Reaction Rate LabInvestigating the effect of concentration and temperature on reaction rate for an iodine clock reaction

Anthony XieIB HL Chemistry

: Dr.Johnson December 17 th , 2010

Data Processing

Raw Data:

Table 1.0

*Time in seconds it took for the mixtures to turn blue *Solution A is dilute iodate ion solution and Solution B is a starch and hydrogen sulphite ion solution

Mixture Volume (mL ± 0.5) Duration of Reactions (±0.005 Seconds)

Solution A Solution B Trial 1 Trial 2 Trial 3

1 10.0 10.0 13.94 14.10 15.06

2 8.0 10.0 17.76 18.30 19.87

3 6.0 10.0 21.12 21.57 23.70

4 4.0 10.0 31.50 32.80 35.80

5 2.0 10.0 66.37 71.48 79.20

Chemical Composition of Solution A

Solution A: 4.30 g ± 0.01g KIO3, 1.000 ± 0.005 L of water

Chemical Composition of Solution B

0.20g ± 0.01g Na2S2O5, 4.00 ± 0.01g starch, 5.0mL ±0.5 mL H2SO4(aq), 1.000 ± 0.005 L of water

Sample Calculations

Mixture Volume (mL ± 0.5) Duration of Reactions (±0.005 Seconds)

Solution A Solution B Trial 1 Trial 2 Trial 3

1 10.0 10.0 13.94 14.10 15.06

Calculation for Average Time

Average time it takes for mixture to turn blue in experiment 1

(13.94 )+(14.10 )+(15.06)3 =14.37

Sum of the trials divided by number of trials

Calculation for Uncertainty of Average Time

15.06−13.942

=0.56

Range (max-min) divided by 2

0.5614.37= 3.89%

Calculation for Concentration and Concentration Uncertainty in Experiment 1 (Solution A)

Concentration=Number of MolesVolume

Number of Moles= Mas sMolar Mass

Number of Moles= 4.3±0.23%214.0

= 0.0200… ±2.3%

Concentration=0.200…±0.23%1.00±0.5%

= 0.02 ±0.73% (relative uncertainty)

Initial Concentration of Solution A in Mixture 1

C2 = C1V1/V2

= (0.02±0.73%)(0.0100±5%)

0.0200±2.5%

=0.01±8.23% (relative uncertainty)

Calculated Concentrations of Solution A in other Mixtures

Mixture Volume (mL ± 0.5)

Solution A Solution B

2 8.0 10.0

(1 x 10-2 ± 8.23%) (80% or 0.8)

=

Rate of Reaction

To calculate the rate of reaction, the concentration of iodate ions was divided by average time for the reaction to complete for each mixture.

Mixture

Volume (mL ± 0.5) Concentration of Solution A

Concentration of Solution A Uncertainty

Average time Average Time

Uncertainty

Solution A

Solution B (8.2%)

1 10.0 10.0 0.008 14.37 3.89%

Order of Reaction Percentage Error

Experimental Rate Constant with Uncertainty

Average Rate Constant

Average Rate Uncertainty

=31.6%

Percentage Error of Rate Constant

Data Analysis

Table 2.0

The following table displays the processed data from the earlier raw data. It shows the volumes of solution A and solution B in mixtures 1-5, the concentration of solution a, the average time to the mixtures to react and turn blue for said mixtures, and the calculated uncertainties.

Mixture

Volume (mL ± 0.5) Concentration of Solution A

Concentration of Solution A Uncertainty

Average time Average Time

Uncertainty

Solution A

Solution B

1 10.0 10.0 8.23% 14.37 3.89%

2 8.0 10.0 8.23% 18.64 5.68%

3 6.0 10.0 8.23% 22.13 5.83%

4 4.0 10.0 8.23% 33.36 6.44%

5 2.0 10.0 8.23% 72.35 9.01%

Table 2.1

Mixture

Volume (mL ± 0.5) Concentration of Solution A

Concentration of Solution A Uncertainty

Reaction Rate Reaction Rate

Uncertainty

Solution A

Solution B (8.2%)

1 10.0 10.0 8.23% 12.2%

2 8.0 10.0 8.23% 4.29 13.9%

3 6.0 10.0 8.23% 2.71 14.1%

4 4.0 10.0 8.23% 1.20 14.7%

5 2.0 10.0 8.23% 2.76 17.2%

Figure 1.0

Since the concentration of hydrogen sulphite does not affect the reaction, n = 0.

However, mixture 4 is double the concentration of mixture 5 in terms of Solution A, comparing the rate of reactions of these two mixtures shows the order of the reaction.

When this value was compared to the theoretical value which was 2, the percentage error was calculated to be 6%.

Table 3

Mixture Rate Constant Average Rate Constant

Reaction Order

(K)

1 13.6 ± 31.6% 2.12

2

3

4

5

Using the experimental order of reaction value, the rate constant was calculated to be 13.6 ± 31.6%. In

comparison to the given theoretical value of 8.8, the percentage error is 54%.

Graph 1.0

Graph 1.1

Conclusion

From the analysis of raw data in both iodate clock experiments 1 and 2, it can be concluded that

an increase in temperature and concentration of the iodate ions results in the decrease of reaction time

and consequently an increase in reaction rate.

This relationship for concentration vs. duration of reaction as mentioned previously can be

deduced from the processed data. By observing the average duration of reaction time (seconds) and the

concentration of Solution A (mL), table 3 shows a general trend that as concentration decreases,

duration time increases and hence reaction rate decreases. Furthermore by comparing mixtures 4-5

where the concentration of solution A in mixture 4 is double that of mixture 5, it was deduced the

reaction was second order. This also corresponded to figure 1.0. This trend is further represented in

graphs 1.0 and 1.1. The relationship in graph 1.0 shows the square relationship between reaction rate

and concentration. Logger Pro calculated the equation to be Y= AxB where A is 4.181 1.423, B is 1.895

0.07. The root mean standard error (RMSE) for the graph was 1.25, which suggests that the fit is

relatively accurate. According to this relationship, reaction rates become exponentially large at every

interval where concentration is increased. The graph also shows that if concentration levels are very

low, the reaction rate is also extremely slow as well. Moreover this suggests that the x is a horizontal

asymptote which cannot be crosses. This makes sense since there cannot be negative rate of reaction,

or negative concentration rates. Graph 1.1 is linear regression of graph 1.0. Concentration2 is graphed

against reaction in which the linear equation is y = 6.727x – 1.035 x 10-5 in which the RMSE is 1.391. In

this particular equation x again represents concentration and 0.93 is the y intercept. The linear

relationship when concentration2 is plotted against reaction rate suggests that the concentration is

inversely proportional to reaction time and directly proportional to rate of reaction. This relationship fits

the collision theory since the initial increase of concentration results in greater number of particles per

unit volume which are more probable to collide in a fixed space. Since twice as many particles means

twice as many collisions, the rate of reaction is generally proportional to concentration of the reactant

(Van Kessel 2003). This trend is supported by the analysis of data in experiment 1. This relationship

between concentration and reaction time for a second order reaction provides an understanding of

reaction rates and concentration which is quintessential on an industrial level. The experiment allows

scientists to create systems by increasing the concentration of the substance that the reaction is

dependent on to produce yields of product in the shortest time possible.

Evaluation of Weaknesses and Limitations

The relatively large 54% percentage error is due to the weaknesses and limitations of the lab.

Firstly, human reaction time was a limitation in both experiments. Furthermore, the stirring in the

experiment which affected the time for the reaction to complete could not be measured. Mixtures were

stirred more than the others thus resulting in accuracy in time. It is impossible to stop the timer

precisely when the colour change occurred in the iodate clock reaction. It was also difficult to determine

when the reaction was completed and turned blue. Spectrometry should be used since it can

instantaneously determine when the ion changed color. However, in a high school setting this is not

viable so to improve accuracy; the experiment can be carried through using a burette and a flask like a

titration lab.

Secondly, the concentration of bisulphate was never changed. It was assumed that the order of

reaction was zero. It could have potentially affected the final results. To fix this source of error, the

volumes added of solution B can be changed to effectively determine if the bisulphate actually is a zero

order reaction.

Lastly, a significant source of error is the impurity of solutions used. Solutions B and A were not

completely pure since there is no way to guarantee this. Even exposure from the air could result in

disrupting the purity of the substances. The water used in the experiment also came from a tap and

where the minerals and chemicals in tap water could have potentially affected the results. Therefore to

fix this source of random error, water should be used from a distilled source and solution B and A in an

ideal setting from a more controlled source, such as the manufacturer. However, in a school setting this

is not practical, so students should take more precaution in not polluting solution A and B while using

distilled water instead of tap water.

Works Cited

Neuss, Goeffery. (2007) IB Diploma Chemistry Course Companion. Glasgow, Great Britain: Oxford

University Press.

Hans van kessel, D. F. (2003). Chemistry 12. Toronto: Nelson.