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Introduction

EXTENDED ESSAY - Chemistry - How does the introduction of xanthan gum into a solution and the resulting increased viscosity affect the rates of reactions occurring within that solution? Word Count: 3731 ANDREW PELLY IB NUMBER 000834 027 CONTENTS SECTION TITLE PAGE Abstract 2 1 Introduction 3 2 Research question 4 3 Background information 4 i. Xanthan gum in solution 4 ii. Electrolytic refinement 5 iii. Na-H2O ionisation reactions 6 4 Method 6 i. Viscosity measurements 6 ii. Rate of reaction measurement: electrolytic refinement 7 iii. Rate of reaction measurement: neutralisation reactions 7 5 Data 8 i. Relationship between xanthan gum concentrations and time taken for burette to empty, in order to model viscosity 8 ii. Comparison of mass change of the cathode in an electrolytic purification reaction involving a copper anode and a copper cathode in a copper sulphate solution 9 iii. Peak temperatures achieved during Na/H2O ionisation reaction 11 6 Analysis 12 i. The homogeneity assumption 12 ii. Sodium and water reaction 12 iii. Hydrogen bonding in water 13 7 Conclusion 15 i. Xanthan gum solution viscosity testing 15 ii. Electrolytic refinement testing 15 iii. Na/H2O ionisation reaction 15 Appendix 16 i. Bibliography 16 Abstract In this essay, I researched the question "How does the introduction of xanthan gum into a solution and the resulting increased viscosity affect the rates of reactions occurring within that solution?" Xanthan gum is a standard food additive used as thickening agent. It is very stable and only reacts at extreme pH and temperature values. In the experiments described in this essay, it was used as it is in food, as a thickener and the effect of the increased solution viscosity on the rates of oxidation and reduction was measured in two different experiments. The first was the electrolytic refinement of copper, electrolysed with an external power source in copper sulphate solutions, and the second was the ionisation of solid sodium in water. ...read more.

Middle

4. Method 4.1 Viscosity Measurements Usually a Couette instrument11 would be used to measure the viscosity of a solution. Due to the lack of a Couette instrument, an alternative method had to be found. 1. The xanthan gum solution to be tested was prepared and the temperature was measured. 2. A standard burette used for titration was placed vertically in a clamp stand. 3. 30 ml of the solution were poured into the top of the closed burette and allowed to settle. 4. The tap at the base of the burette was opened and the time taken for the burette to empty completely was measured. 5. Steps 1-4 were repeated for all 5 solutions to be tested. A comparative analysis of the times taken for the burettes to empty will yield values relative to each other for the viscosity of the solutions. 4.2 Rate of reaction measurement: Electrolytic refinement 1. 100 ml of a solution of 0.1M CuSO4- was mixed with 100ml of the solution to be tested in a 250ml beaker. 2. Two small sheets of copper of roughly equal size were weighed, and the mass was recorded. 3. The two copper sheets were placed in the beaker filled with CuSO4- solution in such a way that the two sheets did not touch directly 4. A 12V power supply was connected to the two copper sheets to form a circuit in such a way that one copper sheet became the cathode and the other became the anode. 5. The power supply was set to produce 12V of direct current and then switched on. 6. After 15 minutes the power supply was switched off. 7. The copper sheets were then removed from the solution, dried off, and the mass was once again recorded. The electrolytic refinement experiment was repeated for all 5 test solutions, and each solution was given an equal amount of time to react. ...read more.

Conclusion

7. Conclusion 7.1 Xanthan gum solution viscosity testing Unsurprisingly, a xanthan gum solution takes longer than a standard water solution to empty through a thin burette tap. This is due to the thickness of the solution being increased by the presence of xanthan gum within the solution. The greatest difference between two values occurred between a concentration by mass of 0.6% and 0.8%. This is in accordance with Zantz et al.'s research in "Xanthan Gum solutions at low shear rates" which states that a xanthan gum solution's viscosity does not increase in a linear fashion when related to its concentration gradient, but in an exponential fashion. 7.2 Electrolytic refinement testing The results of the refinement testing points towards a tendency for the xanthan gum solutions to slow refinement, indicating that the presence of xanthan gum, and the resulting increase in viscosity, reduces the rate of reaction within the solution. The value for the mass change of the anode and cathode for the highest concentration gradient of xanthan gum, 0.8%, was approximately half the value for the mass change occurring in unadulterated water. The other factors that could have caused this cannot account for such a large difference (approximately 50%) unless the viscosity factor played a part in slowing the reaction. 7.3 Na/H2O ionisation reaction The differences between the peak temperatures obtained in unadulterated water and those obtained in one of the treated solutions are significant. The values of the peak temperatures showed a steady reduction as the concentration gradient of xanthan gum rose, totalling a reduction of over 10% of the initial value across the concentration spectrum. Although the presence of xanthan gum could have reduced the diffusion constant for the solution in which the temperature was measured, this change is no more than a 4.8% reduction in diffusion, as per Fick's first law, and could not account for a 10% or greater change in the peak temperature values. The trend shows that the presence of xanthan gum, and the increased viscosity which occurs as a result, reduces the rate of ionisation for sodium atoms in water. ...read more.

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