4.2: Reactions of acids

Question 1

What are redox reactions?

Answer 1

This​ ​means​ ​that​ ​one​ ​substance​ ​is​ ​reduced​ ​and
another​ ​substance​ ​is​ ​oxidised.

You​ ​should​ ​be​ ​able​ ​to​ ​identify​ ​which​ ​substances​ ​are​ ​which​ ​by​ ​looking​ ​at electrons​ ​gained​ ​and​ ​lost​ ​(following​ ​OIL​ ​RIG)

Question 2

What ions do acids and alkalis produce in aqueous solutions?

Answer 2

• Acids​ ​produce​ ​H​+​​ ​ions​ ​in​ ​aqueous​ ​solutions

- Alkalis​ ​produce​ ​OH​-​​ ​ions​ ​in​ ​aqueous​ ​solutions

Question 3

How do you carry out a titration?

TRIPLE-EXTENDED

Answer 3

1. Wash​ ​burette​ ​using​ ​dilute​ ​hydrochloric​ ​acid​ ​and​ ​then​ ​water
2. Fill​ ​burette​ ​to​ ​100cm3​ ​​ with​ ​acid​ ​with​ ​the​ ​meniscus’​ ​base​ ​on​ ​the​ ​100cm3​ ​​​line
3. Use 25cm3​ pipette to add 25cm3​ of alkali into a conical flask, drawing alkali into the pipette​ ​using​ ​a​ ​pipette​ ​filler
4. Add a few drops of a suitable indicator to the conical flask (eg: phenolphthalein which​ ​is​ ​pink​ ​when​ ​alkaline​ ​and​ ​colourless​ ​when​ ​acidic)
5. Add​ ​acid​ ​from​ ​burette​ ​to​ ​alkali​ ​until​ ​end-point​ ​is​ ​reached​ ​(as​ ​shown​ ​by​ ​indicator)
6. The titre (volume of acid needed to exactly neutralise the acid) is the difference between​ ​the​ ​first​ ​(100cm3​ )​ ​ ​and​ ​second​ ​readings​ ​on​ ​the​ ​burette
7. Repeat​ ​the​ ​experiment​ ​to​ ​gain​ ​more​ ​precise​ ​results

Question 4

What is the difference between a strong acid and a weak acid?

Answer 4

● Strong​ ​acid​ ​=​ ​completely​ ​ionised​ ​in​ ​aqueous​ ​solution
o e.g.​ ​hydrochloric,​ ​nitric​ ​and​ ​sulphuric​ ​acids
● Weak​ ​acid​ ​=​ ​partially​ ​ionised​ ​in​ ​aqueous​ ​solution
o Ethanoic,​ ​citric​ ​and​ ​carbonic​ ​acids
● Stronger​ ​an​ ​acid,​ ​lower​ ​the​ ​pH​ ​(for​ ​a​ ​given​ ​conc.​ ​of​ ​aq.​ ​solutions)