2.4 acid, base and redox reactions

what is the formula for hydrochloric acid?

HCl (strong)

what is the formula for sulphuric acid?

H2SO4 (strong)

what is the formula for nitric acid?

HNO3 (strong)

what is the formula for ethanoic acid?

CH3COOH (weak)

what is a base?

substance that can react with an acid to form a salt

what is an alkali?

base that is soluble in water

what does a strong acid do in water?

dissociate/ ionise fully into H+ ions

what does a weak acid do in water?

partially dissociate/ionise into H+ ions

what are some examples of common bases?

• sodium hydroxide

• potassium hydroxide

• ammonia

what are three types of bases?

• metal hydroxides

• metal carbonates

• alkalis

what does acid and metal oxide make?

• salt

• water

what does acid and metal hydroxide make?

• salt 

• water

what does acid and metal carbonate make?

• salt

• water

• carbon dioxide

what does metal and acid make?

• hydrogen

• salt

why is metal and acid reaction NOT a neutralisation reaction?

• water is not formed

What type of reaction is metal and acid?

• redox reaction

what is formed when ammonia reacts with an acid?

• ammonium salt

what is the simplified ionic equation for neutralisation between acid and alkali?

• H⁺+OH^- = H₂O

what is an oxidation state?

• tells us the charge of an element

• gives an indication of the number of electrons a element has lost or gained

why are oxidation states helpful?

• helps us see what has been oxidised or reduced in redox reaction

what is oxidation state of element in uncombined state?

• 0

what does a positive oxidation state show?

• element has lost electrons

what does a negative oxidation state show?

• element has gained electrons

what does variable oxidation states mean?

• usually the group number of an element determines the oxidation state

• but some elements can have different oxidation states depending on the type of element they are bonded to 

what is the oxidation state of oxygen in peroxide?

• -1

what is oxidation state of oxygen when bonded to fluorine

• +2

what is oxidation state of hydrogen in metal hydrides?

• -1

how do you know if element has been oxidised using oxidation states?

• oxidation number has increased from _ to  _  

how do you know if element has been reduced using oxidation states?

• oxidation number has decreased  from _ to _

what is disproportionation?

• when the same element have been oxidised and reduced

what is the oxidation state for Group 1 element?

• +1

what is oxidation state for Group 2 element?

• +2

what is oxidation state for Group 3 element?

• +3

what is the formula for hydrogen peroxide?

• H₂O₂

what is normal oxidation state of oxygen?

• -2

what is the oxidation state of fluorine?

• -1 always

what is normal oxidation state of chlorine?

• -1

when does chlorine have a different oxidation state than -1?

• when bonded to F or O it has positive value

what are peroxides?

• compounds with oxygen and hydrogen only

what are metal hydrides?

• compounds with metal and hydrogen only

what is charge of nitrate ion?

• NO₃^-

what is charge of carbonate ion?

• CO₃^2-

what is charge of sulphate ion?

• SO₄^2-

what is charge of hydroxide ion?

• OH^-

what is charge of ammonium ion?

• NH₄^-

what is charge of zinc ion?

• Zn²⁺

what is charge of silver ion?

• Ag⁺

what is charge of iron ion?

• Fe³⁺

• Fe²⁺

what is charge of copper ion?

• Cu²⁺

what is a oxidising agent?

• substance that gets accepts electrons and therefore gets reduced in order to oxidise another substance

what is a reducing agent?

• substance that donates electrons and therefore gets oxidised in order to reduce another substance

what is titration used for?

• finding the concentration of a solution

• identification of unknown chemicals

• finding the purity of a substance

why is finding the purity of a substance important?

• important aspect of quality control

• especially compounds manufactured for human uses e.g. medicines, food, cosmetics

• pharmaceuticals should have high purity level as even the tiniest impurity can lead to a lot of harm for patients

what is a standard solution?

• solution of known concentration

what is the volumetric flask used for?

• make standard solution accurately

how would you prepare a standard solution?

1. solid is first weighed accurately

2. solid is dissolved in beaker using distilled water

3. solution is transferred to volumetric flask, last traces are rinsed into flask with distilled water

4. flask is carefully filled until graduation line using distilled water until bottom of meniscus lines up with mark

5. volumetric flask is inverted several times to mix the solution thoroughly

what is the effect of the volumetric flask being filled with water past the graduation line?

• solution is too dilute

• so must be prepared again

what is the effect of the volumetric flask not being inverted?

• solution not mixed thoroughly

• titration results are unlikely to be consistent

what is the acid-base titration procedure?

1. add measured volume of one solution into a conical flask using a pipette

2. add the other solution into burette and record initial burette reaction

3. add indicator to solution in conical flask

4. run solution in burrette into solution in a conical flask, swirling the conical flask to mix, repeating until end point is reached shown by colour change of indicator

5. record burette reading

6. repeat until 2 accurate results are concordant

what is the volume of solution added to burette called?

• titre

what is the range for concordant results for titre?

• 0.10cm³

if oxidation number decreases is that oxidation or reduction?

• reduction

if oxidation number increases is that oxidation or reduction?

• oxidisation