Chapter 4 Understanding Acid-Base Properties
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Who was the first person to outline the characteristics of acid and bases?
Robert Boyle
What properties did Robert Boyle state that acid and bases had?
Acids -Sour taste -Corrosive to metal -Change colour of certain vegies dyes - Litmus blue to red Base (Boyle used the term alkalis) -Slippery -Litmus red to blue
What does Arrhenius’s theory state about acids and bases?
-An acid is a substance that will ionise in a solution producing H+ ions -A base is a substance that will dissociate in a solution producing OH- ions
According to Arrhenius, what is a strong acid?
A substance that completely ionises in water
In terms of ionisation and weak/strong acids and Arrhenius’s theory, what does a single arrow and a double arrow indicate about the strength of the acids?
A single arrow is used to show complete ionisation that is a strong acid. A double arrow indicates partial ionisation that is a weak acid
According to Arrhenius, what is a weak acid?
A substance that partially ionises in water
What is Arrhenius’s theory limited to?
It only limited to acid-base behaviour in aqueous solutions
What does Bronsted-Lowry theory explain about acids and bases?
Explain the behaviour of acids and bases in terms of proton transfer between the two species. Acids are substances that donates a proton Bases are substances that accepts a proton
What is a conjugate base?
The species that is formed when an acid donate a proton
What is a conjugate acid?
The species that is formed when a base accepts a proton
What is the acidity constant (Ka
An equilibrium constant that measures how much an acid donates protons in water.
What does a large Ka value mean?
Strong acid (greater ionisation, more H⁺ donated).
What does a small Ka value mean?
Weak acid (less ionisation, less H⁺ donated).
How is water treated in the Ka expression?
Water is a liquid with constant concentration, so it’s excluded from the expression.
What is the relationship between acid strength and its conjugate base?
Strong acid → weak conjugate base; Weak acid → stronger conjugate base.
What are monoprotic acids?
Acids that donate one proton per molecule (e.g. HCl, HNO₃).
What are polyprotic acids?
Acids that donate more than one proton (e.g. H₂SO₄, H₃PO₄).
How does acid strength change in polyprotic acids?
Each successive proton is harder to remove, so Ka₁ > Ka₂ > Ka₃.
Is the conjugate base of a polyprotic acid always neutral?
No, it’s usually still acidic but weaker than the original acid.
What happens when an acid reacts with a base?
A salt and water are formed.
Are all salts neutral?
No. Salts can be acidic, basic, or neutral depending on their ions.
What makes a salt solution acidic?
If the cation (e.g. NH₄⁺) acts as a weak acid.
What makes a salt solution basic?
If the anion (e.g. CH₃COO⁻) acts as a weak base.
What is a neutral salt made from?
A strong acid and a strong base (e.g. NaCl).