E29 Textbook Answer [ENDORSED]

[Madeleine Farrington 1B]

Question E.29 part d reads: A chemist measured out 8.61 g of copper(II) chloride tetrahydrate, CuCl2 * 4H2). d) What fraction of the total mass of the samplewas due to oxygen?

The answer manual lists the answer as 0.3099 because they used 16.00g.mol^-1 as the molar mass for oxygen. I used 15.999g.mol^-1 as the molar mass in my calculations, so I included 5 significant figures rather than 4. Would this be marked incorrect on an exam/ how do we know how many decimal spaces to use for the molar masses of elements?

[OrAmar-1L]

We are provided a periodic table of elements for each exam. Use the atomic mass given on that table and you will get full points. :)