Chapter 4: Calculations

How can concentration in mol / dm³ be calculated?

Concentration = moles / volume (dm³)

What is a mole?

A mole is a mass of a substance that contains 6.02 × 10²³ particles.

Give the value for Avogadro's constant.

6.02 x 10²³

What is a titration?

A titration is a method used to determine the concentration of an unknown solution.

What is the end-point?

The point at which the reaction is complete, indicated by a color change.

Which formula is used to calculate the number of moles from mass and M?

moles = mass / M.

Which formula is used to calculate the mass of a substance from number of moles and M?

mass = moles x M.

How should solution be added from the burette to reach the end point?

Add drop by drop, swirling in between.

Why is a white tile used in titration?

To see the colour change better.

What is a titre?

Volume of solution added from the burette

What is a limiting reactant?

The reactant that is completely used up in a chemical reaction.

What volume does one mole of any gas occupy at room temperature and pressure?

24 dm³ or 24000 cm³.

What is a unit for concentration?

g/dm³ or mol/dm³.

Which formula is used to calculate concentration from mass and volume?

concentration (g/dm³) = mass / volume (dm³).

Which formula is used to calculate volume from concentration and mass?

volume (dm³) = mass / concentration (g/dm³).

Which formula is used to calculate mass from concentration and volume?

mass (g) = concentration (g/dm³) x volume (dm³).

How can you convert a volume reading in cm³ to dm³?

Divide by 1000.

If the amount of solute in a solution is increased, what happens to its concentration?

The concentration increases.

If the volume of water in a solution is increased, what happens to its concentration?

The concentration decreases.

What is the yield of a reaction?

The mass of product obtained from the reaction.

What is the theoretical yield of a reaction?

The maximum mass of the product that could have been produced.

Why is the actual yield always less than the theoretical yield?

• Some of the product can be lost on separation

• Unexpected side reactions between reactants

• Reactions may be reversible

What is the percentage yield?

The actual yield as a proportion of the theoretical yield.

How is percentage yield calculated?

(actual yield / theoretical yield) x 100.

What is atom economy?

A measure of how many atoms of the reactants end up as useful products.

Why is a high atom economy desirable?

It results in less waste and is more sustainable.

How is percentage atom economy calculated?

(M of useful product / M of all products) x 100.