Bio 206L Expt #1 - Group Members_Exercise_Date LI Unique...

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Group Members: _____ _______________ _____________________________Exercise_______Date: ___________ LI ______________________ Unique __________ Day: __________ Room: _______ Lab Start Time ________ Exercise 1 Analysis (1) Which device used in Section 1.3 seems to be the most accurate for measuring a 60-mL volume? State some reasons why this device might be more accurate compared to the others . We first found the weight of the water using the density (mass/volume) and because the density of water is 1g/ml, therefore, 1 ml of water equals to 1 g of water. The device that seemed to be the most accurate for measuring a 60-ml volume was the 100-ml graduated cylinder because the weight of a 60 ml volume of water (H2O) is equivalent to 60 g of water, and using a graduated cylinder after 3 trials the weights were 59.39g, 60.49g and 59.5g with a mean of 59.79g that is the closer to 60g then the mean of the other average weights measured by the Erlenmeyer flask and the beaker of 56.07g and 52.49g. We then also calculated the percent error of mean (PEM) by this formula % error of mean = (calculated ave. vol.) – 60 ml) x 100% 60 ml The PEM of the graduated cylinder was 0.34%, which was less then the Erlenmeyer flask or the beaker with PEM values of 6.54 % and 12.52 %, respectively. The other groups had similar average results as well as similar PEM values, to conclude that the 100-mL graduated cylinder was the most accurate for measuring a 60-mL volume. The graduated cylinder was the most accurate device for measurement in this experiment because of the way it is designed. It goes by small markings with increments of 1ml; therefore, it was easier for us to estimate the level of water at 60-ml. For the beaker and Erlenmeyer flask have increments of 10 ml and 25ml respectively, so these devices are harder to estimate. Another reason for why the graduated cylinder was the most accurate device, is because of its smaller size implying a less surface area (smaller diameter); therefore, the less amount of water attached to the walls of the container (adhesion ability) reduced the inaccuracy of the water level. Also, using a small sized graduated cylinder helped us estimate and visualize the water and meniscus levels more accurately. -Why can’t one determine which device seems to be the most precise based on the data collected in Section 1.3? What would one need to do to determine this? State the calculation one could use and rationale to decide? Precision is how measured values are consistent with one another, and it is based as well on the observations of each viewer. By just looking at the data we collected, it is difficult to conclude the most Spring 2011 Ex 1 Analysis Page 1 of 8
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Group Members: _____ _______________ _____________________________Exercise_______Date: ___________ LI ______________________ Unique __________ Day: __________ Room: _______ Lab Start Time ________ precise device. Therefore, we needed to use the standard deviation measurement, that shows how much variation there is from the mean. Standard deviation is a measurement of precision as well, so we used it to determine the most precise device. The standard deviation formula is ∑(value of each obs. – mean of those observations)^2/ total number of observations, then take the square root of the result. The smaller the standard deviation, the more precise the values are.
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