RP2: Titrations Flashcards
What is the aim of this experiment?
- Carry out an investigation to find the conc of a dilute sulphuric acid solution, using a sodium hydroxide solution of known concentration
How would you find out the volume of sulfric acid that will exactly neutralise 25cm3 of sodium hydroxide solution?
1) use pipette and pipette filler to put exactly 25cm³ sodium hydroxide solution into conical flask. stand flask on white tile
2) clamp burette vertically in clamp stand about halfway up its long so that there is enough room underneath for conical flask and tile
3) ensure burette tap is closed and use small funnel to carefully fill burette with dilute sulphuric acid to 0cm³ line. do this at a low level so that you are not pouring acid from above head height
4) add 5 drops of phenolphthalein indicator into conical flask, swirl to mix and place under burette with tile
5) carefully open tap so that sulphuric acid flows into flask at drowse rate. whilst adding acid, constantly swirl flask and look for colour change from pink to colourless
6) slow drops down when colour change almost happened. shut tap immediately after a single drop of acid causes colour to become permanently colourless
7) read burette scale carefully and record volume of acid added
8) repeat investigation twice and calculate mean value for volume of acid needed to neutralise 25cm³ of sodium hydroxide solution
If you’re determining the volume of acid needed to neutralise an alkali, what goes in the burette and what goes in the conical flask?
- alkali goes in conical flask, acid goes in burette
If you’re determining the volume of alkali needed to neutralise an acid, what goes in the burette and what goes in the conical flask?
*acid goes in conical flask, alkali goes in burette
You should repeat your experiment until your results are […] and why?
- concordant (within 0.1cm³ of each other)
- this increases the accuracy of your results
- this helps you spot any anomalous results
- mean titre can be calculated reducing the effect of random error
What safety precautions should be taken?
- Wear safety goggles when working with acids
- Tie hair back
- Report any broken glassware immediately
- Burette filled below eye level so there is no risk of spilling or splashing on face
Why should a white tile be used in a titration experiment?
- placed under the reacting. mixture making the colour easier to see
Why might a volumetric Papeete and a pipette filler be used to measure 25cm3 rather than a measuring cylinder?
- aa volumetric pipette will measure more accurately
What colour is phenolphthalein in acid and alkali?
- Acid - colourless
- Alkali - pink
Why is the first trail in a titration often called a rough trial?
- the first trial gives an approximate idea of where the end point is so then of further tires you can be more precise as you know approx what volume will be required for neutralisation
Why are burettes used for titrations
- allow the solution to be added drop by drop in very small quantities
Apart from phenolphthalein what other indicator could be used titration?
- Methyl Orange: Red (acid) to yellow (alkali)
- Litmus Blue: Red (acid) to blue (alkali)
If you know the volume of acid required to neutralise an alkali, how could you calculate the conc of the acid given the alkali conc and volume?
- Calc the number of moles of the alkali using the own volume and conc
- Use the chemical equation to work out the ratio of acid and alkali that react and hence work out how many moles of acid have reacted
- Divide the moles of acid by the volume used in neutralisation
If you know the conc of an acid in mol/dm3, how could you convert this to g/dm3?
- Multiply the conc in mol/dm3 by the molar mass (Mr) of the acid to give the value in g/dm3
If you know the conc of an acid in mol/dm3, how could you convert this to g/dm3?
- Multiply the conc in mol/dm3 by the molar mass (Mr) of the acid to give the value in g/dm3
