Specifications

Core Practicals

Core Practical 3

Preparing copper sulfate

Introducing the Practical

Excess copper oxide must be added to warm dilute sulfuric acid (warmed using a water bath), which will react to produce a blue solution of the salt copper(II) sulfate.

  

The solution then needs to be filtered using filter paper and evaporated using an evaporating basin and Bunsen burner, followed by final drying using a watch glass to allow all the water to evaporate.

Risk Assessment

As a general rule, eye protection (goggles) must be worn for all practicals.

  

This risk assessment is provided as an example only, and you must perform your own risk assessment before doing this experiment.

Apparatus

Each group will need:

  • evaporating basin

  • spatula

  • stirring rod

  • filter funnel

  • filter paper

  • tongs

  • sulfuric acid

  • copper(II) oxide

  • electric waterbath

  • 250 ml conical flask

  • 100 ml beaker

  • Bunsen burner

  • gauze

  • tripod stand

  • heat-resistant mat

  • watch glass

  • 100 ml measuring cylinder

Experiment Set-up

Method

  1. use a measuring cylinder to add 40 ml of sulfuric acid in a beaker

  2. place the beaker in a waterbath to heat up the sulfuric acid

  3. add a spatula of copper oxide powder to the beaker

  4. stir the solution with a glass rod, and add more copper oxide powder until it no longer disappears (add in excess)

  5. filter the mixture to remove the excess copper oxide, then pour the filtrate (the copper sulfate solution) into an evaporating basin

  6. place the evaporating basin above a water bath, and heat the copper sulfate solution to evaporate off half of the water

  7. pour the solution into a watch glass and leave on the side to allow all of the water to evaporate

Results and Analysis

Why was it necessary to warm the sulfuric acid?

  
How did you know when the copper oxide was present in excess?

  
Why is a water bath used to evaporate the water from the copper sulfate solution instead of heating the evaporating basin directly with a Bunsen burner?

  
Why should you not evaporate all of the water from the copper sulfate solution?

Exam Question and Model Answer

This question is about making copper salts. Outline a safe plan the student could use to make pure, dry, crystals of the soluble salt copper sulfate from an insoluble metal oxide and dilute acid.
(Apparatus available: stirring rod, spatula, beaker, filter paper and funnel, evaporating basin, Bunsen burner, tripod, gauze and mat, and conical flask)

[6 marks}

Level 1 (1-2 marks)

Add the metal oxide to the dilute acid.

Stir them.Filter the solution and then evaporate off the water.

Level 2 (3-4 marks)

Safely measure 25 ml sulfuric acid into a conical flask.
Add copper oxide to the flask, and then heat the acid until no more copper oxide will react.
Pour the contents of the conical flask into an evaporating basin.
Filter the solution.
Heat this gently and stop heating once crystals start to form.
Leave the solution to evaporate overnight.

Level 3 (5-6 marks)

Ensure you are wearing safety goggles and measure 25 ml sulfuric acid into a conical flask. Sulfuric acid is corrosive.
Add excess copper oxide to the flask, and then heat the acid gently using the Bunsen burner, whilst stirring the solution, until no more copper oxide will react.
Allow the solution to cool, then any remaining copper oxide must be removed using a funnel/filter paper, by filtration.
Pour the contents of the conical flask into an evaporating basin. Heat this gently on a tripod and gauze, on top of a beaker half-filled with water. Stop heating once crystals start to form.
Leave the solution to evaporate overnight, then remove the crystals and dry them.

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