Required practical 3: Effect of temp on rate of reaction Flashcards
We are reacting sodium thiosulfate with hydrochloric acid, and measuring the temperature change of it.
Write out the equation
Na2S2O3 + 2HCl —>
2NaCl + SO2 + S + H2O
Write out the method for this practical
- Add 10cm of 1Moldm3 HCl to a test tube, and place this test tube into a plastic container which has a lid with two holes in it for space for two test tubes to slot in
There is also a piece of paper under it with a drawn cross under one test tube and no cross under the other.
Put this HCl in the hole without a cross under it - Use a measuring cylinder to add 10cm of 0.05moldm3 sodium thiosulfate solution to the second tube. Place this tube into the plastic container with a cross under it
Place the thermometer into the tube
. Record start temperature of this solution, then add 1cm of the HCl from the other test tube into it and immediately press start on timer
. Look down the tube from above and time how long it takes for the cross to disappear from view
- Record the final temperature of the reaction mixture, then pour the cloudy content of tube into sodium carbonate solution. This acts as a stop bath.
Now repeat but with hot water:
- Now add water from a hot tap to the plastic container (make sure it is no hotter than 55 degrees)
- Now measure out another 10cm of 0.05moldm3 sodium thiosulfate into a clean tube, and insert into plastic container hole with a cross under it
. Let it warm up for 3 minutes
Repeat steps 3 to 6 to obtain results for at least 5 temperatures
Why should you wear gloves and goggles
Because HCl is an irritant
Why should a lid be put over the plastic container with hot water in it
It will minimise the amount of toxic sulfur dioxide released that we could breathe in
Why is a sodium carbonate stop bath utilised in this reaction
Where do you keep it
Stop baths will be available throughout the whole reaction to neutralise the reactants at any point
Keep it in a fume cupboard
When the sodium thiosulfate / HCl mixture is poured into it, it stops the reaction occurring so no more toxic sulfur dioxide will be produced as gas, as the acid will be neutralised
How do you know when the stop bath has to be replenished
It is usually a pink colour, but when this fades (like in a titration) due to the acid being added, this means the sodium carbonate has been neutralised so will no longer work.
How should you draw your table for this reaction
Have initial temperature and final temperature recorded, and then calculate mean temperature the reaction was carried out in.
You want the initial and final temperatures to stay the same to keep temp constant
Then have the time taken for solution to go cloudy, under the temperature changes
How do you calculate the initial rate of reaction
It is directly proportional to the amount of sulphur produced divided by time taken for it to go cloudy
So basically 1/time because the amount of sulphur produced is fixed.
So use this to calculate rate of reaction for each temperature
How do you make the initial rate of reactions more easy to plot on a graph
Multiply each rate of reaction value by 1000 as before they were 0.003 etc
What do you plot on your graph
. Plot mean temperature on x axis, and rate of reaction on y axis
Why do higher temperatures increase rate of reaction
At a higher temperature, the particles have more kinetic energy so move around more so will collide more with each other which will transfer energy.
