AQA A-Level Chemistry - Amount of Substance, Amount of Substance - AQA ALevel Chemistry Questions and Answers

AQA A-Level Chemistry - Amount of
Substance, Amount of Substance - AQA A-
Level Chemistry Questions and Answers

Why is Percentage Yield never 100%? -Loss by mechanical transfer (e.g. when moving from

one container to another)

-Loss during separation (e.g. filtration)

-Reaction not completing

-Side reaction




Calculating Moles of a Solvent Dissolved in a Solution Moles = (solution volume(cm^3) x

concentration(mol/dm^3))/1000




Calculating Solution Volume Volume = (moles x 1000)/concentration




Calculating Solution Concentration Concentration = (moles x 1000)/volume




Deducing the Identity of an Unknown in an Equation 1 ) Calculate the moles of the reactant

you are given the most information about

,2 ) Calculate the moles of the reactant containing the unknown

3 ) Calculate the amount in moles of the reactant containing the unknown

4 ) Find the Mr of the reactant containing the unknown (mass/moles)

5 ) Work out the Mr of the part of the reactant known

6 ) Subtract this from the calculated Mr and use this value to identify the unknown




Solutions Reacting Together For example, neutralisation reactions (an acid and an alkali), an

indicator can be used to identify the end-point




Preparing a Burette for Use 1 ) Rinse with deionised water


2 ) Ensure the water flows through the jet then discard the water

3 ) Rinse the burette with the solution you will be filling it with

4 ) Ensure the solution runs through the jet and then discard

5 ) Charge (fill) the burette with the solution you will be using in it




Preparing a Pipette for Use in a Titration 1 ) Use a pipette filler to fill the pipette with

deionised water and then discard the water

2 ) Rinse the pipette with the solution you will be filling it with and then discard

, Using a Burette - Volume of the solution is read at the bottom of the meniscus


- Operate with left hand and swirl conical flask with right hand




Using a Pipette 1 ) Attach pipette filler to top of pipette


2 ) Place pipette in the solution and solution is drawn up using suction to above the line on the

pipette

3 ) The solution is released until the meniscus sits on the line

4 ) The solution is released into a conical flask

-Pipettes measure out exactly 25cm^3 or 10cm^3 - having the exact amount is essential




Conical Flasks -Can be easily swirled so good to use in titrations


-Sloped sides prevent solution from being spat out when it is added

-Rinse with deionised water before using - does not have to be completely dry before use




Volumetric Flasks -Used to dilute a solution before a titration is carried out


-Also used when preparing a solution of a solid

-Has a line indicating an exact volume