C3 : Quantitative Chemistry

What is relative atomic mass (A_r)?

The number of neutrons and protons (mass number)

What is relative formula mass (M_r)?

The sum of all of the atomic masses of each element present in the formula

What is the M_r of MgCl₂?

( A_r of Mg = 24 ) ( A_r of Cl = 35.5)

95

What is the formula for percentage mass of an element in a compound?

What is a mole?

An amount of a substance

What is Avogadro’s constant + what does it show?

6.02 × 10²³

How many atoms there are in a molecule

3 moles of atoms

5 moles of atoms

5 moles of atoms

2 x 6.02 × 10²³ = 1.024 × 10²⁴

3 × 6.02 × 10²³ = 1.806 × 10²⁴

6.02×10²³

1.806 × 10²⁴

What is the unit for moles?

mol

What is the mass of one mole of an atom in relation to its relative formula mass (M_{r) ?}

Mass of one mole of an atom is equal to M_r the of that atom

What is the mass one mole of carbon?

What is the mass one mole of nitrogen?

What is the mass one mole of carbon dioxide?

What is the formula for the number of moles in a given mass?

Moles = mass/M_r

( A_r of Carbon = 12) ( A_r of Oxygen = 16)

1.5mol

( A_r of Carbon = 12) ( A_r of Oxygen = 16)

48g

What is the formula for the mass of products and reactants in a chemical reaction in terms of mass?

Mass of products = Mass of reactants

Why would mass decrease in a chemical reaction?

Because one of the reactants or products is a gas

What is a limiting reactant + why is it called this?

• The reactant is the reactant that is completely used up during a reaction

• It limits the amount of product made

What does it mean when a reactant is in excess + why are reactants used in excess?

• A reactant that has not been used up when the limiting reactant has been used up

• This is to make sure the limiting reactant has been used

What is the relationship between the amount of product and the amount of limiting reactant?

The amount of product formed is directly proportional to the amount of limiting reactant

159.5g

14.6(25)g

31.75g

272g

190g

426g

136g

At room temperature and pressure what does one mole of any atom occupy?

24dm³

What is the formula for the volume of a known mass of any gas at room temperature?

(Cl₂)

120 dm³

48 dm³

What is concentration?

The amount of substance (mass or the number of moles in a substance) in a certain volume of a solution

What is a solute + what is the relationship between the amount of solute + the concentration?

• Solute → Substance that is dissolved

• More solute there is in a given volume means more concentrated the solution is

What is the formula for the concentration in terms of mass of solute?

What is the formula for the concentration in terms of number of moles of solute?

0.1 moles

88.8g

34 mol/dm³

0.71 mol/dm³

What is atom economy?

The measure of the amount of starting materials that end up as useful products

What is the formula for atom economy?

Why is a higher atom economy better? (4)

• Less waste

• Low atom economy use resources very quickly

• Materials are expensive

• Waste is hard to get rid of

What do scientist try to do with unwanted side products?

They try to repurpose them in other reactions

What is the relationship between the amount of products and the atom economy?

The more the products, the lower the atom economy

What is a yield?

The amount of product made

What is the formula for percentage yield?

What does 100% yield mean?

All the products expected to be made were made

What is the benefits of a high percentage yield? (2)

• Reduce waste

• Reduce costs

What are 3 reasons as to why there will never be 100% yield?

• Reversable reactions

• Side reactions

• Product lost from separation (filtration)

240g

62.5%

20%

60%