23 Laboratory Manual for General Organk, and lochemlstry, Seventh Editon 19 Lock

Question

23 Laboratory Manual for General Organk, and lochemlstry, Seventh Editon 19 Locker Number Date Name Please pink last ne rs Experiment 1 Measurement and Density 1. Why should weighing data or any other measurement data be recorded immediately in PRELIMINARY EXERCISES: your laboratory manual and not on a scrap of paper? 2.- An object was carefully weighed five times on a mnltiple-beam balance. The balance was zeroed each time. The masses were: 11.36 g 11.37 g: 11.40 g 11.38 g: and 11.39 g a. Calculate the average valueof these measurements. ease show all work) average b. Calculate the standard deviation, s.d., of this set of measurements using the range of the data and the sauare root of the number of measurements averaged. (Please show all work.) Calculate the density of a solid if it lhas a mass of 8.47 g and a volume of 3.24 cm. Please show your calculations, with units, below. 3. density

Explanation / Answer

1) All experimental data must be entered straightway in laboratory notebook or manual and not on a piece of scrap paper. This is mainly due to two purposes. A piece of paper may be easily lost and the experimenter will lose the data and may need to re-perform the entire experiment to acquire the data again. The second factor somewhat relates to ethical lab practices. Any data on scrap paper can be easily modified or altered and hence must be recorded in lab manuals and preferably signed by the instructor right away to avoid such malpractices.

2a) The average value of all the measurements = sum of the values obtained in each measurement/number of measurements = (11.36 + 11.37 + 11.40 + 11.38 + 11.39)/5 g = 11.38 g (ans).

2b) The standard deviation of the data set is given as

s.d. = (x - x)2/(N – 1) where x is the individual measurement and x is the mean of the measurements; N is the total number of measurements.

Plug in values and obtain

s.d. = [{(11.36 – 11.38)2 + (11.37 – 11.38)2 + (11.40 – 11.38)2 + (11.38 – 11.38)2 + (11.39 – 11.38)2}/(5 – 1)]1/2 g = [(0.001)/4]1/2 g = (0.00025)1/2 g = 0.0158 g (ans).

3) The density of an object is defined as mass per unit volume, i.e., density = mass/volume.

Mass of the solid = 8.47 g; volume of the solid = 3.24 cm3; density of the solid = (8.47 g)/(3.24 cm3) = 2.614 g/cm3 (ans).

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