Three isotopes of argon occur in nature – 36 18ar, 38 18ar, 40 18ar. calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and the abundances of each of the isotopes: argon36 (35.97 amu; 0.337%), argon-38 (37.96 amu; 0.063%), argon-40 (39.96 amu; 99.600%). 1. 119.89 amu 2. 39.95 amu 3. 39.96 amu 4. 35.97 amu 5. none of these 6. 37.96 amu 7. 37.95 amu 8. 35.96 amu

3) 39.96 amu

Explanation:

Mass of isotope Ar- 36 = 35.97 amu

% abundance of isotope Ar- 36= 0.337% =

Mass of isotope Ar- 38 = 37.96 amu

% abundance of isotope 2 = 0.063 % =

Mass of isotope Ar- 40 = 39.96 amu

% abundance of isotope 2 = 99.600 % =

Formula used for average atomic mass of an element :

Therefore, the average atomic mass of argon is 39.96 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"

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