2.1.3 Amount of Substance: Module 2: Foundations In Chemistry: Chemistry OCR A A Level

What is the symbol for amount of substance?

n

What is the unit used to measure amount of substance?

Mole

What does the Avogadro constant represent?

The number of atoms per mole of the carbon-12 isotope.

How to calculate the mass of 1 mole of the element?

Mass of 1 mole = Relative atomic mass in grams

How to calculate moles when mass and molar mass are given?

Moles (mol) = mass (g) / molar mass (g•mol^-1)

State Avogadro’s Law

Under the same temperature and pressure, one mole of any gas would occupy the same volume.

How much volume does a gas occupy, at room temperature and pressure?

24 dm^3 or 24000 cm^3

Define molar gas volume.

The volume per mole of gas molecules.

Why do different gas particles occupy the same volume?

The gas particles are very spread out, hence individual differences has no effect.

How to calculate moles when gas volume is given?

Moles (mol) = Volume (dm^3 ) / 24 or Moles (mol) = Volume (cm^3 ) / 24,000

What are the ideal ways in which gases behave?

● They are in continuous motion.

● No intermolecular forces experienced.

● Exert pressure when they collide with each other or container.

● No kinetic energy is lost in the collisions.

● When temperature increases, kinetic energy of gases also

increase.

Write down the ideal gas equation (in words and symbols, including the units).

pV = nRT

Pressure (Pa) x Volume (m^3) = Number of Moles (mol) x Gas Constant (8.314 J mol^-1) x Temperature (K)

1 atmospheric pressure is equal to how many pascal?

1 atm = 101,325 Pa

0℃ is equal to how many kelvin?

273 K

What does concentration of a solution mean?

It is the amount of solute dissolved in 1 dm^3 of solvent.

How do you calculate moles when concentration and volume are given?

Moles (mol) = Concentration (mol⋅dm^-3) × Volume (dm^3)

What is a standard solution?

A solution of known concentration.

Write down the steps to prepare a standard solution.

1. Weigh the solute using the weigh by difference method.

2. In a beaker dissolve the solute using the solvent.

3. Pour the solution into a volumetric flask.

4. Rinse the beaker using the solution and add it to the flask.

5. Add solvent to the flask carefully until it reaches the graduation line.

6. Mix the solution thoroughly to ensure complete mixing.

What does the terms concentrated and dilute mean?

Concentrated - large amount of solute per dm 3 of solvent.

Dilute - small amount of solute per dm 3 of solvent.

What is a species in a chemical reaction?

Any particle that takes part in a reaction.

What are the four common state symbols?

1. Solid (s)

2. Liquid (l)

3. Gaseous (g)

4. Aqueous (aq)

What does the percentage yield mean?

The efficiency of which reactants are converted into products.

What are the reasons for not obtaining 100% yield?

● Reaction may be at equilibrium.

● The reactants may be impure.

● Side reactions could happen.

● Reactants or products may be left behind while transferring.

● Loss of products during separation and purification.

How is percentage yield calculated?

Percentage yield = [Actual amount of product (mol) / Theoretical amount of product (mol)] x 100

What does atom economy tell us about?

The proportion of desired products compared with all the products formed in the reaction.

How is atom economy calculated?

Atom economy = [Molecular mass of desired product / Sum of the molecular masses of all products] x 100

Does 100% yield mean 100% atom economy?

No, even if all the reactants are converted into products, not all products of the reaction will be the required products.

Which type of reaction has 100% atom economy?

Addition reactions (two or more reactants are combined to form a product).