the line, name the part, then add its job in three or four words — the job is usually the mark you are actually being tested on.