Welcome to today's lesson.

This lesson's about the pH scale and universal indicator solution.

It's part of the "Acid and Bases" unit.

My name's Mrs. Mytum-Smithson, and today we're going to look at the pH scale.

You might have heard of this before, but if not, don't worry, because we're going to work through this lesson step by step.

And by the end of the lesson, you should be able to measure the pH of an acid or alkali using the pH scale.

Today's keywords are pH scale, acidic, alkaline, neutral solution, concentration.

On the next slide, there's some sentences that include these keywords, so if you wish to read them, pause that slide, and then press Play when you're ready to start the lesson.

Today's lesson consists of two learning cycles.

Firstly, we're gonna do about the pH scale, and then we're going to learn all about universal indicator.

So let's get going now with the pH scale, our first learning cycle.

pH stands for potential of hydrogen.

When you see it written down, it should always start with a lowercase p and have a capital H.

The H stands for hydrogen, 'cause that's the chemical symbol of hydrogen.

So the pH scales is the numerical scale, and it goes from pH 1 to pH 14.

So here's our scale there.

Now acids contain hydrogen.

That's why we've got potential of hydrogen there.

The higher the concentration of hydrogen, so the more hydrogen there is, the lower the pH.

The lower the concentration of hydrogen, so the less hydrogen there is, the higher the pH.

So we can see that more hydrogen will lower the pH, less hydrogen will increase the pH.

Now less than pH 7, that is considered acidic, and more than pH 7 is alkaline.

And right there in the middle, exactly pH 7 is neutral.

Quick check for understanding for you now.

The pH scale goes from 1 to 10, 1 to 100, 1 to 7, or 1 to 14.

Pause the video now, choose your answer, and then press Play, and we'll see if you right or not.

Well done if you said D, the pH scale goes from 1 to 14.

So one being the most acidic, 14 being the most alkaline.

I've got another quick check here.

A solution with a pH of exactly seven is, is it acidic? Is it neutral? Or is it alkaline? Pause the video, decide which answer you're going to choose, and then press Play, and I'll let you know if you're right.

Well done if you said a solution with a pH of exactly seven is neutral.

Well done.

You're doing really well with these checks for understanding, I'm sure.

So here's another one.

The higher the concentration of hydrogen, the lower the pH? The higher the pH? The concentration of hydrogen does not change the pH.

Select your answer.

So pause the video whilst you do that, and then press Play, and we'll go through the answer together.

Well done if you said the higher the concentration of hydrogen, so the more hydrogen there is, the lower the pH.

Well done if you got that correct.

The pH scale goes up and down in factors of 10.

So if you take an acid of a pH 2, that is 10 times more acidic than a pH of three, and a pH of one would be 10 times more acidic than a pH of two.

So as we go from three to two, we go by a factor of 10.

So if we have a look at pH 4, pH 4 is 10 times more acidic than pH 5.

An alkali of pH 9 is 10 times more alkaline than pH 8.

So as we go from eight to nine, that increases the alkalinity, so it increases it by 10 times, so it's 10 times more alkaline pH 9 than pH 8.

So if you go from pH 11 to pH 13, you'll increase that by two factors of 10.

So 10 times 10 is 100, so pH 13 is 100 times more alkaline than pH 11.

Here's a true or false for you.

True or false? The pH scale goes up and down in factors of 14.

Pause the video, select if it's true or false, and I'll tell you the answer in a minute.

Well done if you said that that was false.

Now on to justification for that.

So choose one of these answers.

A solution of pH 5 is 10 times more acidic than a solution with a pH of six.

Or a solution of pH 5 is 10 times less acidic than a solution with pH of six.

Pause a video while you have a think about your answer, then press Play, and I'll tell you if you're right.

Well done if you said A.

A solution of pH 5 is 10 times more acidic than a solution with pH of six.

Remember, as you go down the scale, each pH you go down increases the acidity by a factor of 10.

What I'd like you to do now for this check for understanding is select all the correct statements.

The more alkaline a solution is, the higher the pH.

So pH 9 is 10 times more alkaline than pH 8.

pH 9 is 14 times more alkaline than pH 8.

pH 9 is 10 times less alkaline than pH 8.

pH 11 is 100 times more alkaline than pH 9.

Pause the video for some thinking time, and press Play, and we'll go through the answer or answers together.

Well done if you said pH 9 is 10 times more alkaline than pH 8.

So as we go from eight to nine, the alkalinity, so how alkaline something is, increases by 10 times.

pH 11 is 100 times more alkaline than pH 9, because as you go from 9 to 10, that's 10 times more alkaline, and then as you go from 10 to 11, that's another factor of 10, so 10 times 10 is 100, so pH 11 is 100 times more alkaline than pH 9.

Well done if you've got both of those correct.

What I'd like you to do now is state if the solution is acidic, neutral, or alkaline.

So all you're going to do for each solution, you're going to write acidic, neutral, or alkaline.

So a solution has a pH of five.

A cleaning solution has a pH of eight.

Water has a pH of exactly seven.

Milk has a pH of 6.

5.

Vinegar has a pH of three.

A drain unblocker solution has a pH of 10.

A facial cleanser has a pH of 7.

5.

Pause the video while you complete that task, then press Play, and we'll go through the answers together.

Well done for working hard and completing that task.

Let's see how you got on.

So a solution has a pH of five.

That's going to be acidic, because that's less than seven.

A cleaning solution has a pH of eight.

That's going to be alkaline, because it's got a pH of greater than seven.

Water has a pH of exactly seven.

So only things have got a pH of exactly seven are neutral.

So you should have written neutral there.

Milk has a pH of 6.

5, so that's less than seven, so that's actually acidic.

Vinegar has a pH of three.

That's definitely acidic, 'cause pretty low on the scale.

A drain unblocker solution has a pH of 10.

So that's greater than seven, so that's alkaline.

A facial cleanser has a pH of 7.

5.

So this is going to be alkaline.

So it's only going to be slightly alkaline 'cause it's only just over seven, but it is alkaline.

So well done if you've got all of those answers correct.

What I'd like you to do for task two of part A is tell me are Jacob and Alex's statements true or false? So all I want you to do for this bit is say true or false.

So Alex has said a solution with a pH of two is more acidic than a solution with a pH of seven.

His second statement is, solution A has a pH of three, solution B is 100 times more acidic.

So solution B has a pH of two.

Jacob said the pH scale goes from 1 to 20.

And he's also said pH stands for potential of helium.

Pause the video while you decide if these statements are true or false, then press Play, and we'll go through the answers together.

Well done if you said that the first statement, a solution with a pH of two is more acidic than a solution with a pH of seven.

Absolutely true because that pH is lower than seven, it's more acidic, because the lower the pH, the more acidic it is.

Solution A has a pH of three.

Solution B is 100 times more acidic.

So solution B has a pH of two.

That was false.

Jacob said the pH scale goes from 1 to 20.

That was also false.

And pH stands for potential of helium.

That's also false.

So well done if you've got those four statements correct.

Now what I want you to do is take those three false statements and make them scientifically correct.

So pause the video while you do that, then press Play, and we'll have a look and see how well you've done.

What we were doing here is we were correcting the false statements to make them scientifically correct.

So Alex just had one false statement, and there's two ways that this answer could be written.

So you could have written solution A has a pH of three, solution B is 100 times more acidic.

So solution B has a pH of one.

Or you could have written it this way.

Solution A has a pH of three, solution B is 10 times more acidic.

So solution B has a pH of two.

So well done if you got that one correct.

Jacob's got two statements.

They said the pH scale goes from 1 to 14, not 1 to 20 that he said earlier.

And also pH stands for potential of hydrogen.

Remember that capital H is a chemical symbol for hydrogen.

So well done if you've got all of those correct.

You're doing really well so far.

Here's the final part of task A, part four.

You're doing really well so far this lesson.

What I want you to do for this task is write the pH of the solutions.

Solution A has a pH of three, solution B is 10 times more acidic.

What is the pH of solution B? Solution C is neutral.

What is the pH of solution C? Solution D has a pH of eight.

Solution E is 1,000 times more alkaline.

What is the pH of solution E? Solution F has a pH of seven, solution G is 100 times more acidic.

What is a pH of solution G? Pause the video while you complete this task, then press Play, and we'll go through the answers together.

Well done for completing part four of task A.

Let's go through the answers together.

So solution A has got a pH of three, and solution B is 10 times more acidic.

So we need to go down the pH scale just by one, because it's 10 times more acidic.

So that gets us to pH 2.

Solution C is neutral.

So the pH of a neutral solution is pH 7.

Solution D has got a pH of eight, and solution E is 1,000 times more alkaline.

So we need to move from 8 to pH 11 going up each time by a factor of 10, because 10 multiplied by 10 multiplied by 10 is 1,000.

So solution F has got a pH of seven, and solution G is 100 times more acidic.

So this time we're going down the scale, we need to go down two points, because 10 times 10 is 100.

So the pH of solution G is pH 5.

Well done if you've got all of those correct.

Well done for completing our first learning cycle all about the pH scale.

Now we're going to look at universal indicator.

Most acids and alkalis are colourless solutions.

So that means that they don't have any colour to them.

So we can't tell just by looking at them if they're an acid or an alkali.

So what we need to do is we use something called an indicator.

So an indicator can be used to identify if something is acidic, or alkaline, or even neutral.

So we've got some universal indicator.

You can see this goes from red all the way through orange, yellow, green, blue, and finally purple at the end.

And this is called universal indicator paper.

That's a scale at the top of the picture, and then at the bottom you can see two pieces, and it comes in, it is kind of a yellowish colour paper.

We've got some universal indicator solution.

Again, this is a very dark colour.

You can see at the bottom it's a very dark colour.

You just pop that into your solution, and that'll tell you if it's an acid or an alkali.

And we've also used before in previous lessons, we've used red and blue litmus paper.

Universal indicator, it's available in a solution or in a paper form.

So that's just some paper that's been soaked in that solution and then dried, and it's made from a mixture of dyes that will change to a different colour depending on the pH of the solution.

So here's our scale.

You can see we've got the numbers of pHs along the bottom from 1 to 14, and we've got the colours along the top, so they go from red to orange through yellow and green, and then all the way up to blue and purple.

You can see as we go from pH 7 down to pH 1, it's acidic.

So if it's yellow, orange, or red, it's going to be an acidic solution.

Neutral is this green colour.

It's quite a yellowish green on this scale.

It can be a more vivid green if you use a universal indicator solution.

And at the top end of the scale, we've got the alkaline solution.

So if it's an alkaline solution, it's going to turn blue or purple.

So that's the paper will turn blue or purple, or the solution will turn blue or purple.

The paper can be dipped into the solution being tested, or drops of the solution form can be added to the solution being tested.

So you've got two ways that you can use universal indicator.

You can either add drops to your solution that you're testing to see if it's an acid or an alkali, or you can take a drop out.

Now the advantage of taking a drop of the solution that you're testing out of the solution and placing it on some universal indicator paper is it prevents contamination, because sometimes you want your solution to not have universal indicator in it.

Let's have a quick check for understanding now.

Universal indicator solution in an acidic solution.

Will it be red, orange, or yellow? Will it be green? Will it be blue or purple? Pause the video, have a little think, choose your answer, and then press Play, and I'll tell you if you're right.

Well done if you said red, orange, or yellow.

Remember, universal indicator will turn red, orange, or yellow in acidic solutions, it will be green if it's neutral, and it will be blue or purple if it's in an alkaline solution.

So well done if you said red, orange, or yellow.

Now I've got a true or false for you.

True or false? Universal indicator has a wide range of colours in different pH solutions.

Is that true or is that false? Pause the video while you have a little think, and then press Play, and I'll tell you if you're right or not.

Well done if you said that that was true.

Universal indicator does have a wide range of colours in different pH solutions.

Now onto justification.

The colour of the indicator solution or paper will tell you the pH of the solution you are testing.

Or you cannot tell the difference between solutions that have a different pH.

Pause the video while you have a think, press Play, and we'll go through the answers together.

So well done if you said the colour of the indicator solution or paper will tell you the pH of the solution you are testing.

So you can tell the difference between solutions that have got different pHs.

Well done if you got that one right.

I've got a quick check for understanding for you now.

So which is the indicator paper that has been dipped in an alkaline solution? What I want you to do is use a universal indicator pH chart to help you decide which one.

Is it the green one, the red one, or the dark blue one? Pause the video while you have a think, choose your answer, and then press Play, and we'll go through the answer together.

Well done if you said dark blue.

So this piece of universal indicator paper has changed from yellow to dark blue where it's been dipped into the alkaline solution.

Well done if got that one correct.

Here's part one of task B.

What I want you to do is draw a results table for the experiment that I'm just about to describe.

Then I want you to test the series of solutions to determine their pHs using either universal indicator solution or paper.

So here's the method.

Using a pipette, place three or four drops of the test solutions in a well of a spotting tile.

Either add one to two drops of universal indicator solution, or place the end of universal indicator paper into each well of the spotting tile.

Using a pH scale chart, observe and note down the colour and the pH of the solution in your results table.

So pause the video while you carry out this practical, and then press Play, and we'll go through the answers.

So your results table might look similar to this.

Now I'm going to just go through some of the solutions that I've tested, but you might have tested different solutions, and have slightly different results.

So lemon juice, vinegar, cleaner, toothpaste, pure water, and fizzy drinks were tested.

So for lemon juice, the colour of the universal indicator was red.

And it was orange for vinegar.

The cleaner turned dark blue.

The toothpaste was dark green.

Pure water was pale green.

And a fizzy drink was yellow.

So you could have then looked at the chart, and then said what pH you thought it was.

So lemon juice got pH of two.

Vinegar, a pH of three.

The cleaner was alkaline, so that was pH of 11.

Toothpaste, that was dark green, so that was pH 9.

So that was alkaline.

Pure water, that's pale green, so that's seven.

And the fizzy drink at yellow, that was a pH of two.

So well done if you've got results similar to these.

What I'd like you to do now is write a conclusion for your experiment by completing these sentence starters.

So the most acidic solution I tested was, and then you're going to name the solution there.

I know this because, and you're going to give me a reason, some evidence.

The most alkaline solution I tested was, and you're going to write the name of that solution there.

And you're going to say, I know this because, and you're going to give me an answer there.

And then you're going to tell me if you did or did not test a neutral solution, and tell me how you know that.

So I want some evidence there.

So write your conclusion.

So pause the video whilst you do this, then we'll go through the answers together in a minute.

Well done for writing your conclusion.

It should be similar to mine.

So the most acidic solution I tested was, and you're going to name a solution there.

And then you're going to tell me how you know it.

And it should be something like this, that the solution went a red colour, or that you had a low pH of one.

The most alkaline solution that you tested, and you're going to name that solution there.

And you're going to say, I know this because, and you're going to say the solution was a purple colour, or a dark blue colour, and had a high pH of 12.

So whatever you've written there, well done.

And if you tested a neutral solution, I did test a neutral solution, and I know this because the solution went green, or I had a pH of seven.

Or you might not have had a neutral solution, in which case your conclusion would've been I did not test a neutral solution, and I know this because no solutions went green, and no solutions had a pH of seven.

So well done for writing your conclusion there.

Here's a summary for today's lesson.

Most acids and alkalis are colourless solutions, so indicators can be used to identify them.

pH stands for potential of hydrogen, and acids contain hydrogen.

The higher the concentration of hydrogen, the lower the pH.

The pH scale goes up and down in factors of 10, so an acid of pH 2 is 10 times more acidic than pH 3.

A low pH means acidic.

A high pH means alkaline.

And solutions with a pH of seven are neutral.

Well done for working really hard this lesson.

I hope you now understand more about the pH scale, and how to measure the pH of a solution with universal indicator paper or solution.

So well done for working really hard this lesson.

Hope to see you soon.