IGCSE CHEM_CHAP 3.3_ The mole and the Avogadro constant

Mole

the unit for the amount of substance

Avogadro constant

the number of particles (atoms, molecules, or ions) in one mole of a given substance, equal to 6.02 × 10^23

Molar mass

the mass of one mole of a substance expressed in g/mol, which is numerically the same as the Mr

Relative molecular mass (Mr)

a unitless quantity representing the sum of the relative atomic masses in a formula

Concentration

the amount of solute dissolved in a measured volume of solution

Molar gas volume

the volume occupied by one mole of any gas at room temperature and pressure (r.t.p), taken as 24 dm³

Stoichiometry

the calculation of reacting masses and volumes based on balancing numbers in a chemical equation

Limiting reactant

the reactant that is completely used up first and determines how much product is formed

Excess reactant

the reactant that is leftover after the reaction has finished

Empirical formula

the simplest whole number ratio of atoms of each element in a compound

Molecular formula

the actual number of atoms of each element in a compound

Percentage yield

the ratio of the actual amount of product produced to the theoretical amount possible, multiplied by 100

Theoretical yield

the maximum mass of a substance calculated using the formula Mr × moles

Titration

an experimental technique using a formula triangle (n, c, v) to calculate concentration or volume

Percentage purity

the mass of the pure substance divided by the total mass of the sample, multiplied by 100

Amount of substance

What is the definition of a mole?

6.02 × 10^23

What is the value of the Avogadro constant?

Unitless

What is the unit for relative molecular mass, Mr?

g/mol

What is the unit for molar mass?

180 g/mol

If the Mr of a compound is 180, what is its molar mass?

Mass divided by Mr

How do you calculate the number of moles from mass?

Mr multiplied by moles

How do you calculate the mass of a substance?

Mass divided by moles

How do you calculate the molar mass from experimental data?

1.204 × 10^24

How many atoms are in 2 moles of a monatomic element?

1.806 × 10^24

How many molecules are in 3 moles of carbon dioxide?

3.01 × 10^23

How many molecules are in 0.5 moles of oxygen?

24 dm³

What is the volume of 1 mole of any gas at r.t.p?

24000 cm³

What is the molar gas volume at r.t.p in cubic centimeters?

Divide by 1000

How do you convert a volume from cm³ to dm³?

Multiply by 1000

How do you convert a volume from dm³ to cm³?

Volume divided by 24

How do you calculate moles of a gas at r.t.p using dm³?

Moles multiplied by 24

How do you find the volume of a gas in dm³ at r.t.p?

Solute amount per volume

What is the general definition of concentration?

g/dm³ and mol/dm³

What are the two common units for concentration?

Multiply by Mr

How do you convert concentration from mol/dm³ to g/dm³?

Divide by Mr

How do you convert concentration from g/dm³ to mol/dm³?

n

c × v

Limiting reactant

Which reactant determines the maximum amount of product formed?

Excess reactant

What is the term for the reactant that is not used up?

Molar ratio

What do the balancing numbers in a chemical equation represent?

1:1

In the reaction HCl + NaOH, what is the molar ratio of the reactants?

Empirical formula

What is the term for the simplest whole number ratio of atoms?

Molecular formula

Which formula shows the actual number of atoms in a molecule?

CH2O

What is the empirical formula of glucose, C6H12O6?

6

If the empirical Mr is 30 and the actual Mr is 180, what is the multiplier?

Theoretical yield

What is the maximum possible mass of a product calculated from an equation?

Actual yield

What is the mass of product produced in a real reaction?

Percentage yield

What is actual amount divided by theoretical amount times 100?

Reversible reaction

Why might a reaction not go to 100% completion?

Loss during separation

Why might the actual yield be lower than theoretical?

Side reactions

What happens when reactants react in unexpected ways?

Percentage purity

What is mass of pure substance divided by total mass times 100?

Total Ar / Mr × 100

What is the formula for percentage composition by mass?

28.6%

What is the percentage of magnesium in MgCO3 if Mg

0.64%

If 0.64 g of NaCl is in 100 g of water, what is the percentage purity?

Titration

What process uses experimental data to find a solution's concentration?

0.5 moles

How many moles are in 12 dm³ of gas at r.t.p?

48 dm³

What is the volume of 2 moles of gas at r.t.p?

11.5 g

What is the mass of 0.5 moles of sodium if Ar

3 moles

How many moles are in 426 g of Na2SO4 if Mr

2.71 × 10^24

How many total atoms are in 1.5 moles of CO2?

1.25 mol/dm³

What is the concentration if 0.25 mol is in 0.2 dm³?

M

What unit symbol is sometimes used for molar concentration?

20°C and 1 atmosphere

What are the room temperature and pressure (r.t.p) conditions?

Stoichiometric mass

What is the mass of reactant needed to react exactly according to the equation?

Amount of substance

What is the definition of a mole?

6.02 x 10^23

What is the value of the Avogadro constant?

N

n x NA

n

N / NA

1.204 x 10^24

How many atoms are in 2 moles of Sodium (Na)?

0.5 mol

How many moles are in 3.01 x 10^23 molecules of O2?

n

m / Mr

m

n x Mr

N

(m / Mr) x NA

1 mol

How many moles are in 12g of Carbon (Ar

6.02 x 10^23

How many atoms are in 12g of Carbon?

3 atoms

How many total atoms are in one molecule of CO2?

9.03 x 10^23

How many molecules are in 1.5 moles of CO2?

2.71 x 10^24

How many total atoms are in 1.5 moles of CO2?

Unitless

What is the unit for relative molecular mass (Mr)?

g/mol

What is the unit for molar mass?

24 dm3

What is the volume of 1 mole of any gas at r.t.p?

24000 cm3

What is the molar gas volume at r.t.p in cubic centimeters?

Divide by 1000

How do you convert cm3 to dm3?

Volume / 24

How do you calculate moles of a gas at r.t.p using dm3?

n

c x v