Maximise chemistry and minimise washing up

This activity is a microscale version of a common test-tube practical. The main advantages of the microscale version are the tiny quantities of chemicals consumed and the lack of test tubes to wash up.

Two student sheets are provided:

  • Reactions of positive ions with sodium hydroxide
  • Reactions of transition metal ions with sodium hydroxide – a shorter version of the positive ion activity using only transition metal ions.

The student sheet should be laminated or placed inside a plastic document wallet. It can then be wiped clean over the sink and the residues washed away with plenty of water.

Equipment required

Bottles of those chemicals from the list below that are appropriate to the student sheet you have chosen to use will be required for each group of students. If enough bottles are supplied, students will not need to wander around looking for the reagents they need. Dropper bottles are best.

The concentrations are not crucial, and all are minimal hazard at the concentrations specified but the sodium hydroxide should be below 0.5 mol dm–3 to minimise the hazard.

Exactly which salt is used is also not critical.

  • Laminated worksheets, or photocopied worksheets and plastic wallets 
  • Red litmus paper
  • Sodium hydroxide < 0.5 mol dm–3 (Irritant)
  • Iron(II) sulfate 0.2 mol dm–3
  • Iron(III) nitrate 0.2 mol dm–3
  • Copper(II) sulfate 0.2 mol dm–3  
  • Aluminium sulfate 0.2 mol dm–3
  • Calcium chloride 0.2 mol dm–3
  • Magnesium chloride 0.2 mol dm–3
  • Ammonium chloride 0.2 mol dm–3

Health, safety and technical notes

What to do

You are going to investigate the reactions that occur between positive metal ions and sodium hydroxide in solution. As you work, try to decide what is happening and what reaction is taking place. If this sheet is not laminated, put it into a plastic pocket. Onto each of the empty boxes in the table below put one drop of the positive ion solution and add one drop of sodium hydroxide solution. Observe what happens. Hold a piece of damp red litmus paper over the ammonium and sodium hydroxide box and note your observations. After you have observed the aluminium and sodium hydroxide reaction, add a few more drops of sodium hydroxide and observe what happens.

 Positive ion solution Sodium hydroxide
 Iron(II), Fe2+  
 Iron(III), Fe3+  
 Copper(II), Cu2+  
 Aluminium, Al3+  
 Calcium, Ca2+  
Magnesium, Mg2+    
 Ammonium, NH4+  

Questions

  1. Write down your observations for each of the reactions above
  2. What is the name given to a solid made by a reaction between two solutions?
  3. Suggest names for each of the solids made in the reactions above.
  4. The first reaction can be simplified to: Fe2+ + 2 OH–→ Fe(OH)2 Write similar equations for three of the other reactions:
  5. Which gas is made in the reaction between ammonium ions and hydroxide ions?
  6. Complete and balance the equation - NH4+         +         OH–          →

Answers

  1. Reactions of positive ions table 1
  1. A solid formed by reacting two solutions is a precipitate.
  2. The solids made are: iron(II) hydroxide, iron(III) hydroxide, copper(II) hydroxide, aluminium hydroxide, calcium hydroxide and magnesium hydroxide.
  3. Students could give any three of the following equations: 
  • Fe3+ + 3 OH– → Fe(OH)3
  • Cu2+ + 2 OH– → Cu(OH)2 
  • Al3+ + 3 OH– → Al(OH)3
  • Ca2+ + 2 OH– → Ca(OH)2
  • Mg2+ + 2 OH– → Mg(OH)2
  1. The gas formed by the reaction between the ammonium and hydroxide ions is ammonia.
  2. NH4 + + OH– → NH3 + H2O

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Additional information

This resource is a part of our Inspirational chemistry collection.

Inspirational chemistry book