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Find the Ar of lithium.

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Introduction

Evaluation. Was my experiment suitable? My experiments enabled me to gain results, which then with the aid of calculations I could find the Ar of lithium. From this perspective you can say the experiment was suitable as I achieved this. Were my results what I expected? Looking at the results they do not match the expected Ar of lithium (6.9). Method 1, measuring the volume of hydrogen produced, gave the result of 19.76 (a factor of 12.86 out). Method 2, titrating the lithium hydroxide produced, gave the result of 8.65 (a factor of 1.75 out). So looking at these results not only we can see they are out, but one method is more inaccurate than the other. The titration is far more accurate than the collecting of gas. Comparing both methods, and recognising sources of error. Method1. Sources of error in the collection of gas practical were: When the lithium was weighed I had to place it on filter paper first to remove the oil from it. ...read more.

Middle

Also 250 ml measuring cylinders are only accurate to 2 ml -anything under this had to be estimated, which by its very nature lacks accuracy. Parallax may have been a problem when gauging the volume in the 250ml measuring cylinder (it has a relatively large cross-sectional area compared to a burette). This allows for a greater % inaccuracy if you do not line your eye up correctly with the meniscus. Method2. Sources of error in the titration of lithium hydroxide were: because the Li was not weighed accurately (see above) this would of affected my calculations at the end. Air bubbles in the burette will have affected the titre as will have parallax -this may have been a problem when gauging the volume in the burette (however it has a relatively small cross-sectional area compared to a 250ml measuring cylinder- so is more accurate). But if you do not line your eye up correctly with the meniscus there could be a % inaccuracy. ...read more.

Conclusion

etc. Ways to minimise errors, and practical adaptations to improve my experiment. * Reliability could easily be improved for method 1 by performing more repeats (I only did this experiment once!). I feel method 2 was fairly reliable but again it could be argued that repeats could improve this further. * On method one if you tilt the flask at and angle and place the Li inside so it is not touching the water, and then place the bung and level the tube upwards, the chemicals should mix without gas loss. * Also making sure the Li was as pure as possible before weighing to eliminate all oil possible. * Make sure eye is lined with the meniscus and use the smallest instrument possible (with the smallest cross-sectional area possible) to eliminate parallax. * Use instruments with the finest possible gradations to measure volume. * Remove the funnel whilst performing the titration. This will prevent extra acid from being added during the titration * Use the same batch of acid. Then the concentrations will be the same. * Air bubbles in the burette removed be titrating. ...read more.

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