Investiging the change in temperature which happens during the process of neutralisation
Investiging the change in temperature which happens during the process of neutralisation
Planning
The Aim
I intent to investigate the change in temperature which happens during the process of neutralisation. I shall use Hydrochloric acid as my acid, and Sodium Hydroxide as my alkali.
Variables
There are a number of factors, which I could investigate in this experiment, that would effect the temperature change of the solution;
* The concentration of the Hydrochloric acid
* The concentration of Sodium Hydroxide
* The volume of acid and alkali
Independent Variable
The factor that I will change during this investigation shall be the concentration of the Hydrochloric acid used. I intend to use five different concentrations;
1. 0.1M
2. 0.5M
3. 1.0M
4. 1.5M
5. 2.0M
Dependant Variable
The factor that I shall measure throughout my experiment, will be the temperature change in the solution of alkali and acid. I intend to do this by
1. Measuring the initial temperature change in the solution of acid
2. Adding the alkali
3. Measuring the temperature after it levels off
4. Record the difference between the two in a table
Controlled Variables
There are a number of factors that must be kept the same throughout the experiment;
* Concentration of Sodium Hydroxide
* Volume of acid
* Volume of alkali
I intend to keep the volumes constant throughout the experiment by using a measuring cylinder to measure out the quantities of each liquid, while taking the meniscus level into account in each case.
Hypothesis
Before stating my prediction of what will happen within this experiment, I will demonstrate and make reference to my background knowledge.
Acids and alkali's react together to form neutral substances, a process scientifically known as neutralisation. The strength or weakness of an acid or alkali is measured on a scale of pH. E.g. A strong acid will be of a pH about the 1.5 mark, whereas a strong alkali will have a pH of approximately 14, (a pH value of 7 is neutral).
Acids are soluble in water, and produce solutions with a pH of less than 7. They will turn litmus paper red and turn universal indicator an orange/red colour. Acids react with metals which are above Copper in the reactivity series, to form a metal + a salt; e.g.
Magnesium + Sulphuric Acid ( Magnesium Sulphate + Hydrogen
Acids also react with metal oxides, but produce salts and water;
Magnesium Oxide + Sulphuric Acid ( Magnesium Sulphate + Water
Acids react with carbonates to give a salt, carbon dioxide and water. Acid solutions also conduct ...
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Acids are soluble in water, and produce solutions with a pH of less than 7. They will turn litmus paper red and turn universal indicator an orange/red colour. Acids react with metals which are above Copper in the reactivity series, to form a metal + a salt; e.g.
Magnesium + Sulphuric Acid ( Magnesium Sulphate + Hydrogen
Acids also react with metal oxides, but produce salts and water;
Magnesium Oxide + Sulphuric Acid ( Magnesium Sulphate + Water
Acids react with carbonates to give a salt, carbon dioxide and water. Acid solutions also conduct electricity but are also decomposed by it, which shows that the acids consist of ions, which suggests that all acids contain H+ ions. Acids are defined as substances that can denote H+ ions.
Bases are the chemical opposite to acids. Bases take H+ ions rather than donate them. Alkali's are a special kind of base (bases that are soluble in water). All alkali's, except for ammonia are the hydroxides of highly reactive metals. Alkalis have similar properties to acids, they are soluble in water and they are electrolytes..
Alkalis form solutions with a pH value above 7. They turn litmus paper blue and also turn universal indicator a green, purple or blue colour. Alkali's react with acids to give a salt and water. This is called a neutralisation. For example;
Nitric acid + Calcium Hydroxide ( Calcium Nitrate + water
Alkalis also react with metal ions, and when they do, a solid precipitate is formed.
Redox reactions are reactions, which involve oxidisation and reduction. Oxidation can be defined in three ways;
1. The gain of electrons by a substance
2. The loss of hydrogen by a substance
3. The loss of electrons by a substance
Hydrochloric Acid + Magnesium oxide ( Magnesium Chloride + Water
In the previous example, the Hydrochloric acid has been oxidised, due to the fact that it has lost hydrogen. The magnesium oxide has been reduced, as it has lost oxygen.
In a redox reaction there are both reducing and oxidising agents at work. The reducing agent itself is normally oxidised and the oxidising agent is usually reduced. Therefore in the above example, the Hydrochloric acid was the reducing agent and the Magnesium Oxide was the oxidising agent.
If a chemical reaction produces heat in the surroundings, it is called an exothermic reaction. If, however, the reaction takes in heat, it is called an endothermic reaction. In these (endothermic) reactions, bonds are broken which takes in energy. In exothermic reactions, new bonds are made which produces energy.
When fuel is burnt, bonds have to be broken, which takes in energy. New bonds are then formed, which gives out energy. If more energy is given out than taken in, the resultant reaction is exothermic.
Exothermic and endothermic reactions can be shown as energy diagrams.
Reaction rates can be measured in a number of ways. The simplest way is to just measure the time that it takes for the reaction to be completed i.e.
Reaction Rate =1/Time Taken
When we increase the concentration of the reactant particles, the reaction rate increases. If the concentration is increased, it means that there are no more reactant particles in the substance, which are needed for the reaction to successfully occur. The reaction occurs when the particles collide, and the greater the concentration of the particles, the more likely it is and the more frequently (in theory anyway) they will collide. When the reaction takes place, bonds are formed and broken. The faster the reactions take place, the more bonds can be made , therefore giving off more heat. Therefore, the greater the concentration, the faster the reaction, and therefore more heat given off.
Apparatus
Measuring cylinder (100ml)
Hydrochloric acid (0.1M, 0.5M, 1.0M, 1.5M, 2.0M)
Sodium Hydroxide (1M)
Beaker (100ml)
Plastic cup
Thermometer
Method
. Collect apparatus
2. Measure 25ml of Hydrochloric acid using a measuring cylinder and pour it into the plastic cup
3. Place the plastic cup into the beaker
4. Using a thermometer, measure the temperature of the acid and record it
5. Measure 25ml of Sodium Hydroxide using another measuring cylinder , so the neutralisation process will not start yet
6. Add the sodium hydroxide to the acid and stir it with the thermometer
7. When the new temperature levels off, record the final temperature
8. Work out the change in temperature between the two measurements
9. Repeat steps 2-8 using the different concentrations of Hydrochloric acid stated previously
0. Combine the two sets of results into one single set of average results
1. Put these results into a graph, with concentration along the x-axis and temperature change along the y-axis
Safety
. Handle acid with care, as it could be dangerous
2. Wear safety glasses to protect your eyes
3. Obey standard classroom experimental procedures
Results:
25cm Acid
25cm Alkali
Temperature change (oC)
Average temperature Change(oC)
0.25M
M
+4
+3.5
+3
0.5M
M
+5
+5
+5
.0M
M
+8
+8
+8
.5M
M
+8
+7.5
+7
2.0M
M
+7
+6.5
+6
Interpreting and evaluating
From my results, it is obvious that a clear pattern has emerged. The pattern was as follows;
As the concentration of the acid was increased, the temperature change went up.
This occurred until a certain point when the temperature changed levelled off at approximately 8 degrees centigrade. This explains why the graph which I have drawn, initially is rising but becomes flat at the end. This co-insides with my hypothesis.
Previously, I predicted that as the concentration of the acid was increased, that the temperature change would also rise, again this would only occur up until a certain point.
Explanation
Within chemical reactions we measure the reaction rate or its speed. There are many factors that can be altered in order to increase the reaction rate for example temperature and concentration. When we increase the concentration of the acid, there are more reactant particles in the substance. For the reaction to take place, these particles must collide and when there are more particles there shall be more collisions and therefore a faster reaction rate.
When a reaction takes place, bonds are formed and also broken, this both takes in and produces heat. When the reaction rate is increased, there are more bonds formed, which generates heat. Therefore when the concentration of the reactant is increased, the reaction rate increases and therefore there is a greater heat gain. After certain point, the heat change will remain the same. A higher concentration would continue to give the same result, in this case, 8 degrees centigrade
I believe that my method was a good and efficient way of carrying out the experiment, it provided me with good convincing results. There was however one renegade result as it was just outside what I believe from my experiment to be the correct curve, the result was for 0.75M acid. This however, could have been because this specific concentration of acid, I had to prepare myself. I still believe however that my results are convincing as they form a clear cut curve, and that is the result of two sets of results which were both taken to minimise error.
If I were to repeat the experiment I would look very carefully at the meniscus of the acids and alkalis in order to achieve more accurate measurements. I would also take more time to take care of cleaning beakers and test tubes.
Conclusion
In conclusion I can say that the concentration of acid is directly proportional to the temperature change of the solution, up to a certain point after which the temperature remains constant.
