Soluble salts: apply the ideas
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Each correct first selection can count as one self-check point, with six available. Keep your own tally if useful. No total or answers are saved by this page; retries help you learn. These are not official marks, a grade prediction or a measure of practical competence. Written working and partial method credit are not automatically assessed.
Difficulty labels describe the type of task, not an exam-board rating. The questions and data are original. Specialist review has not been completed. Grade 8 is StudyForA’s suggested placement; salt preparation is an introductory extension toward GCSE, not an official Grade 8 requirement.
Foundation · Predict products
Zinc oxide is allowed to react with nitric acid. The resulting zinc salt is soluble in water.
Question 1
Which word equation names the products correctly?
Check the reasoning
zinc oxide + nitric acid → zinc nitrate + water
- Identify the metal in the base: zinc.
- Match nitric acid to nitrate, then use salt + water for this oxide–acid reaction. Do not substitute the products of a metal–acid reaction.
Apply · Track the collected substance
An insoluble oxide is added in excess to make a soluble salt. After the reaction, filter 1 removes the unused oxide. Crystals then grow from the concentrated filtrate. Filter 2 separates those crystals from the liquid that remains.
Question 2
What is retained on each filter paper?
Check the reasoning
Filter 1: unused oxide; filter 2: salt crystals.
- Locate each filtration in the sequence, rather than memorising “keep the residue”.
- Identify which substance is solid at that stage. Some salt can remain dissolved after filter 2.
Apply · Account for water leaving
Use this new idealised dataset. The reaction has finished, the unused oxide is removed, and only water leaves during the later concentration stage. Assume no spills or material left on apparatus. The data do not describe a practical recipe or establish saturation.
| Quantity | Mass (g) |
|---|---|
| Starting acid solution | 72.5 |
| Oxide added | 6.0 |
| Unused oxide removed | 1.5 |
| Mass remaining after concentration | 67.0 |
Question 3
How much water left during concentration?
Check the reasoning
10.0 g
- Before concentration: 72.5 + 6.0 − 1.5 = 77.0 g.
- Subtract final mass: 77.0 − 67.0 = 10.0 g. Check the full balance: 67.0 + 10.0 + 1.5 = 78.5 g, equal to the starting solution plus oxide.
- This inference depends on only water leaving at that stage; a real spill would invalidate the interpretation.
Evaluate · Evaluate a recovery claim
Two groups start with equivalent reactant amounts and aim to recover the same salt. Group P reports 11.2 g of crystals with liquid still on their surfaces. Group Q reports 9.4 g after a defined procedure to remove surface liquid. Neither group has tested purity.
Question 4
Which conclusion is supported?
Check the reasoning
The masses cannot establish which group recovered more pure salt.
- Name the comparison problem: P includes surface liquid while Q has undergone a defined surface-drying procedure.
- Do not turn the 1.8 g difference into a salt yield. Even comparable dry masses alone would not establish purity.
Apply · Interpret remaining solution
After collecting an initial batch of crystals, a student retains the liquid that passed through the second filter. Later, some water evaporates and additional crystals of the same identified salt appear. No new reactants are added.
Question 5
What does this show about the liquid retained after the first crystal collection?
Check the reasoning
It still contained dissolved salt that could crystallise later.
- Distinguish recovery from purity: leaving some salt in solution can reduce collected mass without proving contamination.
- No further neutralisation is needed to explain the observation: salt already present in solution can crystallise.
Evaluate · Challenge a separation claim
A student uses too little zinc oxide with nitric acid. All the oxide reacts, and a suitable test confirms acid is still present. The student passes the clear solution through ordinary filter paper and says the excess acid has now been removed.
Question 6
What is the flaw in that claim?
Check the reasoning
Dissolved acid passes through with the solution, so filtering does not remove it.
- Use the positive acid test as evidence; clarity alone is not evidence of purity.
- Explain the separation limitation. Do not claim that filtration substitutes for completing or controlling the reaction.
Choose your next step
Return to the explanation for any question you could not justify. The linked lesson retains its separate recall check; completing this page does not mark that lesson mastered.
Return to the soluble-salts lesson · Back to Chemistry and materials · Explore the soluble-salts mind map