Practicals Flashcards
How do you prepare a standard solution from a solid
Weigh an empty weighing bottle
Add the required amount of the solid into weighing bottle
Add enough water for the solid to dissolve
Transfer solution to volumetric flask, make up to mark with distilled water and invert flask repeatedly
Why do you Rinse the weighing boat after use and pour the rinsings into the beaker
Ensure all of the solid gets transferred from boat to beaker
Why do you Ensure the bottom of the meniscus lies on the line
To ensure that the volume of solution is exactly 250 cm3
Explain the process of Titrating the sodium hydroxide against the acid
- Pipette 25.0 cm3 of 0.10 moldm-3 sodium hydroxide into a conical flask.
- Add a few drops of phenolphthalein indicator.
- Rinse the burette in the acid solution, and then fill the burette with fresh solution.
- Titrate the alkali sample against the acid solution.
- Repeat until 2 concordant values are obtained.
- Record your titration results in a table.
Why should you Rinse the burette with acid before use
Ensure that any water or other substance left in the burette is washed out
State the method for RP2 to find the molar enthalpy change for the reaction of zinc with aqueous copper (II) sulphate
- Place a clean, dry polystyrene cup inside a glass beaker.
- Pipette 50.0 cm3 of 1.0 moldm-3 copper (II) sulphate into the cup.
- Start the stopclock and record the temperature, to 1 decimal place, of the solution every 30 seconds for 2.5 minutes.
- While you are waiting, weigh a weighing boat and then add approximately 5 g of zinc powder into it. Weigh the boat again.
- After the timer has been running for 3 minutes add the zinc to the solution. Weigh the weighing boat again.
- Place a lid on the cup and continue to measure the temperature of the solution every 30 seconds for 10 minutes, starting from 3.5 minutes. Continue to stir gently using the thermometer.
What is the graph used for and how in RP2
- Plot a graph of temperature against time.
- Extrapolate the part of the graph with a negative gradient to find out what the temperature would have been after 3 minutes. Use this as your final temperature.
- Calculate the temperature rise using your initial and final temperatures.
Why should you use a polystyrene cup, with a glass beaker for support
Polystyrene is a good insulator with a low heat capacity. The glass beaker stops the cup falling over
Why should you record the temp change over a 10 min period (RP2)
To allow the solution time to cool, so a cooling curve can be plotted
State the tests for Halide Ions
Add Nitric Acid to the test tube that contains the sample, then add silver nitrate. You can then add dilute ammonia solution and conc. ammonia solution
What are the observations when adding the silver nitrate to the sample
Chloride ions = White ppt
Bromide Ions = Cream ppt
Iodide ions - Yellow ppt
What happens when you add dilute and then conc. ammonia solution
The Chloride ions will dissolve in dilute whereas the others wont. the bromide ions will dissolve in the conc. ammonia solution. Iodide ions insoluble
Why is Nitric Acid added?
It will remove any unwanted ions that may contaminate ions
What is the tests for Ammonium ions
• Add sodium hydroxide
NH4+ + OH- –> NH3 + H2O
• Warm mixture
• Test with- damp red litmus paper, if present, it will turn blue
How do you test for carbonate ions
Add Hydrochloric Acid to a solution of sodium carbonate and then bubble through a test tube of limewater and if present, it will turn cloudy
