2
$\begingroup$

I am curious why there were changes in molar mass of lithium in the past.

The values were like 9 to 10 before 1830. But suddenly after 1830, the range of molar masses seems similar to the molar mass that is used now. I thought there might be some technical issues in the past. But, from 1830, the values were consistent and stable. So, I cannot assume there were lack of development in equipments and technics.

So, my questions are:

1. why the values were around 9-10 before 1830, not around 6.941?

2. why the values suddenly became similar to the molar mass which is used now?

$\endgroup$
3
$\begingroup$

This doesn't necessarily completely answer the question, but it at least moves closer to the root of the problem. From the Wikipedia article that MaxW included in his comment:

Brande also described some pure salts of lithium, such as the chloride, and, estimating that lithia (lithium oxide) contained about 55% metal, estimated the atomic weight of lithium to be around 9.8 g/mol (modern value ~6.94 g/mol)

So it seems to stem from an erroneous estimation of the percent composition of lithium oxide. If we go to the source (Brande's manual of chemistry:https://books.google.com/books/reader?id=zkIAAAAAYAAJ&printsec=frontcover&output=reader&pg=GBS.PA190), we find that this error likely stems from the fact that lithium oxide was difficult to obtain and so very limited experimentation had been done to characterize it.

| improve this answer | |
$\endgroup$
1
$\begingroup$

According to http://www.rsc.org/periodic-table/element/3/lithium

In 1821 William Brande obtained a tiny amount this way but not enough on which to make measurements. It was not until 1855 that the German chemist Robert Bunsen and the British chemist Augustus Matthiessen obtained it in bulk by the electrolysis of molten lithium chloride.

So I think that it could just be related to the small isolated amounts.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.