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Moles & Molar Mass
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Moles & Molar Mass
A sample of magnesium weighs 12.0 g. Magnesium reacts with oxygen to form magnesium oxide (MgO).
i) Write the formula for calculating mass using moles and molar mass.
ii) Calculate the number of moles of magnesium in the sample.
How did you do?
Using the mole ratio, determine the number of moles of MgO formed.
How did you do?
Calculate the mass of MgO produced. (Molar masses: Mg = 24.30 g/mol, MgO = 40.30 g/mol)
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A container holds 4.5 g of water (H2O).
Calculate the number of moles of water in the container.
How did you do?
Calculate the total number of water molecules in the sample (Avogadro’s number = 6.022 × 1023).
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Determine the total number of hydrogen atoms in the sample.
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Determine the ratio of oxygen atoms to hydrogen atoms in the sample.
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A sample of a hydrated salt, MgSO4⋅xH2O, is heated to remove all the water of crystallization, leaving an anhydrous salt.
Mass of hydrated salt: 4.93 g
Mass of anhydrous MgSO4: 2.41g
Calculate the mass of water lost during heating.
How did you do?
Calculate the number of moles of water lost.
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Determine the number of water molecules (x) in the formula of the hydrated salt.
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A student is tasked with preparing a solution containing 0.5 moles of sodium chloride (NaCl).
Calculate the mass of sodium chloride required.
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If the student uses 35.0 g of sodium chloride, calculate the molarity of the solution if the final volume is 500.0 mL.
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Suggest one way the student could correct the solution in part (b) to meet the original molarity target.
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A reaction occurs between aluminum and chlorine gas to form aluminum chloride (AlCl3):
2Al + 3Cl2 → 2AlCl3
Calculate the number of moles in a 4.92 g sample of aluminum.
How did you do?
If 19.08 g of chlorine gas (Cl2) is used, determine the limiting reactant. Justify your answer.
How did you do?
Calculate the maximum mass of AlCl3 produced. (Molar mass: AlCl3 = 133.30 g/mol)
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A 50.0 g sample of a compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
Calculate the number of moles of each element in the sample.
How did you do?
Determine the simplest whole-number ratio of the elements and state the empirical formula of the compound.
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