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AQA GCSE · Question 06.1 · Chemical changes
A student investigated the voltage produced by different pairs of metal electrodes in a chemical cell. Figure 6 shows the apparatus and Table 3 shows the results.
<br/><br/>
<table border="1" cellpadding="12" cellspacing="0" style="border-collapse: collapse; font-family: Arial, sans-serif; font-size: 15px; border: 2px solid black;">
<caption style="font-weight: bold; font-size: 18px; margin-bottom: 10px;">Table 3</caption>
<tr>
<th style="border: 1px solid black; padding: 12px; text-align: left; font-weight: bold;">Electrode A</th>
<th style="border: 1px solid black; padding: 12px; text-align: center; font-weight: bold;">Symbol of metal</th>
<th style="border: 1px solid black; padding: 12px; text-align: center; font-weight: bold;">Voltage in volts</th>
</tr>
<tr>
<td style="border: 1px solid black; padding: 12px; font-weight: bold;">Copper</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">Cu</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">−0.59</td>
</tr>
<tr>
<td style="border: 1px solid black; padding: 12px; font-weight: bold;">Magnesium</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">Mg</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">2.12</td>
</tr>
<tr>
<td style="border: 1px solid black; padding: 12px; font-weight: bold;">Nickel</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">Ni</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">0.00</td>
</tr>
<tr>
<td style="border: 1px solid black; padding: 12px; font-weight: bold;">Silver</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">Ag</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">−1.05</td>
</tr>
<tr>
<td style="border: 1px solid black; padding: 12px; font-weight: bold;">Zinc</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">Zn</td>
<td style="border: 1px solid black; padding: 12px; text-align: center;">0.51</td>
</tr>
</table>
<br/><br/>
This is the method used.<br/><br/>
- Place a nickel electrode and an electrode made from a different metal (electrode A) in 1.0 mol/dm3 sodium chloride solution.<br/><br/>
- Measure the voltage produced.<br/><br/>
- Repeat using different metals for electrode A.<br/><br/>
Write the symbols of the five metals in Table 3 in order of reactivity.<br/><br/>
Justify your answer.<br/><br/>
Most reactive __ __ __ __ __ <br/><br/>Least reactive __ __ __ __ __ <br/><br/>
Justification: __ __ __ __ __
A student investigated the voltage produced by different pairs of metal electrodes in a chemical cell. Figure 6 shows the apparatus and Table 3 shows the results.
<br/><br/>
This is the method used.<br/><br/>
- Place a nickel electrode and an electrode made from a different metal (electrode A) in 1.0 mol/dm3 sodium chloride solution.<br/><br/>
- Measure the voltage produced.<br/><br/>
- Repeat using different metals for electrode A.<br/><br/>
Write the symbols of the five metals in Table 3 in order of reactivity.<br/><br/>
Justify your answer.<br/><br/>
Most reactive __ __ __ __ __ <br/><br/>Least reactive __ __ __ __ __ <br/><br/>
Justification: __ __ __ __ __
How to approach this question
1. **Understand the setup:** A chemical cell is made with Nickel and another metal (Electrode A). The voltage is measured.
2. **Relate voltage to reactivity:** In a chemical cell, the voltage produced depends on the difference in reactivity between the two metals. The more reactive metal will be the negative electrode and will have a more positive potential relative to the less reactive metal.
3. **Order the metals:** The table shows the voltage of each metal relative to Nickel (which has a voltage of 0.00). A more positive voltage means the metal is more reactive than Nickel. A more negative voltage means it is less reactive than Nickel.
4. **List the metals:** Arrange the metals in order from the most positive voltage to the most negative voltage. This will be the order of reactivity from most to least reactive.
5. **Justify:** Explain the link between the size/sign of the voltage and the reactivity difference compared to the reference electrode (Nickel).
Full Answer
Most reactive: Mg, Zn, Ni, Cu, Ag :Least reactive
Justification: The greater the difference in reactivity between the two metals, the larger the voltage produced. Magnesium produces the largest positive voltage (2.12 V) so it is the most reactive. Silver produces the most negative voltage (-1.05 V) so it is the least reactive.
In this electrochemical cell, all metals are being compared to Nickel. The voltage reading indicates the relative tendency of a metal to lose electrons compared to Nickel.
- A more reactive metal loses electrons more readily. This results in a larger potential difference.
- The sign of the voltage tells us whether the metal is more or less reactive than Nickel. A positive voltage means Electrode A is more reactive than Nickel. A negative voltage means it is less reactive.
Ordering the voltages from most positive to most negative:
- Magnesium (Mg): +2.12 V
- Zinc (Zn): +0.51 V
- Nickel (Ni): 0.00 V (the reference)
- Copper (Cu): -0.59 V
- Silver (Ag): -1.05 V
This order of voltage corresponds directly to the order of reactivity.
**Therefore, the reactivity order is: Mg > Zn > Ni > Cu > Ag.**
**Justification:** The magnitude of the voltage is proportional to the difference in reactivity between the two electrodes. Since Magnesium gives the largest positive voltage, it is the most reactive metal in the list. Silver gives the most negative voltage, meaning it is the least reactive.
Common mistakes
✗ Reversing the order of reactivity.
✗ Justification is simply restating the order without explaining the principle (link between voltage and reactivity difference).
✗ Ignoring the signs of the voltages.
Practice the full AQA GCSE Chemistry Higher Tier Paper 1
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