Introduction:
Acid rain has an acidity of around 4, which is 1000 times more acidic than normal rain.
When humans burn fossil fuels, sulphur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere. Those air pollutants react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. Winds may spread these acidic compounds through the atmosphere and over hundreds of miles. When acid rain reaches Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil. Acid rain and fog also damage forests, especially those at higher elevations. The acid deposits rob the soil of essential nutrients such as calcium and causes the aluminum to be released in the soil, which makes it hard for trees to take up water. Trees’ leaves and needles are also harmed by acids.
The chemical equation of acid rain is:
Chemical equation for the formation of sulphuric acid:
Aim:
This experiment aims to see how fast metal corrodes with different acids. My hypothesis is that the sulfuric acid will have the highest temperature at the end of the 15 minutes because it had the lowest pH out of the liquids being tested.
The pH scale measures how acidic or basic a liquid is. The range goes from 0-14, with 7 being neutral (water). pH is a measure of the relative amount of free hydrogen and hydroxyl ions in the water.
Dependant: The temperature because that is what is being measured. Because the reaction is exothermic, the higher the temperature, the faster the corrosion.
Control: Steel Wool.
Independent: The acids that are being used.
Materials:
- Gloves
- Lab coat
- Safety glasses
- 9 test tubes
- Test tube rack
- 3 rubber stoppers (for test tube)
- 3 thermometers
- Steel wool
- Scissors
- Ruler
- 3 Beakers
- 250mL distilled water exposed to air
- 250mL vinegar
- 250mL 1M H2SO4
Method:
- Put on your disposable gloves to help prevent you from getting splinters from the steel wool.
- Using the ruler, measure 2.5cm along the length of a steel wool pad. Cut across the width of the pad with the scissors at the 2.5cm mark. Set the cut strip aside. Continue through the width of the pad, at 2.5cm intervals, until it is used up. Repeat this step for two or more pads, or until you have a total of nine 2.5cm strips of steel wool.
- Pour approximately 250mL of the vinegar, distilled water, and H2SO4 into separate beakers.
- Thread the rubber stopper onto each thermometer.
- Place each rubber stopper, with its attached probe, inside the test tube. Record the temperature of the thermometer in your data table. This will be your temperature at “time equals zero.”
- Soak a strip of steel wool in the beaker of each substance for 30 seconds (sec). It might float to the top of the liquid, so hold it under the surface with your fingers (gloves are important here. Do each liquid at the same time otherwise, you will run out of time.
- Remove the steel wool from each beaker and squeeze out the excess liquid for a couple of seconds over a sink.
- Immediately, remove the thermometer from the test tube and thread the soaked steel wool onto the end of the thermometer, below the rubber stopper. Twisting the probe as you thread it through the steel wool may help it go on more easily.
- Place the thermometer back into the test tube and press the stopper closed.
- Start the timer and record the temperature every minute for 10 min., and then once more 5 min. later.
- Stop and reset the timer.
- Remove the thermometer and examine the steel wool. Record any observations. Use the ruler to measure the greatest length of rusting observed.
- Repeat steps 5-13 two more times with each liquid.
- Using the collected data, find the average temperature for each liquid at each minute.
- Pack up all equipment.
Results:
| Sulphuric Acid | Temperature (OC) | |||
| Time (min) | Trial 1 | Trial 2 | Trial 3 | Average |
| 16 | 17 | 18 | 17 | |
| 1 | 20 | 20 | 18 | 19.3 |
| 2 | 21 | 20 | 18 | 19.6 |
| 3 | 21.5 | 20.5 | 18.5 | 20.2 |
| 4 | 21.5 | 20.5 | 19 | 20.3 |
| 5 | 21.5 | 20.5 | 29 | 20.3 |
| 6 | 21.5 | 20.5 | 19 | 20.3 |
| 7 | 21.5 | 21 | 19 | 20.5 |
| 8 | 22 | 21 | 19 | 20.6 |
| 9 | 22 | 21 | 19 | 20.6 |
| 10 | 22 | 20.5 | 19 | 20.5 |
| 15 | 22.5 | 21 | 19 | 20.8 |
| Vinegar | Temperature (oC) | |||
| Time (min) | Trial 1 | Trial 2 | Trial 3 | Average |
| 0 | 15 | 15 | 15 | 15 |
| 1 | 17 | 21 | 22 | 20 |
| 2 | 17 | 20 | 22 | 19.6 |
| 3 | 16 | 20 | 22 | 19.3 |
| 4 | 16 | 20 | 22 | 19.3 |
| 5 | 17 | 20 | 22 | 19.6 |
| 6 | 16 | 20 | 22 | 19.3 |
| 7 | 15.5 | 20 | 22 | 19.17 |
| 8 | 15.5 | 20.5 | 22.5 | 19.5 |
| 9 | 15.5 | 20.7 | 22.5 | 19.57 |
| 10 | 16 | 21 | 22.5 | 19.83 |
| 15 | 16 | 21 | 23 | 20 |
| WATER | Temperature (oC) | |||
| Time (min) | Trial 1 | Trial 2 | Trial 3 | Average |
| 0 | 19 | 19 | 18 | 18.67 |
| 1 | 20 | 21 | 20 | 20.33 |
| 2 | 19 | 20 | 19 | 19.33 |
| 3 | 19 | 20 | 19 | 19.33 |
| 4 | 19 | 20 | 19 | 19.33 |
| 5 | 19 | 20 | 19 | 19.33 |
| 6 | 18.5 | 20 | 19 | 19.17 |
| 7 | 18.5 | 20 | 19 | 19.17 |
| 8 | 18.5 | 20 | 19 | 19.17 |
| 9 | 18.5 | 20 | 19.5 | 19.33 |
| 10 | 18 | 19 | 19 | 18.67 |
| 15 | 18 | 19 | 19.5 | 18.83 |
Discussion:
All three acids are exothermic reactions, meaning that energy is produced. We can see this in the results because, in all 3 tested acids, the temperature rises as time passes.
Consistently throughout the 3 trials is an initial spike in temperature within the first minute. Looking at all acids, vinegar had the biggest spike in temperature, and after the initial spike, it remained consistent in overall temperature throughout the experiment.
Sulphuric acid, with a pH of 0.5, corroded the steel wool the fastest because, at the end of the 15 minutes, the temperature of the steel wool was at 20.8℃. Vinegar, with a pH of 2.5, corroded the wool the second fastest, with a temperature of 20℃. Distilled water was all over the place, with a big initial spike, but it fluctuated up and down from there.
These results were expected, because Sulphuric acid has the lowest pH, meaning it corrodes metal the fastest.
If this experiment was to be done again, making sure that the 3 pieces of steel wool were soaked for the same amount of time, to get a more accurate result.
Conclusion:
In conclusion, the hypothesis that Sulphuric acid will corrode the steel wool the fastest is indeed true. This is because it has the lowest pH of the tested acids.
