Hello, I'm Mrs. Adcock, and today's lesson is on acid rain and chemical weathering.

We are going to look at what is acid rain, what produces acid rain and what are the impacts of acid rain? In today's lesson, the outcome is I can describe how acid rain is formed and the effects that acid rain can cause.

Some keywords that we will be using in today's lesson include pH, pH scale, acid rain and chemical weathering.

You can see those keywords written here in a sentence, so you might want to pause the video and read through those sentences now, or make some notes, and then you can refer back to those later on in the lesson when needed.

Our lesson today on acid rain and chemical weathering is split into three parts.

Part one is acids, part two is about acid rain, and part three, we're going to look at the effects of acid rain.

So let's get started on the first part of our lesson on acids.

Commonly used acids in scientific labs are hydrochloric acid, which has the formula, HCL, sulfuric acid, which has the formula H2SO4, and nitric acid, which has the formula, HNO3.

So you might be familiar with the names of those three acids.

Acids are substances that produce hydrogen ions when dissolved in water.

So for example, when we have hydrochloric acid and that's in solution, then it forms H+ ions and CL- ions.

But you can see there that it's forming those H+ ions.

H2SO4, that's our sulfuric acid in solution forms, H+ ions.

And SO42- ions and HNO3, that's nitric acid in solution forms H+, so our hydrogen ions and NO3- ions.

So you can see there that acids produce hydrogen ions when they're dissolved in water.

Time for a check.

When acids are in solution, they produce A, hydroxide ions, which are OH-, B, hydrogen ions, which are H+ or C, water, which is H2O.

The correct answer is B.

So well done, if you chose B.

Acids in solution produce hydrogen ions.

pH is a measure of the hydrogen ion concentration in a solution, and the pH scale is used as a measure of how acidic or alkaline a solution is.

So we can see a diagram there of the pH scale, and if something has a pH of seven, we describe it as neutral.

So anything higher than seven, so eight up to 14, then they are described as alkalines.

And as you go from eight up to 14, we've got increasing alkalinity.

Below pH seven, so pH six and lower, they are our acids.

And as you go from six down to zero, we've got increasing acidity.

Approximate pH values of samples can be measured by adding universal indicator solution and comparing the resultant colour with a pH chart.

So we've got a picture here of a pH chart, and you can see that neutral on our pH chart is green.

As we have increasing alkalinity, we go to from green to blue to purple.

And then for our acids, as something becomes more acidic, we're going from green to yellow to orange to red.

What is the pH of acids? Is it A, less than seven, B, seven, or C more than seven? The correct answer is less than seven.

Well, then if you've got that correct and chose option A, knowing that acids have a pH of less than seven.

So if you have a pH of one or two, we would consider that a strong acid and a pH of five or six, we would consider a weak acid.

If something has a pH of seven, it will be neutral, and if it's more than seven, it'll be an alkaline.

Time for our first practise task of today's lesson.

Question one, what is pH a measure of? And question two, you need to use the pH values to work out if the following substances are an acid, alkali or neutral.

So you've got sodium hydroxide that has a pH of 14, is that an acid alkali or neutral? And then if you work it out for water, wine and baking soda as well.

Pause the video and then I'll see you back in a moment to go over the answers.

pH is a measure of the hydrogen ion.

It's a H+, that's a hydrogen ion, hydrogen ion concentration in a solution.

Now, sodium hydroxide has a pH of 14, so that'll be an alkali.

Water has a pH of seven, that's neutral.

Wine has a pH of four, so that's acid, and baking soda has a pH of nine, so that will be an alkali.

So well done if you've got those correct.

Time for us to move on to the second part of our lesson, which is on acid rain.

Rain water is naturally slightly acidic due to a reaction with carbon dioxide.

And the formula for carbon dioxide is CO2.

So rainwater can react with carbon dioxide in the air.

And we can see there we've got that written as a symbol equation H2O, which is a liquid, reacts with carbon dioxide, which is gaseous in the air, to form H2C0E, and that H2CO3 is an acid called carbonic acid.

And you can see it's got the state symbol aq to show that this is aqueous or in solution.

Pollutants such as sulphur oxide and nitrogen oxide in the atmosphere can cause rainwater to become even more acidic.

So although rainwater is naturally slightly acidic due to the carbon dioxide in the air, sulphur oxide and nitrogen oxide, which are pollutants, they can make the rainwater even more acidic.

The sulphur oxide and nitrogen oxides react with oxygen and water in the atmosphere to produce sulfuric acid and nitric acid.

So we can see diagrams there of our H2S04 that we saw earlier on in the lesson.

So that's sulfuric acid and HNO3, that's nitric acid.

So sulfuric acid and nitric acid dissolve in atmospheric water to lower the pH and form acidic rain.

The pollutants, sulphur dioxide and nitrogen oxides, can travel really long distances with the wind, and therefore, areas without pollutants can still experience acid rain.

Which air pollutants or pollutants may cause acid rain? Is it A, sulphur dioxide.

B, carbon particulates.

C, carbon monoxide, or D nitrogen oxides? So the correct answer is A, sulphur dioxide, and D nitrogen oxides.

So well done if you identified those two pollutants that can cause acid rain.

The pH of acidic rainwater is seven.

Is that statement true or false? So that statement is false.

And see if you can justify your answer.

Is that false because A, the pH acid rain is higher than seven, or B, the pH of acid rain is lower than seven? So well done if you put B because the pH of acids is lower than seven.

So the pH of acid rain will also be lower than seven.

Time for a practise task.

And this is an scientific investigation.

So you need to follow the method to investigate how the pH of acid rain compares to other commonly used acids.

And what you need to do for this is firstly place five drops of acidic rain in a spotting tile.

Then secondly, add two drops of universal indicator solution.

Then we are on to C, which is use a pH colour chart to measure the pH, D, record your results in the results table, and then E, repeat steps A to D for the other acids that you have available.

If you do not have the equipment available to complete the investigation yourself, then there is some sample results included, which you can use to help you answer question two and three.

So question two, how does the pH of acid rainwater compare to normal rainwater? And three, how does the pH of acid rainwater compare to citric acid, which is found in lemons and oranges? And how does the pH of acid rainwater compare to the pH of vinegar? Pause the video now and you can either have a go at the investigation and then answer the questions, or you can make a note of the questions and then move on to see the sample results table.

And then you can complete the questions before we go over the answers.

Here is a results table that you may use to complete the investigation and to fill in the pH for those different solutions.

Here is a set of sample results that you can use if you were unable to complete the investigation yourself.

Let's go over the answers.

Question two.

How does the pH of acid rainwater compare to normal rainwater? Normal rainwater is slightly acidic with a pH of about six, however, acidic rainwater is more acidic, so it has a lower pH with a pH of about four.

And how does the pH of acid rainwater compare to citric acid found in lemons and oranges and how does it compare to vinegar? The pH of the acid rain was higher than citric acid that we find in lemons and orange juice and also higher than vinegar.

So acid rain is a weaker acid than citric acid and vinegar.

Time to move on to the final part of our lesson, which is on the effects of acid rain.

Acid rain decreases the pH of soil, and this makes it more difficult for plants to absorb water and the essential nutrients that they need, such as calcium and magnesium.

Now, these are particularly important to plant so that they can resist infection and withstand cold temperatures.

Acid rain also causes aluminium to be released from soil particles, and this can wash into rivers and lakes.

We've got a photo there showing lots of trees that have been killed, because the rain was more acidic than normal, so the plants were unable to absorb water and the essential nutrients that they need.

So therefore, the plants, in this case trees, have died.

Acid rain makes lakes, streams and other aquatic environments toxic.

And this can partly be because some of that aluminium that got released from the soil, has now washed into these aquatic environments and makes them toxic to some organisms such as algae.

Now, if algae die, this will have a knock on effect to other organisms in a food web, including land animals such as birds.

So if we have a lip there, this is just one example of an aquatic food web where we've got algae at the bottom and we can see that they're mid larvae, the aquatic worms and mayfly all feed on the algae.

And then you can see the beetles and dragonflies and caddis flies that feed on those organisms. And the fish feed on the great diving beetle and the dragonfly and the caddis fly.

And at the top we've got the heron and kingfishers that feed on the fish.

So if the water becomes toxic to the algae, you can see of all the organisms that can be impacted by the acid rain.

Which of the following are effects of acid rain? Is it A, plants dying as the absorption of water is more difficult? B, plants dying as they struggle to absorb enough essential nutrients.

C, algae dying due to toxic water or D, food webs impacted due to the death of producers.

Now read through those and decide which of them you think are effects of acid rain.

You may think that it's more than one answer.

So the correct answers are A, plants dying as the absorption of water is more difficult.

Plants dying because they can't get those essential nutrients they need, algae dying due to toxic water.

And then food webs are then impacted too.

So they are all effects of acid rain.

So well done if you identified all four of them.

Chemical weathering is when rocks are broken down by a chemical change.

For example, reactions with acid rain.

And we've got a picture there showing some statues, and they have been damaged by acid rain.

So we've already seen the impacts of acid rain on living organisms. Now we're going to look at the impact of acid rain on rocks.

Many sedimentary rocks contain carbonate minerals such as calcium carbonate in limestone and calcium magnesium carbonate in dolomite.

And you might have heard of these rocks before.

So we've got a diagram there sharing limestone.

So the white cliffs of Dover contain lots of limestone, and the dolomite mountains contain the rock dolomite.

Acid rain contains sulfuric and nitric acid, chemically reacts with carbonates in rocks to break down that carbonate mineral and produces salt water and carbon dioxide.

So we have our metal carbonates in our rocks, and that reacts with the acid in our acid rain, and they react to produce a salt, plus water, plus carbon dioxide.

And we can look at an example there of that reaction happening.

So we've got calcium carbonate, which is found in limestone, and that reacts with sulfuric acid from our acid rain to produce calcium sulphate plus water plus carbon dioxide.

What are the products when a carbonate in rocks reacts with acid rain? Is it A, salt and water, B, salt and hydrogen, or C, salt and water and carbon dioxide? Well done if you choose C.

When a carbonate reacts with acid, it forms salt plus water plus carbon dioxide.

Time for our final practise task of today's lesson.

Question one, what is chemical weathering? Question two, can you state the products when a limestone rock containing calcium carbonate reacts with sulfuric acid in acid rain? And question three, apart from weathering of rocks, can you state another environmental impact of acid rain? So if you pause the video now, have a go at those three questions and I'll see you when you're ready to go over the answers.

Question one, what is chemical weathering? Chemical weathering is when chemicals such as acid react with minerals in the rocks.

That may be all you've got, but you might have gone on further to say this will alter the molecular structure.

Question two, state the products when a limestone rock containing calcium carbonate reacts with sulfuric acid in acid rain.

So the products will be a salt plus water plus carbon dioxide while done, if you were able to actually name the salt and the salt would be calcium sulphate.

Question three, apart from weathering of rocks, state another environmental impact of acid rain.

So your answer may have included the ones we've looked at today which are damaged to plants and impacting food webs.

Well done.

That's excellent understanding from the final part of our lesson on the effects of acid rain.

If you were able to correctly define chemical weathering, know the products when a carbonate from the rocks reacts with acid rain.

And if you could identify some of the environmental impacts of acid rain.

We've reached the end of our lesson today.

So let's summarise some of the key points we have covered in today's lesson on acid rain, and chemical weathering.

The pH of rainwater is naturally below seven.

Chemical reactions between certain pollutants and water in the atmosphere may cause a decrease in the pH of rainwater.

Acid tain is not as acidic as vinegar or citric acid that is found in lemons and oranges.

Acid rain chemically reacts with carbonates that form many rocks to produce a salt water and carbon dioxide.

Acid rain can have long-term effects on habitats and ecosystems. Well done for all your hard work in today's lesson on acid rain, and chemical weathering.

I've really enjoyed the lesson and I hope you have too and I hope you're able to join me for another lesson soon.