One type of ‘breathalyser’ instrument used by police for the measurement of the concentration of alcohol in a driver’s breath is a fuel cell - VCE - SSCE Chemistry - Question 8 - 2005 - Paper 1

To calculate the maximum current, we first need to find the moles of ethanol being provided per second. The molar mass of ethanol (C2H5OH) is approximately 46 g/mol.

Moles of ethanol per second: $n = \frac{mass}{molar \: mass} = \frac{3.0 \times 10^{-5} \: g}{46 \: g/mol} = 6.52 \times 10^{-7} \: mol$

Next, we need to find the total charge produced. The half reaction at the anode shows that 4 moles of electrons are produced for every mole of ethanol oxidized.

Total moles of electrons per second: $electrons = 6.52 \times 10^{-7} imes 4 = 2.608 \times 10^{-6} \: mol$

Using Faraday’s constant ($F \approx 96485 \: C/mol$), we can find the total charge: $Q = n \times F = 2.608 \times 10^{-6} imes 96485 = 0.25 \: C$

To find the current (I), we use the formula: $I = \frac{Q}{t}$

Since the charge is produced per second, the current is: $I = 0.25 \: A$

1. Carry current: The electrodes need to conduct electricity effectively to allow the current generated by the reactions to flow.

2. Catalyse electrode reactions: The electrodes must facilitate the oxidation of ethanol and the reduction of oxygen efficiently to ensure accurate and reliable measurement of alcohol concentration.