Calculations General Formulas s x x n 1 CV relative standard deviation error 100 s x o e e s sample standard deviation x sample mean o observed value e expected value 1 29 5740 29 5739 29 5737 29 5742 29 5738 5 29 5739 g s x x n 1 trial weight of 50mL beaker 1 2 3 4 5 avg range sd rsd 29 574 29 5739 29 5737 29 5742 29 5738 29 57392 0 0005 0 000192354 6 50417E 06 2 v mL m g g mL d T 1 T 2 T 3 T 4 4 xof volume trial weight of 5mL water Volume delivered 4 9162 4 927170345 1 2 3 4 avg sd 4 951 4 9326 4 9427 4 962048 4 943606941 4 953729479 4 946638691 0 015010375 rsd Percent error 0 00303446 1 07 trial weight of 10mL water Volume delivered 1 2 3 4 9 9564 9 9606 9 9457 9 9557 avg sd rsd Percent error 9 978617392 9 982826764 9 967893515 9 97791583 9 976813375 0 006329682 0 000634439 0 23 3 trial avg sd rsd error 1 2 3 4 5 avg sd rsd error 1 2 3 4 5 Mass of 500 microL water 0 4998 0 5068 0 5037 0 4988 0 4894 0 4997 0 006582553 0 013173009 0 06 0 9997 0 9823 0 983 1 002 0 9955 0 9925 0 009292201 0 009362419 0 75 trial Mass of 1 mL water 0 0505 0 0503 0 0501 0 0504 0 0508 0 05042 0 000258844 0 005133748 0 84 0 099 0 1006 0 099 0 0996 0 1002 0 09968 0 000715542 0 007178388 0 32 trial Mass of 50 microL water trial Mass of 100 microL water 1 2 3 4 5 1 2 3 4 5 avg sd rsd error avg sd rsd error Questions 4 Almost all of the pipettes performed better than the values provided in the table except for the 1 mL micropipette This can be attributed to improper technique used in the lab which would lead to a systematic error 1 Systematic error comes because of a flaw from equipment or design of experiment so if the experiment is replicated the error is reproducible For example a poorly calibrated instrument such as a thermometer that reads 102 oC when immersed in boiling water and 2 oC when immersed in ice water at atmospheric pressure Such a thermometer would result in measured values that are consistently too high Random error occurs because of uncontrollable variables in the measurements such as the task of reading a scale For example different people will report there subjective reading between the markings when reading the scale measurement Improving technique can reduce these types of errors but they will always be present 2 It is advisable to report the median instead of the mean when outliers are present in the sample that can skew the mean The median is resistant to outliers so it will not be affected in the manner the mean is 3 TC glassware refers to glassware used to Contain liquid like volumetric flasks and graduated cylinders TD glassware refers to glassware that is used to deliver liquid such as pipettes and burets 4 I would propose to calibrate the volumetric flask to contain I would propose to calibrate by measuring the mass of water filled in a flask and then using the density of water at that particular temperature to calculate volume Dry the flask with acetone and vacuum not in the oven and weigh it with its top Then fill the flask to the line with water at the desired temperature and reweigh A large volumetric flask probably will not fit onto the pan of an analytical balance In such a case a good top loading balance may be used because a tenth gram uncertainty is acceptable when the weight of water is 100 g or more 5 A volumetric pipette is used to transfer a desired volume of solution from one container to another A Mohr pipette is graduated for delivery from the zero mark to the final graduation mark 6 7 One of the most important rules of weighing is that the sample must never come in direct contact with the balance pan The best way to keep the balance pan clean is to use the method of weighting by difference The weighing bottle plus dried sample is weighed then the required weight of sample is removed to a suitable receiver the weighing bottle and contents are then reweighed The weight of the sample in the receiver is simply the difference in the two weights The sample can be removed from the weighing bottle by either of two methods If the solid is crystalline gentle tapping of the weighing bottle with its cap Figure 5 3 will remove a controlled number of crystals at a time To prevent fingerprints from changing the weight of the weighing bottle it is usually handled with a paper loop With powdery solids it is usually easier to remove the sample with a small spatula With this method make sure that no sample spills from the spatula and that the spatula is rinsed with deionized waterbefore use In an experimental procedure a typical weighing instruction might be Accurately weigh about 0 4 grams of sample where the actual number of grams will vary according to the experiment This statement means that a sample of about 0 4 grams usually within10 is to be weighed to the nearest tenth of a milligram A notebook entry for this weighing procedure might look as follows Initial weight21 9683 gFinal weight21 5537 gWeight of sample0 4146 gNote that the actual weights are recorded not just the difference If by accident too much sample is removed that sample must be discarded and not returned to the weighing bottle Of course in the case of very expensive or otherwise irreplaceable substances a discarded sample would be saved and redried The method of weighing by difference may at first seem cumbersome but with practice samples can be weighed efficiently This method is used because 1 The balance pan is kept clean because only the weighing bottle touches it 2 The sample is kept clean because it remains in a capped weighing bottle as much as possible 3 The exact zero of the balance is not critical because only the difference in weights is used 4 The sample can be weighed into a wet receiver 5 Time is saved when weighing several samples because the final weight for sample 1 becomes the initial weight for sample 2 etc If samples were weighed on paper two weighings would be required for each sample Found in Canvas Files 8 Average 0 1283 M Standard deviation 0 0009 See equations above G1 0 5556 Keep data point G2 0 1111 Keep data point G3 0 8889 Keep data point G4 1 444 Keep data point 9 La2O3 6HNO3 2La NO3 3 3H2O Moles La2O3 Molar mass 325 81g mol 0 1968g 1mol 325 81g 6 04 10 moles La2O3 Moles La NO3 3 Molarity 1 208 10 M …