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More on Acids

More about acids

Strong and Weak Acids 1

What you need to know:

What is meant by the dissociation of acids.

What makes an acid weak or strong.

Dissociation of acids

When an acid is added to water (or an aqueous solution), the molecules within the acid let go of a H+, hydrogen ion.

For example:

More on Acids, figure 1

Strong acids

Strong acids are acids which completely ionise in aqueous solution. This means that all of the acid molecules lose a H+ ion completely.

Weak acids

Weak acids are acids which partly ionise in aqueous solution. This means that only some of the acid molecules lose a H+ ion.

More on Acids, figure 2

Strong and Weak Acids 2

What you need to know:

How acid strength affects the reactivity of said acid.

How acid strength and pH are related

How acid strength affects reactivity

When acids react with other substances, it’s the Hion in the acid which is reacting with the molecules in the other substance. Therefore, the more Havailable, the more vigorously the acid reacts with other substances. For this reason, strong acids react more vigorously than weak acids.

Acid strength and pH

The pH scale is actually a measurement of the concentration of Hions within the acid. The higher the concentration of Hions, the lower the pH and the stronger the acid.

For every decrease of 1 on the pH scale, the Hion concentration increases by a factor of 10 (10x more than before).

You can work out how many more ____H+__ ions there are with the equation:__

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Acid strength and concentration

Acid strength and concentration are two different things. The strength of the acid tells you what proportion of the molecules ionise in water. The concentration tells you how much of the solution is made up of the acid.

Acidic Reactions

What you need to know:

How acids react with different types of substances and the generic equations for each.

Reactions with metal oxides and metal hydroxides

__Difference between base and alkali: __

  1. Alkalis are substances that form OH- ions when they dissolve in water.
  2. A base is something that can neutralise acids.
  3. All alkalis are bases but not all bases are alkaline.
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What do you call the salt?

The salt is very easy to name, if you have the name of the reactants. The metal (from the metal oxide or metal hydroxide) will tell you the first half of the name, and the acid will tell you the last half!

For example:

More on Acids, figure 2

Metal carbonates reacting with acids

Metal carbonates are bases too. They reactant with acids to form a salt, water and carbon dioxide.

More on Acids, figure 3

Just like before, the type of salt depends on the metal and the salt involved. The only difference is that now there is carbon dioxide released as well!

Making Soluble Salts

What you need to know:

How to make a soluble salt and how to purify the salt that is produced.

To make a soluble salt, you need to react an acid with a metal oxide/hydroxide/carbonate. You can work out which acid and base you will need by the name of the salt you want to form.

To form a soluble salt, you need to do the following steps:

  1. Put the acid in a beaker and gently warm the acid with the bunsen burner. Once the acid has been warming up for about a minute, turn off the bunsen burner.
  2. Place the insoluble base (metal oxide/carbonate) into the beaker and stir. You will see that the product is soluble.
  3. Keep adding the insoluble base until it is saturated. This happens when no more product can be formed and you will see that there will be some base left over which won’t react.
  4. Filter out the insoluble reactant using filter paper and a funnel. This will leave you with the salt solution.
More on Acids, figure 1