≫3.1-3.6 Required Practicals 1-12 ✔ Flashcards
R/P 01 - 3.1 - Making up a volumetric solution:
Outline the method and ways to reduce uncertainties for this practical:
Method:
⓵Weigh the weighing boat containing the solid on a 2d.p balance.
⓶Transfer solid to beaker and reweigh the weighing boat, record the difference in mass.
⓷Add approximately 100cm³ of distilled water and use a glass rod to stir the contents until all the solid has dissolved.
⓸Using a funnel pour the contents of the beaker into a 250cm³ volumetric flask, using further distilled water wash out the beaker and funnel transferring all washings into the volumetric flask.
⓹Make the volumetric flask up to a graduated mark by adding distilled water.
⓺Stopper the flask and invert to combine thoroughly.
Reducing Uncertainties:
- Using a more accurate balance or a larger mass will reduce the uncertainty in weighing a solid.
- Weighing sample before and after addition and then calculating difference will ensure a more accurate measurement of the mass added.
R/P 01 - 3.1 - Carrying out a simple acid-base titration:
Outline the method and ways to reduce uncertainties for this practical:
Method:
⓵Fill the burette with the standard solution of known concentration.
⓶Pour approximately 100cm³ of the solution with unknown concentration into a beaker, using a pipette filler and pipette transfer exactly 25cm³ of solution into a 250cm³ conical flask.
⓷Add 2-3 drops of phenolphthalein indicator to the solution in the conical flask, turning it pink in alkali conditions.
⓸Record the initial burette reading and do a rough titration to get an idea of the amount of solution needed to neutralise.
⓹Record initial burette reading and titrate the contents of the conical flask whilst swirling the contents until the indicator undergoes a definite colour change to colourless. Calculate the titre volume.
⓺Repeat until three concordant results are obtained and calculate a mean titre volume.
Reducing Uncertainties:
- To reduce uncertainty in a burette reading the titre volume needs to be made larger, this could be done by increasing the volume and concentration of the substance in the conical flask or by decreasing the concentration of the substance in the burette.
- Replacing measuring cylinders with pipettes or burettes which have lower apparatus uncertainty will lower the overall error.
R/P 06 - 3.3 - Organic Tests:
Outline the test and result for the test for an alkene:
- Add about 1 cm³ of bromine water to 2 drops of alkene.
- Shake the contents of the tube vigorously from side to side.
- Bromine water decolourised from orange if an alkene is present.
- If an alkane was present no visible change is observed.
R/P 02 - 3.1 - Measuring Enthalpy Change:
Outline the method for measuring the enthalpy change of a neutralisation:
- Measure out a set volume of acid using a measuring cylinder and add it to the polystyrene cup (good insulator.)
- As density of water is 1.00kgdm⁻³ the volume of liquid = the mass of both the acid and alkali
- Record initial temperature once a minute for 3 minutes (control measure.)
- On the 4th minute add alkali but do not record the temperature.
- From 5th-15th minute record temperature every minute.
- Draw a graph of Temp v Time, extrapolate both lines back to the time of mixing (4m) and work out ∆T - the vertical line section.
- Work out q=mc∆T
- Work out moles (mass of solid) or (moles of liquid used.)
- Calculate ∆H=q/n if heat is given out then the value is negative.
R/P 02 - 3.1 - Measuring Enthalpy Change:
Outline the method for measuring the enthalpy change of a solid and a liquid:
- Measure the weighing boat and record in a table.
- Add the mass of metal or metal carbonate to weighing boat and record in a table.
- Transfer the solid to the beaker.
- Measure the weighing boat again and work out the difference to get the actual mass.
- Work out the Mr of the substance and the number of moles.
- Add a set volume of liquid e.g: 25cm³ of water or acid using a measuring cylinder to a polystyrene cup.
- Record the temperature every minute for the first three minutes and record.
- As density of water is 1.00kgdm⁻³ the volume of liquid = the mass of the liquid in the equation.
- On the 4th minute add the solid and from the 5th-15th minute record the temperature every minute.
- Draw a graph of Temp v Time, extrapolate both lines back to the time of mixing (4m) and work out ∆T - the vertical line section.
- Work out q=mc∆T
- Calculate ∆H=q/n if heat is given out then the value is negative.
R/P 02 - 3.1 - Measuring Enthalpy Change:
Outline the method for measuring the enthalpy change of combustion:
- Measure out a set volume of water using a measuring cylinder and add it to the beaker.
- Could add a lid to reduce loss of heat by evaporation and screens to reduce draught.
- As density of water is 1.00kgdm⁻³ the volume of liquid = the mass of the liquid in the equation.
- Record initial temperature and record this in a table.
- Fix height of beaker a set distance from the flame.
- Burn alcohol for a set time.
- Record the highest temperature.
- Calculate the difference in temperature.
- Work out q=mc∆T where c = specific heat capacity of water 4.18
- Work out moles (mass of solid) or (moles of liquid used.)
- Calculate ∆H=q/n if heat is given out then the value is negative.
R/P 03 - 3.1 - Investigation of how the rate of a reaction changes with temperature:
Outline the method and safety precautions for this practical:
Method:
⓵Add about 10cm³ of 1moldm⁻³ hydrochloric acid to the ‘acid’ tube. Place this tube into a plastic container (without the cross under it).
⓶Use a measuring cylinder to add 10cm³ o f 0.05 moldm⁻³ sodium thiosulfate solution to the second tube. Place this tube into the plastic container with the cross under it and carefully place a thermometer in this tube.
⓷Record the start temperature and then add 1cm³ of the acid to the thiosulfate solution and start timing.
⓸Look down through the tube from above and record the time for the cross to disappear from view.
⓹Record the final temperature of the reaction mixture, then pour the cloudy contents of the tube into the sodium carbonate solution.
⓺Now add water from a very hot water tap (or kettle) to the plastic container. The water should be no hotter than 55°C. Add cold water if necessary.
⓻Measure another 10cm³ of 0.05moldm⁻³ sodium thiosulfate solution into a clean tube. Insert this tube into the correct hole in the plastic container (i.e the one with the cross under it).
⓼Leave the tube to warm up for about 3 minutes.
⓽Repeat steps (3) to (6) in order to obtain results for at least 5 different temperatures in total.
Safety:
- Wear eye protection, a lab coat and gloves as HCl is an irritant.
- Ensure that the investigation is carried out in a well-ventilated room and that appropriate measures are taken to dispose of waste
solutions.
R/P 07 - 3.4 - Measuring the rate of reaction - Initial Rate Method:
Outline the method and improvements for this practical:
Method:
⓵Rinse a 50cm³ burette with KI and then fill out with KI solution.
⓶Transfer 10cm³ of hydrogen peroxide solution from a burette to a 100cm³ beaker.
⓷Use a 50cm³ measuring cylinder to add 25cm³ of sulfuric acid to a 250cm³ beaker.
⓸Use a 25cm³ measuring cylinder to add 20cm³ of distilled water into the 250cm³ beaker.
⓹Use a plastic pipette to add about 1cm³ of starch solution to the beaker.
⓺Use the burette to add 5.0cm³ of KI solution to the mixture in the 250cm³ beaker.
⓻Finally add 5.0cm³ of sodium thiosulfate solution from a burette to the mixture in the 250cm³ beaker.
⓼Stir the mixture in the 250cm³ beaker. Pour the hydrogen peroxide solution from the 100cm³ beaker into the 250cm³ beaker and immediately start the timer.
⓽Stop the timer when the mixture in the 250cm³ beaker turns blue-black, record the time.
⓾Rinse the 250cm³ beaker with distilled water and dry it with a paper towel, repeat steps in four further experiments, changing the concentration of KI by increasing its volume by 5cm³ each time and reducing the volume of water by 5cm³. Plot a graph of initial rate (y) against concentration (x) to determine the order.
Improvements:
- Use a colorimeter to minimise human error in timing.
