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Investigating the effect of different liquid densities on the time taken to release 25 ml of alcohols

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DESIGN * Research question: * Does the change in liquid densities at the same temperature affect the time taken to release 25 ml of the alcohol from a 50 ml burette? * Variables: * Independent variable: The liquid density / g ml-1. * Dependent variable: The time taken to release 25 ml of the alcohol from a burette / s. * Controlled variables: * The volume of alcohol in a burette / ml. * The temperature of the alcohols / oC. * The absence of unnecessary substances or ions. * The same burette for the entire experiment. * Prediction: * The time taken to release 25 ml of the alcohol from a 50 ml burette is, stated by F. Weinberg (1984) [1], dependent on flow velocity and in particular are very sensitive to small changes in the density difference between the two liquids. * My prediction is, the higher the liquid density is, the more time taken for 25 ml of the alcohol to be released from the burette. The time taken to release 25 ml of alcohol increases in order: Methanol, Ethanol, Propan-1-ol, Butan-1-ol and Octan-1-ol. * Method: * Apparatus: * 50 ml burette (Uncertainty: � 0.500 ml). * Retort stand. * 125 ml ethanol C2H5OH 95.0%. * 125 ml methanol CH3OH 99.5%. * 125 ml propan-1-ol CH3(CH2)2OH 98%. * 125 ml butan-1-ol CH3(CH2)3OH 99%. * 125 ml octan-1-ol CH3(CH2)7OH 94%. ...read more.


* The burettes and funnels are rinsed carefully with distilled water prior to the experiment to ensure that inside the burettes do not contain any unnecessary substances/ions. If present, they may react with the alcohols to form products which have different liquid density, as opposed to original liquid densities of the alcohols at 20 oC (293 K). * The same burette is used for every measurement. This is because burettes from the same manufacturer cannot be guaranteed to have the same radius of the tips (possessing relatively small values). The use of different burettes can result differences in the time taken for the alcohol to be released. DATA COLLECTION AND PROCESSING * Raw data table: Alcohols Dependent & independent variables Ethanol Methanol Propan-1-ol Butan-1-ol Octan-1-ol Liquid density / g ml-1 at 20 oC (293 K) [4] 0.789 0.791 0.804 0.810 0.826 1st repetition: Time taken to release 25 ml of alcohol from a burette / seconds � 0.0100 39.0 43.0 67.0 82.0 112 2nd repetition: Time taken / seconds � 0.0100 41.0 44.0 69.0 81.0 115 3rd repetition: Time taken / seconds � 0.0100 38.0 46.0 70.0 83.0 111 4th repetition: Time taken / seconds � 0.0100 39.0 42.0 71.0 80.0 114 5th repetition: Time taken / seconds � 0.0100 40.0 45.0 70.0 79.0 110. ...read more.


Overall there are 15 times to add 25 alcohol samples since I decide to investigate 5 different alcohols. The more time I need to add more alcohols into the burette, the more likely inaccuracies to occur. * Improving the investigation: * The procedures can be partially replaced by computer data logging suggested by Laurence Rogers (1995) [5] to prevent uncertainties from human errors when stopping the watch. The experiment can be programmed to collect the data (Time taken for 25 ml of the alcohol to be released from the burette) automatically. * More alcohols with liquid densities within the ranges (The lowest value: 0.789 g ml-1 & the highest value: 0.826 g ml-1) can be tested to fill the 2 gaps between methanol and propan-1-ol, butan-1-ol and octan-1-ol in the presented graph. For instance, penta-1-ol has the liquid density of 0.815 g ml-1 at 20 oC (293 K) [6]. * Pure alcohols should be bought in the same concentration to ensure the reliability of the collected data. Otherwise, diluting the alcohols to the same concentration can be less expensive, yet time consuming. * A larger burette, for instance, with measuring volume of 75 ml (only 2 times to add 5 alcohol samples, 25 ml each) will reduce the times need to pour more alcohols into the burette to 10. Not only this change in equipment may save time of experimenting, but also minimise the uncertainties. ...read more.

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