Topic 3 - Quantitative chemistry

How to workout the % mass of an element in a compound?

What is Avogadro constant?

6.02 X 10²³

What is one mole of any substance?

1. One mole of any substance has 6.02 X 10²³ particles - can be atoms, molecules, ion…

2. One mole of any substance will have a mass in grams that = relative formula mass

How to work out number of moles in a given mass?

What is conservation of mass in a reaction?

No atoms are destroyed and no atoms are created - mass is conserved?

What can explain if the mass does increase in a reaction?

1. The reactants is a gas and products are solids or aqueous

2. Reactant can react with the air in the reaction vessel

What are the explanations if the mass decreases in a reaction?

If the reaction vessel isn’t contained then gas can escape

Why are reactants usually in excess

To make sure that all of the other reactant is used up

What is a limiting reactant?

The reactant that gets used up first

How to calculate moles?

moles = mass/relative formula mass

What is the mass of product called?

Yield of a reaction

How to calculate volume of gas using moles?

Volume of gas = (Mass of gas/ relative formula mass) X 24

What can concentration be defined as?

The amount of a substance in a certain volume of a solution

What is the formula for concentration? (g/dm³ )

Concentration = mass of solute/volume of solvent

What is the formula for concentration? (mol/dm³ )

concenctration = moles of solute/ volume of solvent

How to convert from mol/dm³ to g/dm³ ?

Use the formula mass = moles X M (rearrange it)

What is the atom economy?

The atom economy of a reaction tells you how much of the mass of the reactants is wasted and how much ends up as the desired product.

What is the formula for atom economy?

atom economy = (relative formula mass of desired product/relative formula mass of all reactants) X 100

What is the formula for percentage yield?

(mass of product actually made/ maximum theoretical mass of product) X 100

Why are yields always less than 100%?

1. Not all reactants react to make a product

2. There might be side reactions

3. You lose some product when you separate it form the reaction mixture