For this investigation I will be doing a neutralisation reaction. The neutralisation reaction will need an acid and an alkali to be reacted together. This will produce a salt and water.
Acid + Alkali → Salt + water
The acid I will decide to use is hydrochloric acid. The alkali I will use is sodium hydroxide. I will react these two together in a polythene cup and record the temperature to tell weather it’s an exothermic or endothermic reaction.
The factor I will choose to vary is the concentration of the hydrochloric acid. To keep this a fair test I will have to keep the other the factors constant. The temperature will remain constant by using the room temperature (25°c). The concentration of the sodium hydroxide will be constant. I will only use one type of acid, which is hydrochloric acid and one type of alkali, which is sodium hydroxide. The only factor that will vary is the concentration of the hydrochloric acid by diluting it with water in order to investigate in this.
I will collect the apparatus needed to start my investigation. A diagram of the experiment will need to be drawn and from this I can then set up the experiment to start collecting evidence.
When a detailed diagram is drawn of the experiment I can then be able to collect evidence. To collect my evidence needed I will need to have the same volume of acid and alkali each time. Both the acid and alkali will measure 10cm3 each time. The two solutions will both be poured in a polythene cup to measure the temperature of the solutions when reacting. Before the acid and alkali react together I will obtain both their temperatures and then react them together.
To measure the hydrochloric acid and sodium hydroxide a measuring cylinder will be used. A polythene cup will be used because it is a good insulator of heat and therefore when the reaction occurs heat will not be lost to the surrounding. A thermometer is used to measure the temperature to help me find out weather the reaction is exothermic or endothermic.
Apparatus list
∗ Polythene cup
∗ Measuring cylinder
∗ Beaker
∗ Thermometer
∗ Stopwatch
Diagram
Hydrochloric acid and Sodium hydroxide
Thermometer
Stopwatch Polythene cup
The apparatus will be collected and set up as indicated form the diagram. Once the experiment is set up and ready to go I can then start to collect the evidence needed for my investigation. When I measure the hydrochloric acid and sodium hydroxide in a separate measuring cylinder then they will be put together in the polythene cup to react. The thermometer will be put inside to measure the temperature of the energy transfer. The hydrochloric acid will measure 10cm3 and be poured into a beaker. I will record its temperature for two minutes and do the same method for the sodium hydroxide. Then they will be poured together to react.
Fair test
To keep this investigation fair, I must vary the temperature and keep the other factors constant. Separate measuring cylinders were used. One was used for the hydrochloric acid, another used for the sodium hydroxide and the last one for the water. The acid and alkali both measure 10cm3 each time.
Safety
While doing this experiment safety precautions must be taken seriously:
∗ During the experiment I stood up in case of any accidents.
∗ Goggles were worn in case of any acid or alkali splashed into my eye.
∗ Any bags or coats were put aside.
The evidence I am planning to obtain is weather a neutralisation reaction is affected by concentration. The hydrochloric acid will be diluted to make the concentration weaker. I will use a 1.0 molar hydrochloric acid and dilute this.
Here is how I diluted the acid.
Method
- Collect all the apparatus needed as indicated from the apparatus list.
- Set up the experiment by following the diagram.
- Pour 10cm3 of hydrochloric acid using a measuring cylinder.
- Pour the hydrochloric acid into a beaker and measure its temperature for two minutes by using a thermometer.
- Pour 10cm3 of sodium hydroxide using a measuring cylinder.
- Pour the sodium hydroxide into a beaker and measure its temperature by using a thermometer.
- Pour both hydrochloric acid and sodium hydroxide into the polythene cup.
- Stick in a thermometer to measure its temperature for two minutes by using a stopwatch.
- Collect the evidence and record it in a neat table.
- Do this procedure each time.
The plan I produced should help me get through this experiment nice and easy, as it has been analysed carefully. To get accurate results I will repeat the test five times and calculate an average reading by using the equipment as accurately as possible.
Hypothesis
My prediction is that as the concentration increases the temperature also increases. A neutralisation reaction will be an exothermic reaction because its making bonds. Bond making produces lots of energy and this energy is lost to the surrounding as heat. The reason for my prediction is because as the concentration becomes more diluted it will not contain much hydrogen and chloride ions and therefore not much bond making will occur. As a result of this not much energy will be created and heat will not be lost to the surrounding. If the hydrochloric acid is to be concentrated it will contain more hydrogen and chloride ions. As a result of this there will be much bond making and therefore more heat will be produced as a result of this. When heat is being produced it indicates a reaction is taken place. A reaction between two solutions is when bonds are being made and gives out heat. These reactions are called exothermic.
To plan this investigation I had to analyse this in more detail. To achieve this I used secondary sources:
A book called “Edexcel Modular Science”.
From this book I obtained some relevant information that will help me plan my investigation. I also did preliminary work to see what changes I had to make to my plan in order to have the best plan as possible. From this preliminary work I decided to use a suitable range of
- 0.8, 0.6, 0.4 and 0.2 molar.
This range is perfect to obtain the evidence needed. I will do five repeats for each concentration, which will make a total reading of 25.
I have obtained the evidence needed including repeats.
Results Obtained from Neutralisation Reaction
From this I was able to calculate the average.
Here is an example how I worked out the average.
1.0 molar
29 + 28 + 29 + 28 + 29 ÷ 5 = 28.6°c.
The results I obtained are enough to help me draw a conclusion. The equipment was used accurately to get the best possible results. The range I used was good as I got good reliable results.
The results I obtained were plotted on a graph to analyse the results in great detail. The results were plotted on a scatter graph with an appropriate line of best fit. From my graph I found out that as the concentration increases the temperature also increases. So I can say that the temperature is proportional to the concentration. A scatter graph was used because it will show any sort of trend in a clear way and will allow me to draw a line of best fit. The trend it shows is that as the concentration increases the temperature also increases.
Conclusion
From the graph I spotted a trend from the line of best fit. The concentration has an affect on the temperature as shown from the graph. When the reaction is taking place it is giving out energy in the form of heat. This means the reaction is exothermic. When heat is given out it means its making bonds. When a bond is being made it gives out a lot of energy from the work it’s done.
The bond making in the reaction I investigated is when the Na + (positive sodium) ions bond with the Cl• (negative chlorine) ions. These two ions react together to form a salt. The H + (positive hydrogen ion) ions bond with the O• (negative oxygen ions) ions to form water. This is a neutralisation reaction.
Acid + Alkali → Salt + Water
Hcl + Naoh → Nacl + H20
To from a salt the Na + ions must bond with Cl• .
Na + + Cl• → Nacl
To from water H + ions must bond with the 02• ions.
H+ + 02• → H20
I know this has happened because it is making bonds and as a result of this energy is being created to make bonds, giving out energy. The temperature increase, which is indicated by the thermometer. My results show an exothermic reaction.
My prediction I made was correct and was exactly what I expected, which is proved by my graph. My prediction matches my evidence well enough to say so and means I obtained correct and sufficient results.
Evaluation
My task did work out well. The reason it was good is because the results I obtained were accurate. This indicates that my task was done correctly. The method I created was done as accurately as possible just before starting the actual experiment. This is important because the procedures must be correct in order to obtain enough and accurate evidence. Overall my planning was good as I got through the experiment smoothly and getting the evidence needed, which were fair.
My evidence was accurate as shown by my graph I created and was accurate enough for the task. I drew a line of best fit, which was appropriate. From this I found out that my results show a strong relationship because some points on the graph were exactly on the line of best fit and some were just off.
As the line of best fit was drawn I spotted one anomaly and this indicates in a human error. There are a few possible ways that a human error could of occurred.
Reading the temperature of the thermometer incorrectly.
Measuring the quantities incorrectly.
A mistake in making the concentration.
This anomaly was just off the line of best fit, which clearly means it is not a bad result but not perfect. Overall the results I obtained were correct and is sufficient to support my conclusion and prediction. My evidence is enough to support my conclusion because the prediction I made was correct as shown from my results.
To improve my method to get more accurate evidence I would change steps 3 and 5. I would change them to “ Pour 10cm3 of hydrochloric acid using a measuring cylinder and pipette”. This change to step 3 would also apply to step 5. By doing this I could measure the quantities more accurately and obtain more reliable results.
The main problem with this investigation was reading the thermometer incorrectly. This would have an affect on my results. To over come this problem I could have used a digital thermometer. This is more accurate than a normal thermometer. By using this I could get rid of that anomaly to make it fit in with the line of best fit.
Further work could have been carried out to get additional relevant evidence. I could of done this experiment with different acids. By doing this I could see if different acids have any affect on a neutralisation reaction and if they follow the same rules as the hydrochloric acid.
