Acids and Redox

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  • Created by: jp3louis
  • Created on: 16-01-17 21:03

Acids

All acids contain hydrogen in their formulae.

When dissolved in water, an acid releases hydrogen ions as protons into the solution.

In this equation, hydrogen chloride gas releases H+ ions as it dissolves in water:

HCl (g) + aq --> H+(aq) + Cl- (aq)

In this equation, +aq has been included to show that an excess of water is present.

A strong acid releases all its hydrogen atoms into solution as H+ ions and completley dissociates in aqueous solution.

HCl (aq) --> H+ (aq) + Cl- (aq)

A weak acid only releases a small amount of H+ ions and partially dissociates in aqueous solution.

Ch3COOH(aq) <=> H+(aq) + CH3COO- (aq)

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Bases and alkalis

Metal oxids, metal hydroxides, metal carbonates and ammonia, Nh3 are bases. 

A base neutralises an acid to form a salt.

An alkali is a base that dissolves in water releasing hydroxide ions (OH-) into the solution. 

NaOH(s) + aq --> Na+ (aq) + OH-(aq)

Metal oxides                            Metal carbonates                           Alkalis

MgO                                              Na2CO3                                 NaOH

CaO                                               CaCO3                                   KOH

CuO                                               CuCO3                                    NH3

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Neutralisation

In neutralisation of an acid, H+ (aq) ions react with a base to form a salt and neutral water.

The H+ ions from the acid are replaced by metal or ammonium ions from the base.

Hydrochloric acid: HCL                    Sodium chloride - NaCl

Sulfuric acid: H2SO4                      Sodium sulfate - Na2SO4

Nitric acid: HNO3                            Calcium nitrate - Ca(NO3)2

Ethanoic acid: CH3COOH                Ammonium ethanoate - CH3COONH4

To form a salt, the hydrogen in the acid is replaced by a metal or ammonium ion.

Acid+ Alkali --> salt + water

Acid + carbonate --> salt + water

Acid + metal oxide/metal hydroxide --> Salt + water

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Few equations

n= C X V / 1000

C = 1000 x n/v

N = mass x mr

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Oxidation numbers and redox

The number of electrons involved in bonding to a different element.

Rules for element:

The oxidation number is always 0 for elements.(H2, o2, P4, S8, Na and Fe)

Rules for compounds and ions

Sum of oxidation numbers = total charge.

Polyatomic ions : N02- has the oxidation of +3 for nitrogen. N03- is +5

Redox reactions

Redox involves reduction and oxidation (if something is reduce, something must be oxidised)

Dilute acid ungergo redox with some metals to produce salts and hydrogen gas.

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