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lab report

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Introduction

Experiment 9 Aim A. To investigate the existence of hydrogen bonds between ethanol molecules. B. To measure the strength of hydrogen bond formed between ethanol molecules C. To investigate the formation of hydrogen bonds between molecules of ethyl ethanoate and trichloromethane. D. To measure the strength of hydrogen bond formed between molecules of ethyl ethanoate and trichloromethane. Procedure A. 1. 10 cm3 of ethanol was added into an insulated 50 cm3 beaker by using a measuring cylinder. The temperature of the liquid was measured. 2. 10 cm3 of cyclohexane was added to the ethanol in the beaker. It was then mixed well and the lowest temperature attained was recorded. ...read more.

Middle

The highest temperature attained was recorded. Result Temperature change of solution A B C D Initial(oC) 19.5 20.5 20 18 Final(oC) 16 16.5 27 26 Net(oC) -3.5 -4 7 8 Calculation Liquid Formula Relative Molecular mass Density /kg dm3 Specific heat capacity /kJ kg-1 K-1 Ethanol CH3CH2OH 46 0.81 2.44 Cyclohexane C6H12 84 0.78 1.83 Trichloromethane CHCl3 119.5 1.48 0.98 Ethyl ethanoate CH3CO2CH2CH3 88 0.9 1.92 B. Mass of Ethanol: 0.81?(10?10-6)=0.0000081kg Mass of Cyclohexane: 0.78?(20?10-6)=0.0000156kg Total heat absorbed: 4?(0.0000081?2.44+0.0000156?1.83) =0.000193248 kJ mole of limiting reactant (i.e. ethanol): 0.0000081?1000/46=0.000176086 mole The enthalpy change for one mole of ethanol that the hydrogen bond was broken is: 0.000193248/0.000176086 =1.09746 kJ/mole D. ...read more.

Conclusion

The mixing of the two liquid break the hydrogen bonds. As bonds are broken, energy is needed. Therefore, heat is absorbed and temperature drops. B. * Cyclohexane has to be used in excess in order to ensure that no hydrogen bond is presented. * The hydrogen bond strength obtained was not accurate because there is heat lost to surroundings and to the beaker, which was not considered in calculation. C. * The temperature rises. During mixing, the electropositive hydrogen atom in trichloromethane formed hydrogen bonds with the electronegative oxygen atom in ethyl ethanoate. As bonds are formed, energy is given out. Therefore the temperature rises. D. * It does not matter whether using trichloromethane or ethyl ethanoate in excess because using trichloromethane or ethyl ethanoate in excess does not affect the no. of hydrogen bonds per molecule. ...read more.

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