Chemistry SC1 Investigation: How does the temperature affect the rate of reaction between sodium thiosulphate and hydrochloric acid?
Chemistry SC1 Investigation: How does the temperature affect the rate of reaction between sodium thiosulphate and hydrochloric acid?
Skill P - Planning:
Background:
Sodium Thiosulphate is white solid with the chemical formula Na2S2O3. It can be made by reacting sulphur dioxide with sulphur in boiling sodium hydroxide solution.
S + SO2 + 2NaOH › Na2S2O3 + H2O
Hydrochloric acid is a colourless, corrosive, non-flammable liquid. Its formula is HCl.
Factors that could affect the rate of reaction between sodium thiosulphate and hydrochloric acid:
* The concentration of the hydrochloric acid. If the acid has a high concentration e.g. 5moles/litre, it will react quicker than a less concentrated, more dilute acid.
* The concentration of the sodium thiosulphate will also affect the rate of reaction in the same way.
* The temperature of the sodium thiosulphate, thus the temperature the reaction will take place at, will affect the rate of the reaction. At lower temperatures, the reaction will take a long time, as little heat energy is available for the hydrochloric acid and sodium thiosulphate molecules to convert into kinetic energy. However, at higher temperatures, lots of heat energy will be converted into kinetic energy. The molecules will be moving around at higher speeds. This increases the chance of a successful collision, and hydrochloric acid and sodium thiosulphate molecules will easily have enough activation energy to join together. Temperature will be used as the factor in the final experiment.
* Whether a catalyst is present or not will, also, affect the rate of reaction. A catalyst speeds up the rate of a reaction and can be retrieves at the end chemically unchanged.
Trial experiments carried out:
A trial experiment was carried out to determine what concentration of sodium thiosulphate is to be used. Several concentrations were tested at room temperature, then at 50°C, (the thiosulphate concentration is 40g/litre):
* 20% sodium thiosulphate to 80% water
* 40% sodium thiosulphate to 60% water
* 60% sodium thiosulphate to 40% water
* 80% ...
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* Whether a catalyst is present or not will, also, affect the rate of reaction. A catalyst speeds up the rate of a reaction and can be retrieves at the end chemically unchanged.
Trial experiments carried out:
A trial experiment was carried out to determine what concentration of sodium thiosulphate is to be used. Several concentrations were tested at room temperature, then at 50°C, (the thiosulphate concentration is 40g/litre):
* 20% sodium thiosulphate to 80% water
* 40% sodium thiosulphate to 60% water
* 60% sodium thiosulphate to 40% water
* 80% sodium thiosulphate to 20% water
* 100% sodium thiosulphate to 0% water
These were all tested over a range of temperatures to find which concentration provided a suitable reaction time. In the end a 40% concentration of sodium thiosulphate was chosen.
Results of trial experiment:
Thiosulphate/water concentration
Time taken at room temperature (23°C)
Time taken at 50°C
20% / 80%
:25
0:37
40% / 60%
:10
0:23
60% / 40%
0:50
0:15
80% / 20%
0:35
0:12
00% / 0%
0:25
0:05
The thiosulphate/water concentration of 40% / 60% was chosen (this was made up of 20cm3 thiosulphate and 30cm3 water.) This concentration gave us will spread out results. Higher concentrations took very little time, and a larger % error if we were to get any anomalous results. More dilute mixtures took too long and, thus, were ruled out due to time restrictions when doing the actual experiment.
How the experiment will be carried out:
Apparatus required:
* 1x Tripod
* 1x Bunsen burner
* 1x Gauze
* 1x Heat-proof mat
* 1x Tile with black cross on it
* 1x Stopwatch
* 1x 100°C thermometer
* 6x 150cm3 beakers
* 6x 50cm3 water/sodium thiosulphate mixture (20cm3 thiosulphate and 30cm water)
* 6x 5cm3 2M/litre hydrochloric acid
Diagram of how the apparatus will be set up:
Method:
The apparatus will be set up as shown on the previous page. The sodium thiosulphate (40g/litre) / water mixture (20cm3 thiosulphate and 30cm3 water) will be heated to the desired temperature, then placed on the tile with a thick, black cross drawn on it. The cross will be observed from above, the 5cm3 of 2M/litre hydrochloric acid added and the timer started. The reaction will be observed and the timer will be stopped when the reaction is completed and turns so murky, that the cross will no longer be visible from above. Each experiment at each temperature will be repeated twice. This is so we can get an average in results, rather than just one anomalous one. The results will first be recorded into a rough table, before being presented in neat table and graph form. The experiment will be carried out with the sodium thiosulphate at the following temperatures:
> 20°C
> 30°C
> 40°C
> 50°C
> 60°C
> 70°C
Control variables:
To make sure that this experiment is a fair test, the following procedures will be used:
* Different beakers will be used for each experiment at different temperatures (washing beakers out thoroughly and drying them is too time consuming.)
* The same concentration of hydrochloric acid and sodium thiosulphate will be used at each temperature. Only the independent variable, the temperature will be changed.
* The same person will observe the cross on the tile at each temperature until the reaction is completed. Some people's eyesight is impaired, thus it is important to have the same person observe the cross through the reaction at each temperature.
Safety procedures to be followed:
* Normal laboratory safety procedures will be followed, i.e. Lab coats to be worn along with safety goggles. Carrying out the experiment standing up, so if an accident were to occur, we could move away safely.
* Heatproof mats will be used to prevent the bench surface from becoming too hot.
* Care will be taken when operating the Bunsen burners.
* Extreme care will be taken when moving the beaker with the sodium thiosulphate in it, off the gauze and onto the tile, after it has been heated.
Treatment of results:
The results will first be noted down into a rough table. They will then be presented in a neat, well laid out table, and in a graph, with the temperature (°C) on the X-axis and the time taken (minutes and seconds) on the Y-axis.
My prediction of the results:
The independent variable chosen for this experiment is the temperature that the reaction will take place at. The dependant variable, the one we will record in our results is the time taken for the completed reaction. The temperature will affect the rate of the reaction. The higher the temperature, the quicker the rate of reaction, thus the reaction time will be less. At low temperatures e.g. 20°C and 30°C, the reaction will take much longer. This is because little heat energy is being given out from the sodium thiosulphate. Thus, little is transferred into kinetic energy for the hydrochloric acid and sodium thiosulphate molecules. The reaction time is longer, because, with little kinetic energy, the molecules are moving around slowly, the chances of a successful collision between molecules is low, and even so, in some collisions, there wont even be enough activation energy for the molecules to combine and react.
At higher temperatures, however, there is a lot of heat energy being converted into kinetic energy for the molecules. As they are moving around much faster, the chance of collisions between molecules is increased, and there will almost certainly be enough activation energy to combine the molecules. Thus the reaction time will be a lot less than the same experiment done at a lower temperature.
Olek Zydron 10MS