acids and redox

what is an acid?

a species that donates a proton
it releases H+ ions in aqueous solution

what are some examples of common acids?

hydrochloric acid HCl
sulfuric acid H2SO4
nitric acid HNO3
ethanoic acid CH3COOH

what is a strong acid?

it completely dissociates in aqueous solution

what is a weak acid?

it partially dissociates in aqueous solution

what is a base?

a species that accepts a proton
it neutralises an acid to form a salt

what is an alkali?

a base that dissolves in water releasing OH- ions into the solution

what are some examples of common alkalis?

sodium hydroxide NaOH
potassium hydroxide KOH
ammonia NH3

what is a salt?

a compound that is formed when H+ of an ion is replaced by a metal ion

what are three ways acids can be neutralised?

neutralised by metal oxides/hydroxides, alkalis, or carbonates

what happens when an acid is neutralised by a metal oxide or hydroxide?

they react to form a salt and water only

what happens when an acid is neutralised by an alkali?

they react to form a salt and water only

what happens when an acid is neutralised by a carbonate?

they react to form a salt, water, and carbon dioxide 

what are titrations?

techniques used to accurately measure the volume of solution that reacts exactly with another solution

what are three things titrations can be used for?

finding the concentration of a solution, identification of unknown chemicals, finding the purity of a substance

what are the steps to prepare a standard solution?

1. calculate the mass of the solid using the weigh-by-difference method

2. dissolve the solid using a small amount of distilled water; stir with a glass rod

3. using a funnel, transfer solution to a volumetric flask; rinse the beaker + glass rod with distilled water into the flask

4. add distilled water until the bottom of the meniscus lines up exactly with the mark on the neck of the flask

5. place a stopper on and invert the solution slowly several times

why should the volumetric flask not be filled with water above the graduation line?

if too much water is added, the solution will be too dilute and must be prepared again

why should the flask be inverted?

to ensure that the solution is mixed evenly for consistent titration results

what is the colour of methyl orange in acid, base, and at end point?

acid - red
base - yellow
end point - orange

what is the colour of phenolphthalein in acid, base, and at end point?

acid - colourless
base - pink
end point - pale pink

what is an oxidation number?

a measure of the number of electrons an atom uses to bond with any other atom

what is the oxidation number for an uncombined element?

O

what is the oxidation number for combined oxygen?

-2 (-1 in peroxides, +2 bonded to fluorine)

what is the oxidation number for combined hydrogen?

+1

what is the oxidation number for a simple ion? e.g. Na+, Mg2+, Cl-

the charge on the ion e.g. Na+ = +1

what is the oxidation number of combined fluorine?

-1

what is the oxidation number of sulphur in sulphate?

+6

what is the sum of oxidation states in a neutral molecule?

0

what is the sum of oxidation states in an ion?

it equals the charge on the ion

what oxidation number does iron (II) have?

+2

what is reduction?

the removal of oxygen and the gain of electrons

what is oxidarion?

the addition of oxygen and the loss of electrons

what are redox reactions?

involve both reduction and oxidation

what is redox in terms of oxidation number?

reduction is a decrease in oxidation number, oxidation is an increase in oxidation number