calculation

Question

2c Determine the mass of a one-trillion (1.0x10^12) atom sample of copper.
My ans:1.0x10^12/L x 63.5 = 1.05 x10^-10g
The answer from the book = 1.08x10^-11g

3e Calculate the number of e- contained in 2.8g of nitrogen gas
My ans: 2.8/28xLx2x5(as each N atom 5e-)=6.022x10^23
The answer from the book =8.43x10^23

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3q

Answer 1

2c
Your answer is correct, but the answer from the book is incorrect.

Possible reason : Key in “6.5” instead of “63.5” when using the calculator.

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3e
The answer from the book is correct, but your answer is incorrect.

In the expression "2.8/28xLx2x5" :
(1) "28" (the relative molecular mass of N2 molecules) should be "14" (the relative atomic mass of N atom).
(2) "5" (the number of outermost shell electrons in N atom) should be "7" (the number of electrons in N atom).

No. of moles of N atoms = mass/(molar mass) = 2.8/14 = 0.2 (mol)
No. of N atoms = 0.2L = 0.2 x (6.02 x 1023) = 1.204 x 1023 (atoms)
No. of e- = (1.204 x 1023) x 7 = 8.43 x 1023 (e-)