Question 1

Multiple choiceEasy1 mark

A sample contains 0.0400 mol0.0400\ \text{mol} of O2\mathrm{O_2} molecules. What is the number of oxygen atoms in the sample? Use NA=6.02×1023 mol−1N_\mathrm{A}=6.02\times10^{23}\ \text{mol}^{-1}

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Answer: C. Each O2\mathrm{O_2} molecule contains two oxygen atoms. Thus, 0.0400×6.02×1023×2=4.82×10220.0400\times6.02\times10^{23}\times2=4.82\times10^{22} oxygen atoms.

A: uses 0.00400 mol0.00400\ \text{mol} and counts O2\mathrm{O_2} molecules rather than oxygen atoms.
B: counts O2\mathrm{O_2} molecules but omits the two oxygen atoms in each molecule.
D: shifts the amount one place too high, using 0.400 mol0.400\ \text{mol}

Remember: multiply by the number of specified entities in each molecule when counting atoms.

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