quantitative chemistry part 2

gcse aqa march 2025

moles calculation mass and RFM

moles = mass/RFM

moles calculation volume and concentration (in moldm^-3)

moles = concentration x volume (n = cv)

What do pipettes measure?

Measure one fixed volume accurately

What do burettes measure?

Measures variable volumes accurately

concentration calculation (in gdm^-3)

concentration = mass/volume

cm³ to dm³

divide by 1000 = dm³

dm³ to cm³

multiply by 1000 = cm³

gdm^-3 to moldm^-3

divide by RFM = moldm^-3

moldm^-3 to gdm^-3

multiply by RFM = gdm^-3

How is the concentration of a solution related to the mass of a solute and the volume of the solution?

The more the solute (the thing you dissolve), the higher the concentration. The higher volume of the solution, the lower the concentration.

How is the concentration of a solution in moldm^-3 related to the mass of the solute and volume of the solution?

The concentration (in moldm^-3) is the mass of solute in moles over the volume of the solution

What is the volume of 1 mole of gas at room temperature and pressure?

24dm³ (24,000cm³)

What is molar volume?

The volume occupied by 1 mole of gas (24cm³ at room temperature and pressure)

molar volume calculation (moles for gases, input 24 for volume at room temp/pressure)

molar volume = volume/moles

gases volume calculation using moles

Volume (cm³) = moles x 24000cm³

What is the mole train for concentration and volume?

Find moles of known → use balanced equation to form molar ratio → find moles of unknown → find volume/concentration of unknown using moles

What is uncertainty in a chemistry measurement?

The range of values in which the true value lies (estimated degree of error)

How do you calculate uncertainty?

Range of values/2

What symbol must you always put in front of uncertainty measurements?

± (plus-minus sign)

How do you carry out titration? (10)

Rinse burette and pipette with distilled water, then burette with acid and pipette with alkali, discard solution used to rinse, use pipette to transfer (25cm³) of alkali to conical flask (which should be on a white tile), add 3 drops of (methyl orange) indicator, fill the burette with the acid and note the starting volume, add the acid to the alkali while swirling the flask, and stop when the indicator changes colour, take the final volume of the acid, repeat 3 times and make a table of results

What is a random error?

An error that occurs due to unpredictable changes in measurements

What is a zero error?

A type of systematic error that occurs when a piece of equipment measures 0 when it should not or doesn’t measure 0 when it should

What is a systematic error?

A consistent error that occurs in the same direction each time, likely due to malfunctioning equipment