Amount of substances

• What is the key concept for chemical calculations?

  The mole
• What is the definition of molar mass?

  Molar mass is the mass in grams of 1 mole of a substance, given in units of g mol^-1.
• How can molar mass for a compound be calculated?

  By adding up the mass numbers of each element in the compound from the periodic table.
• What is the molar mass of calcium carbonate (CaCO₃)?

  The molar mass of CaCO₃ is 100.1 g mol^-1.
• What is the definition of a mole?

  The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.
• What is relative atomic mass?

  Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.
• What is the molar gas volume at room temperature and pressure?

  The molar gas volume is 24 dm³ mol^-1.
• What is Avogadro's constant?

  Avogadro's constant is 6.02 x 10²³ particles in one mole of any specified entity.
• How many atoms are in 1 mole of copper atoms?

  1 mole of copper atoms contains 6.02 x 10²³ atoms.
• How many molecules are in 1 mole of carbon dioxide (CO₂)?

  1 mole of carbon dioxide molecules contains 6.02 x 10²³ molecules.
• How many ions are in 1 mole of sodium ions?

  1 mole of sodium ions contains 6.02 x 10²³ ions.
• How do you calculate the amount in moles from mass and molar mass?

  Amount in moles = mass / molar mass.
• Calculate the amount in moles in 35.0 g of CuSO₄.

  The amount is 0.219 mol.
• What is the conversion factor between milligrams and grams?

  1000 mg = 1 g.
• What is the conversion factor between grams and kilograms?

  1000 g = 1 kg.
• What is the conversion factor between kilograms and tonnes?

  1000 kg = 1 tonne.
• How should answers be given in relation to significant figures?

  Answers should be given to the same number of significant figures as the data provided in the question.
• Calculate the amount in moles in 75.0 mg of CaSO₄.2H₂O.

  The amount is 4.36 x 10^-4 mol.
• What is an empirical formula?

  An empirical formula is the simplest ratio of atoms of each element in the compound.
• What is the general method to calculate an empirical formula?

  1. Divide each mass (or % mass) by the atomic mass of the element.
  2. Divide each of the answers from step 1 by the smallest one of those numbers.
  3. Multiply to give whole numbers if necessary.
• Calculate the empirical formula for a compound containing 1.82 g of K, 5.93 g of I, and 2.24 g of O.

  The empirical formula is KIO₃.
• What is a molecular formula?

  A molecular formula is the actual number of atoms of each element in the compound.
• How do you determine the molecular formula from the empirical formula?


  By calculating how many times the mass of the empirical formula fits into the relative molecular mass (Mr).
• What is the molecular formula for a compound with an empirical formula of C₃H₆O and a Mr of 116?


  The molecular formula is C₆H₁₂O₂.
• Does the Mr need to be exact to convert an empirical formula to a molecular formula?

  No, the Mr does not need to be exact because the molecular formula will be a whole number multiple of the empirical formula.