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John Nash

on 23 April 2010

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Transcript of Chemistry

Acids and Bases 8.1.1: Define acids and bases
according to the Bronsted-Lowry
and Lewis theories Bronsted-Lowry:
Bronsted-Lowry theory revolves around the donation and acceptance of protons. Lewis:
Lewis theory revolves around electron pairs. 8.1.2: Deduce whether or not a species could act as a Bronsted-Lowry and/or a Lewis acid or base As mentioned before a Bronsted-Lowry acid is a proton donor and a base is a proton acceptor. Using this theory the following reaction reactant and products can be labeled an acid or base.

HNO3 + H2SO4 -> H2NO3+ + HSO4-
The following can be done the same as a Lewis acid will accept a pair of electrons and a Lewis base donates a pair of electrons.

H+ + NH3 -> NH4+
8.1.3. Deduce the formula of the conjugate acid (or base) of any Bronsted-Lowry base (or acid) CH3COOH(aq) + H2O(l) -> H3O+(aq) + CH3COO-(aq) 8.2.1: Outline the characteristic properties of acids and bases in aqueous solution. Acids
- Acids on litmus paper will turn it red
- Phenolphthalein will turn it colorless
- It has a pH of less than 7
- When acids react with either carbonate or hydrogen carbonate, carbon dioxide is created with water and a salt.

- CaCO3(aq) + 2HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l)
- NaHCO3(aq) + HCl(aq) -> NaCl(aq) + CO2(g) + H2O(l)

- Acids reacting with metals produce salts and hydrogen gas
- Zn(aq) + HCl(aq) -> ZnCl2(aq) + H2(g)
- Bases on litmus paper will turn it blue
- Phenolphthalein will turn it pink
- It has a pH of higher than 7
- When a base reacts with water, it releases hydrogen gas and also creates a metal hydroxide.
- 2Na + 2H2O -> 2NaOH + H2
Acids and bases
- Acids and bases neutralize each other to form salt and water, while being exothermic, which are called neutralization reactions.
- HCl + NaOH → NaCl + H2O
8.3.1 Distinguish between strong and weak acids and bases in terms of the extent of dissociation, reaction with water and electrical conductivity

8.3.2 State whether a given acid or base is strong or weak

8.3.3 Distinguish between strong and weak acids and bases, and determine the relative strengths of acids and bases, using experimental data

Strong and weak acids are distinguished by their dissociation in water. Conductivity
A strong acid/base fully dissociates; therefore, it has more ions allowing better conductivity. Reaction rates
The rate of reaction can also distinguish between strong/weak acid/base. Strong acids:

Weak acids:
-H3PO4 Strong bases:
-Group 1 hydroxide (NaOH)
-Lower group 2 hydroxides Ba(OH)2

Weak bases:
8.4.1 Distinguish between aqueous solutions that are acidic, neutral or alkaline using the pH scale.

8.4.2 Identify which of two or more aqueous solutions is more acidic or alkaline using pH values.

8.4.3 State that each change of on pH unit represents a 10-fold change in the hydrogen ion concentration [H+]

8.4.4 Deduce changes in [H+] when the pH of a solution changes by more than one pH unit.
Using the pH scale
The idea of pH comes from the presence of H+ ions in the water. pH = - log [H+] - pH 1 strong acid
- pH 7 is neutral, water
- pH 14 strong base There are different methods of measuring the pH, the most common methods are
-A pH meter
-Indicator solution, e.g. Phenolphthalein
-Indicator paper, e.g. Universal paper
Full transcript