Question

1. complete the following table and use it for the calculations below.

a)

b) calculate the number of moles in the sample.

c) calculate the number of molecules in the sample.

d) using the number of sodium atoms in the formula, calculate the number of sodium atoms in the sample.

Explanation:

Step1: Calculate the molar mass of \(Na_2SO_4\)

• Molar mass of \(Na = 22.99\ g/mol\), \(S=32.07\ g/mol\), \(O = 16.00\ g/mol\)
• \(M(Na_2SO_4)=2\times22.99+32.07 + 4\times16.00\)
• \(M(Na_2SO_4)=45.98+32.07+64.00 = 142.05\ g/mol\)

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

• Formula \(n=\frac{m}{M}\), where \(m = 13.42\ g\) and \(M = 142.05\ g/mol\)
• \(n=\frac{13.42}{142.05}\approx0.0945\ mol\)

Step3: Calculate the number of molecules (\(N\))

• Use \(N=n\times N_A\), \(N_A = 6.022\times10^{23}\ mol^{-1}\)
• \(N=0.0945\times6.022\times 10^{23}\)
• \(N = 5.69\times10^{22}\) molecules

Step4: Calculate the number of sodium atoms

• In \(Na_2SO_4\), there are 2 \(Na\) atoms per molecule
• Number of \(Na\) atoms \(=2\times N\)
• \(=2\times5.69\times10^{22}=1.14\times10^{23}\) atoms

Answer:

a) \(142.05\ g/mol\)
b) \(0.0945\ mol\)
c) \(5.69\times10^{22}\) molecules
d) \(1.14\times10^{23}\) atoms