You have taken a certain amount of data for your coursework. However, to be fully certain of the conclusion you reach, you would want to look at some other sources. This extra information is known as secondary data. You take information from other people who have done the same experiment as you.
To get the minimum marks for this section, you will need to mention at least one extra set of data (you get given some by the exam board) and comment on the similarities and differences between this information and your own in your conclusion.
To get full marks for the secondary data, you will have to include data from several different sources (which you then reference). So take data from different groups as well as the exam board, and reference where the information is from. Describe and explain how much it supports or undermines your conclusion and explain how confident you are in this data, as well as why you are confident.
This is the section in which students struggle the most to get high marks
Showing posts with label Coursework. Show all posts
Showing posts with label Coursework. Show all posts
Tuesday, 4 February 2014
What's the Difference between a Conclusion and Evaluation?
There's often a lot of confusion about what goes into a conclusion and what is in an evaluation, and whether they are the same thing. Most of the confusion stems from the fact that they both talk about the experiment and the results (although given that we've spent so long working up to the experiment, it would be weird if they didn't). So what's the difference?
The evaluation involves looking at your experiment and seeing how you could have improved your technique. Evaluation looks at your results and asks if they show your experiment to have been performed well. It's like feedback on your performance - if you did the experiment again, what would you change? What new equipment might you use? Alternatively, explain why you think your method could not be improved.
If you had any outliers, mention them, or explain why you don't think you have any. Mention the range of data and error bars, and whether you feel they are acceptable (do the error bars overlap?). The evaluation looks at the accuracy and repeatability of the results. The exam board prefers the word 'repeatable' to 'reliable'. Repeatable means that if you did the experiment again, you could expect to get the same results and explain why.
The conclusion will relate back to the hypothesis. Did you prove your hypothesis correct? If you did, why are you so sure? The conclusion will also mention the results (the degree of scatter etc), but this time it's to do with how confident you are in the fact that they have proved your hypothesis. You need to bring in scientific knowledge again, this time to explain why you think the hypothesis is supported by your results. You could also talk about what extra data or further experiments would make you even more confident in your results. The conclusion will also bring in secondary data to prove your point. What is secondary data, I hear you ask? That's for another post...
The evaluation involves looking at your experiment and seeing how you could have improved your technique. Evaluation looks at your results and asks if they show your experiment to have been performed well. It's like feedback on your performance - if you did the experiment again, what would you change? What new equipment might you use? Alternatively, explain why you think your method could not be improved.
If you had any outliers, mention them, or explain why you don't think you have any. Mention the range of data and error bars, and whether you feel they are acceptable (do the error bars overlap?). The evaluation looks at the accuracy and repeatability of the results. The exam board prefers the word 'repeatable' to 'reliable'. Repeatable means that if you did the experiment again, you could expect to get the same results and explain why.
The conclusion will relate back to the hypothesis. Did you prove your hypothesis correct? If you did, why are you so sure? The conclusion will also mention the results (the degree of scatter etc), but this time it's to do with how confident you are in the fact that they have proved your hypothesis. You need to bring in scientific knowledge again, this time to explain why you think the hypothesis is supported by your results. You could also talk about what extra data or further experiments would make you even more confident in your results. The conclusion will also bring in secondary data to prove your point. What is secondary data, I hear you ask? That's for another post...
Monday, 3 February 2014
Evaluation: How Could I Be More Accurate in my Coursework?
There are a lot of things we could have done to improve the accuracy of our coursework. For example, we could have used different beakers for each concentration to avoid cross-contamination. We could have pre-mixed the different dilutions in the lab, to ensure we did it correctly, rather than diluting as we went.The temperature is another factor that may have changed during the experiment - how could we have prevented this happening?
There are a few pieces of equipment we could have used instead:
Volumetric flask (Pictures available here) - this piece of equipment is used to dilute solutions, and the long neck allows us to be very accurate about the amount of liquid that we add. It would have allowed us to dilute the acid with much greater accuracy
Colorimeter (Pictures available here) - a colorimeter is a fancy machine that shoots lasers at a solution and calculates how much of the laser is able to pass through the liquid. From this you can work out how much of the light is blocked, or how cloudy the liquid is. We could have performed a much more rigorous experiment in which we took a colorimeter reading of the different reactions every 10 or 30 seconds.
As this equipment is expensive, we could instead have used a simple colorimeter, which consists of a light dependent resistor attached to a multimeter and power pack. We could have placed the resistor under the beaker and noted the current through the resistor at different times in the experiment, or stopped our stopwatch whenever the current reached a certain value.
Electric Stirrer (there are a lot of different variations of this - type magnetic stirrer or laboratory shaker into Google Images) - if you stirred your solution, there is a chance that you stirred different ones with a different amount of force. To prevent this happening, you could have used one of these specialised pieces of equipment. It would be a little bit of overkill in our experiment, but there's no harm in mentioning it, just to show that you're aware of how to improve.
There are a few pieces of equipment we could have used instead:
Volumetric flask (Pictures available here) - this piece of equipment is used to dilute solutions, and the long neck allows us to be very accurate about the amount of liquid that we add. It would have allowed us to dilute the acid with much greater accuracy
Colorimeter (Pictures available here) - a colorimeter is a fancy machine that shoots lasers at a solution and calculates how much of the laser is able to pass through the liquid. From this you can work out how much of the light is blocked, or how cloudy the liquid is. We could have performed a much more rigorous experiment in which we took a colorimeter reading of the different reactions every 10 or 30 seconds.
As this equipment is expensive, we could instead have used a simple colorimeter, which consists of a light dependent resistor attached to a multimeter and power pack. We could have placed the resistor under the beaker and noted the current through the resistor at different times in the experiment, or stopped our stopwatch whenever the current reached a certain value.
Electric Stirrer (there are a lot of different variations of this - type magnetic stirrer or laboratory shaker into Google Images) - if you stirred your solution, there is a chance that you stirred different ones with a different amount of force. To prevent this happening, you could have used one of these specialised pieces of equipment. It would be a little bit of overkill in our experiment, but there's no harm in mentioning it, just to show that you're aware of how to improve.
Tuesday, 28 January 2014
How to calculate concentration
The acid we used was 20g/dm3. This means that there were 20g of HCl for every 1 dm3 (a dm3 is 1000cm3, which means it's 1 litre). This is a measure of concentration.
If we dilute the acid, we can work out the new concentration. To do this, we must first work out how strong it is compared to the original solution. Do this by dividing the volume of acid in the solution by the the total volume. For example, if you used 10cm3 of acid, mixed with 10cm3 of water, that gives a total volume of 20cm3. Volume of acid / Total volume = 10 / 20 = 0.5
This tells us that the solution is half as strong as the full strength acid (this makes sense - half of the volume of the solution was acid).
As another example, if we used 5cm3 of acid and 10cm3 of water, that means 5cm3 (acid) / 15cm3 (total volume) = 0.333 or 1/3
Once we've calculated the ratio, then we can multiply this by the original concentration. Our original concentration was 20g/dm3, so in our first example: 0.5 x 20g/dm3 gives us a new concentration of 10g/dm3.
ALTERNATIVELY: concentration is also displayed like this: 0.5M [the capital M stands for moles per dm3, where a mole is the name given to a specific number of atoms or molecules]. If you prefer, you can use this as a value of concentration. The full strength acid is 0.5M, so in our first example, the solution would have a concentration of 0.5 x 0.5 = 0.25M
If you put a column in your results table showing the concentration of the acid solution, that'll make your results look a lot more professional.
If we dilute the acid, we can work out the new concentration. To do this, we must first work out how strong it is compared to the original solution. Do this by dividing the volume of acid in the solution by the the total volume. For example, if you used 10cm3 of acid, mixed with 10cm3 of water, that gives a total volume of 20cm3. Volume of acid / Total volume = 10 / 20 = 0.5
This tells us that the solution is half as strong as the full strength acid (this makes sense - half of the volume of the solution was acid).
As another example, if we used 5cm3 of acid and 10cm3 of water, that means 5cm3 (acid) / 15cm3 (total volume) = 0.333 or 1/3
Once we've calculated the ratio, then we can multiply this by the original concentration. Our original concentration was 20g/dm3, so in our first example: 0.5 x 20g/dm3 gives us a new concentration of 10g/dm3.
ALTERNATIVELY: concentration is also displayed like this: 0.5M [the capital M stands for moles per dm3, where a mole is the name given to a specific number of atoms or molecules]. If you prefer, you can use this as a value of concentration. The full strength acid is 0.5M, so in our first example, the solution would have a concentration of 0.5 x 0.5 = 0.25M
If you put a column in your results table showing the concentration of the acid solution, that'll make your results look a lot more professional.
Friday, 24 January 2014
Boosting your grade in the coursework
There are a number of things that you can include in the coursework to boost your grade.
Rate column in the table: the rate of a reaction is the speed at which a reaction takes place. So a faster reaction will take less time than a slow reaction. The rate of a reaction can be expressed by finding 1 / time. If you add a column to your table showing Rate as 1/ time, this will net you some bonus points, especially if you make a graph of this vs concentration.
Preliminary investigation: many experiments do a preliminary investigation to check and see what quantities are required before they perform the full experiment. For example, there's no point planning lots of different dilutions of acid if the time difference between each dilution was around 2 seconds... Before you do an experiment, if you're going to be very scientific, you need to check that you're using a suitable range of data. You could write in a section between your introduction and method that you did a preliminary test. In this preliminary test you used some rough dilutions to get an idea of how long it would take, and this would then allow you to decide the dilutions you would need for your final version.
There are some other examples of extra things we can put in, but they fit into the later sections, like the Conclusion and Evaluation, so we'll save them for later.
Rate column in the table: the rate of a reaction is the speed at which a reaction takes place. So a faster reaction will take less time than a slow reaction. The rate of a reaction can be expressed by finding 1 / time. If you add a column to your table showing Rate as 1/ time, this will net you some bonus points, especially if you make a graph of this vs concentration.
Preliminary investigation: many experiments do a preliminary investigation to check and see what quantities are required before they perform the full experiment. For example, there's no point planning lots of different dilutions of acid if the time difference between each dilution was around 2 seconds... Before you do an experiment, if you're going to be very scientific, you need to check that you're using a suitable range of data. You could write in a section between your introduction and method that you did a preliminary test. In this preliminary test you used some rough dilutions to get an idea of how long it would take, and this would then allow you to decide the dilutions you would need for your final version.
There are some other examples of extra things we can put in, but they fit into the later sections, like the Conclusion and Evaluation, so we'll save them for later.
Calculating Averages for Coursework
As you know, an average is calculated by finding the sum of all the values, and then dividing this by the number of different values (so if there are 3 different results, divide the total by 3).
When we take a reading on a stopwatch, we have to be careful when calculating the average. First you have to convert the value to seconds, then add up. Here's an example:
If I took two readings, one was 3:42:07 (that's 3 minutes, 42.07 seconds) and one was 2:56:39, if we tried calculating the average in minutes, we would probably do (3.4207 + 2.5639) / 2. That would give an answer of 2.9923. 2 minutes and 99 seconds? That can't be right, and it's because there are 60 seconds in a minute, whereas decimals work in 100s.
Instead we need to convert the values to seconds. 3:42:07 becomes 222.07 seconds (because 3 minutes is 180 seconds, and 180 + 42 = 222). 2:56:39 becomes 176.39 seconds. The average is 199.23 seconds.
To be honest, it's probably neater and easier to keep your answer in seconds...
When we take a reading on a stopwatch, we have to be careful when calculating the average. First you have to convert the value to seconds, then add up. Here's an example:
If I took two readings, one was 3:42:07 (that's 3 minutes, 42.07 seconds) and one was 2:56:39, if we tried calculating the average in minutes, we would probably do (3.4207 + 2.5639) / 2. That would give an answer of 2.9923. 2 minutes and 99 seconds? That can't be right, and it's because there are 60 seconds in a minute, whereas decimals work in 100s.
Instead we need to convert the values to seconds. 3:42:07 becomes 222.07 seconds (because 3 minutes is 180 seconds, and 180 + 42 = 222). 2:56:39 becomes 176.39 seconds. The average is 199.23 seconds.
To be honest, it's probably neater and easier to keep your answer in seconds...
Wednesday, 22 January 2014
Any other questions about the Coursework?
If you have any other questions about the coursework, email them to the usual address (westfieldacademyscience dot gmail dot com)
What's in an Investigation?
I've taken some of the wording from the mark scheme and put it up here. The S stands for Strategy, and so these marks are given for your planning and background knowledge.
S(a) – Write information about what affects a rate of reaction and
pick one factor to test. What is your hypothesis, and prediction and why have
you made this prediction.
This is your introduction. In it you can show off your knowledge about reactions, and even throw in a few diagrams to explain your points. Remember your hypothesis uses scientific knowledge to explain what you think will happen in your investigation from a theoretical perspective (think of particles and collisions), whereas your prediction is explaining the actual thing you will see (think of time taken for the beaker to change).
S(b) – Select and use appropriate techniques – how will you
do the experiment. Justify the technique, and explain your range of data
(including how many repeats). Complete full risk assessment, including how to
minimise any harm.
This will be your method. Your range of data is the different solutions you will use (this depends on what variable you pick). Remember to explain the repeats you will use and why. A good risk assessment can come separately to the method, as a separate section. Don't just mention the risks but explain how you can avoid them and stay safe.
Coursework Reaction
The reaction in this video is very similar to the reaction we will be doing in our investigation: http://www.youtube.com/watch?v=r4IZDPpN-bk
This video shows a variation on the reaction, some of the terms will be unfamiliar (the capital M eg 0.5M, refers to concentration): http://www.youtube.com/watch?v=HWvf7HUshJY
This video shows a variation on the reaction, some of the terms will be unfamiliar (the capital M eg 0.5M, refers to concentration): http://www.youtube.com/watch?v=HWvf7HUshJY
Monday, 20 January 2014
Coursework Example
Here is an example of a write-up by a student that has done a similar investigation to the one we're doing this year. It is very detailed and there's a lot more in there than you would be expected to do, but it helps to see what a finished piece might look like. The biggest difference is that we are only changing one variable, whereas the student investigated several different variables.
If you can't open this link, email me and I will send you a copy (the address is westfieldacademyscience [at] gmail [dot] com )
If you can't open this link, email me and I will send you a copy (the address is westfieldacademyscience [at] gmail [dot] com )
Sunday, 19 January 2014
Additional Coursework: Simulating Reactions
This simulation allows you to have a look at how changing different components in a reaction can have an effect on the rate. It's a little complicated, and more detailed than you'll need for your coursework, but playing with it will help you get comfortable with how to control a reaction: http://phet.colorado.edu/en/simulation/reactions-and-rates
The Rate Experiments tab is probably the best one for the coursework.
The Rate Experiments tab is probably the best one for the coursework.
Additional Science Coursework: Rates of Reaction
This year's Additional coursework is investigating the factors that affect how quickly a reaction takes place. As part of the write-up you will need to explain why the rate of a reaction is affected by these factors. While this link from BBC Bitesize is based on a different exam board (AQA rather than OCR), it covers the basics of a reaction well: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/reaction/ratesrev1.shtml
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