P1C8 - Acids and alkalis

Question 1

What is formed when acid reacts with an alkali?

Answer 1

Water

Question 2

What does an alkali form?

Answer 2

It forms a hydroxide ions
OH-

Question 3

What does an acid form?

Answer 3

Hydrogen ions
H+

Question 4

What is a strong acid?

Answer 4

Fully ionise in water

Question 5

What is a weak acid?

Answer 5

Partially ionise in water

Question 6

Methyl orange

Answer 6

Red in acid
Yellow in alkali

Question 7

Litmus paper

Answer 7

Red in acid
Blue in alkali

Question 8

Phenolphthalein

Answer 8

Colourless in acid
Pink in alkali

Question 9

How do you test for carbon dioxide

Answer 9

Take an aqueous solution of limewater (calcium hydroxide) and bubble through the gas.

If the gas is carbon dioxide, the limewater solution will turn from clear to cloudy.

Question 10

What is titration?

Answer 10

A technique that measures the volumes of acid and alkali solutions that are needed in a neutralisation reaction.

Question 11

What are the 2 titration indicators?

Answer 11

Methyl orange - yellow AL = red AC
Phenolphthalein - pink AL = colourless AC

Question 12

Titration method

Answer 12

1. Using a pipette, add a set volume of a strong alkali to a conical flask.
2. Add a few drops of a suitable indicator.
3. Place a strong acid (sulfuric, hydrochloric or nitric acid) of known concentration in a burette.
4. Take an initial reading of the volume of acid in the burette.
5. Gradually add the acid to the alkali.
6. Make sure that you are regularly swirling the conical flask as you add the acid. As you get closer to the end point, start to add the acid at a slower rate.
7. As soon as the indicator changes colour, stop adding acid.
8. Take a final reading of the volume of acid in the burette.
9. Subtract the final reading from the initial reading to calculate the volume of acid needed to neutralise the alkali.