Question

Copper has two naturally occurring isotopes. Copper-63, with an atomic mass of 62.94 u, makes up 69.17 percent of the sample, and Copper-65, with an atomic mass of 64.93 u, makes up the other 30.83 percent. Calculate the weighted average atomic mass of copper based on the given information.

Answer 1

@akash123

Answer 2

i have the solution, but i have one question on this

Answer 3

ok..tell

Answer 4

an element can have atomic mass as non-whole-numer, becoz its average of all isotopes the element is available in

Answer 5

but in this question, they gave the atomic mass of isotope Carbon-63 as 62.94

Answer 6

which looks weird to me

Answer 7

i mean, the atomic mass of an isotope of an element must always be whole number right ?

Answer 8

becoz we are not taking any average, it would be just number of protons & neutrons

Answer 9

actually mass number is a whole no
and mass no= no of neutrons+ no of prontons

Answer 10

yea, but mass of an isotope must also be an wholenumber right ?

Answer 11

atomic mass of a element= total mass of all the constituents ( e, p and n)

Answer 12

yea in units amu, it should wholenumber right ?

Answer 13

then atomic mass of any isotope must be whole number (in units amu)

Answer 14

im sorry we just started chemistry module 2.. these things look very confusing :s

Answer 15

yes u r right

Answer 16

the mass of isotopes given in the question i posted is misleading then

Answer 17

from where did u get this Q?

Answer 18

from my notes

Answer 19

flvs

Answer 20

flvs?

Answer 21

should i ask my teacher about this

Answer 22

but mass no is a whole no and I think if u represent atomic mass in amu then it can be in fraction.

Answer 23

mass number is always whole number, there no ambiguity there

Answer 24

yes...but now...how do we define atomic mass?

Answer 25

atomic mass of an element can be a fraction too becoz we take average of isotopes

Answer 26

but how can an isotope have fraction mass

Answer 27

u mean atomic mass unit ?

Answer 28

that's true that atomic mass of an element can be a fraction because of different isotopes

Answer 29

I mean..what do u mean by atomic mass of an element?

Answer 30

weighted average of number of neutrons + protons of all the isotopes

Answer 31

is that right ?

Answer 32

im not so sure

Answer 33

can u give me some time? I'll be back in 10 or 15 min.

Answer 34

okay thnks for ur time appreciate very much :)

Answer 35

as we agree that mass no is a whole no
now what is atomic mass--it is total mass of e, p and n

Answer 36

but u have been given in ur question copper-63 has atomic mass 62.94 u.

Answer 37

if we add the masses of all the constituents of Cu-63 then it should come out more than 63 amu

Answer 38

so if atomic mass = total mass of all the constituents- mass defect

Answer 39

so if u express atomic mass in amu then it can be in fraction

Answer 40

proton mass = 1.00727638 amu and neutron mass = 1.0086649156 amu

Answer 41

so if we add mass of all the constituents then we'll definitely get the fraction..but i can understand...where d glitch is?
as we r told that atomic mass of an element is in fraction because of different isotopes of that element existing in nature.

Answer 42

mass no n atomic mass of an element are two different things.
mass no= no of n + no of p...so it must be a whole no
but atomic mass of an element= (total mass of it's constituents) - mass defect