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# Chemistry Help watch

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1. Hey I was just wondering If anyone can help with these 2 questions

1)Why is carbon-12 the only atom with a relative atomic mass which is an exact whole number?

2) Calculate the mass of 1 mol of H+ ions ( but then in the question it states the weight of one electron - which i dont understand as i thought a H+ ion had no electrons, just a single proton? so why state the mass of an electron?)

Cheers.
2. (Original post by Rob92)
Hey I was just wondering If anyone can help with these 2 questions

1)Why is carbon-12 the only atom with a relative atomic mass which is an exact whole number?

2) Calculate the mass of 1 mol of H+ ions ( but then in the question it states the weight of one electron - which i dont understand as i thought a H+ ion had no electroncs, just a single proton? so why state the mass of an electron?)

Cheers.
I'm not 100% on question one, so I better hadn't corrupt your mind with false info.

But question (2) is quite simple. They've given you the weight of an electron, because to deduce the weight of a proton, you'll need to subtract this value from the weight of a normal Hydrogen atom (these are composed of one electron and one proton). This will give you the weight of a proton. Then, multiply this vale with Avagadro's number (6.02 X 10^23), which'll give you the weight of one mole of H+.
3. The answer to question 1 lies in the definiton of relative atomic mass:

The mass of 1 mole of an element on a scale where the mass of 1 mole of Carbon atoms is 12 units.

Therefore, the scale is standardised by Carbon, which has a given value of 12, everything else will be slightly, if not, significantly off a whole number.
4. (Original post by Rob92)
1)Why is carbon-12 the only atom with a relative atomic mass which is an exact whole number?.
One carbon-12 atom is an exact whole number by international agreement because one atom of the carbon-12 isotope has been assigned a mass of 12 atomic mass units.

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