Video: GCSE Chemistry Foundation Tier Pack 1 • Paper 2 • Question 5

GCSE Chemistry Foundation Tier Pack 1 • Paper 2 • Question 5

10:15

Video Transcript

The emission of certain gases into the atmosphere can lead to acid rain. Which of the following gases can cause acid rain? Tick one box. Nitrogen oxides, oxygen, ammonia, or argon.

Before we look at the statements, let’s review what acid rain is. Firstly, rain is obviously made of water. Water, in its natural state, has a pH of seven. It’s neutral overall. The pH of acid rain is less than seven; it’s acidic. Within each drop of acid rain, there is water and there are other dissolved gases which make it acidic. So in order to answer this question, we need to consider what happens as each of these gases dissolves in water.

Nitrogen oxides here refers to common nitrogen oxides like nitrogen oxide and nitrogen dioxide. The main reaction we have to consider here is what happens when nitrogen dioxide interacts with water. It reacts to produce nitric acid and nitrous acid. Nitrogen monoxide interacts with other species in the atmosphere to form nitrogen dioxide and so can be equally dangerous. So nitrogen monoxide and nitrogen dioxide are both culprits of acid rain. Therefore, nitrogen oxides is a correct answer.

Just to be safe, we’ll look at the other three options. Oxygen gas does not react directly with water but it does dissolve to a very small degree. However, it does not produce an acidic solution. Therefore, it is not a correct answer. Ammonia, on the other hand, does react with water to produce ammonium hydroxide. However, ammonium hydroxide is a base not an acid. Since ammonium hydroxide is basic rather than acidic, ammonia cannot be the correct answer. Now, what about argon? Argon is a noble gas and therefore is not reactive. Therefore, it is not going to produce either an acid or a base. It does dissolve ever so slightly in water, but this has no effect on the pH. Therefore, argon is not a correct answer. Therefore, of the gases given, only nitrogen oxides produce acid rain.

There are many sources of energy. Which of the following energy sources is the most likely to produce gases that cause acid rain? Tick one box. Nuclear power, burning fossil fuels, wind power, and hydroelectric power.

To answer this question, we should look at each option and consider what is omitted as waste by the process. In nuclear power, radioactive sources like uranium are used to heat large amounts of water to drive steam turbines. So besides the radioactive slurry that’s produced, water is the only gas output. Fossil fuels, on the other hand, like coal, natural gas, and oil have contaminants in them. Because of the contaminants in fossil fuels as well as the high temperatures in internal combustion engines, burning fossil fuels produces, as well as carbon dioxide, sulfur dioxide and nitrogen oxides.

Meanwhile, wind power, which turns wind energy into mechanical motion and from mechanical motion into electrical energy, generates no gases. Similarly, hydroelectric power, where gravity draws water through electricity turbines, releases no gas. Therefore, wind power and hydroelectric power are not correct answers. As for nuclear power, as the only gas output is water vapor and water is neutral and does not contribute to acid rain, nuclear power is not a correct answer.

This leaves us with burning fossil fuels. The gases output from fossil fuels due to contaminants are acidic gases like sulfur dioxide and nitrogen oxides. Therefore, burning fossil fuels is the correct answer.

Now, realistically, all these forms of energy will generate acidic gases. For nuclear power, fossil fuels are burned in order to move fuel to the nuclear power plant. In wind power, acidic gases will be generated during the manufacture of the turbines. Similarly, for hydroelectric power. However, what we’re being asked here is what energy source is the most likely to produce gases that cause acid rain. And that is definitely burning fossil fuels.

Sulfur dioxide is a dangerous pollutant with strong potential to cause acid rain. Figure one shows the annual production of sulfur dioxide in the United Kingdom between 1985 and 2010. Using the data in figure one, what was the annual emission of sulfur dioxide in the UK in 1995?

This question requires us to look at figure one, read up from 1995, and read along to the 𝑥-axis to the annual emission of sulfur dioxide. Here, we have to take note that the units of the 𝑦-axis is kilotons. So we need to be sure to include those units in our answer. Let’s start by reading off the value from 1995. You may find it helpful to mark on the graph, the way I have. Marking upwards from 1995 until the data point and then marking along to the 𝑦-axis.

Reading from the graph, we can see that the value we obtain is four-fifths of the way between 2000 and 2500. The difference between 2500 and 2000 is 500. So 2000 plus four-fifths times 500 equals 2400. So the answer to what was the annual emission of sulfur dioxide in the UK in 1995 was 2400 kilotons.

There are a number of trends and regions in the data in figure one. Give three statements that describe the behavior of the data.

Remember that this graph describes the annual emission of sulfur dioxide in the UK in kilotons. The first thing we need to understand is we’re being asked to give three statements. The question says that there are a number of trends and regions. Combining these two suggests that there are at least three regions in the data that we can describe. So let’s look at figure one and see what regions we can break it down into.

The first region we can see on the graph is the region between 1985 and 1987. During this period, the annual emission of sulfur dioxide in the UK was constant. In the next region of the data, we can see that the annual emission of sulfur dioxide in the UK starts to reduce, but slowly. I placed the boundaries of this region up until about 1992. But you could judge that it was a little bit sooner.

The next region of the data is between about 1992 and 1999. During this period, there was a rapid decrease in the annual emission of sulfur dioxide gas. By your eye, you could judge the end of this period a little bit differently and that’s okay. The important point is to recognize there’s a transition between a slow decrease and a fast decrease in the annual emissions.

The fourth and final region is between about 1999 and the year 2010. This is a period where the slow decrease in annual emission of sulfur dioxide resumes. Just to recap, region one was steady. In region two, there was a slow decrease in the annual emission of sulfur dioxide. During region three, the annual emission of sulfur dioxide fell much faster. And in region four, there was once again a slow decrease.

For this question, we’ve been asked to give three statements. So we only need to describe three out of the four regions. For simplicity’s sake, I’m going to select one, two, and three.

Describing region one between 1985 and 1987, sulfur dioxide emission in the UK was constant. Describing region two between 1987 and 1992, sulfur dioxide emission in the UK decreased slowly. And finally, describing region three between 1992 and 1999, sulfur dioxide emission in the UK decreased quickly. If you had selected region four, your statement would have been similar to that for region two. Therefore, we’ve given three statements that describe the behavior of the data.

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