4.2 Acid-Base Titrations Flashcards
What is a titration
A technique used to accurately measure the volume of one solution that exactly reacts with another solution
What can titrations be used for?
-Finding the concentration of a solution
-Identifying unknown chemicals
-Finding the purity of a substance
What is a standard solution?
A solution of known concentration and volume.
What equipment is used to make up a standard solution?
A volumetric flask
State how to prepare a standard solution
1- Solid is weighed accurately
2- Solid is dissolved in a beaker, using less distilled water than will be used to fil the volumetric flask to the mark
3- Solution is transferred into a volumetric flask, any traces of the solution are rinsed with distilled water
4- Flask is filled to the graduation line by adding distilled water a drop at a time, until the bottom of the meniscus lines up exactly
5- Volumetric flask is inverted several times to mix the solution thoroughly
What equipment is used to titrate an acid against a solution of a base?
Pipette and a burette.
How can you get the closest accurate titre value?
Repeat the titres until 2 values are within 0.1cm^3 of eachother.
What should you know from the results of a titration?
-Both the concentration and reacting volume of one of the solutions
-Only the reacting volume of the other solution
What should you do once you have the results of a titration? (Calculations)
-Work out the amount, in moles, of the solute in the solution for which you know both the volume and conc
-Use the equation to work out the amount in moles of the solute in the other solution
-Work out the unknown information about the solute in the other solution (conc)
State the instructions for an acid-base titration.
1- Add a measured volume of one soluton to a conical flask using a pipette
2- Add the other solution to a burette, and record the initial burette reading to the nearest 0.05cm^3
3- Add a few drops of an indicator to the solution in the conical flask
4- Run the solution in the burette into the solution in the conical flask, swirling the conical flask to mix the solutions. At the end point, the indicator changes colour, indicating when the volume of one solution has exactly reacted with the other
5- Record the final burette reading (volume of solution added to the flask from the burette is called the titre)
6- A quick, trial titration is carried out first to find the approximate titre
7- A titration is repeated accurately, until 2 accurate titres are concordant
How does rinsing a burette with the solution it will be filled with help reduce percentage uncertainty?
To prevent residual water in the burette diluting the solution, and to prevent the solution from reacting with substances left from a previous titration
Which substance is placed in the conical flask during titration?
Generally the one we don’t know the concentration of.
Why is a conical flask often used instead of a beaker in a titration?
Because it is easier to swirl the mixture in a conical
flask without spilling the contents.
Would increasing the volume in a burette increase or decrease percentage uncertainty? Why?
Decrease, because larger volumes have a lower percentage error due to uncertainty.
Why shouldn’t you leave the funnel in the burette during a titration?
Because small drops of liquid may fall from the funnel during the titration, leading to a false burette reading, that would give a lower titre volume.
Why is it important to make sure that the jet space in the burette is filled with solution before the titration?
Because if it is not filled properly, there will be a larger than expected titre reading
Why is it important to read the meniscus line at eye-level?
To get accurate results, and prevent parallax errors.
How does phenolphthalein change colour?
Pink in alkali, to colourless in acid.
How does Methyl orange change colour?
Red in acid, to yellow in alkali.
Why is it okay to use distilled water to wash out conical flasks before use?
Because any dilution of the solution in the conical flask will not affect the number of moles of the substance.
What does anhydrous mean?
Not containing water of crystallisation
What should be done with the weighing boat after all of the powder has been removed from it?
Should be rinsed with distilled water, and these rinsings should be added to the volumetric flask.
