Acids, bases and neutralisation

What is an acid

An acid is a species that is a proton donor

What is a base

A base is a proton acceptor

Amphoteric

When a substance has both acidic and basic components, such as an amino acid

Preparing a standard solution

1. Accurately weigh out mass of solid using weighing boat and scale and record.

2. Transfer solid to a 250cm³ beaker, rinse weighing boat with distilled water to ensure all solid is transferred

3. Transfer solution to a 250cm³ flask using a funnel. Rinse funnel and beaker with distilled water to ensure all solution has been transferred.

4. Add 50-100cm³ of distilled water and swirl around to mix. Then add distilled water until below calibration mark.

5. Then using a dropping pipette add distilled water until meniscus sits on the mark.

6. Place stopper on flask and invert at least 10 times to fully mix.

Carrying out titration

1. Rinse burette with solution that will fill it, HCl, then fill burette with solution. Ensur3e burette tip is full with no air bubbles.

2. Record initial burette reading to 0.05cm²

3. Rinse a pipette with the solution you will transfer to the conical flask (CacO₃). Use a pipette + safety filler to transfer 25.0 cm³ of the other solution into a 250 cm³ conical flask (the acid).

4. Add 2-3 drops of suitable indicator. Phenolphthalein for weak acid vs strong base. Methyl orange for strong acid vs weak base.

5. Place a white tile under the conical flask to see the colour change more clearly.

6. Run the burette solution slowly into the flask while swirling. As you approach the end point, add the solution dropwise.

7. Stop when the first permanent colour change is observed:

   • Phenolphthalein: pink → colourless or colourless → pale pink

   • Methyl orange: yellow → orange/red or vice versa

Record the final burette reading to 2 d.p.

8. Calculate the titre (final − initial).

9. Repeat until concordant results obtained (0.10cm³ of each other. Find mean.

Strong acid vs weak acid

A strong acid fully dissociate in water whilst a weak acid partially dissociates in water. Most weak acids are organic