This question focuses on chemical bonding and structure.

Calcium chloride is formed when calcium reacts with chlorine gas.

Describe, in terms of electrons, what happens to the calcium atoms and chlorine atoms when this ionic compound is produced.

[4 marks]

  • Calcium is in group 2, so 2 electrons.

    Chlorine is in group 7, so 7 electrons.

Calcium and Chlorine atom configurations showing 2 electrons in outer shell of Calcium and 7 in outer shell of Chlorine.

  • Calcium loses 2 electrons. (1 mark)

    Each Chlorine gains 1 electron. (1 mark)

    We need two Chlorines for one Calcium. (1 mark)

Electron transfer from Calcium (two) to two atoms of Chlorine which receive one each so they all have a full outer shell of eight now.

  • Calcium now has 2+ charge (since it lost 2 negative electrons).

    Each Chlorine now has 1+ charge (since each gained 1 negative electron).

    (1 mark)

Calcium 2+ ion and two Chlorine 1- ions after the electron transfer showing result of ionic bonding.

How do we write the final chemical formula?

[1 mark]

Calcium Chloride (CaCl2)

When Calcium Chloride solution is electrolysed, what is formed at the Cathode (negative electrode)?

[1 mark]

  • Ca2+

    Cl-

positive and negative ions in Calcium Chloride.

  • Aqueous means dissolved in Water.

    Water splits up into H+ and OH-

Water broken down into negative Hydroxide ion and positive Hydrogen ion.

  • Negative ions (OH- and Cl-) are attracted to the positive Anode.

    Positive ions (Ca2+ and H+) are attracted to the negative Cathode.

Electrolysis setup with negative Hydroxide and Chloride ions attracted to positive electrode (anode) and positive Hydrogen and Calcium ions attracted to negative electrode (Cathode).

  • At the negative electrode (Cathode), the LESS reactive ion wins.

    H+ wins.

Hydrogen ion being discharged at the negative electrode since it is less reactive than Calcium.
Reactivity series highlighting positions of Calcium and Hydrogen, showing that Hydrogen is less reactive and will be discharged first.

  • H+ ions gain negative electrons at the Cathode - so Hydrogen gas if formed.

Hydrogen ions being discharged (gaining electrons) at the Cathode to form Hydrogen, seen as a visual half-equation.

What is formed at the Anode (positive electrode)?

[1 mark]

  • At the Anode, a Halide ion (from Group 7) wins. Otherwise, OH- wins.

Calcium ion being discharged at the positive electrode (anode) since it is a Halogen.
Group 7 (Halogens) highlighting Chlorine to show it is a halogen and should be discharged at the Anode instead of the Hydroxide ion.

  • The Chlorine ions have too much negative charge.

    They let go of electrons at the Anode.

    Chlorine gas if formed.

Chlorine ions being discharged at the anode (losing electrons) to form Chlorine gas seen as a visual half-equation.
--> Cl2 + 2e-
2Cl-

Investigate the effect of electrolyte concentration on chemical cell voltage.

Plan a valid method using the following starter materials:

  • Metal electrodes

  • Pure water

  • 1.0 mol/dm³ Sodium Chloride solution

[6 marks]

  • • Sodium Chloride solution as the electrolyte

    • Two different metals as electrodes

    • Measure Voltage

Sodium Chloride solution with two different metals as electrodes to make a fuel cell.
Sodium Chloride solution in a beaker.
Sodium Chloride solution with two metal electrodes connected to a volt meter to form a fuel cell.

  • Dilute the Sodium Chloride solution with water by:

    • Measuring volumes of sodium chloride solution and water using measuring cylinder and mixing

Measuring cylinders with water and sodium chloride forming diluted sodium chloride in a beaker to be used for fuel cell.

  • • Repeat at different concentrations of electrolyte solution

    • Use the same two metals each time

    • Use the same volume of electrolyte solution

Three different Sodium Chloride concentrations with their electrodes and volt meters used for fuel cells experiment.