The Rate At Which Aspirins Dissolve Essay, Research Paper

SKILL P: PLANNINGInput Variables (things that will affect the rates of reaction):·

Surface area of Alka-Seltzer tablets-can vary, i.e. if

crushed it will increase the surface area. ·

Amount of Water used (ml) ·

Amount of Alka-Seltzer tablets used-quantity. ·

Stirring same number of times. ·

Temperature of Water-°C Output Variables:·

If the surface area of the tablets is increased, the

particles around it in the solution will have more area to work on, and the

rates of reactions will increase because there will be more collisions. ·

The more amount of water used the quicker the tablets

will dissolve because they will be in contact with more particles of water. ·

If the amount of tablets being used is increased, then

the reactions will take longer, because there will be more tablets but less

water to dissolve them. ·

If the water with Alka-Seltzer tablets are stirred

during the reaction, then the rates of reactions will increase because the

particles will be forced to make contact much quicker, rather than take their

time to make contact, and therefore the number collisions will increase. ·

If the temperature is increased, then the particles

will move much quicker because they are hot and therefore vibrate a lot, and so

the number of collisions will increase.The input variable that I am going to test is the

temperature. All the other input variables are going to remain constant to

ensure that the experiment is a fair test. The output variable that I am going

to measure is the rate of reaction, i.e. time in seconds. Relevant Scientific Background:There are different speeds at which reactions can occur as

they vary. Firstly there is chemical weathering of rocks. This takes years to

occur, so this is a very slow reaction. Then there is also the rusting of iron.

This is fairly slow and it happens in a matter of weeks. There are also the

reactions between metals and acids. These are quicker and happen in a matter of

minutes, but the quickest reactions are explosions, which are instantaneous and

are all over in a fraction of a second. Rates can be measured in different ways. They can be

measured at the rate at which a reactant reacts, also the rate at which the

product forms and the volume of carbon dioxide can be measured against

time-i.e. the decrease in mass against time. It can also be measured by the

time taken for a tablet to dissolve. This is how I am going to measure the rate

of reaction in this particular experiment. Rates of Reactions depend on: 1.

Temperature: As the temperature increases so

does the rate of reaction.??????????????????????????????????????????????????????????????????????? activation

energy (EA)???????????????

↑????? ? energy? ?? marble + acid Product + CO2 + H20

(Exothermic

reaction)??????????????????????????????????????????????????????????? ??????????? Time???? →EA (activation energy) is the minimum energy

particles must have on collisions for them to react. By increasing the temperature,

particles move faster, i.e. they have more energy. So, they collide with more energy

and more particles have the required EA (and also they collide more frequently.2.

Surface Area: If the surface area is

increases (more powdered) the rate of reaction also increases. This means that

there are more collisions between the solid and liquid. The smaller the particles

involved the greater the surface area where the reaction can take place and the

faster is the reaction.3.

Concentration: If the concentration is increased, the rate

increases. There are more collisions because there are a greater number of

particles in the same volume. 4.

Pressure (for

reactions between gases): If the pressure is increased, the

rate increases. There are more collisions because there are a greater number of

particles in the same volume.5.

Catalysts: If a catalyst is added the rate

increases. The EA is

lowered. These change the rate by providing an alternative reaction pathway

along which the reaction can occur. A catalyst works by giving the

reacting particles a surface to stick to where they can bump into each other.

This increases the number of collisions Marble + acidThere is a curve because the temperature changes two things. Time (s) (i.e. rate)??????????????????????????????????????????????????????????????????????????????????? ??????????? things

go wrong at higher temperatures Temperature (°C) ??????????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????

?????? 1?????? ?? time(s) (i.e. rate) Temperature (°C)Alka-Seltzer tablets contain sodium bicarbonate (base) and

citric acid (acid). Both of these are solids, so no reaction will occur until

the tablet gets wet. Once wet, protons transfer from the acid to the base

according to the neutralisation reaction: 3NaHCO3 + C6O7H6 Na3C6O7H + 3CO2 + 3H2O Sodium Citric Sodium Carbon Water Bicarbonate Acid Citrate Dioxide As a consequence of this reaction, bubbles of carbon dioxide

are produced (the fizz) and a basic solution (due to the excess of sodium

bicarbonate as well as the sodium citrate in solution) which will neutralise

excess stomach acid. Alka-Seltzer tablets also contain aspirin (acetyl

salicylic acid which is covalent). Alka-Seltzer tablets dissolve in warm water, so therefore

the warmer the water the quicker the reaction will be.The Q10 Theory states that with every 10°C

rise in temperature the rates of reaction double.Tap water is hard water. Dissolved Ca2+ and Mg2+

ions cause hardness. Due to the anion HCO3- being

present, it is only temporary hardness and can be removed by heating. Heat has

a great effect on it. At temperatures of about 60°C and over, calcium

hydrogen carbonate starts to decompose. ??????????????????????? ???????? HEAT Ca(HCO3)2

(aq) ????????? ????????CaCO3 (s) + CO2 (g)

+ H2O (l)This removes the dissolved calcium hydrogen carbonate and

hence removes the hardness. This is why things tend to go wrong at higher

temperatures (i.e. 60°C +).Hypothesis:As the temperature increases, so will the rate of reaction,

but at higher temperatures the pattern (link) will break down (giving us

unreliable results and the trend in the graph will show this). Therefore the Alka-Seltzer tablets dropped into the hottest

water will dissolve the fastest. This is due to the fact that the atoms, ions or particles

(reactants) of something must physically touch each other to produce a chemical

reaction. Increasing the temperature of the reactants can increase the rate of

chemical reaction.Prediction From my scientific knowledge I know that as the temperature

is increased the rate of reaction is also increased. By increasing the

temperature the particles will have more energy to collide with and therefore

they will do so more frequently, increasing the rate of reaction. The Q10 Theory

states that with every 10°C rise in temperature, the rate of reaction will double,

so therefore I predict that with every 10°C rise in temperature the

rate of reaction will approximately double. Therefore I have decided to

increase the temperature by 10°C each time to see whether the results that I obtain

support this prediction. Preliminary Work:Some Preliminary Work was carried out to help me to decide

how to approach the problem. Here are the results that I obtained from the experiment: For the actual experiment, I have decided to use 2

Alka-Seltzer tablets. So, 2 Alka-Seltzer tablets will be dropped into the water

at the same time at different temperatures (input variable to be tested) and

the rate of reaction (output variable to be tested) will be timed.The temperatures that I am going to investigate are:??????? 20°C ??????????????????????????????????????????????????????????????????????????????????? 30°C ??????????????????????????????????????????????????????????????????????????????????? 40°C ??????????????????????????????????????????????????????????????????????????????????? 50°C ??????????????????????????????????????????????????????????????????????????????????? 60°C ??????????????????????????????????????????????????????????????????????????????????? 70°C ??????????????????????????????????????????????????????????????????????????????????? 80°C Safety:·

Safety goggles will be worn throughout the whole

experiment. ·

Only a roaring (blue) flame will be used on the Bunsen

to heat the water, and when no water is being heated a safety (yellow) flame

will be put on. ·

During the experiment ties will have to be tucked in. Apparatus: ·

100ml measuring cylinder ·

Burette ·

100 ml beaker ·

Timer (stopwatch) ·

Funnel ·

Tap Water ·

Alka-Seltzer Tablets ·

Thermometer ·

Bunsen Burner ·

100 Beaker ·

250 Beaker ·

400 Beaker ·

Heat mat ·

Gauze ·

Tripod Method:·

A burette will be filled with water using a 250ml

beaker. This will be used to measure out 20ml of water in a 100ml beaker. ·

A timer and some Alka-Seltzer tablets will be obtained.

A thermometer will be placed in the beaker of water to measure the temperature

(°C)

of the water. ·

Two Alka-Seltzer tablets will be dropped into the

beaker. The time taken for the tablets to dissolve will be timed and recorded. ·

The experiment will be carried out at different

temperatures. To heat the water, the 100ml beaker will be placed in a 400ml

beaker containing a small amount of water (water bath). Again a thermometer

will be placed in it. A Bunsen on a roaring flame will be placed directly

underneath it to heat it with the beaker being supported by a tripod and gauze. ·

Once the temperature reaches 80°C, two Alka-Seltzer

tablets will be dropped in, and again the time for the tablets to dissolve will

be timed. The beaker will be taken off the Bunsen, but will still remain in the

water bath to maintain its temperature. ·

The water will be allowed to cool and then lower

temperatures will be investigated using the same method. ·

The temperatures to be investigated are:????? 20°C 30°C 40°C 50°C 60°C 70°C 80°C ·

Repeat results will be obtained for all the above

temperatures once at least one result has been obtained for each temperature. Diagram: ??????????????????????????????????????????????? Thermometer ??????????????????????????????????????????????????????????????????????? Alka-Seltzer

??????????????????????????????????????????????????????????????????????? Tablets Temperature Reading????????????????????????????????????????????????????????????????????????? 400ml

Beaker e.g. 20°C??????????????????????????????????????????????????????????????????????? (Water

Bath) 100ml Beaker ????????????????????????????????????????????????????????????????????????????????????? containing

????????????????????????????????????????????????????????????????????????????????????? 20ml

of Tap ????????????????????????????????????????????????????????? ???????????????????????????? Water 100ml

approx. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx??????????? Gauze ??????????????????????????????????? ???????? HEAT Pre-Evaluation: Already I can see some weaknesses in this experiment.

Firstly, when the Alka-Seltzer tablets are dissolving, the temperature rises or

decreases rapidly, which can affect the rate of reaction by either slowing it

down or making it faster. Also, it is impossible to decide exactly when the

Alka-Seltzer tablet has dissolved, and carry this out consistently throughout

the whole experiment. This will make the results slightly unreliable, as the

point where the Alka-Seltzer tablet has dissolved will not always be the same

and there will be some variation each time. SKILL O, A & E-OBSERVATION, ANALYSIS & EVALUATION Method: ·

A burette was filled with water using a 250ml beaker.

This was used to measure out 20ml of water in a 100ml beaker. ·

A timer and some Alka-Seltzer tablets were obtained. A

thermometer was placed in the beaker of water to measure the temperature (°C) of

the water. ·

Two Alka-Seltzer tablets were dropped into the beaker.

The time taken for the tablets to dissolve was timed and recorded. ·

The experiment was carried out at different

temperatures. To heat the water, the 100ml beaker was placed in a 400ml beaker

containing water (water bath). Again a thermometer was placed in it. A Bunsen

on a roaring flame was placed directly underneath it to heat it with the beaker

being supported by a tripod and gauze. ·

Once the temperature reaches 80°C, two Alka-Seltzer

tablets were dropped in, and again the time taken for the tablets to dissolve

was timed. The beaker was taken off the Bunsen, but still remained in the water

bath to maintain its temperature. ·

The water was allowed to cool and then lower

temperatures were investigated using the same method. ·

The temperatures which were investigated were:????? 20°C 30°C 40°C 50°C 60°C 70°C 80°C ·

Repeat results were obtained for all the above

temperatures once at least one result had been obtained for each temperature. ·

N.B. when taking repeat results a measuring cylinder was

used instead of a burette to speed up the process. My observations were that as the Alka-Seltzer tablets came

into contact with the water a vigorous reaction took place. In the water at

higher temperatures there was a very vigorous reaction that lasted for most of

the reaction and the froth produced had risen, and then quickly went back down

as the reaction slowed down. However in the water at lower temperatures there

was a vigorous reaction at first, with the froth rising, but then it slowly

started to go down as the reaction started to calm down. Results: N.B. the row

highlighted represents a set of anomalous results.

Conclusion: From the results obtained it has

been seen that the rate of reaction increases as the temperature increases,

supporting my hypothesis in which I stated that??As the temperature increases, so will the rate of

reaction, but at higher temperatures the pattern (link) will break down (giving

us unreliable results and the trend in the graph will show this). Therefore the Alka-Seltzer tablets

dropped into the hottest water will dissolve the fastest.?? As you can see

from the graph, at 80°C the link breaks down, giving us a result that does not

fit in with the general trend of results. This is not an anomalous result and

there is a reason behind this. Things tend to go wrong at higher temperatures

because at higher temperatures (60°C+) the dissolved calcium hydrogen carbonate starts to

decompose. This removes the temporary hardness and therefore removes the

dissolved Ca2+ and Mg2+ ions, therefore making the test

unfair because at lower temperatures there was hardness in the water. The graph showing

the time in seconds (rate of reaction), against the temperature shows the rate

of reaction increasing with the temperature, and there is a curve that at first

goes down steeply, but then becomes straighter. At 80°C the link breaks down,

giving us an odd result, which can be explained by the fact that the Ca2+

and Mg2+ ions are removed due to the decomposing of the calcium

hydrogen carbonate. As you can see from the graph and my table of results, the

result obtained at 30°C is an anomalous result (i.e. it doesn?t follow the

general trend). This again supports my hypothesis in which I stated this by

saying that the link would break down giving us unreliable results. The link

did not break down at 60°C as I had stated that it would because that is only the

temperature at which the Ca2+ and Mg2+ ions started to

decompose and once they had fully decomposed the results showed this.For the 1/time(s) against the

temperature (°C)

graph I got a straight line, which was the line of best fit. Again it shows how

unreliable the results are at higher temperatures, as the results for 70°C and

80°C

do not fit in. showing how the link breaks down due to dissolved substances in

the water. This shows that the temperature is inversely proportional to the

time. Also I predicted

that as the temperature increased by 10°C the rate of reaction

would approximately double. The results do not clearly show this happening, but

I believe that it shows some signs of this happening. At 20°C the

average time is 97.5 seconds. When the temperature was increased to 30°C it

approximately doubled (x 2.17 to 3 significant figures) to 45 seconds. However

this is an anomalous result and should be higher. Even so, this still supports

my prediction. The next result obtained is for 40°C, which is 37 seconds.

There is no sign of the rate doubling (x 1.22 to 3 significant figures), but if

we take into account that the previous result should have been higher, then it

would appear to approximately double. From here onwards it does not double for

every 10°C.

This is due to my theory (scientific background knowledge) that things go wrong

at higher temperatures due to the decomposing of calcium hydrogen carbonate at

temperatures of 60°C

and above. Evaluation: I have obtained a reliable set of results, with repeats of

the evidence obtained. An accurate procedure was used, with this being shown by

the results obtained which all agree with each other. By using a burette, it

allowed me to work up to a very accurate degree of accuracy, rather than simply

using a beaker or a measuring cylinder. However, I did use a measuring cylinder

for repeat results and this did not seem to affect my results.I obtained one set of anomalous results. These were obtained

for a temperature of 30°C and did not fit in with the general trend. According

to the best-fit line on my graph, the rate of reaction should have been longer

and it should have taken about 58 seconds for the Alka-Seltzer tablets to

dissolve in water with a temperature of 30°C.? A reason for me obtaining this anomalous

result could have been due to the fact that whilst the reaction was taking

place the 100ml beaker was still in the water bath. This would have caused the

temperature to rise slowly and slowly increase the rate while the tablets were

dissolving, therefore causing more collisions and increasing the rate. This did not happen however at higher temperatures, because

the temperature of the water bath was about the same, and so it did not really

have much effect, and it just kept the temperature constant (i.e. stopped it

rising or falling).Although I tried my best to make the experiment perfect

there were some unavoidable inaccuracies with the experiment. Firstly, when

testing lower temperatures, the temperature of the water bath, which was much

higher than the actual temperature being tested, caused a rapid increase in the

temperature, or if it were lower it would cause it to decrease rapidly,

especially when taken off the Bunsen. These gave us results for inaccurate

temperatures to which were we testing. To overcome this problem, a thermostatic

water bath would need to have been used, since it can be set to a certain

temperature, and it will stop when it reaches there. Also it would mean that

the solution inside it would reach the exact temperature or close to it., and

not increase or decrease once the water inside it has reached equilibration. Secondly, it was impossible to say when exactly the

Alka-Seltzer tablets had completely dissolved and consistently decide this for

every result obtained. This was a huge flaw in the experiment and affected the

results in a big way. To overcome this problem a special piece of apparatus

would be needed to decide exactly when they had dissolved each time and give us

the same measure of consistency each time.To improve the quality of the results, the same piece of

apparatus would have needed to be used throughout the whole experiment, and not

changed for repeat results. To extend my inquiry and provide additional

evidence for this experiment, I think that I could have investigated up to

higher temperatures and see how the link would break down, and how the results

would fit in with the trend of results. Also, it would have helped me to see

how the decomposing of the dissolved substances affected the results. To

improve the experiment and make it fair, distilled water should have been used

instead of tap water because it is purer than tap water and does not contain

impurities.