Question

How many neutrons are present in 0.760 moles of 18O atoms (the oxygen 18 isotope)? Report your answer to 3 significant figures.

Answer 1

CONCEPT: Calculate the no. of neutrons in one ¹⁸O atom. Then calculate no. of atoms in 0.760 moles of ¹⁸O atom .

No. of neutrons in ¹⁸O atom = mass number - Atomic Number = 18 - 8 = 10

No. of atoms in 0.76 moles of ¹⁸O atom. = No. of moles of ¹⁸O atom X No. of atoms in one mole

No. of atoms in 0.76 moles of ¹⁸O atom. = 0.760 X 6.022 X 10²³X = 4.577 X 10²³ atoms

Therefore no. of neutrons in 4.577 X 10²³ = No. of neutrons in one atom X No. of atoms

No. of neutrons in 4.577 X 10²³ = 10 X 4.577 X 10²³ = 45.7 X 10²³ neutrons.

(Answer has three significant figures)