4.2 Acid-Base Titrations

Question 1

What is titration

Answer 1

A technique used to accurately measure the volume of one solution that reacts exactly with another solution

Question 2

What can titration be used for

Answer 2

Finding the concentration of a solution, identification of unknown chemicals, and finding the purity of a substance

Question 3

What equipment is used to make up a standard solution very accurately?

Answer 3

A volumetric flask

Filled so that the bottom of the meniscus just touches the graduation line

Question 4

Tolerances of a 100cm^3 and 250cm^3 volumetric flask

Answer 4

100cm^3 - ±0.20cm^3

250cm^3 - ±0.30cm^3

Question 5

Method to prepare a standard solution

Answer 5

1. Accurately weigh the solid
2. Dissolve the solid in a beaker using less distilled water than will be needed to fill the volumetric flask to the mark
3. Solution is transferred to a volumetric flask. The last traces of the solution are rinsed into the flask with distilled water
4. The flask is carefully filled to the graduation line by adding distilled water a drop at a time until the bottom of the meniscus lines up exactly with the mark
5. The volumetric flask is slowly inverted several times to mix the solution. Without doing this, results will not be consistent

Question 6

What equipment is used for an acid-bast titration

Answer 6

Pipette and a burette

Question 7

Tolerances for a 10cm^3 and 25cm^3 pipette, and a 50cm^3 burette

Answer 7

10cm^3 pipette - ±0.04cm^3
25cm^3 pipette - ±0.06cm^3
50cm^3 burette - ±0.10cm^3

Question 8

How are burette readings recorded

Answer 8

To the nearest half division with the bottom of the meniscus on a mark or between two marks
Measured to the nearest ±0.05cm^3 so that the reading always has two decimal places, the last being either 0 or 5

Question 9

Method of acid-base titration

Answer 9

1. Add a measured volume of one solution 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, SWIRL the conical flask to mix
5. Indicator eventually changes colour at the END POINT of the titration. Used to indicate the volume of one solution that exactly reacts with the volume of the second solution
6. Record the final burette reading, volume of solution added from burette is called the titre
7. Quick trial titration is carried out first to find approximate titre
8. Repeated accurately adding it dropwise nearing the end point
9. Carry out more until two accurate titres are concordant

Question 10

What is a titre

Answer 10

The volume of solution added from the burette

Calculated by subtracting the initial from the final burette reading

Question 11

What to remember when working out the mean titre

Answer 11

ONLY use the closest accurate titres

• By repeating titres until two agree within 0.10cm^3, can reject inaccurate titres
• If you were to include all titres in the mean, you have lost the accuracy of the titration technique

Question 12

What do you know from the results of a titration

Answer 12

Both the concentration c1 and the reacting volume V1 of the solution
Only the reacting volume V2 of the other solution

Question 13

Pattern of method to analyse results

Answer 13

Step 1 - Work out the amount in mol of the solute in the solution for which you know BOTH the concentration c1 and volume V1
Step 2 - Use the equation to work out the amount in mol of the solute in the other solution
Step 3 - Work out the unknown information about the solute in the other solution

Question 14

How to identify an unknown carbonate using titration

Answer 14

1. Prepare a solution of an unknown carbonate X2CO3 in a volumetric flask
2. Using a pipette, measure 25.00cm^3 of your prepared solution into a conical flask
3. Using a buratte, titrate the solution using 0.100moldm^-3 hydrochloric acid
4. Analyse your results to identify the carbonate