Chemistry - Quantative chemistry

formula for moles

number of moles = mass(g) / mr

limiting reagent

the chemical that runs out 1st in a reaction, stopping it

moles

are the standard base counting unit for the amount of a substance.

How many particles are in a mole of a substance

6.022 x 10²³

percentage yield

A measure of the actual yield of a reaction.

formula for percentage yield

percentage yield = actual mass / theoretical mass

Factors that affect percentage yield

-side reactions may occur

- Some residue of the product may be left on the equipment

-the reaction may be reversible ( the product turns back into the reactants)

-the reactants may not be pure

atom economy

A measure of the proportion of reactants that have been converted into products. It is calcualted by using the formula, atom economy = mass of desired product over total ass of reactants x 100. Reactions with a high atom economy are desirable.

Formula for atom economy

atom economy = (mr of desired product / total mr of compound) x 100

formula percentage composition

percentage composition = (total Ar of element / Mr of the compound) x 100

percentage composition

The percentage by mass of a compound that is due to a particular element

What is 1 dm³ in cm³?

1000 cm³

molar gas volume at room temperature

24 dm³ or 24000 cm³

What does 1 molecule of gas occupy at room temperature

24 dm³ or 24000 cm³

formula for molar gas volume

volume (dm) = moles x 24 (at RTP) or

volume (cm) = moles x 24000 (at RTP)

concentration

the amount of solute in a volume of soultion

Formula for concentration in g/dm³

concentration (g/dm³) = amount of solute (g) / volume of solution (dm³)

or

concentration (g/dm³) = amount of solute (g) / volume of solution (cm³) x 1000

Formula for concentration in mol/dm³

concentration (mol/dm³) = amount of solute (mol) / volume of solution (dm³)

titration

a practical used to find out how much acid is used to neutralise an alkali with a given volume and concentration.

titration steps

1. Use a pipette to measure a fixed volume (25cm³) of an alkali with a known concentration and put it in a conical flask

2. Add a few drops of indicator

3. Fill the burette with the acid of an unknown concentration

4. Add the acid whilst swirling the flask until the indicator shows it has reached the end point

5. Record the volume of the acid used

6. Repeat the experiment until you get 3 concordant results and find the average