The average atomic masses of some elements may vary, depending upon souces of their ores. naturally occurring boron consist of two isotopes with accurately known masses (10 b, 10.0129 amu and 11b, 11.0931 amu). the actual atomic mass of boron can vary grom 10.807 to 10819, depending on whether the mineral source is from turkey or the united states. calculate the percent abundances leading to the two values of the average atomic masses of boron from these two countries.

1) atomic mass 10.807

Percentage of 10B= 26.48%

Percentage of 11B= 73.52%

2) atomic mass 10.819

Percentage of 10B= 25.37%

Percentage of 11B= 74.63%

Explanation:

The average atomic mass of an element is the weighted average of the atomic masses of the isotopes of the element.

If a sources is rich in one kind of isotope then the atomic mass will be nearer to its value and if it is rich in another kind then the atomic mass will be nearer to its value.

Let us calculate the percentage abundance in each case.

a) Average atomic mass =

Average atomic mass = 10.807

Let the % of 10B isotope = x

% of 11B isotope =100-x

putting in the formula

Percentage of 11B= 100-26.48= 73.52%

a) Average atomic mass =

Average atomic mass = 10.819

Let the % of 10B isotope = x

% of 11B isotope =100-x

putting in the formula

Percentage of 11B= 100-25.37= 74.63%

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-