5.1 - Moles II
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in a lab what are volumes of gas usually measured in
cubic centimetres (cm^3)
what more common unit is used in mole calculations for volume
cubic decimetres (dm^3)
what is the scale factor to convert between cm^3 and dm^3
1000
how do you get from cm^3 to dm^3
divide by 1000
how do you get from dm^3 to cm^3
multiply by 1000
what is the equation to calculate the moles of a gas
moles = volume (dm^3) / 24 dm^3
what is the concentration of a solution
a measure of how much solute is dissolved per unit volume
what is the concentration of a solution measured in
mol/dm^3
what formula is used to calculate the concentration of a solution
concentration (mol/dm^3) = moles (mol) of solute / volume (dm^3) of solvent
what is titration used to measure
the volume or ‘titre’ of acid needed to neutralise a particular volume of alkali or vice-versa
what are the two special pieces of equipment used in titrations
volumetric pipette and burette
what is a volumetric pipette
measures out 25cm^3 very accurately
what is a burette
measures any volume to the nearest 0.05 cm^3
how do you set up a titration
• use a volumetric pipette to place 25cm^3 of the unknown alkali into a conical flask • add a few drops of phenolphthalein indicator to the flask • fill a burette with known acid and clamp it above the conical flask
how do you use a titration
• measure the initial volume of known acid on the burette, to the nearest 0.05 cm^3 • use the burette to add acid into the conical flask drop-by-drop and swirling the flask • close the burette tap as soon as the colour in the conical flask changes — the start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise) • measure the final volume of known acid on the burette, to the nearest 0.05 cm^3 • calculate titre (final volume - initial volume) • repeat to get concordant (within 0.2 cm^3) titres
explain the process of doing a titration
• use a volumetric pipette to place 25cm^3 of the unknown alkali into a conical flask • add a few drops of phenolphthalein indicator to the flask • fill a burette with known acid and clamp it above the conical flask • measure the initial volume of known acid on the burette, to the nearest 0.05 cm^3 • use the burette to add acid into the conical flask drop-by-drop and swirling the flask • close the burette tap as soon as the colour in the conical flask changes — the start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise) • measure the final volume of known acid on the burette, to the nearest 0.05 cm^3 • calculate titre (final volume - initial volume) • repeat to get concordant (within 0.2 cm^3) titres