Chemistry Homework

[andymacdcfc]

I have this chemstry homework but I have never done this sort of quesiton before and I was hpoing you could helf me. This is it:

Element X has 2 isotopes. One istope has a mass number of 26 and an abundance of 80%. The other isotope has a mass number 28.

(a) What is meane by the term isotope?

(b) Calculate the Relative Atomic Mass of element X.

[maelogman]

a)isotopes are forms of an element with the same atomic number but different mass numbers,,,OR.. atoms with the same number of protons but different numbers of neutrons

 

b) of every hundred atoms 80 have mass 26, and the other 20 have mass 28

total mass is (80 x 26) + (20 x 28) = 2080 + 560 = 2640

R.A.M. is average mass, i.e. 2640/100 = 26.4

[Piper-AK]

Relative Atomic Mass is the mass of an atom compared to Hydrogen which is given a mass of 1.  So your atom weight an avarage of 26.4 times more than Hydrogen in the above calculation.

[ursula62]

True, although if you wanted to be pedantic... there are isotopes of hydrogen (e.g. deuterium and tritium) that have a mass of 2 and 3 respectively, so the actual mean atomic mass of hydrogen is not exactly one!

[Piper-AK]

I know!  How on earth do we ever calculate anything??? 

[brachiopod]

I thought RAM was calculated with respect to Carbon-12, not hydrogen? I am open to contradiction.

[samz90]

You are right. Atomic masses are always given relative to a standard mass. This standard mass is C-12 = 12.000000. Abundance = 98.93%.