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.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"

the answer your looking for is c).