C5 - strong and weak acids

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  • Created by: Hapsa
  • Created on: 21-03-13 20:28
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Strong and weak acids
Strong acids ­ hydrochloric, nitric, sulphuric
Weak acids ­ citric, ethanoic (in vinegar)
Strong acids = low pH, react quicker, ionise completely in water
Weak acids = high pH, react slower, ionise partially in water
Strong and weak acids will produce the same amount of products, but at different rates
Reaction with magnesium = hydrogen
Reaction with calcium carbonate = carbon dioxide
Strong acid hydrogen ions + other ions
HCl H+ + Cl-
Weak acid hydrogen ions + other ions (equilibrium arrow)
C6H7O7H H+ + C6H7O7-
In water, acid molecules ionise and form hydrogen ions. (H+)
Low pH = high concentration and high pH = low concentration
The equilibrium arrow position is on the left because the mixture contains lots of acid
molecules but not many H+ ions, so weak acids do not seem to be so acidic. Reactants are
more concentrated.
The rate of reaction
Strong acid rate is fast high concentration of H+ ions increases collision frequency
Weak acid rare is slow few H+ ions are available to react
Electrolysis ­ the ions move
Acids produce hydrogen at the cathode (negative electrode). Positive ions go to the cathode
(hydrogen goes there)
The same amount of concentration of strong and weak acids produces the same amount of
hydrogen gas in electrolysis.
Conductivity
Harder for current to flow in weak acids as they have a low electrical conductivity slower
rate creating slow rate of hydrogen being made because =====
Weak acids fewer hydrogen ions to move in the liquid do not conduct as well as strong
acids. (H+ ions carry the charge)
Descaling agents the concentration of H+ ions in a weak acid is enough to attack the lime
scale on a kettle = not enough to attack the kettle material, strong acids would damage the
metal.
Concentration ­ the concentration of an acid tells us how many moles of acid there are in dm3
of a solution.
Strength - The strength of an acid tells us how much of an acid ionises
A strong acid can be diluted with water to increase the pH.

Comments

Tanaz

Hello Hapsa, the notes are very helpful.

I think you can add diagrams to make it more effective

Thanks 

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