Titrations

Question 1

What is the difference between a Primary standard solution and a secondary standard solution?

Answer 1

Primary standard solution: standard solution prepared from a solid

Secondary standard solution: a standard solution whose concentration was determined using titration/other quantitative analysis

Question 2

What are the properties of primary standard solutions:

Answer 2

• very pure
• stable mass
• no moisture
• Soluble
• Reads completely
• high molar mass

As for accurate concentration we need accurate mass and volume

Question 3

What are good primary standards!

Answer 3

Oxalic acid is a good acid primary standard (C2H2O2)

Sodium carbonate and sodium hydrogen carbonate are good base standards

*sodium hydroxide is a poor primary standard as it is hygroscopic( absorbs water &sincerases in mass)

Question 4

What is the definition of titration?

Answer 4

A technique used to determine the concentration of a solution by adding a solution of known concentration with an indicator

Question 5

What is the difference between an end point and an equivalence point?

Answer 5

End point: the colour change of an indicator

Equivalence Point: reactants have neutralised eachother completely

Question 6

Why is the end point the same as the equivalence point?

Answer 6

When Equivalence is reached: there is a big jump in pH
(At the exact point of equivalence the pH will rapidly change
*the right indicator will change colour when equivalence is reached**

When the end point is reached: when the colour changes
Eg, from a yellow to blue

Question 7

What is the method for titration?

Answer 7

1. Pour standard solution into a clean burette using a clean funnel. Ensure solution goes above ml line.
2. rinse excess solution out of burette
3. rinse a cleanconical flask with distilled water.
4. Add the unknown solution to the flask and place it under the burette
5. Slowly add the standard solution in the burette to the flask, swirling continuously until the indicator just changes colour (end point)
6. Read volume of burette.
   Repeat 3 times. Calculate average

Question 8

steps for preparing a standard solution?

Answer 8

1. calculate mass of solid required using N=CV and m=nM
2. weigh out mass of solid required on a clear plastic tray on electronic balance
3. Wash a funnel and volumetric flask 3 x with distilled water
4. transfer solid into volumetric flask (using funnel and wash bottle)
5. Add distilled water until the bottom of the miniscus just reaches the calibration line (avoiding parallax error)
6. stopper the flask and invert 3 times and label.