- temperature rise
- size of particles
- catalyst
- pressure
- turbulence
- pH
- surface area
- electric current
- concentration
- light.
There are three ways to measure the speed of a reaction and these are precipitation, change in mass and the volume of gas given off. The four things that are suitable for the magnesium reaction to affect how fast it takes place are temperature, turbulence, concentration and surface area. Concentration is the best for this magnesium reaction because it is easy to undertake.
The sorts of changes that normally take place during a chemical reaction are a colour change in the solution or the substance of the reaction, you might see bubbles and cloud and eventually the product disappear. You might also see a change in mass and the volume of the gas given off. In the case of magnesium and hydrochloric acid experiment you would see bubbles and cloud and the product disappear in a certain amount of time.
All reactions proceed at different speeds for example; one of the slowest is the rusting of iron and also slow is chemical weathering, like acid rain damage to limestone buildings. A really quick reaction is an explosion. Magnesium reacting with hydrochloric acid to produce a gentle stream of bubbles is a moderate speed.
Reactants are chemicals and substances that react when they are combined together and show that they are reacting by it bubbling, change of colour or the substance dissolves. Products are the gases that are given off when a reaction is taking place. The particles of the reactants during the chemical reaction move quicker and faster, are more squashed up, and are broken into smaller pieces.
We can change speeds of reactions in three ways:
- increasing the surface area
- increasing concentration
- raising the temperature
Surface area is increased to make the reactant that is a solid break up into smaller pieces. This is to create a bigger surface area for the particles around it to work on which will make more useful collisions.
Concentration is increased to make the particles of the reactant knock about between the water molecules, which makes the collisions between the important particles more likely.
The temperature is raised to make the particles move quicker, which will make more collisions to make the reaction go faster.
The chemical I will be using for my coursework is Hydrochloric acid. Magnesium will react with the chemical hydrochloric acid as follows:
My Experiment
Experiment 1
Aim
To show that changing the concentration of the hydrochloric acid with the magnesium ribbon will affect the rate of reaction. I will measure this reaction by timing how long it takes for the ribbon to dissolve completely in the acid with high to low concentration.
Preliminary work
Things we have done in class before we had started the experiment have helped me understand the whole idea of rates. We had been given a worksheet to do called ‘How Fast, How Slow?’ In this it had questions asking us to put some reactions they have named that take place at home and place them in order of the fastest one first, e.g. Cooking gas burning, Food digesting in the stomach, Gloss paint drying, Flesh decomposing, etc. I knew that 20cm³ and 2cm ribbon were the right amounts of acid and magnesium to use in my coursework. I found this out by trying various amounts and realised that this amount was just right as it lasted the right amount of time for me to finish the practical in the short time I have.
Prediction
I think that in my experiment when I change the acid by 2cm³ the time will double every time. This is my prediction because I know that magnesium reacts with acid so if the concentration is less then it will take more time for the magnesium to dissolve. Therefore, I predict that it will probably take double the time for every time the concentration is changed.
Apparatus list
30cm Ruler- to measure 2cm of the magnesium
Scissors- to cut the magnesium
Stopclock- measure the rate of each reaction
Beaker- for the solution to react in
2 measuring cylinders- 1 for the acid and the other for water to get the exact amount
2cm of magnesium
Hydrochloric Acid
Plan
- I will measure the acid using the measuring cylinder, this will give the exact amount of acid that the solution needs
- I will measure the water using the measuring cylinder, this will give the exact amount of water that the solution needs
- I will pour both the acid and water into the beaker, the compound is ready
- I will now add the 2cm magnesium to the beaker
- I will straight after measure the time the magnesium takes to dissolve using a stop-clock, this will give the time in seconds
- I will record the times in a table on a piece of paper.
Safety
- Wear safety goggles so that if the reaction spits you definitely wont get acid in your eyes
- Hold the acid bottle by the label so that if the acid spills down the side of the bottle it wont be the label side it will always be the other side
- Wipe it up immediately if the corrosive acid spills
Method
We will follow the plan. We shall change the amount of acid and water for each reaction we do. We shall also do this experiment again on each reaction to find out the average.
Observations
- First the solution was bubbling and so was the magnesium
- The solution then started to get cloudy and the magnesium had started to break down into smaller pieces
- The magnesium had after a certain amount of time depending on the amounts of water and acid had dissolved. Except when there was no hydrochloric acid in the solution
- At the end the magnesium had totally dissolved and had left the solution cloudy.
Analysis
I decided not to do some of the experiments because it took too long, like the last one I did not do 20cm³ water and 0cm³ HCl because the reaction would take infinity. I’ve found out that it takes more time for the magnesium ribbon to dissolve in diluted acid and takes less time in concentrated acid. For example the magnesium ribbon takes days to dissolve in 0.2m(diluted acid), and the ribbon takes 103.5s to dissolve in 1.8m(concentrated acid). The concentration affects the measured results alot. Changing the acid by 2cm³ each time made the times change in an irregular way. I have found this out by doing some simple sums:
I have not done the sums of 0.4m, 0.2m and 0m because they did not have digits to do a sum on they were ‘days’ and ‘infinity’. The sums I have done above tell me that changing the concentration by 2cm³ does not make the time double every time. Finding this out tells me that my prediction was wrong.
I think my results of this experiment have given these results because on the reaction with more acid there were more particles of reactant, which gives more chances of collisions. So that’s why the reactions with high concentration are quicker.
Conclusion
My results weren’t what I was expecting it to be I was expecting the time to double every time the concentration was changed. I think that maybe it hadn’t doubled every time I changed the concentration because of human error with measuring or timing. The results were really telling me that this is evidence that it has proven the theory made to be correct! Chemical reactions occur when particles of the reactants collide.
Evaluation
My method had worked to follow my plan and had gone all to plan. One time my plan had gone wrong because I had measured the wrong amount of acid to go in the beaker. I had started the stop-clock, the magnesium dissolved quite quickly, and then I realised that I predicted it was not meant to be quicker then the one I did before. So I had poured the whole solution back into the sink and done another one this time with the right amount.
The results I have are quite reliable because I had been making accurate measurements the whole time and had repeated it as well. To make my results more reliable I could have repeated it more times, but then that would need more time and I only had a certain amount of time to finish it in. In addition, I could have collected class results from other groups who did the exact same experiment as me.
There was one anomalous result when there was 0.6m acid and the time it took had risen more than double than the time it took for 0.4m acid. I think this had maybe happened because I had measured the timing wrong.
And thanks to WWW.COURSEWORK.INFO.COM
Deepak Tailor
11GS
Beal High School