Hello, I am Mrs. Adcock and welcome to today's lesson on concentration and rate practical using gas collection method.

We are going to think about how we can investigate the effect of concentration on the rate of reaction using a gas collection method.

Today's lesson outcome is: I can carry out a fair test to investigate how the rate of reaction depends on the concentration of a reacting solution.

Some of the key words we will be using in today's lesson include rate of reaction, independent variable, dependent variable, and control variable.

Here you can see each of those keywords written in a sentence.

It would be a good idea to pause the video now and read through those sentences.

You might even like to make some notes so that you can refer back to them later in the lesson if needed.

Today's lesson on concentration and rate practical using gas collection is split into three main parts.

First of all, we are going to be looking at concentration and rate theory.

Then we are going to move on to look at concentration and rate variables.

And finally we will move on to look at the concentration and rate equipment and method.

Let's get started on the first part of our lesson where we are going to look at the theory of concentration and rate of reaction.

For chemical reaction to take place, particles in the reactants must collide with each other and the minimum energy that the particles must have in order to react when they collide is known as the activation energy.

Here we can see some reactant particles colliding together and these particles have the activation energy.

Therefore, when they collide, they are able to react and they form a new product.

So we can see we have the reactant particles A, B, and these react with C.

And when they collide with each other, they have enough energy in order to react and form new products.

And the new products are A and B, C.

The rate of reaction, and this is the speed with which a chemical reaction takes place, can be affected by changing the concentration of the reactants.

When we increase the concentration of a solution, there are more reactant particles per unit volume.

Here we can see an animation and we have a low concentration of reactant in solution.

If we increase the concentration, you can see in this animation we have a high concentration of reactant in solution, and at a high concentration we have got more reactant particles, but in the same volume.

At a higher concentration, because we have more reactant particles in that same volume, the particles in a solution are closer together and therefore they are more likely to collide.

And remember, in order for the reaction to take place, these reactant particles need to collide with each other.

We have our low concentration of reactant solution and our high concentration of reactant in solution.

Increasing the concentration increases the rate of reaction.

As those particles are closer together, they are more likely to collide and therefore, we increase the frequency of successful collisions.

Time for a question.

What effect does decreasing the concentration of reacting solutions have on the rate of reaction? If we decrease the concentration of reacting solutions, will A, the rate of reaction decrease, B, the rate of reaction stay the same, or C, the rate of reaction increase.

The correct answer is A.

So we saw previously how if we increase the concentration of reacting solutions, we increase the frequency of successful collisions and therefore the rate of reaction increases.

The opposite then happens if we decrease the concentration.

If we decrease the concentration of reacting solutions, then we will decrease the frequency of successful collisions and the rate of reaction decreases.

Well done if you got that correct.

Time for a practise task and for this task, you need to complete the following sentences, using the words increases or decreases only.

Read through those sentences, decide whether those missing words are increases or whether they are decreases, and then come back when you're ready to go over the answers.

Let's see how you got on.

When the concentration of reacting solutions increases, the rate of reaction increases.

This is because at higher concentrations, the number of particles in the same volume increases and therefore the distance between the reacting particles decreases.

As a result of this, at higher concentrations, the frequency of successful collisions increases.

Well done if you filled in those missing gaps correctly.

We've had a look at the theory about how concentration can affect the rate of reaction.

Now we are going to move on to have a look at what the variables are when we are investigating the effect of concentration on the rate of reaction.

Izzy wants to investigate whether increasing the concentration increases the rate of reaction.

She reacts hydrochloric acid with magnesium and measures the volume of hydrogen gas formed over time, and we can see the reaction there.

We have magnesium and hydrochloric acid reacting together to produce magnesium chloride and hydrogen.

Izzy plans to repeat her experiment, changing the concentration of hydrochloric acid and investigating the effect this has on the rate of reaction.

To ensure this is a fair test investigation, Izzy needs to consider three main variables.

The independent variable, and this is the variable that we change or select values for.

The dependent variable, this is the variable that we measure or observe to get our results.

And the control variables and these are variables that must remain the same or constant throughout an investigation.

So the independent variable starts with an I, so we can think that's the thing that I change.

The dependent variable starts with D, that's the data that we are collecting and the control variable starts with con, that's the thing.

We are keeping constant.

Time for a question.

Izzy wants to investigate how changing the concentration of a reacting solution affects the rate of reaction.

Which of the following is a control variable for this investigation? Is it A, the time taken for the reaction? B, the concentration of the reacting solution? Or C, the temperature? A control variable for this investigation will be C, the temperature.

So well done If you chose option C.

Izzy is investigating how changing the concentration of hydrochloric acid affects the rate of the reaction.

And we can see the reaction that Izzy's using written there as a word equation for us.

She uses an upturned measuring cylinder to measure the volume of hydrogen gas produced in a certain time period.

And we can see an image there showing us how she will set up her equipment with the upturned measuring cylinder used to measure the volume of hydrogen gas that is produced.

Can you identify the independent, dependent, and control variables in Izzy's investigation? If you pause the video now and have a go at writing down these variables, then when you come back, we'll see how you got on.

Let's see if you were able to identify the independent, dependent, and control variables in Izzy's investigation.

The independent variable is the concentration of the hydrochloric acid.

That's the variable that she will be changing.

The dependent variable is the volume of hydrogen gas produced.

These are the measurements that Izzy is going to be recording and the control variables include the surface area and mass of magnesium.

She needs to keep these constant throughout the investigation.

The volume of hydrochloric acid that's used and also the temperature.

Hopefully you got the independent and dependent variable correct and you were able to identify some of those control variables.

We have had a look at the theory and the variables.

Now we are going to move on to have a look at the equipment and method for investigating the effect of concentration on the rate of reaction.

To determine the rate of reaction, we need to know the amount of reactant that's used in a given time.

And we can use this equation here to work out the rate of reaction.

We can do the amount of reactant used divided by the time taken.

Or to work out the rate of reaction, we can use the amount of product made in a given time so we could do the amount of product made divided by the time taken to work out the rate of reaction.

If one of the products is a gas, we can use an upturned measuring cylinder like Izzy did to measure the volume of gas produced in a given time.

Here we can see the equipment set up for us.

We have the reaction mixture.

Here we have a strip of magnesium and hydrochloric acid in our reaction mixture.

These are in a conical flask.

We have a bun placed on the top and a delivery tube so the hydrogen gas that is produced can travel out of the conical flask and down the delivery tube.

We have water in a water trough and an upturned measuring cylinder.

And our upturned measuring cylinder will be filled with water.

And as our gas is produced, it'll bubble up through the measuring cylinder and displace the water and we will at the top have our collected volume of gas.

This method works well for chemical reactions that produce large volumes of gas at moderate rates.

Gas syringes are another way we can measure the volume of gas produced during a chemical reaction.

So we don't always have to use an upturned measuring cylinder.

We could use a gas syringe.

Gas syringes are ideal for chemical reactions that produce a small volume of gas.

And here we can see the apparatus set up.

We have our conical flask, which would have our reaction mixture inside and then the hydrogen gas or the gas that is produced in your reaction would travel up out of the conical flask through the delivery tube and to the gas syringe and here you could measure the volume of gas that's being produced.

Which equipment can be used to measure the volume of gas produced in a reaction? Can we use A a gas syringe, B a pipette, C a conical flask, or D a measuring cylinder? The equipment that we can use to measure the volume of gas produced in a reaction is a gas syringe or an upturned measuring cylinder.

So well done if you identified both of those answers.

When measuring the production of gas over the course of a reaction, the results may look similar to this graph and we have the volume of gas in centimetres cubed on the Y axis and we have the time in seconds on the X axis.

And hopefully you can notice that the volume of gas that's produced per second is initially high.

So our curve starts off with a steep gradient.

And this is because initially for most reactions, we have a high rate of reaction.

And then as the reaction progresses, less gas is produced per second, so the rate of reaction decreases.

And finally we can see that the volume of gas remains constant.

And this is because no more gas is being produced because the reaction has ended.

When excess solution reacts with equal amounts of another reactant, the same volume of gas is produced for all concentrations of the solution.

Because we are using excess of our solution, it is not the solution that is determining the amount of gas product that we make.

Because this reactant is in excess, it is gonna be the other reactant that is going to be the limiting reactant.

So it doesn't matter what concentration we use of our solution that is in excess, we will still produce the same amount of product for each concentration.

Here we can see this shown on the graph.

We've got the volume of hydrogen gas that is produced in centimetres cubed and we've got the time in seconds and we have a high concentration of solution that has been reacted and a low concentration of solution that has been reacted.

And the final volume of hydrogen gas produced for the high and low concentration is the same because these reacting solutions are in excess.

Remember, it is the limiting reactant that is going to limit how much of the product that we produce.

What volume of gas will be produced when this experiment is repeated, changing only the concentration of the reacting solution that is in excess? We have a table and it shows us the concentration of the reacting solution.

We have one mole per decimeter cubed and a solution that has a concentration of two moles per decimeter cubed.

And we can see that when we used one mole per decimeter cubed concentration, the volume of gas produced was 25 centimetres cubed.

So what will be the volume of gas produced when we increase that concentration of the reacting solution? Will it be A 12.

5 centimetres cubed, B 25 centimetres cubed, or C 50 centimetres cubed? The correct answer is B, because this reacting solution was in excess, increasing the concentration from one mole per decimeter cubed to two mole per decimeter cubed does not have any effect on the volume of gas that we produce.

So we still produce 25 centimetres cubed even though we've changed the concentration of the reacting solution.

Well done if you got that question correct.

Time for another practise task.

And for the first part of this task, you need to plan a method to investigate the effect of changing the concentration of acid on the rate of this reaction.

And the reaction is magnesium reacting with hydrochloric acid and these react together to produce magnesium chloride and hydrogen gas.

So we are going to investigate the effect of changing the concentration of the hydrochloric acid and seeing the effect it has on the rate of this reaction.

You are provided with the equipment shown and you do not need to use it all, but you need to plan a method for this investigation.

If you pause the video now, have a go at answering this question.

Take your time making sure that you've got a detailed method that someone else would be able to follow.

Then come back when you're ready to go over the answer.

Let's see how you got on with planning a method to investigate the effect of changing the concentration of acid on the rate of a reaction.

Your method may be similar to this one here.

You can see from the diagram there, we are going to use an upturned measuring cylinder to measure the volume of gas produced.

You may have used a gas syringe as part of your method.

Step one, set up the water trough and upturned measuring cylinder using a clamp and clamp stand to secure in place.

Step two, place a strip of magnesium into a conical flask.

Step three, add 25 centimetres cubed of hydrochloric acid to the conical flask.

Step four, immediately add the bung and delivery tube.

Step five, record the volume of gas produced every 10 seconds until the volume remains constant.

And step six, then repeat the experiment using a different concentration of hydrochloric acid.

And you may have mentioned different concentrations of hydrochloric acid that could be used.

For the second part of this task, we are going to follow the method to collect results on the effect of concentration on the rate of reaction.

You will set up your apparatus as shown in the image and then work through those steps.

You will notice that we are going to use one mole per decimeter cubed of hydrochloric acid, first of all, and then we are going to change and use a different concentration of hydrochloric acid.

Remember to record your data in a results table.

Good luck on this investigation and I will see you when you have finished.

Here we have a sample set of results if you were unable to carry out the investigation or if you were unable to collect a full set of data.

We have got the time in seconds in the first row and we recorded measurements every 10 seconds.

We then in the second row have the volume of gas that was made using a 1.

0 moles per decimeter cubed concentration of hydrochloric acid.

In the final row, you can see that we have the volume of gas that was made using a different concentration.

We used a higher concentration of 1.

5 moles per decimeter cubed of hydrochloric acid.

And you will notice that we kept recording measurements every 10 seconds until the reactions had ended and we knew the reactions had ended because the volume of gas that was produced remained constant.

We have reached the end of today's lesson on concentration and rate practical using gas collection.

I hope that you've enjoyed the lesson.

Before you go, let's just summarise some of the key points we have covered in today's lesson.

The changing rate of a reaction can be found by measuring the amount of gas produced as the reaction progresses.

Increasing concentration of a reacting solution introduces more reactant particles so they collide more frequently.

And when reacting excess acid with equal amounts of magnesium, the same volume is produced for all concentrations of acid.

Well done for your hard work during today's lesson.

I hope that you're able to join me for another lesson soon.