(2.28-2.33) Acids, Alkalis and Titrations

What is an acid?

A substance that is a source of H+ ions in solution

What is an alkali?

A soluble base that is a source of OH- ions in solution.

What can alkalis do?

Neutralise acids

How do alkalis neutralise acids?

OH- reacts with H+ to create H2O which is neutral

What are the four indicators?

Litmus, phenolphthalein, methyl orange, universal indicator

What is the colour of litmus in acids?

Red

What is the colour of litmus in alkalis?

Blue

what is the colour of phenolphthalein in acids?

Colourless

what is the colour of phenolphthalein in alkalis?

Pink

What is the colour of methyl orange in acids?

Red

What is the colour of methyl orange in alkalis?

Yellow

Strongly acidic values + colour on the pH scale

0-3 and red/orange

Weakly acidic values + colour on the pH scale

4-6 and yellow/light green

Neutral values + colour on the pH scale

7 and green

Weakly alkaline values + colour on the pH scale

8-10 and dark green/blue

Strongly alkaline values + colour on the pH scale

11-14 and dark blue/purple

Describe how to use universal indicator to measure pH of an aqueous solution.

Add drops of solution onto a piece of universal indicator paper and observe the colour change. Match it to the pH scale.

What is a titration?

the slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration until the reaction reaches neutralization, which is often indicated by a color change.

List the equipment needed for titration.

filter funnel, burette, beaker, alkali, acid, glass pipette, pipette filler, conical flask, phenolphthalein indicator, white tile, distilled water

Detail steps of titration

1. Rinse burette with acid and record to nearest 0.05cm3

2. Use pipette filler to rinse glass pipette with alkali and transfer 25.0cm3 to a conical flask.

3. Add 2-3 drops of indicator to conical flask and place on white tile.

4. Run acid from burette to flask, swirling until solution is colourless. (trial so overshooting is fine.) Record to nearest 0.05cm3.

5. Wash with distilled water, re-fill and repeat. Record starting and end volume of acid. When close to last volume, add in acid in drops.

6. Repeat 5 at least twice more.

7. Clean and put away equipment.

What are concordant results?

Values (excluding trial run) that are within 0.20cm3 of each other.