Topic 3 - Primary Cell Features and Explanations

Question 1

Feature: Electrolytes in paste/gel, not a dilute solution

Answer 1

Explanation: reactants last longer, limits moistures and leaks

Question 2

Feature: separator used instead of salt bridge (gelled elecrolyte, microporous plastic film, or porous inert material filed with electrolyte)

Answer 2

Explanation: salt bridge physicall incompatible, battery allows electrolyte ions to move across, porous material allows migration (of ions), but not mixing of oxidant and reductant

Question 3

Feature: total surface area of electrodes is increased as much as possible

Answer 3

Explanation: increased rate of reaction (may or may not be bad in primary, but in fuel good because reactants constantly supplied), reactants attach to electrode better to provide a constant voltage

Question 4

Feature: Oxidant is a metal and sometimes serves as the external container

Answer 4

Explanation: so that metals don’t oxidise (and thus corrode), container is intact

Question 5

Feature: Products of electrode reactions are removed from electrode surfaces if possible

Answer 5

Explanation: so that cell doesn’t reach equilibrium (goes flat)

Question 6

Feature: anode and cathode separated by an insulator

Answer 6

Explanation: prevents the cell from heating up (related to rate of reaction, may be good or bad) and they can occur in separate places

Question 7

Disadvantages (2) & improvements

Answer 7

Polarisation: When products build up around electrodes.
Improvement: Remove products from electrodes, allow the cell to rest so products migrate away from electrodes, using a gel or paste.

Electrolyte being acidic: metals can corrode
Improvement: Use a basic electrolyte