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 Graphical accounts for heat lost to surroundings Sources of error for spirit lamp experiment + modifications to minimise the error Incomplete combustion  Flush more to ensure complete combustion Burning of wick produces heat, which accounts for the temperature rise → use a fibre wick that does not burn. Ensures that heat transferred to calorimeter is entirely due to combustion of (substance in spirit lamp) only Reaction Kinetics Homogeneous catalyst  Consumed by the reaction & gets regenerated Heterogeneous catalyst  Catalyst is different phase from reactants & products Tables: Average temperature T of reaction mixture = ( + ) / °C Time (t) for blotting out the cross / s cm3 cm3 cm3 O 2 21 T initial T final

Practic al not es 3 Possible question types: Explain why water is added to the reaction mixtures To keep the total reaction volume constant across all experiments. This allows concentration of reactants used to be directly proportional to its volume added Explain why is a measure of the rate of reaction Since the same end point is reached, it means that the same fixed amount of (product) is formed in each reaction. Thus, is directly proportional to rate of reaction Inorganic Test for Description  Observations Add (aq) Effervescence is observed. Gas liberated forms white ppt when bubbled through (aq) , , Add (aq), followed by (aq) dropwise until in excess  White ppt that is soluble in forms  Pale cream ppt that is sparingly soluble in  Yellow ppt that is insoluble in forms Add (aq), followed by (aq) dropwise until in excess White ppt forms Complex ions Organic Test name Procedure Iodoform Add 1 cm depth of (aq) in a test tube, followed by (aq) dropwise until a permanent yellow colour is obtained. Add 1 cm depth of organic compound. Heat in hot water bath. t1 t1 CO 32− HNO 3 Ca(OH) 2 Cl−Br−I− Ag(NO) 3 NH 3 Cl− NH 3 Br− NH 3 I− NH 3 SO 42− Ba(NO ) 3 2 HNO 3 [Al(OH) ]4− [Zn(OH) ]42− [Pb(OH) ]42− [Cr(OH) ]63− [Zn(NH ) ]3 42+ [Cu(NH ) ]3 42+ [Ag(NH ) ]3 2+ NaOHI 2

Practic al not es 4 Yellow ppt ( ) forms Tollenʼs Test Add 1 cm depth of (aq) to 2 cm depth of (aq). Then add (aq) dropwise until ppt dissolves. Add 2 cm depth of organic compound. Heat in hot water bath. Silver mirror forms Fehlingʼs Test Mix 5 drops of (aq) and 5 drops of aq solution containing (aq) and Potassium tartrate (aq). Add 1 cm depth of organic compound. Heat in hot water bath. Red ppt ( ) forms Planning Structure: Pre-calculations  Procedure Include measuring capacity of instrument Tip: Visualise yourself doing the experiment. Practice more questions to remember the phrasing Instrument Measuring capacities available Measuring cylinder 10 , 50 , 100 Beaker 100.0 , 250.0 , 500 Conical flask 50 , 100 , 250 , 500 Pipette 10 , 25 % error Formula: % error = ±(max error)/ volume measured x 100% Max error = half the smallest division on instrument x no. Of times you read the instrument ** Exception to the above max error: Measuring cylinder (can read smallest division instrument) ** From the formula, observe that greater volume measured would decrease % error Some words of encouragement/ advice: Stay calm. Donʼt panic. Fretting = shaky hands = have to redo experiments ☹ Spend about 2025 mins on planning. To practice, try 30 mins first then slowly reduce the time limit. Do planning first cos your mind can still function the best at this time. After 25 mins, die die must stop planning already. Do 2 perfect titrations. Donʼt waste time on a rough one Still need refill burette). How to know when going to change colour soon: the colour in the solution starting to take longer time to turn back to original colour. CHI 3 NaOHAgNO 3 NH 3 Cu2+ NaOH Cu O2 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3

Practic al not es 5 Your bunsen burner is working fine. They checked prior to the exam, so donʼt ask for help. Invigilator will only on to show you it works then off for you to on by yourself. Outcome: You know that your bunsen burner works even though that was already known from the start & you may potentially have lost some marks. All the best for practical! 😃🌟