CP3.17: Hydrated Copper Sulfate Crystals
An appropriate insoluble oxide or carbonate can react with a dilute acid to form a soluble salt. For the copper oxide and sulfuric acid example, copper(II) sulfate and water form. Adding a suitable excess of the insoluble solid helps use up the acid; the remaining solid can subsequently be removed. An excess soluble alkali cannot be removed by the same filtration step.
Before you start
- Use your teacher’s tier checklist: this overview can include Higher-only material, and is not a tier-specific revision list.
- Pearson Edexcel separate GCSE Chemistry 1CH0. Preserve the specification’s core-practical reference and any explicitly required subparts.
- Recall acid–base reactions, solubility and the difference between a solution and a suspension.
- Use the centre’s approved supervised method, apparatus, heating and disposal arrangements. Written preparation does not replace performing and recording the practical activities.
Watch, pause, try
Video by Malmesbury Education. Use the demonstration alongside this lesson’s specification reference and written explanations.
Viewing focus: Explain excess insoluble reactant, filtration and crystallisation
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Why use excess insoluble oxide?
Show answer and reasoning
To consume the acid while leaving removable solid. The preparation relies on removing the unreacted solid afterwards.
After watching 2: Where is the dissolved product immediately after filtration?
Show answer and reasoning
In the filtrate. Filtration separates an insoluble solid from the liquid containing dissolved ions.
What you'll be able to do
- Explain excess insoluble reactant, filtration and crystallisation
- Distinguish pure crystals from a concentrated or contaminated solution
- Process original yield data and evaluate losses
Choose the preparation route from solubility
An appropriate insoluble oxide or carbonate can react with a dilute acid to form a soluble salt. For the copper oxide and sulfuric acid example, copper(II) sulfate and water form. Adding a suitable excess of the insoluble solid helps use up the acid; the remaining solid can subsequently be removed. An excess soluble alkali cannot be removed by the same filtration step.
Use the heating and addition arrangements in the approved method. Warming can help the reaction proceed, but boiling or vigorous addition is not the purpose. Record the appearance and the point at which further solid remains rather than assuming that the first colour change proves all acid has reacted. The intended salt determines which acid and base are suitable.
Give each separation step a different job
Filter to remove unreacted insoluble solid. The liquid that passes through is the filtrate and contains the dissolved salt; the residue is the retained solid. Filter paper does not remove the dissolved product from a true solution. Label the fractions so the product-containing liquid is not discarded.
Concentrate the filtrate using the specified gentle heating method, then allow suitable crystallisation. Cooling a sufficiently concentrated solution can produce crystals while some dissolved material remains in the mother liquor. Separate and dry the crystals as directed. For a hydrated salt, forcing complete dryness by strong heating can alter the product rather than merely removing surface water.
Connect purity, dryness and yield
A wet crystal sample can give an inflated mass because surface solution or water is included. Contamination also affects mass and purity. Conversely, product may remain dissolved or be lost during transfers and separation, giving a lower recovered yield. A high mass is not sufficient evidence of a successful preparation.
When a theoretical yield is supplied or appropriately calculated, percentage yield = actual yield ÷ theoretical yield × 100. Compare like chemical forms: anhydrous and hydrated formulas have different formula masses. Explain a specific source of loss or excess mass rather than treating every departure as an unexplained experimental error.
Retain the specified copper-oxide route
Pearson CP3.17 starts from copper oxide and dilute sulfuric acid. The specified method warms the acid in a water bath, reacts a suitable excess of copper oxide, filters and concentrates the copper sulfate solution using the stated evaporating-basin and Bunsen arrangement before final drying on a watch glass.
Explain the role of each heating and separation stage. The target is pure, dry hydrated copper sulfate crystals, so removing adhering solution is different from driving water from the compound. Retain the teacher-approved handling and heating instructions and avoid treating intense heating to dryness as a universal crystallisation method.
Worked applications
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Example 1A stated preparation should give 5.00 g of the specified hydrated salt. The dry recovered mass is 3.80 g. Calculate percentage yield.
Example 2A supposedly pure sample gives 5.40 g against that 5.00 g theoretical yield. What should be investigated?
Common mistakes to avoid
Key takeaways
- You can explain excess insoluble reactant, filtration and crystallisation.
- You can distinguish pure crystals from a concentrated or contaminated solution.
- You can process original yield data and evaluate losses.
Apply it in an exam
Question 1: A supposedly pure sample gives 5.40 g against that 5.00 g theoretical yield. What should be investigated?
Show answer and reasoning
The result does not demonstrate creation of extra product; investigate the mass and model.
- The calculated percentage is 108%.
- Check surface water, trapped solution, contamination and the assumed chemical form.
Explore further
- Edexcel 1CH0 official specification (opens in a new tab)
Check the assessed scope and practical or mathematical requirements.
- Read or explore this topic (opens in a new tab)
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Return to this tomorrow
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
- Where is the dissolved product immediately after filtration?
- Why can strong heating be unsuitable for hydrated crystals?
Test yourself
Answer a few questions, then review anything you missed.
Keep practising
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.