Question

3 how many molecules are in a sample of water, h2o, which has a mass of 60.0 g?
a) 1.67 × 1024 molecules

Explanation:

Step1: Calculate the molar mass of \(H_2O\)

The molar mass of \(H\) is \(1.008\space g/mol\) and for \(O\) is \(16.00\space g/mol\).
For \(H_2O\), \(M=(2\times1.008 + 16.00)\space g/mol=18.016\space g/mol\)

Step2: Calculate the number of moles of \(H_2O\)

Use the formula \(n=\frac{m}{M}\), where \(m = 50.0\space g\) and \(M = 18.016\space g/mol\)
\(n=\frac{50.0\space g}{18.016\space g/mol}\approx2.775\space mol\)

Step3: Calculate the number of molecules

Use Avogadro's number \(N_A = 6.022\times 10^{23}\space molecules/mol\)
\(N=n\times N_A\)
\(N = 2.775\space mol\times6.022\times 10^{23}\space molecules/mol\approx1.67\times 10^{24}\space molecules\)

Answer:

A. \(1.67\times 10^{24}\space molecules\)