Salts from metals Flashcards
What is salt?
Salt is a general name for a compound formed when the hydrogen in a acid is wholly, or partially, replaced by metal or ammonium ions.
What is the formula for salts?
Metal + acid ——> salt + hydrogen
Why are alkali metals never added to acid?
The metal is very reactive, the reaction with acid is too violent to be carried out safely.
The acid used to provide the negative ions present in all salts:
1) The salts formed when you react a metal with hydrochloric acid are always chlorides (containing Cl- ions)
2) Sulfuric acid makes sulfates
3) Nitric acid always makes nitrates.
Explain the reaction between a metal and an acid.
In the reaction between magnesium, and dilute sulfuric acid, the ions will be displaced from solution by magnesium. This is because magnesium is more reactive than hydrogen. Magnesium has a stronger tendency to form positive ions than hydrogen has, so the following reaction takes place:
Mg(s) + H2SO4(aq) —–> MgSO4 + H2
You can summarize this reaction as an ionic equation:
Mg(s) + 2H+(aq) —> Mg2+ + H2(g)
The sulfate ions in solution do not change in the reaction so are not included in the ionic equation. They are called spectator ions.
A magnesium atoms loses two of its electrons from its outer shell. It gives these electrons to two hydrogens ions from the acidic solution. Theses bond to each other.
Oxidation is loss of electrons and reduction is gain of electrons so you can conclude that electrons have been transferred to hydrogen ions in the reaction:
The magnesium atoms have lost electrons, so magnesium is oxidized in this reaction
The hydrogen ions have gained electrons so have been reduced in this reaction.
The reaction of a metal with an acid is always a redox reaction. The metal atoms will always donate electrons to hydrogen ions, displacing hydrogen as a gas and leaving positive metal ions in the solution.
