atomic mass, and isotopes?

Question

1. There are four naturally occurring isotopes of the element Copper. The perent abundance of each is :
^60 Cu= 4.31%
^63 Cu = 83.76%
^65 Cu = 9.55%
^66 Cu = 2.38%

Calculate the average atomis mass of copper: (please show work so i cant figure out how it was done thank you so much!!!)

2. Determine average atomic mass of the following mixtures of isotopes:

A. 80.0 % ^127 I,
17.0 % ^ 126 I,
3.00 % ^128 I

B. 95.00% ^14 N
3.00% ^15 N
2.oo% ^ 16 N

Answer 1

Well you have to look up the EXACT masses of the four isotopes of copper. For the sake of argument, I'm going to use round numbers. You can look up and plug in the exact figures in place of 60, 63, 65, and 66.

60(0.0431) + 63(0.8376) + 65(0.0955) + 66(0.0238) = average mass

For the others,

A 127(0.8) + 126(0.17) + 128(0.03).
Again you need to look up the exact masses to use in place of 127, 126, and 128

B 14(0.95) + 15(0.03) + 16(0.02)

Again you need to look up the exact isotopic masses to use in place of 14, 15, and 16.

Answer 2

1.
{[60 x 4.31] +[63 x 83.76] + [65 x 9.55] + [66 x 2.38]}/100
63.1331 for Cu

2.A.
{[80 x 127] + [ 17 x 126] + [3 x 128]}/100 = 126.86 => I

2.B.
{[95 x 14] + [3 x 15] + [2 x 16]}/100 = 14.07 => N

Answer 3

1)K...this is how you would do this:
4.31/100 x 60=2.586
83.76/100 x 63=52.7688
9.55/100 x 65=6.2075
2.38/100 x 66=1.5708

2.586+52.7688+ 6.2075+1.5708=63.1331(average atomic mass of Copper)

2) 80/100 x 127=101.6
17/100 x 126=21.42
3/100 x 128=3.84

101.6+21.42+3.84=126.86(average atomic mass of Iodine)

3) 95/100 x 14=13.3
3/100 x 15=.45
2/100 x 15=.3

13.3+.45+.3=14.05(average atomic mass of Nitrogen)

:)