Mole Concept

What is the actual mass of a proton in kg?

1.67 × 10^-27

What is the actual mass of a neutron in kg?

1.67 × 10^-27

What is the actual mass of an electron in kg?

9.11 × 10^-31

Charge of proton

+1

Charge of neutron

0

Charge of electron

-1

Relative mass of protons and neutrons

1

Relative mass of electrons

1/1840

Definition: Atomic number

Number of protons in the nucleus of an atom

Definition: Nucleon number / Mass number

Total number of protons and neutrons in the nucleus of an atom

Definition: Isotopes

Atoms of the same element having same number of protons but different number of neutrons

Why was carbon 12 chosen as the standard?

• Carbon exists as a stable solid at rtp → suitable for storage, transportation

• Most abundant isotope of Carbon → readily available

Isotopes have the ______ chemical properties but _______ physical properties (e.g. boiling point, density)

the same chemical properties, different physical properties

Definition: Relative abundance

Percentage of isotopes in naturally occurring element (e.g. ³⁵Cl:³⁷Cl = 75:25)

Q) Calculate the A_r of chlorine using the data: ³⁵Cl:³⁷Cl = 75:25

Definition: Relative Isotopic Mass

Mass of one atom of an isotope of an element compared to 1/12 the mass of one carbon-12 atom

Definition: Relative Atomic Mass

Average mass of one atom of an element compared to 1/12 the mass of one carbon-12 atom

Definition: Relative Molecular Mass

Average mass of one molecule of an element or compound compared to 1/12 the mass of one carbon-12 atom

Definition: Relative Formula Mass (only for ionic compounds)

Average mass of one formula unit of an ionic compound compared to 1/12 the mass of a carbon-12 atom

Definition: Avogadro Constant (L)

Number of particles per mole of a substance with the value of 6.02 × 10²³

Definition: Mole

Amount of substance that contains 6.02 × 10²³ elementary entities

Definition: Molar mass (M_r)

Mass of one mole of substance

Unit: g mol^-1

Formula: Amount from Mass and M_r

Definition: Molar Volume

Volume occupied by one mole of any gas at a particular temperature and pressure

Definition: Avogadro’s Law

Equal volumes of all gases at the same temperature and pressure contain equal number of moles irrespective of the gas type

Molar Volume for Standard Temperature and Pressure

273K, 10⁵ Pa [1 bar] → 22.7dm³

Molar Volume for Room Temperature and Pressure

293K, 101325 Pa [1 atm] → 24.0dm³

Formula: Amount from Volume and Molar Volume (22.7 or 24.0)

Formula: Ideal Gas Equation

Definition: Empirical Formula

Formula that shows the simplest whole number ratio of atoms of each element present in the compound

Definition: Molecular Formula

Formula that shows the actual number of atoms of each element present in one molecule of the compound

Q) A hydrocarbon had 92.3% carbon, 7.7% hydrogen and a M_r of 78. Calculate its empirical and molecular formula.

Formula: Combustion Equation

Q) 10cm³ of a gaseous hydrocarbon was mixed with 100cm³ of oxygen and ignited. 80cm³ of gas remained which was reduced to 50cm³ on shaking with excess aqueous KOH. Find molecular formula of the hydrocarbon assuming all volumes are at room temperature and pressure.

Definition: Stoichiometric amount

Amount used in the exact proportion as shown in the equation

Definition: Excess Reagent

Reagent that is not completely used up in a chemical reaction

Definition: Limiting Reagent

Reagent that is completely used up in a chemical reaction

Definition: Theoretical Yield

Quantity of product that will be formed if all limiting reagent reacts

Definition: Actual Yield

Quantity of product that is actually obtained during an experiment

Formula: Percentage Yield

Definition: Concentration

Amount of solute dissolved in 1 dm³ of solution (mol dm^-3)

Mass of solute dissolved in 1 dm³ of solution (g dm^-3)

Formula: Convert mol dm^-3 to g dm^-3

Formula: Amount from Concentration and Volume

When a solution is diluted by adding more solvent, the number of moles in the solute in the diluted solvent ________

remains the same

Formula: Dilution Factor

Definition: Parts per million (ppm)

Number of parts out of a total of one million parts (10⁶)

Formula: PPM

In aqueous → grams of substance per million grams of solution

In gaseous → number of volume units of gas per million volume units of gaseous mixture

Q) A particular study showed that SO₂ can be detected at 2.65 × 10^-6 g in 1 dm³ of an air sample.

(i) What is the volume of SO₂ at rtp?

(ii) How many parts per million (ppm) by volume of SO₂ be detected in the air sample?

Prefixes

Unit Conversions