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Chemistry determination of RAM of lithium

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Introduction

ANALYSIS: Method 1: Measure the volume of hydrogen produced when a known mass of lithium reacts with water. Set up apparatus. 250cm� conical flask must contain 100cm� of distilled water. Weigh between 0.08g and 0.13g of lithium. Record the exact mass of lithium. Remove the stopper, add lithium to the flask and quickly replace stopper. Collect the gas and record final volume of hydrogen. RESULTS: I used 0.08g of lithium, this produced 168cm� of hydrogen gas. Treatment of results: Assuming that 1 mole of gas occupies 24,000cm3 at room temperature and pressure Calculating the number of moles of hydrogen: 168 / 24000 = 0.007 mol Number of moles of lithium: 0.007 x 2 = 0.014 mol Using above info and original mass of lithium, RAM of lithium can be calculated as: 1 / 0.014 x 0.08 = 5.7142 Method 2: Titration of aqueous LiOH with 0.100 mol dm HCl. ...read more.

Middle

Chronic (long-term) occupational exposure to hydrochloric acid has been reported to cause gastritis, chronic bronchitis, dermatitis, and photosensitization in workers. Prolonged exposure to low concentrations may also cause dental discoloration and erosion Evaluation: The overall accuracy of the experiment was not very high due to apparatus and methodological errors. The main source of error procedure-wise was titrating the LiOH solution and determining when the solution became clear. Measurements of lithium metal were fairly accurate due to use of digital weighing scales, however, when using a water bath to determine amount of hydrogen released, accuracy was not superb. Repetition of the titration allowed for more reliable results as 2 results became 0.2cm� off each other. Calculation of a mean titre also helped accuracy. APPARATUS ERROR IN ACCURACY EFFECT OF ERROR ON RESULT IMPROVEMENT REASON FOR IMPROVEMENT Upside down gas cylinder in water bath Measured to 1 cm�. ...read more.

Conclusion

solution taking longer to titrate and vice-versa Add a specific amount of phenolphthalein, for example 10cm� If consistent amount of phenolphthalein is added then titration will be more reliable Shaking of solution Whilst titrating, the flask may have been shaken more or shaken less Shaking the flask, distributes molecules more equally so therefore titration is faster Use an electronic shaker Better results can be achieved if consistency is ensured. Equal distribution will result in fair accurate results Validity of results: Although there were some major sources of error, I believe this experiment to be valid. Accuracy was maintained at a level sustainable in a classroom. Extraneous variables were controlled to the best of my ability. Reliability of results: Due to having achieved two results within 0.2cm� of each other I would have to say my results are reliable. Consistency in methodology was sustained and this allowed for greater accuracy of results. Aminul Hoque AS Chemistry Coursework: Determination of the relative atomic mass of Li ...read more.

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