Chemical cells and fuel cells

Required practical 4, investigating temperature changes independent variable

Volume of sodium hydroxide

Required practical 4, investigating temperature changes Dependent variable

Maximum temperature reached

Required practical 4, investigating temperature changes Control variables

Volume of hydrochloric acid, concentration of both hydrochloric acid and sodium hydroxide solution

Steps for the required practical to investigate temperature changes in Exothermic reaction

1. Using a measuring cylinder to measure 30cm³ of dilute hydrochloric acid

2. Transfer acid into polystyrene cup

3. Stand the cup in beaker to stop cup from falling

4. Thermometer to measure temperature of acid, record in table

5. Measuring cylinder to measure 5cm³ of sodium hydroxide solution

6. Transfer this to polystyrene cup

7. Fit plastic lid to cup And place thermometer through hole in the lid. Bulb of thermometer must be in solution

8. Use thermometer to stir the solution

9. Temperature of solution will increase

10. When reading on thermometer stops changing, we record highest temperature reached

11. Rinse out and dry cup, repeat experiment using 10cm³ of sodium hydroxide solution. Carry out experiment several times, increase volume of sodium hydroxide by 5cm³, until we reach 40cm³ of sodium hydroxide solution.

12. Repeat experiment one more time for 2 sets of results to calculate mean maximum temperature reached for each volume of sodium hydroxide

Results for practical

As you increase volume of sodium hydroxide, maximum temperature reached increases. This is because when we add more particles of sodium hydroxide they react with the hydrochloric acid. This is an Exothermic reaction so more energy is released and maximum temperature increases . However, at a certain volume, maximum temperature reached decreases. At this point, we are adding so much sodium hydroxide that there aren’t enough hydrochloric acid particles. This means some sodium hydroxide particles aren’t able to react. Maximum energy released is reached.

If we take 2 different metals and place them into an electrolyte…

We can produce electricity

Cells

Produce electricity

Cells can only…

Produce electricity for a certain period of time because eventually, th chemicals in the cell run out and reaction stops.

Cells only produce electricity if…

We use metals with different reactivities.

The greater the difference between the reactivity of the metals…

The greater the potential difference produced by the cell

Battery

2 or more cells collected in series, produces greater voltage

Alkaline batteries

The reactants run out, no more electricity is produced. Non rechargeable

Rechargeable batteries

We can reverse the chemical reactions when we apply an electrical current

Fuel cells

We react a fuel, eg hydrogen, with either pure oxygen or air. Chemical reaction takes place, producing an electric curren.

Waste product of hydrogen fuel cell

Water

Advantages of hydrogen fuel cells

Will produce electricity for as long as hydrogen is provided. Hydrogen fuel cells don’t get less efficient the longer they run, unlike rechargeable fuel cells that store less and less electricity the more charging cycles they go through. Can also be a source of drinking water for astronauts on space craft

Disadvantages of hydrogen fuel cells

They run on hydrogen gas, which is explosive and is difficult to store safely. Unlike with rechargeable batteries, Enoch don’t need dangerous fuels (however some can catch fire if manufactured wrong). Hydrogen fuel cells produce low potential difference so more are needed. Rechargeable fuel cells can produce greater potential difference.