Core practical 2 Flashcards
What is CP2?
It is the preparation of a standard solution and titration
What is the aim?
Prepare a standard solution from a solid acid salt and find the concentration of NaOH by titration using this standard solution.
What is the method?
1) Weigh an empty test tube. Scoop approximately 2.5g of sulfamic acid into the test tube.
2) Reweigh the test tube and its contents accurately.
3) Dissolve the sulfamic acid in approximately 100cm3 of water in a beaker.
4) Transfer the solution, including the washings, into a 250cm3 volumetric flask and make the solution up to the mark with deionised water.
4. Stopper the flask, then mix thoroughly by inverting and shaking vigorously.
What errors can be made?
● Be careful not to lose any solid when transferring from the weighing boat to the beaker.
● When weighing out the solid, weigh by difference and then calculate the mass of a solid in a beaker: mass of (weighing bottle + beaker) - (mass of the bottle after emptying solid)
What are some key points?
● Acid must have a high molar mass (to reduce weighing errors).
● Sample must be pure.
● Sample must not be air sensitive or react with air components (e.g. by absorbing CO2 or H2O).
What health and safety points should be noted?
Wear goggles.
Sulfamic acid can be toxic if it is ingested.
Ensure burettes are filled when the top of the burette is below eye level.
What is a standard solution?
It is a solution of known concentration
What equipment is used to carry out this titration?
A pipette and a pipette filler are used to measure out the volume of NaOH before transferring it to a conical flask
A burette is used to add small volumes of sulfamic acid solution to the NaOH until the reaction has reached completion
How do you carry out this titration?
Once the pipette has been used to place the NaOH into the conical flask, fill the burette with the acid solution. Record initial volume
Add a few drops of methyl orange indicator to the conical flask
Open the burette tap and allow the sulfamic acid to flow into the conical flask, swirling it to mix the contents
Close the burette tap once the colour change occurs. Use a white tile so the colour change is easy to identify.
Record the final burette volume
Repeat until you get concordant results, then calculate a mean titre
How would you analyse the results from this titration?
Calculate the concentration of the sulfamic acid solution
Calculate the mean titre using concordant results
Calculate the conc of the burette solution
