S1.4 Counting Particles by Mass: The Mole

Question 1

State how much elementary entities one mole contains: (1)

Answer 1

• 6.02 x 10^23

Question 2

State Avogadro’s constant and include the units: (1)

Answer 2

6.02 x 10^23 mol^-1

Question 3

State examples of elementary entities: (4)

Answer 3

• Atoms (1)
• Molecules (1)
• Ions (1)
• Electrons (1)

Question 4

Define the following terms: (4)

• Relative Atomic Mass (2):
• Relative Molecular Mass: (2)

Answer 4

• The weighted average mass of one atom of an element (1)
• Compared to 1/12th the mass of a carbon-12 atom. (1)
• The weighted average mass of a molecule (1)
• Compared to 1/12th the mass of a carbon-12 atom. (1)

Question 5

State what Relative Formula mass is used for: (1)

Answer 5

Compounds

Question 6

State what molar mass is numerically equal to: (1)

Answer 6

Relative atomic mass (1)

Question 7

State the formula regarding moles, mass and molar mass: (1)

Answer 7

moles = mass/molar mass (n = m/M) (1)

Question 8

State the formula regarding concentration, volume and moles: (1)

Answer 8

concentration = moles/volume (c = n/v)

Question 9

State how to convert from cm3 to dm3: (1)

Answer 9

divide by 1000 (1)

Question 10

State the formula regarding the percentage composition of an element in a compound. (1)

Answer 10

% composition = mol of element x molar mass of element/molar mass of compound x 100 (% = n of e x mr of e/ mr of c x 100) (1)

Question 11

Define the following terms: (4)

• Molecular formula (2)
• Empirical formula (2)

Answer 11

• Actual number of atoms (1)
• in a compound. (1)
• Lowest whole number ratio of atoms (1)
• in a compound (1)

Question 12

State the formula regarding concentration, mass and volume: (1)

Answer 12

• Concentration = mass/volume (c = m/v)

Question 13

State the formula regarding ppm, mass of solute and solution: (1)

Answer 13

ppm = mass of solute/mass of solution x 10^6 (solute/solution x 10^6)

Question 14

State what ppm is equal to: (1)

Answer 14

mg dm 3 (milligrams decimetres cubed)

Question 15

State avogardro’s law: (1)

Answer 15

The volume occupied by a gas is directly proportional to the amount (in mol) of gas (at constant pressure and temperature)

Question 16

State the formula regarding volume and mols: (1)

Answer 16

k = volume/moles (k = v/n) (1)

Question 17

State the formula for 2 volumes and 2 moles: (1)

Answer 17

v1/n1 = v2/n2 (1)

Question 18

State what equal volumes of any gas contains at standard temperature and pressure: (1)

Answer 18

The same number of particles (mol). (1)

Question 19

State the conditions of STP: (2)

Answer 19

• Temperature of 273K
• Pressure of 100 kPa

Question 20

State how to determine the limiting reactant: (1)

Answer 20

mol/volume (if at STP) divided by the coefficient in the equation