Richards and Willard determined the molar mass of lithium and collected the following data.6 Experiment Molar mass, g/mol

1 6.9391

2 6.9407

3 6.9409

4 6.9399

5 6.9407

6 6.9391

7 6.9406

(a) Find the mean molar mass determined by these workers.

(b) Find the median molar mass.

(c) Assuming that the currently accepted value for the molar mass of lithium is the true value, calculate the absolute error and the percent relative error of the mean value determined by Richards and Willard.

(d) Find in the chemical literature at least three values for the molar mass of lithium determined since 1910 and arrange them chronologically in a table or spreadsheet along with the values since 1817 given in the table on page 10 of the paper by Richards and Willard. Construct a graph of molar mass vs. year to illustrate how the molar mass of lithium has changed over the past two centuries. Suggest possible reason(s) why the value changes abruptly about 1830.

(e) The incredibly detailed experiments described by Richards and Willard suggest that it is unlikely that major changes in the molar mass of lithium will occur. Discuss this assertion in light of your calculation in part (c).

(f) What factors have led to changes in molar mass since 1910?

Ans a-

mean atomic mass = 6.9391 + 6.9407 + 6.9409 + 6.9399 + 6.9407 + 6.9391+ 6.9406 /7

mean atomic mass = 6.9401 Ans.

part b)-

median atomic mass is odd number of observations indicated the median.

median atomic mass = 6.9399

part c)

individual value 'xi' = 6.9399

true value 'xt'= 6.9410

Er = (xi - xt)x 100 / xt

Er = (6.9399- 6.9410)x 100 / 6.9410in

Er = - 0.01584 % ans.

part d-

The atomic mass determination of Li has undergo many researches. The ratio analysis of LiCl with AgCl &pure Ag has provided atomic mass data. The accurate determination of at. mass of Li occurs via gradual change.

Since 1910. since 1817

6.01512 6.01012

6.022 6.212

6.941 6.237

The variation of at. mass with time in years

year at.mass

1817 6.0102

1845 6.212

1895 6.237

1910 6.3512

1922 6.6022

1930 6.941

Graph

Part e)

Experiment performed by Richard & Willard shows that no major deviation is possible in atomic measurement.The measurement technique invariably includes purification technique like gravimetric . The method involves mass ratio analysis of LiCl with AgCl & Ag.

Part f)-

The at.mass measurement techniques changes quite a bit after 1910.

The at.mass measurement techniques function only after valid calibration of Li- salt Oxygen & fused perchlorates. Thus accuracy of result changes. These calibration technique are the main cause of this tendency

Graph of part d)-

please use this google drive link to download the answer file.

https://drive.google.com/file/d/1pP-Uup6BUmJ8XjouEpABphOdbp7KEzfu/view?usp=sharing

note: if you have any trouble in viewing/downloading the answer from the given link, please use this below guide to understand the whole process.

https://helpinhomework.org/blog/how-to-obtain-answer-through-google-drive-link