﻿Hello everyone, I hope you're all doing great. It's me again, Dr. Deng. And welcome back to chemistry, where we are going to continue looking at the rates and extent of chemical change. I hope you're excited because in this lesson, we're going to look at the first required practical in this unit. Where we will investigate the effect of changing concentration on the rate of reaction. So before we begin, make sure you find yourself a quiet space where you can sit and work through this lesson without any distractions. Switch off your mobile phones and close all the tabs on your device so you can make the most of this lesson. When you're ready, let's get started. We are going to start this lesson by recapping the different factors that affect the rate of reaction. But focusing on changing concentration of reactants in a solution because this is what we will be looking at in our required practical. Next, we are going to move on to our required practical. Where we will learn what a hypothesis is and how to write a hypothesis for a particular investigation. We will also go over how to write a method for a practical. And we will talk about the variables that are changed, measured, and controlled. Then finally, we are going to look at how to display data from our practical appropriately. And draw conclusions from our results. In terms of equipment that you need for this lesson. You'll need a writing pen, paper, pencil, rubber, and a ruler. If you do not have any of these on you right now, please pause the lesson and go and get your equipment. Then resume when you are ready. So let's go over the five different factors that affect the rate of reaction. Do you remember what they are? Here are the five factors that will affect the rate of reaction. The first one is the concentration of reactants in a solution. Number two, the pressure of reacting gases. Three, the surface area of solid reactants. Four, the temperature. And number five, the presence of catalysts. We are going to focus on the first factor. Which is concentration of reactants in a solution. Now when we talk about how concentration affects rate, we are referring to reactions that take place in solutions. In the diagram on the screen, you can see two containers containing the same volume of solutions. However, we say that the second container on the right side is more concentrated. Why do you think that is? That's right, we can see that it contains more reacting particles than the container on the left. Even though they both contain the same volume of solution. So what happens to rate of reaction when we increase the concentration? The higher the concentration of reactants in a solution, the more number of reacting particles per unit volume. And therefore, particles will collide more frequently and this will increase the rate of reaction. Now it's also important to note that the mean energy of the particles does not change. So these reacting particles do not collide with more energy. They simply collide more frequently. So when we are talking about how frequently these successful collisions are happening, we are referring to the number of collisions over time. So for example, five collisions per second. So before we move on, let's do a quick check to make sure you've understood what we've gone through. Pause the lesson here to answer the question. Then resume when you are finished. Well done, let's take a look at the answer. When the concentration of reactants in a solution increases, the more number of reacting particles per unit volume. The particles will collide more frequently and therefore, the rate of reaction will increase. When we are explaining how different factors affect rate of reaction, we must include key terms. Some of these key terms have been underlined in the answers here. And remember to always make reference to collision theory. Now we are going to move on and look at the required practical. This part of the lesson is extremely important as you can be assessed on this particular required practical in your exams. So you must make sure you learn this well. Let's begin by writing a hypothesis. This is very important before we start carrying out any practicals. So what is a hypothesis? Hypothesis, is a prediction made about a scientific investigation with limited evidence to begin with. However, we can use our scientific knowledge to make these predictions. In this required practical, we will investigate the effect of changing the concentration of hydrochloric acid on the rate of reaction when reacting with magnesium. Magnesium is a solid at room temperature. But hydrochloric acid is a solution. So we can link this back to what we talked about earlier on regarding change in concentration on rate. So in our hypothesis, we need to say what will happen to the rate of reaction when we increase the concentration of hydrochloric acid. Pause the lesson now to have a think. You can also write this down on your piece of paper. Then resume when you are finished. Off you go. Well done, now let's see if you were able to come up with a hypothesis using the knowledge that you have learned previously. For this reaction, the hypothesis is. Increasing the concentration of hydrochloric acid increases the rate of reaction when reacting with magnesium. Well done if you got that right. Now let's take a look at how to plan and write a method to describe this investigation. In our previous lesson, we talked about what a good method should look like. So first, you can either draw a labelled sketch of the equipment setup. Or you can use the one that is already provided to you to help you describe the steps. Typically, we will write the method using numbered stages. And in our method, you must use imperative verb. What this means is that the sentences should sound like you are giving an order, or giving a command. You must also remember to be precise when we are naming the equipment you used. For example, we are going to use conical flask to hold the reactant in our required practical. So the equipment is, conical flask. Remember, we don't just use test tubes and beakers in the lab. There are other equipment too. We must also use precise values when describing an investigation. We must mention the exact quantities of reactants that we are going to use. So the person who is reading the method is absolutely clear when they are following the method. Sometimes the results that we obtain may not be as predicted. So it's good practise to repeat an investigation three times to find a mean to discount any anomalous results. And step four, we are going to list the independent, dependent, and control variables. So first, let's take a look at a labelled sketch for the equipment setup for our required practical. We are going to react magnesium with different concentrations of hydrochloric acid to make magnesium chloride salt and hydrogen gas. Now as hydrogen gas is going to be produced, we can determine the rate of reaction by collecting and measuring the volume of gas produced over time. There are two methods that we can use to collect and measure hydrogen gas. This is the first method. Where we can place an inverted measuring cylinder or a measuring cylinder that is upside down in a trough of water. The measuring cylinder will be filled with water to begin with, but the hydrogen gas produced will displace the water in the measuring cylinder. Which will allow us to measure the volume of hydrogen gas. Let's take a look at the second method. We can also collect and measure hydrogen gas produced over time using a gas syringe. This is the method we are going to use in our required practical, in this lesson. So let's describe this investigation before we carry out the practical. So this is the method to describe our investigation. Please pause the lesson here. So you can read through these steps. Then resume when you have finished. Let's identify the independent, dependent, and control variables for this particular investigation. The independent variable is the variable that we are going to change. Dependent variable refers to the variable that we are going to measure. And control variables are the variables that we are going to keep the same throughout the entire investigation. If you are confident identifying the variables for this required practical, you can pause the lesson now and write these down on your piece of paper. If not, please continue listening so we can identify these variables together. So what is the variable that we are going to change? Remember, we are looking at how different concentrations of hydrochloric acid affect the rate of reaction when it reacts with magnesium. So we are going to be changing the concentration of hydrochloric acid, which is our independent variable. The unit for this is molar. The variable that we are going to be measuring, as we said earlier on, is the volume of hydrogen gas produced. And the unit for this, is centimetre cubed. The variables that we must keep the same in order for our results to be valid and reliable are. The volume of hydrochloric acid must be kept the same. The mass of magnesium ribbon must also be the same. And finally, we must also keep the temperature the same. As any changes in one of these control variables can make our results invalid. Okay, so let's watch a video on how this required practical is carried out. So here we have all equipment ready. We are going to start by measuring out 20 centimetre cubed of one molar hydrochloric acid using a measuring cylinder. Then pouring this into the conical flask. For this practical, we are going to use two two centimetre magnesium ribbon. But before adding them into the acid, we need to clear our workspace. So nothing gets in our way. We are also going to check that the gas syringe is working. Especially the inner plunger. Getting our timer ready. Then adding the magnesium ribbon into the conical flask. Start the timer, and closing the conical flask with a rubber bung that is connected to the gas syringe with a delivery tube. We will start to see the inner plunger of the gas syringe moving outwards as hydrogen gas starts to fill the gas syringe. We're going to record the volume of gas produced every 20 seconds for three minutes. Then we will repeat this three times to find a mean. We will repeat this procedure, using the other two concentrations of hydrochloric acid. This is another method we can use to collect and measure the hydrogen gas produced from this reaction. By displacement using an inverted measuring cylinder in a trough of water. I've got my colleague, Ms. Whittick here. Who's going to demonstrate how this is done. First, she's going to measure out 20 centimetre cubed of one molar hydrochloric acid using a measuring cylinder at eye level before pouring this into the conical flask. She has a stopwatch ready. So she can take a reading every 20 seconds for three minutes. Then, she's going to add the magnesium ribbon into the conical flask and start the timer on the stopwatch. Then closing the conical flask with a rubber bung that is connected to a delivery tube. This will allow the gas to displace the water inside the inverted measuring cylinder. Every 20 seconds she's going to take a reading and record the volume of hydrogen gas produced. She repeats this three times to find a mean. And repeats the entire procedure with the other two concentrations of hydrochloric acid. Okay, now let's head back to the slides so we can take a look at the data that we've collected. So I've collected all this data from the required practical. Which I've recorded in this table. You can see how I have clearly displayed my results in this table which will allow me to plot a graph and find rates of reaction effectively. So let's take a look at how the data is going to look when plotted on a graph. So here's a graph showing the volume of hydrogen gas collected over time for the three different concentrations of hydrochloric acid. Which line do you think represents the reaction with the highest concentration of hydrochloric acid is used? Excellent, it is the line that is the steepest. And also finishes the soonest compared to the reactions using the other two lower concentrations of hydrochloric acid. So we can draw a conclusion from this and referring back to the hypothesis. What is the conclusion for our investigation? The higher the concentration of hydrochloric acid, the greater the rate of reaction with magnesium. And we can explain this using collision theory by saying the higher the concentration of reacting particles, the more particles there are per unit volume. Therefore, the particles will collide more frequently and the rate of reaction will increase. So how confident are we feeling about our results and this conclusion that we've made? This is where we are going to look at reproducibility. So in order to ensure that our results are correct, we can check reproducibility. What this means is that we can get someone else to follow our method and see if they obtain similar results to ours. If the results are similar, we can be confident in the method that we have used. If not, the method that we used might not be suitable. Now what I would like you to do is complete a couple of exam style questions independently. Here's your task. For question two, where you are asked to plot a graph and draw a line of best fit. You can either do this on graph paper that you have at home. If you don't have a graph paper, there's one available for you to download and print out from the downloadable resources, or worksheet. Pause the lesson here to complete this task. Then resume when you have finished. Excellent work. Now let's check your answers. Here are the answers for the first question. You can pause the lesson here to assess your work. Here's the answer for question two, where you have been asked to plot a graph and draw a line of best fit. I have listed the success criteria on the side. So you can check if you have met each one. Pause the lesson now to assess your work. And finally, here are the answers for questions three and four. Pause the lesson again to check your answers. Okay now let's summarise what we have learnt in this lesson. At the beginning, we recapped the five different factors that affect the rate of reaction. Do you still remember them? Then we looked at the required practical, where we learnt what a hypothesis is and how to write a hypothesis for our particular required practical. We then conducted our required practical, where we collected data to plot a graph and then draw conclusions from our results. And finally, we looked at what reproducibility is and how to check for reproducibility. We have now arrived at the end of this lesson. There are downloadable resources and a worksheet for you to complete after watching this lesson. Please make sure you also complete the exit quiz so I know how well you've been listening. I hope you found this lesson useful and I look forward to seeing you in our next lesson. Where we will look at the second required practical in this unit. Thank you for joining me in this lesson and I will see you soon. Bye!

In this lesson, students will complete the required practical: Investigate the effect of concentration on the rate of reaction by a method involving measuring the volume of a gas produced.
Students will go over the variables to change, measure and control. At the end of the required practical, students will learn how to display data appropriately and how to check reproducibility.

Combined Science

Y11 Combined Science (Foundation)

Key Stage 4

Year 11

Rate of reaction required practical (Part 1)

The rate and extent of chemical change (FT)

UNIT

Rate of reaction

Collision theory

Planning an investigation to find rate of reaction

Rate of reaction required practical (Part 2)

Effect of changing surface area on rate of reaction

Effect of changing temperature on rate of reaction

Effect of changing pressure on rate of reaction

Catalysts

Reversible reactions

The Rate and extent of chemical change: Review (Part 1)

Chemistry

Y11 Chemistry

The rate and extent of chemical change

Rate of reaction using graphs and tangents

Le Chatelier's principle: Effect of changing concentration and temperature

Le Chatelier's principle: Effect of changing pressure

Le Chatelier's principle: Uses in industry

The Rate and extent of chemical change: Review (Part 2)

Y11 Combined Science (Higher)

The rate and extent of chemical change (HT)

Lesson overview: Rate of reaction required practical (Part 1)

Intro Quiz

Video

Presentation

Worksheet

Exit Quiz

Transcript

11 lessons in The rate and extent of chemical change (FT):

16 lessons in The rate and extent of chemical change:

16 lessons in The rate and extent of chemical change (HT):