Investigate how the rate of the reaction between Sodium Thiosulphate and Hydrochloric acid can be altered.

To investigate how the rate of the reaction between Sodium Thiosulphate and Hydrochloric acid can be altered.

PLANNING

Sodium thiosulphate and hydrochloric acid are two clear coloured chemical liquids. When reacted together they produce sodium chloride, water, sulphur and sulphur dioxide.

When they react the solution turns cloudy and that is when the cross disappears and shows a reaction has taken place. The cross disappears as the reactants forms sulphur dioxide, this is what turns the solution cloudy.

I could change many key factors to investigate the rate of reaction between Sodium Thiosulphate and dilute hydrochloric acid. These key factors consist of Temperature, concentration or having a catalyst.

For my experiment the independent variables I have choose to investigate is temperature.

AIM: To investigate if temperature affects the rate of reaction between sodium thiosulphate and dilute hydrochloric acid.

PREDICTION: I predict that the higher you increase the temperature of the sodium thiosulphate the faster the reaction will be. I predict this because of the collision theory. The collision theory is when reacting particles collide with enough energy and force to cause a reaction. The reason I think that this will affect the rate of reaction in my experiment is because as we heat the solution the particles are going to be heated with a lot of energy. So this means there are more successful collisions per second therefore a faster reaction.

With less energy

EQUPIMENT: To carry out this experiment safely, accurately and getting reliable readings you will need:

Stop clock

100 ml measuring cylinder

10ml measuring cylinder

Dropper

Beaker

Bunsen burner

Tripod

Fireproof mat

Paper

Felt tip pen

Match

Thermometer

Safety goggles

PROCEDURE:

Measure out 50ml of sodium thiosulphate into the 100ml- measuring cylinder make sure its accurate use the aid of a dropper, to obtain precise volume.

Measure out 5ml of dilute hydrochloric acid into the 10ml-measuring cylinder; once again make sure its accurate use the aid of the dropper.

Then draw a 10cm by 10cm cross (x) onto a piece of plane white paper. The cross in thickness should be as thick as the nib of the pen.

Place the beaker on to the cross making sure the cross is in the centre of the beaker

Pour the two chemicals into the beaker and using the thermometer check the temperature of them.

As you pour the chemicals into the beaker start the stopwatch

Look down from a bird’s eye view into the beaker focusing on the cross

When the solution turns cloudy and you can’t see the cross any longer stop the stop clock immediately for accuracy

This time when repeating the experiment heat the sodium thiosulphate starting with 18’c (which was what out room temperature was) after its been poured into the beaker

Once poured into beaker heat for however long until the desired temperature which is 10 above 18 so therefore 28 is reached

When reached and the beaker ...

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As you pour the chemicals into the beaker start the stopwatch

Look down from a bird’s eye view into the beaker focusing on the cross

When the solution turns cloudy and you can’t see the cross any longer stop the stop clock immediately for accuracy

This time when repeating the experiment heat the sodium thiosulphate starting with 18’c (which was what out room temperature was) after its been poured into the beaker

Once poured into beaker heat for however long until the desired temperature which is 10 above 18 so therefore 28 is reached

When reached and the beaker is on the cross pour the dilute hydrochloric acid into the beaker and start the stop clock

Then carry on the experiment as explained above but after each time thoroughly rinse equipment and increase temp by 10’c until reaching 68’c.

Whilst doing experiment don’t forget to wear safety goggles at all times, tie long hair back and wear appropriate clothing and footwear.

Points being used to help make sure you obtain the most reliable and accurate result possible with the equipment

When measuring out measurements of the chemicals always use a dropper to be accurate so you can keep the volume exactly right, otherwise the test wont be fair and you will not get accurate results. This is because if the concentration of one of the chemicals is higher then the rate of reaction will be speed up.

Also when heating the sodium thiosulphate you must be watching the thermometer at all times to get the temperature as accurate as possible, or your results will not be accurate, there will be a larger decrease or increase depending on if the temperature is higher or lower in the rate of reaction then there is meant to be.

To make my experiment safe I will wear the appropriate clothing, eyewear and have my hair tied back. I will also make sure the Bunsen burner flame is on the safety flame when not in use and is kept away from other objects that could set alight. I will concentrate at all times and keep focused. I will also be careful and if I spill any chemicals then have a cloth ready to mop them up. Also if I get the chemicals on my skin to be ready to rise them off with cold water, for at least two minutes or more to prevent any burns or blistering.

OBTAINING EVIDENCE

Quite reliable well clustered results

ANALYSIS

From my graph (time and temperature) it seems as though my results are going up in tens for the first three sets then there seems to be a drastic change.

I studied my graph to find a mathematical link. I thought that if you increase the temperature by 10 the rate of reaction doubles. Although that is what I thought I could not find the link in my graph, I found no link what so ever.

My graph (time and temperature) shows negative correlation neither weak nor strong.

It also shows how temperature affects the rate of reaction. I predicted this because of the collision theory as you increase the temperature the time decreases as the particles collide more frequently causing more successful collisions per second. This causes a faster reaction.

EVALUATION

Looking at my graph I think I was fairly accurate. I think I could have been more accurate though. As in my graph (time and temperature) I found two anomalies (circled in red on my graph), which did not correlate, with my line of best fit. The only reason I can think of why this happened is because my partner and I changed positions twice throughout the experiment. So one of us could have had better or worst eyesight or even a faster or slower reaction to stopping the clock.

When I look at my reliability from my table of results I think I was very reliable this is because all the results are well clustered.

Although my results weren’t a long way out, they could have been more accurate with a different variety of equipment. Using a Bunsen burner to heat up the solution is not extremely accurate as the temperature could just zoom up past the desired temperature mark that you want. To solve this you could be as accurate as possible and if you accidentally go over the mark take the solution off the flame with the thermometer still in it and wait for it to cool down to the mark you want before adding the hydrochloric acid. When measuring the measurements of the chemicals its almost accurate but you can’t always get the exact amount as you may measure wrong or some of the liquid will stick to the inside of the measuring cylinder when adding. This is an experimental error. When measuring out chemicals into a measuring cylinder you should always measure to the bottom of the curve. To improve getting the exact amount the aid of a syringe may be more exact than the aid of a dropper. As every person has a different eyesight or reaction time to get your results as accurate and reliable as possible the same person should always stay to the same job. This is where my partner and I went wrong and if I were to do the experiment again I would certainly know to keep to my job and my partner to theirs. Another reason the results could not be as accurate as possible is to do with light source. The way the light shines onto the beaker could have an affect on the way the human eye identifies the (X) disappearing, along with many other reasons. Using a light sensor connected to a meter/ computer via interface could solve this problem; you could have the reactants in the beaker as usual but on one side of the beaker have a light sensor. So what happens is as the chemicals react and when no more light can escape through the beaker it will show on the computer device how cloudy the solution has turned. You must time how long it takes though still.

So although my results weren’t too far off they could have been a lot better and thoroughly improved. If I ever repeat the experiment in the future I will make theses changes and investigate in other equipment that can be used.

EXTENDING THE ENQUIRY

Now my experiment is over, I still agree with my prediction that is if temperature goes up than the rate of reaction will go up depending on how much the reactants are heated. I don’t think this will work for all reacting chemicals it will for some but certainly not all. When reacting magnesium and dilute hydrochloric acid, my prediction is true for half of the experiment. Then after it gets to a certain temperature the rate of reaction starts to decrease this is because its heated so much till it reaches its optimum temperature and it can’t let the reactants react as quickly, this as it lets off steam. This is an exothermic reaction. If I were to do the experiment again I would use one of my other independent variables like concentration or having a catalyst.

I could extend the enquiry of my experiment I could cause a temperature change and instead of the temperature increasing it would go down. This would be proven difficult though with the equipment we have for use. We could try and decrease the temperature by fridge or freezer but that certainly wouldn’t be very reliable or accurate. Also the chemicals could freeze making the reaction slow down. This is as when enzymes are colder that they work slower this could have an effect on slowing the whole reaction down. Not making the results very reliable, but for as far as you can go before the reactants freeze I predict that the rate of reaction would increase this meaning the reaction would be slower. I predicted this as I said before because of the collision theory the particles would be cold and therefore not be colliding very frequently with a lot of force. So it would take longer for a reaction to take place.

Also the same experiment with the same chemicals could be used to extend the enquiry but by changing the concentration of the chemicals. So you could dilute them making the concentration weaker than the concentration of the chemicals I used for my experiment. Repeating the experiment with lower concentration would allow me to work out then the compare the differences between the reading from the two different rates of reaction rates of reaction when one is stronger and the other weaker. If I were to do the experiment and compare the two different sets of readings I would expect to find out that the higher the concentration the quicker the reaction. This is because if the concentration is higher there will be more particles compacted together so if they are close together there will be more collisions per second making the reaction faster.