Required Practical Flashcards
(40 cards)
(RP.2) Write the Method to determine the enthalpy of combustion for an alcoholic liquid fuel. (10 steps)
1) Measure 100cm^3 of water into calorimeter
2) Weigh a Spirit burner containing the fuel to be burnt
3) Measure the initial temperature of the water / thermometer note this as T1
4) Use spirit burner to heat liquid
5) Stop Heating after the temperature has rose 15 degrees
6) post switch off keep watching thermometer and record the maximum temperature
7) Reweigh Spirit Burner
8) Calculate Temperature Change & change in Heat energy in joules (q=mc(change in temperature))
9)Calculate change in mass and use that figure to calculate the total moles of fuel used (mass/mr)
10)Calculate Energy change per mole of fuel used
(RP.2) In the enthalpy of combustion for an alcoholic liquid fuel what are the possible reasons why the enthalpy of combustion is frequently less exothermic then the ones within data books? (6 points)
1) Heat losses to surroundings from spirits burner,wick and calorimeter
2) loss of unreacted fuel from the wick or burner from evaporation
3) loss of water from evaporation
4) incomplete combustion of the fuel , denoted by soot being left of the bottom of the calorimeter
5)Heat used to raise temperature of calorimeter before the water
6) Reaction is unlikely to be held under standard conditions
(RP.2) In the enthalpy of combustion for an alcoholic liquid fuel what are the possible ways of improving thr set up to obtain more accurate values? (6 points)
1) Using a draught shield to reduce heat loss to surroundings 
2) using a lid on the calorimeter to reduce evaporation of water into surroundings
3) minimising the distance between the naked flame and calorimeter
4) Insulation of the calorimeter and spirit burner to reduce heat loss
5) using a top on the spirit burner with Protruding wick to minimise evaporation of the fuel
6) burning in a supply of oxygen to prevent incomplete combustion
(RP.2) Write the Method to determine the enthalpy of neutralisation of a solution (9 steps) / enthalpy of solution
1)Place a polystyrene cup in a glass beaker for support
2) Rinse a measuring cylinder with 1moldm^-3 HCl the measure 25cm^3 of this acid
3)Transfer acid to the polystyrene cup
4)Stir the acid and measure initial temperature with a thermometer
5) Measure Temperature from this point at 1 minute intervals
6) Rinse a second measuring cylinder with 1moldm^-3 of NaOH then measure 25cm^3 of the hydroxide
7) add the hydroxide to the acid immediately after a 1 minute interval temperature check
8)Calculate the change in temperature by extrapolating your graphed results and then calculate heat energy using q=mc(change in t)
9) Calculate the amount of mol of acid used, mol of water formed and the enthalpy of neutralisation (energy liberated per mole of water formed during a neutralisation reaction)
How do you Extrapolate?
1) Graph up results of the temperature recorded
2) Draw a line of best fit for initial (unreacted) temperature readings
3)Find your maximum point recorded draw a line of best fit for this and later readings only
4) Your change in temperature is the difference in temperature at the time stamp when the reaction started
Burette
As it can deliver variable volumes
(RP.1) Write out the procedure for preparing a standard Solution
1) Weigh out an accurate mass of a solid in a clean dry beaker
2) Add enough deionised water to dissolve the solid, stirring with a glass rod
3) Transfer the solution with rinsing to a 250CM^3 volumetric flask using a funnel
4)Rinse the beaker, glass rod and funnel with deionised water and add to the volumetric flask
5) Make up to the mark by adding deionised water until the bottom of the meniscus is to the mark
6) Stopper the flask and Invert to mix thoroughly
(RP.1) Describe the Procedure to carry out a titration (7 Steps)
1) Rinse the burette with the solution of unknown concentration , Discard the rinsing and fill the burette.
2) Rinse the pipette with the solution of known concentration, Using a pipette and pipette filler transfer 25cm^3 of this solution to a conical flask
3) Add 2-3 drops of a suitable indicator to the conical flask
4) To conduct a titration: Add the solution from the burette, with constant swirling until the indicator just changes colour
5) Conduct a rough titration first that is an estimate for neutralisation point
6) Conduct further titrations , with a reduced flow rate when nearing the end point. until you achieve 2-3 results that are concordat
7) Calculate mean titre from concordat results excluding the rough titration
(RP.1) What are concordat results
Results that are within 0.1CM^3 of one another
(RP.3) How can the rate of the reaction be determined
Continuous monitoring method ie. Loss of reactant over time / Gain of product over time
Initial Rates method (Iodine clock)
(RP.1) What is a Standard Solution
Solution of Known Concnentration
(RP.1) Describe the weighing by difference technique
Weigh Empty Weighing boat
Zero the scale
Starting weighing substance in weighing boat
After substance is removed reweight the weighing boat
Mass of Substance added = ( Mass of Substance + weighing boat ) - Mass of boat after substance is removed
How can you reduce the uncertainty in the mass measurement
Use a balance with greater resolution
Use Larger Mass
How do you calculate % uncertainty
Absolute uncertainty/calculated value *100
(RP.2) Other then preventing heat loss how can the accuracy of this be improved, (calorimeter & neutralisation)
- Read thermometer at eye level to avoid parallax errors
- Stir solution so the temperature is evenly distributed
-Use a digital thermometer with more accurate and faster readings - Use greater concentrations and masses leading to larger temperature change and smaller uncertainties
Describe accurate data
Data that is closer to the true value
(RP.3) Why does the rate of reaction increase with increasing temperature (4)
Average Kinetic energy of the molecules increase
This results in higher particle velocities, particles now collide more often
Also means a higher proportion of the particles are above the activation energy
Both mean that many more successful collisions are made per second
(RP.3) Describe issues with the hidden cross experiment (4)
Time taken when the cross disappears is judged by eye , unreliable
There could be a delayed reaction time with the stopwatch
At low temperatures the reaction may be too slow
There maybe not enough precipitate for the cross to fully disappear
(RP.3) How could you analyse the data from the hidden cross experiment (4)
Plot a graph for each of the experiments at different temperature
Draw a tangent to the curve when x=0
Measure the gradient of this tangent
The gradient is the initial rate of reaction, compare values with other graphs at different temperatures
What is a control variable
A Variable that is kept constant throughout the experiment
(RP.3) in an experiment investigating the effect of temperature on the rate of reaction what variables will you control?
Concentrations of reactants
Volumes of reactants
Same beaker with same cross under
Same person deciding when the cross has disappeared
(RP.3) Describe the best way of keeping a substance at constant temperature
Using a waterbath
Water has a higher specific heat capacity, small losses in temperature over time
(RP.5) What is Distillation
Separating technique where
Liquid Sample is heated to create a vapour, which travels up the fractionating column
Travels into a condenser and cools forming a liquid in a separate beaker .
Sample separates into different compounds due to different relative volatilities and boiling points
(RP.5) what Equipment is used for distillation?
Pear shaped or round bottomed flask
Liebing condenser
Still head
Stopper
Receiver adaptor fitted with thermometer
Collection vessel
