Chemistry · Year 10 · Chemical Changes and Extraction · Summer Term

Preparation of Soluble Salts (Acid + Metal/Base/Carbonate)

Students will learn experimental methods for preparing soluble salts from acids and reactive metals, bases, or carbonates.

• National Curriculum Attainment Targets
• GCSE: Chemistry - Salts and Neutralisation

About This Topic

Students prepare soluble salts by reacting dilute acids with reactive metals, insoluble bases such as metal oxides, or metal carbonates. Common examples include sulfuric acid with magnesium to form magnesium sulfate and hydrogen, hydrochloric acid with copper oxide to yield copper chloride and water, or citric acid with copper carbonate producing copper citrate, water, and carbon dioxide. Procedures emphasise using excess solid reactant, filtration to remove residues, careful evaporation to form a saturated solution, and cooling for crystallisation to obtain pure, dry crystals.

This topic aligns with GCSE requirements for salts and neutralisation, where students design full experimental methods, justify each step for maximising purity and yield, and compare reaction types by products and observations. It strengthens skills in risk assessment, accurate measurement, and data recording, while linking to quantitative chemistry through mole calculations and percentage yields.

Active learning shines here because students conduct real reactions, witnessing effervescence, colour shifts, and crystal growth. Group-based procedures foster collaboration on troubleshooting, such as adjusting filtration for clearer filtrates, which embeds procedural understanding and builds lab confidence for independent work.

Key Questions

1. Design an experimental procedure to prepare a pure, dry sample of a soluble salt.
2. Explain the purpose of each step in the preparation of soluble salts.
3. Compare the reactions of acids with metals, metal oxides, and metal carbonates.

Learning Objectives

• Design an experimental procedure to prepare a pure, dry sample of magnesium sulfate crystals from sulfuric acid and magnesium oxide.
• Explain the purpose of using excess solid reactant and filtering in the preparation of soluble salts.
• Compare the reaction products and observable changes when acids react with metals, metal oxides, and metal carbonates.
• Calculate the theoretical yield of a soluble salt given the masses of reactants and the balanced chemical equation.

Before You Start

Acids, Bases, and Alkalis

Why: Students need to understand the properties of acids and bases, including neutralisation reactions, before preparing salts.

Reactivity Series of Metals

Why: Knowledge of the reactivity series is essential for predicting which metals will react with acids and for understanding the products formed.

Separation Techniques

Why: Students must be familiar with basic techniques like filtration and evaporation to follow the experimental procedure for salt preparation.

Key Vocabulary

Soluble Salt	A salt that dissolves in water to form a homogeneous solution.
Filtration	A separation technique used to separate insoluble solids from liquids using a filter medium.
Crystallisation	The process of forming solid crystals from a solution, typically by evaporation and cooling.
Saturated Solution	A solution that contains the maximum amount of solute that can be dissolved at a given temperature.

Watch Out for These Misconceptions

Common Misconception

Filtration alone produces pure dry salt.

What to Teach Instead

Filtration removes insoluble residues, but the filtrate contains water and must be evaporated and crystallised for purity. Hands-on trials where students test filtrate conductivity reveal soluble impurities, prompting discussion on full procedures.

Common Misconception

All acid-solid reactions produce the same salt.

What to Teach Instead

The salt depends on acid and cation from the solid; for example, HCl with Na2CO3 gives NaCl, not other salts. Group comparisons of products via flame tests clarify this, building accurate prediction skills.

Common Misconception

Reaction stops when bubbling ends, so salt is ready.

What to Teach Instead

Excess solid ensures completion; bubbling indicates gas evolution only in metal-carbonate reactions. Active excess checks and weighing before/after help students verify completion quantitatively.

Active Learning Ideas

Stations Rotation: Three Salt Reactions

Prepare three stations with acid-metal, acid-base, and acid-carbonate setups using safe reagents like dilute HCl, Mg ribbon, CuO, and chalk. Groups rotate every 10 minutes to react, filter, and note observations. Conclude with class share-out on procedural similarities.

45 min·Small Groups

Pairs: Procedure Design Challenge

Provide pairs with an acid and solid reactant; they outline steps for pure salt crystals on worksheets, including apparatus diagrams. Pairs test one step, like filtration, then swap feedback with another pair before full trials.

35 min·Pairs

Individual: Crystal Growth Optimisation

Students evaporate filtrates from a shared reaction to form crystals, varying cooling rates or seeding. They measure crystal mass and purity by redissolving samples, recording results in tables for peer review.

50 min·Individual

Whole Class: Yield Calculation Relay

Collect class data on actual vs theoretical yields from parallel reactions. Students relay calculations on board, discussing anomalies like losses in transfers, to identify procedural improvements.

25 min·Whole Class

Real-World Connections

• Pharmaceutical chemists use precise salt preparation methods to synthesize active ingredients for medicines, ensuring purity and correct dosage for drugs like aspirin (acetylsalicylic acid).
• Food scientists prepare specific salts, such as calcium chloride, used in cheesemaking or as firming agents in canned vegetables, requiring controlled reactions to achieve desired textures and flavors.

Assessment Ideas

Quick Check

Present students with a list of steps for preparing copper sulfate crystals. Ask them to number the steps in the correct order and write one sentence explaining the purpose of the filtration step.

Discussion Prompt

Pose the question: 'Why is it important to use an excess of the solid reactant (metal, base, or carbonate) when preparing a soluble salt?' Facilitate a brief class discussion, guiding students to explain complete neutralisation of the acid.

Exit Ticket

Students write down the balanced chemical equation for the reaction between hydrochloric acid and zinc carbonate. They then identify one safety precaution they would take when performing this reaction in the lab.

Frequently Asked Questions

How do you prepare pure copper sulfate crystals from sulfuric acid and copper oxide?

Add excess black copper oxide to dilute sulfuric acid, heat gently until blue solution forms and no solid remains. Filter hot to remove unreacted oxide, evaporate half the filtrate, cool for blue crystals, decant, and dry between filter paper. This method ensures purity through excess reactant and stepwise processing, yielding about 80% typically in school labs.

What are the differences in reactions of acids with metals, bases, and carbonates?

Acid-metal reactions produce salt and hydrogen gas; acid-base (oxides/hydroxides) produce salt and water; acid-carbonate produce salt, water, and carbon dioxide. Observations include metal dissolution without residue, colourless filtrates from bases, and effervescence from carbonates. Comparing in parallel experiments highlights gas tests for identification.

How can active learning improve understanding of soluble salt preparation?

Active methods like station rotations let students handle each reaction type, observing unique signs such as gas evolution or colour changes firsthand. Collaborative procedure design encourages justifying steps like excess use, while troubleshooting filtrations builds resilience. These approaches make abstract neutralisation tangible, boosting retention and GCSE practical skills over passive notes.

What safety precautions are needed for preparing soluble salts in Year 10?

Use dilute acids (0.5-1M), eye protection, gloves, and work in well-ventilated areas. Avoid reactive metals like sodium; opt for magnesium or zinc. Supervise heating to prevent splattering, and dispose wastes per school policy. Risk assessments shared pre-lab reinforce student responsibility and hazard awareness.