physical practicals Flashcards
Required practical 2: suggest two disadvantages of using a glass beaker on a tripod and gauze
- Glass is a poor conductor
2.tripod + gauze would transfer heat
3 beaker would be fixed height above flame
Suggest two reasons why the value of enthaloy of combustion is less exothermic than dat booklet
- Heat loss to surroundings
2.Incomplete combustion
Suggest one addition to apparatus that would improve accuracy of enthaloy value obtained
- Add a lid
Required practical 2: Explain how apparatus can be improved
Apparatus
- Use a burette /puppets instead of measuring cylinder
- Use a polystyrene cup
- Reweigh watch glass
- Use powdered solid -reaction is quicker
Temperature
1. Record initial temperature for a few minutes before reacting
2. Measure at regular intervals
Temperature determination
- Plot a graph temp vs time
- Extrapolate to point addition
Required practical two: how can the method be improved
Temperature
1. Record initial temperature for a few minutes before reacting
2. Measure at regular intervals
Temperature determination
- Plot a graph temp vs time
- Extrapolate to point addition
Required practical two : how can experiment be changed to reduce percentage uncertainty
Increase concentration of soluting
Required practical two: describe the steps to determine an accurate minimum temperature
- Start stop clock as reactants are added
2.read the temperature every 30 seconds for 5 minutes
3.
Required practical 6 : outline a practical to determine the enthalpy if combustion
- Weigh alcohol before and after combustion
- Pit water in a colorimeter
3 measure the volume of this water - Burn the alcohol to heat the water
- Measure the temperature raise in water
Suggest one reason other than incomplete combustion or heat transfer to the atmosphere
Heat taken up by the apparatus
Practical three: what is the practical
Investigation of how rate of reaction changes temperature
What is the general method for required practical three
- Measure 10cm 3 hydrochloric acid and 10cm3 of sodium thiosulfate in separate measuring cylinder . Put solution is separate boiling tubes
- Using a water bath get two solutions to the same temperature
- Place the flask on the centre of the large cross ,first add the sodium thiosulfate to flask ,then add hydrochloric acid
- Start stop watch and swirl to mix solutions
- Stop the stopwatch
- Repeat experiment
What is required practical 7
Measuring rate of reaction by initial rate method
What type of reactions are used to find the initial rate
Clocke reactions
What happens in the hydrogen peroxide clock reaction
Hydrogen peroxide reacts with iodide ions to form iodine.
The thiosulfate ion then immediately reacts with iodine
All the iodine has reacted with the thiosulfate and excess iodine remains
How can you determine the order of reaction
By repeating the experiment several times varying the concentrations of a reactant
What is the detailed method for required practical 7
- Measure 50cm3 of 1 mol dm-3 hydrochloric acid
- Set up gas syringe
- Weigh 0.2 g of magnesium
- Add magnesium ribbon to the conical flask
- Record the volume of hydrogen gas collected every 15 seconds for 3 minutes
What is required practical 8
Measuring the EMF of an electrochemical cell
What is the method for required practical 8
1.Clean zinc and copper foils before use
2. Place copper strip into 100cm3 beaker with about 50cm 3 of 1 mol dm-3 CuSO4
3. Place zinc strip into 100cm3 beaker with about 50cm 3 of 1 mol dm-3 ZnSO4
4. He’s strip of filter paper soaked in saturated potassium nitrate solution for the salt bridge
5. Connect Cu(s) | Cu 2+ and Zn (s) | Zn 2+ half cells by connecting the metals using crocodile clips
What is the purpose of the slat bridge
Used to connect up circuit
The free moving ions conduct charge
Describe how a salt bridge would be
Made from filter paper soaked in salt solution , potassium nitrate
Or
Glass U tube containing salt solution
Why is potassium chloride not a suitable electrode solution
Would not be suitable because chloride ions form complexes with copper ions
Why is a wire not used as a slat bridge
Would set up its own electrode system
What is platinum electrode
A platinum electrode is used because it is un reactive and can conduct electricity
Required activity 9 titration curves
