5. the element copper has naturally occurring isotopes with mass numbers of 63
and 65. the relative abundance and atomic masses are 69.2% and 30.8%
respectively. calculate the average atomic mass of copper.

Average atomic mass  = 63.62 amu.

Explanation:

Abundance of Co⁶³ = 69.2%

Abundance of Co⁶⁵ = 30.8%

Atomic mass of Co⁶³ = 63 amu

Atomic mass of  Co⁶⁵  = 65 amu

Average atomic mass = ?

Solution:

Average atomic mass  = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass  = (63×69.2)+(65×30.8) /100

Average atomic mass =  4359.6 + 2002 / 100

Average atomic mass  = 6361.6 / 100

Average atomic mass  = 63.62 amu.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.