Preparing Soluble Salt from Acid and Soluble Base (alkali) by Titration method.

Question 1

How can you remove the phenolphthalein indicator ?

Answer 1

• We can either remove the indicator by using decolourising charcoal

Question 2

Danger of phenolphthalein?

Answer 2

DANGER highly flammable

Question 3

Why is sodium chloride used instead of sodium?

Answer 3

The reaction of sodium with acids is very dangerous. So sodium salts are usually made by starting with sodium hydroxide e.g. sodium chloride:

Question 4

Symbol equation of reaction

Answer 4

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Question 5

Why is an indicator necessary in this reaction ?

Answer 5

Both reactants are soluble and no gas is given off during the reaction. Therefore an indicator is needed to show the reaction end point.

Question 6

Phenolphthalein reaction in acid, alkali and neutral

Answer 6

Phenolphthalein is pink in alkali solution, but turns colourless in neutral and acid solutions.

Question 7

Preparation of Pipette

Answer 7

• Rinse with deionised water
• Rinse it with the solution to be used in the Pipette
• holding the Pipette vertically with the volume line at eye level, use a Pipette filler to draw up the solution and run out the solution until the bottom of the meniscus is on the line
• release the solution into a conical flask, touching the tip of the Pipette onto the surface of the solution

Question 8

Method (11)

Answer 8

• Fill the burette with the hydrochloric acid.
  2. Using the pipette and pipette filler place 25 cm3 of sodium hydroxide solution into a conical flask.
  3. Add 3 drops of phenolphthalein to the conical flask- the solution turns pink.
  4. Carefully add the hydrochloric acid from the burette into the conical flask, swirl gently and rinse any droplets down the flask with deionised water.
  5. Stop adding the hydrochloric acid when the indicator turns colourless.
  6. Record the volume added by carefully reading the burette
  7. The reaction is carried out again, running the acid in steadily until close to the end-point when it is added in very small amounts, until the colour change is observed,
  8. The reaction is carried out once more, this time without the indicator present and using the accurate quality of acid obtained
  9. The solution from the conical flask is poured into a evaporating basin.
  10. Place the evaporating basin onto a tripod and gauze and heat gently using a Bunsen burner until half of the solution remains.
• Leave to cool and crystallise, remove crystals and dry between 2 pieces of filter paper or in a low temperature oven or in a dessicator.

Question 9

How is accuracy in determining the end point in titration obtained? (3)

Answer 9

• Adding The solution in the burette dropwise near the end point
• reading the burette volume at the bottom of the meniscus
• swirling the conical flask during the titration to ensure mixing is complete

Question 10

Preparation of burette (4)

Answer 10

• rinse with deionised water
• Rinse with solution to be used in the burette and ensuring the solution goes through the jet
• Fill with solution, ensuring the jet is filled and there are no air bubbles
• Allow solution to run out until the bottom of the meniscus is on the zero line