A sample of sodium chloride (NaCl) was determined to have a mass of 25.06 g. Cal

Question

A sample of sodium chloride (NaCl) was determined to have a mass of 25.06 g. Calculate the number of moles of NaCl in this sample. Another sample of NaCl has mass of 15.65 g. Calculate the number of sodium atoms present in this sample. A sample of an unknown white solid was analyzed. The sample contains approximately 1.08 Times 10^22 molecules of the unknown substance. Calculate the number of moles of the substance in the sample. If the mass of,he unknown is 1.5044 g. calculate the experimental molar mass of the substance.

Explanation / Answer

1) A sample of sodium chloride (NaCl) was determined to have a mass of 25.06 g. Calculate the number of moles of NaCl in this sample.

MW = 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol

25.06 g x   1 mol = 0.4288 moles NaCl

58.44 g

2) Another sample of NaCl has a mass of 15.65 g. Calculate the number of sodium atoms present in this sample.

15.65 g x   1 mol = 0.2678 moles NaCl

58.44 g

  1 mol Na x 0.2678 moles NaCl = 0.2678 moles Na

1 mol NaCl

6.02 x 1023 atoms Na x 0.2678 moles Na = 1.6122 x 1023 atoms Na

1 mol Na

3) A sample of an unknown white solid was analyzed.

a) The sample contains approximately 1.08 x 1022 molecules of the unknown substance. Calculate the number of moles of the substance in the sample.

1 mol of molecules x 1.08 x 1022 molecules = 0.0179 moles

6.02 x 1023 molecules

b) If the mass of the unknown is 1.5044 g, calculate the experimental molar mass of the substance. Hint: what are the units of molar mass?

MW = 1.5044 g / 0.0179 moles = 84.04 g / mol

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