Titrations

Question 1

Titration

Answer 1

• A practical technique for finding out unknown concentrations of solutions.
• A solution of a known concentration is used to completely NEUTRALISE an unknown concentration of a KNOWN VOLUME of a compound.

Question 2

Volumetric Analysis

Answer 2

• Used for when an acid reacts with a soluble base.
• You know the concentration and the volume of either the acid or the base.
• You will be asked to calculate the concentration, molar mass or volume of the other reactant.
• TITRATIONS are used to calculate unknowns practically.

Question 3

Titration Calculations

Answer 3

1. Write BALANCED EQUATION:
   This tells us how many moles of each compound react with each other.
2. CALCULATE NUMBER OF MOLES:
   This is for your known solution used.
3. MOLAR RATIO:
   Calculate number of moles in the unknown solution.
4. CALCULATE CONCENTRATION:
   As we know both the volume and moles of our unknown , we can use these in the equation ( n = v x c ) to calculate concentration.

Question 4

Indicators

Answer 4

• Change colour when reaction is complete.

END POINT ~ when the colour of the indicator changes and the titration stops.

EQUIVALENCE POINT ~ when the two solutions have full reacted.

A GOOD INDICATOR ~ when the end point of the titration coincides with its equivalence point.

EXAMPLES:

METHYL ORANGE~
acid - red
base - yellow
end point - orange

BROMOTHYMOL BLUE:
acid - yellow
base - blue
end point - green

PHENOLPTHALEIN:
acid - colourless
base - pink
end point - pale pink / colourless

Question 5

Equipment in titration

Answer 5

BURETTE:
- Must be cleaned with solution which it will
be used with.
- Do not overfill
- Using a dirty burette will give a FLAT
MENISCUS.
- Ensure there is no air bubbles.
- Read from eye level to give accurate
readings
- Take funnel out before taking reading.

PIPETTE:
- Ensure the pipette is not broken.
- Clean with solution being used with to
ensure meniscus is visible.
- Ensure you are using a functional pipette
filler.
- Do not shake pipette when draining.
- DIP TIP the pipette after draining the
solution to remove 0.5 cm of our solution.

Question 6

Titration METHOD

Answer 6

1. Fill your burette with your ACID.
2. Use a PIPETTE to add 25cm^3 of your HYDROXIDE solution into a conical flask.
3. Add a few drops of the INDICATOR to the conical flask.
4. TITRATE the contents of the conical flask with the acid.

5.Calculate the TITRE VOLUME by subtracting the INITIAL burette reading from the FINAL burette reading.

6. REPEAT the titration until you have CONCORDANT results (within 0.1cm^3).

7.Record all titration results in a table showing initial and final burette reading, then calculate a MEAN with most ACCURATE results.

Question 7

Titration tables

Answer 7

Titre = final burette reading - initial burette reading

Mean titre = calculated using the titres which are within 0.1cm^3 of each other.

Trial titre should NOT be used.

Question 8

A standard solution

Answer 8

A solution of a PRECISELY known CONCENTRATION which can be used for volumetric analysis.

Question 9

Volumetric flask

Answer 9

• Used to PREPARE standard solutions
• It holds an exact amount of liquid, when filled up to the line.

Question 10

How to prepare a standard solution

Answer 10

1) Place measured washing soda in a 250cm^3 beaker and add 100cm^3 of distilled water.

2) Using a GLASS ROD dissolve the solid , grinding any crystals by pressing rod down on the crystals and twist , adding more distilled water if necessary.

3) TRANSFER solution to the VOLUMETRIC FLASK using a FILTER FUNNEL.

4) RINSE SIDES of beaker using the distilled water and place washings in volumetric flask.

5) Add distilled water to flask 1cm^3 BELOW THE MARK, swirling at intervals.

6) Use a DROPPING PIPETTE to make solution to the mark (bottom of the MENISCUS.

7) Place STOPPER on flask and INVERT 10 times.

When using in titration , add the standard solution to a beaker and pipette from the beaker instead of volumetric flask.