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AQA Chemical Changes 2 (The pH scale (You can use universal indicator or a…
AQA Chemical Changes 2
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Acids
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As the pH decreases by one unit (becoming a stronger acid), the hydrogen ion concentration increases by a factor of 10.
Strong acids are completely ionised in aqueous solutions e.g. hydrochloric, nitric and sulfuric acids.
Soluble salts
They can be made from reacting acids with solid insoluble substances, for example, metal, metal oxides, hydroxides and carbonates.
Production of soluble salts includes adding the solid to the acid until no more dissolves. Then filtering off the excess solid and then crystallise to produce solid salts.
Where do the ions go?
Cations are positive ions and they move to the negative cathode. Anions are negative ions which move to the positive anode.
The pH scale
You can use universal indicator or a pH probe to measure the pH of a solution and determine whether they are acid or alkaline.
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In a neutral pH, hydrogen ions react with hydroxide ions to produce water.
H+ + OH- = H2O
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At the negative electrode metal will be produced on the electrode if it is less reactive than hydrogen. Hydrogen will be produced if the metal is more reactive than hydrogen.
At the positive electrode oxygen is formed. If you have a halide ion then you will get chlorine, bromine or iodine formed at that electrode.
Titrations are used to work out the precise volumes of acid and alkali solutions that react with each other.
Fill the burette with acid and note the starting volume. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
Stop adding the acid when the end point is reached (the appropriate colour change in the indicator happens) note the final volume reading. Repeat steps 1 to 3 until you get consistent readings.
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The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved.