5.8 Strong And Weak Acids
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Strong acid def
Acids that completely ionise in aqueous solutions
Weak acid def
Acids that do not ionise completely in aqueous solutions
Examples of strong acids
• hydrochloric acid • nitric acid • sulphuric acid
Examples of weak acids
• ethanoic acid (found in vinegar) • citric acid (found in citrus fruits) • carbonic acid (found in rainwater, fizzy drinks)
Why do acids have to dissolve in water before showing acidic properties?
• in water all acids ionise (split up) • their molecules split to form H+ ions and negative ions
How does hydrochloric acid (HCl) ionise?
HCl (aq) —> H+(aq) + Cl-(aq)
How do weak acids ionise in a solution?
• only a small proportion of acidic molecules ionise • the reactions in reversible, the molecules will split up and the ions recombine to form original molecules again
Does a weak acid have a higher or lower pH?
Higher
How does the concentration of H+ ions affect the pH?
When the concentration of H+ ions is reduced by a factor of 10, the pH value goes up by one unit
Describe the difference between a strong and weak acid
A strong acid is fully ionised but a weak acid is only partially ionised
Describe the difference between a dilute acid and a concentrated acid
A dilute acid contains a low proportion of acid compared to the total volume of a solution
Write an equation to show how ethanoic acid ionises in water
CH3COOH(aq) —> (reversible) CH3COO(aq)+ H+ (aq)