Each of the Chemistry Required Practicals with real Exam Questions and Answers in note form. Transferrable for flashcard use. Great revision tool. Made and Used by Grade A-A* Student.
RP1a – Making a standard solution
step 1? weigh sample bottle containing required mass of solid on a 2 d.p. balance
step 2? transfer to beaker and reweigh sample bottle
step 3? record difference in mass
what action is carried out by steps 1-3? weigh by difference
step 4? add 100 cm3 of distilled water to beaker
step 5? use glass rod to stir to help dissolve solid
step 6? pour solution into a 250cm3 volumetric flask via a funnel
step 7? rinse beaker and funnel and add washings from the beaker and glass rod
to the volumetric flask
step 8? make up to the mark with distilled water using a dropping pipette for last
few drops
step 9? invert flask several times to ensure uniform solution
why is the beaker and its content sometimes heated gently? [2] substance may not
dissolve well in cold water, ensures all solid has dissolved
where do you fill the line to in volumetric flask? bottom of meniscus sits on line on neck
of flask
what is hard to see with dark liquids, e.g. potassium manganate? meniscus
RP1b – Carrying out an acid-base titration
step 1? rinse equipment
what do you rinse burette with? acid
what do you rinse pipette with? alkali
what do you rinse conical flask with? distilled water
step 2? pipette 25cm of alkali into conical flask
3
step 3? touch surface of alkali with pipette
why do you touch surface of alkali with pipette? ensure correct amount is added
step 4? fill burette with acid
step 5? open tap to get rid of air bubbles and fill space with acid
step 6? record initial burette reading
step 7? add a few drops of suitable indicator
step 8? use a white tile underneath the flask to help observe the colour change
step 9? add acid to alkali whilst swirling the mixture and add acid dropwise near
endpoint
step 10? stop adding acid when relevant sharp colour change is observed
step 11? record final burette reading
step 12? repeat titration until at least 2 concordant results are obtained
what are concordant results? readings within 0.1 of each other
what happens if air space is not filled properly? obtain larger than expected reading in
titration
why are conical flasks used over beakers? easier to swirl
why do you use just a few drops of indicator? usually acids, too much will affect
titration result
colour of phenolphthalein in alkali? pink
colour of phenolphthalein in acid? colourless
end point colour of phenolphthalein? colourless
when do you use phenolphthalein? NaOH
colour of methyl orange in alkali? yellow
colour of methyl orange in acid? red
end point colour of methyl orange? orange
when do you use methyl orange? HCl
, RP2a – Measuring an enthalpy change – combustion
step 1? using measuring cylinder place 50cm3 water into metal calorimeter and
record temperature of water
where do you leave the thermometer after step 1? in the water
step 2? clamp the calorimeter so that its base will be just above the wick of a spirit
burner
step 3? choose a spirit burner noting which alcohol it contains and weigh it
step 4? adjust the wick of the spirit burner so that only about 5mm protrudes from
the neck of the burner
step 5? ignite the alcohol at the wick and immediately place the burner beneath
the clamped calorimeter
step 6? allow the alcohol to burn until the temperature of the water has risen by
approximately 35°C and record the final temperature
step 7? carefully extinguish the spirit burner and reweigh it to determine the mass
of alcohol that has burned in the experiment
step 8? repeat the experiment with a second alcohol
calculation? work out q = mcΔt, where m = mass of water; and ΔH = -q/n, n=m/Mr
where m = mass of alcohol burnt
RP2b – Measuring an enthalpy change – solution
step 1? put polystyrene cup in a beaker for insulation and support
step 2? add 25 or 50ml water to cup using a measuring cylinder
step 3? weigh solid by difference and record precise mass
step 4? construct a suitable table of results to record temperatures at minute
intervals up to 15 min
step 5? clamp thermometer into place making sure the thermometer bulb is
immersed in liquid
step 6? measure the initial temperatures of the water or both solutions if 2 are
used, once a minute for 3 mins
what should you do before you measure the temperature? stir
step 7? add other reagent to cup at fourth min, do not take temperature
step 8? stir mixture
step 9? keep taking temperature every min for another 10 mins
step 10? draw graph of temp vs time, draw two lines of best fit to work out ΔT,
extrapolating lines back over fourth min
errors? [5] 1. heat loss/gain, 2. approximation of specific heat capacity of solution, 3.
neglecting specific heat capacity of calorimeter, 4. reaction incomplete, 5. assuming
density of solution is the same as water
RP3 – Investigating how rate changes with temperature
step 1? using a measuring cylinder, measure out 10cm3 of 0.25 mol dm-3 sodium
thiosulfate solution and 40cm3 water and pour into conical flask
sodium thiosulfate formula? Na2S2O3
step 2? using a measuring cylinder, measure out 5cm3 of 2.0 mol dm-3 HCl into a
test tube
step 3? put the conical flask and test tube in the water bath for 5 mins
temperatures used? room temp, 30, 40, 50, 60
what is the maximum temperature to be used? 60
step 4? remove the conical flask and the test tube from water bath
step 5? place conical flask on the paper marked with a cross
step 6? immediately add acid from the test tube and start the stopwatch
step 7? gently stir the mixture with the thermometer and record the initial
temperature
step 8? observe the cross from above through the solution
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