Question

2.0 mol cu
express your answer using two significant figures.
n =
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part b
5.4×10^{-3} mol c
express your answer using two significant figures.
n =
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part c
25.4 mol he
express your answer using three significant figures.

Explanation:

Step1: Recall the formula for number of atoms

The formula to find the number of atoms \(N\) is \(N = n\times N_{A}\), where \(n\) is the number of moles and \(N_{A}=6.022\times 10^{23}\text{ atoms/mol}\)

Part A: For \(n = 2.0\space mol\space Cu\)

Substitute \(n = 2.0\space mol\) and \(N_{A}=6.022\times 10^{23}\text{ atoms/mol}\) into the formula \(N=n\times N_{A}\)
\(N=(2.0\space mol)\times(6.022\times 10^{23}\text{ atoms/mol})\)
\(N = 1.2044\times 10^{24}\text{ atoms}\)
Rounding to two significant figures, \(N = 1.2\times 10^{24}\text{ atoms}\)

Part B: For \(n = 5.4\times 10^{-3}\space mol\space C\)

Substitute \(n = 5.4\times 10^{-3}\space mol\) and \(N_{A}=6.022\times 10^{23}\text{ atoms/mol}\) into the formula \(N=n\times N_{A}\)
\(N=(5.4\times 10^{-3}\space mol)\times(6.022\times 10^{23}\text{ atoms/mol})\)
\(N=3.25188\times 10^{21}\text{ atoms}\)
Rounding to two significant figures, \(N = 3.3\times 10^{21}\text{ atoms}\)

Part C: For \(n = 25.4\space mol\space He\)

Substitute \(n = 25.4\space mol\) and \(N_{A}=6.022\times 10^{23}\text{ atoms/mol}\) into the formula \(N=n\times N_{A}\)
\(N=(25.4\space mol)\times(6.022\times 10^{23}\text{ atoms/mol})\)
\(N = 1.53\times10^{25}\text{ atoms}\) (rounded to three significant figures)

Answer:

• Part A: \(1.2\times 10^{24}\text{ atoms}\)
• Part B: \(3.3\times 10^{21}\text{ atoms}\)
• Part C: \(1.53\times 10^{25}\text{ atoms}\)