chemistry - quantitative chemistry

topic 3

What is the relative formula mass (Mr)?

The sum of the relative atomic masses (Ar) of the atoms in a formula.

What is the unit of relative formula mass (Mr)?

It has no units (it's a ratio).

What is the law of conservation of mass?

Mass is not lost or gained in a chemical reaction.

Why might mass appear to change in a reaction?

Due to a gas being released or a gas from the air being used.

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

(Ar × number of atoms of that element / Mr of compound) × 100

What is a mole?

The amount of a substance that contains 6.02 x 10^23 particles (Avogadro's number).

What is the formula for number of moles?

Number of moles = mass (g) / Mr

What is the mass of one mole of a substance?

Equal to its relative formula mass in grams.

What is the limiting reactant?

The reactant that is completely used up in a reaction, limiting the amount of product formed.

How can you calculate the mass of a product from a limiting reactant?

1) Work out moles of limiting reactant. 2) Use ratio from equation. 3) Convert moles of product to mass.

What is the concentration of a solution?

Amount of solute in a certain volume of solution.

What is the formula for concentration (g/dm^3)?

Concentration = mass of solute (g) / volume of solution (dm^3)

How do you convert cm^3 to dm^3?

Divide by 1000

What is the formula for number of moles in a solution?

Moles = concentration (mol/dm^3) × volume (dm^3)

What is the atom economy?

(Formula mass of desired product / total formula mass of all products) × 100

Why is a high atom economy important?

Reduces waste, uses resources efficiently, is more sustainable.

What is percentage yield?

(Actual mass of product / maximum theoretical mass) × 100

Why is percentage yield rarely 100%?

Due to incomplete reactions, side reactions, or loss during transfer.

What are the units for concentration in mol/dm^3?

Moles per decimetre cubed.