2024 Chemistry Practical Notes

Practic al not es 1 Practical notes StatusPractical Titration Indicator Acidic Neutral Basic pH range Methyl orange Red Orange Yellow 3.2  4.4 Screened methyl orange Violet Grey Green 3.2  4.4 ThymolphthaleinColourless Colourless (if acidic → neutral)/ pale blue (if basic → neutral) Blue 9.4  10.6 Thymol blue Yellow Green Blue 8.0  9.6 ** Usually, an indicatorʼs neutral colour is a mix of its acidic and basic colour If need to see if reached end point  Record the value first, then add another drop from burette → if colour changed, use the previous value Solution with unknown concentration should be in conical flask Tables: 1 2 Initial burette reading / (2dp) (2dp) Final burette reading / (2dp) (2dp) Volume of (reactant) / (2dp) (2dp) ** Put tick under the values you will use 0.10 ) Mass of empty weighing bottle / g Mass of weighing bottle + (reactant) / g Mass of (reactant) used / g ** If experiment does not expect you to use distilled water to transfer all the reactants in the weighing bottle, insert row “Mass of weighing bottle + residual (reactant) / gˮ under the “Mass of weighing bottle + (reactant) / gˮ ** dp for this table depends on the weighing balance Possible question types: Whether a value calculated from the experimental results will be more accurate if an instrument of a better precision is used to measure out the reactant used in excess Titration Gas Collection Chemic al ener getics/ Calor imetr y R e action K inetics Inor ganic Or ganic Planning % er r or cm3 cm3 cm3 cm3

Practic al not es 2 No, the precision of the volume measured for the reactant does not matter if it is used in excess Why need to dilute some reactants before putting them inside the conical flask If 25.00 of those reactants were used, they require 50.00 of the reactant used inside burette. This exceeds burette capacity 50.00 ) → need to refill  Higher percentage error Gas Collection Possible question types: How to ensure reliability of mass of solid measured Heat solid gently first (prevents solid from splattering), then heat strongly Heat, cool, Reweigh. Repeat this process until a constant mass is obtained Chemical energetics/ Calorimetry Enthalpy change of neutralisation = 57.3kJ/mol Graph drawn need to start from origin Possible question types: Predicting whether replacing a (strong acid) with a (weak acid) will change the enthalpy change Only strong acid + strong alkali reaction will be 57.3kJ/mol. For the remaining acid + alkali reactions, the reaction is less exothermic as some energy from the reaction is absorbed to dissociate the acid completely Predicting whether doubling the volume of both reactants (acid + alkali) will affect temperature change Temperature change remain constant → double the heat produced, distributed double the volume of solution (link to heat capacity) Why graphical method to determine maximum temperature change is more accurate than direct measurement of initial and maximum temperature reached Graphi