C4 - Acids and redox Flashcards
What are acids?
Species that releases H+ ions in aqueous solutions
What is a strong acid?
Acid that dissociates completely in solution
Example of a strong acid
HCl
What is a weak acid?
Acid that dissociates only partially in solution
Example of a weak acid
Ethanoic acid
What is a base
Compound that neutralises ban acid to form a salt
Examples of bases
Metal oxides
Metal hydroxides
Metal carbonates
Ammonia
Examples of alkalis
NaOH
KOH
NH3
What is an alkali
Type of base that dissolves in water forming OH- ions
Acid + alkali
Salt + water
Acid +metal oxide
Salt + water
Acid + carbonate
Salt + water + carbon dioxide
What is a titration?
Technique used to accurately measure the volume of one solution that reflects exactly with another solution
What can titrations be used for?
Finding concentration of solution
Identification of unknown chemicals
Finding purity of substance
How do you prepare a standard solution
1) weigh solid accurately
2) solid dissolved in beaker
3) solution transferred to volumetric flask and beaker contents rinsed into flask
4) flask filled to graduation line using pipette until bottom of meniscus line up with mark
5) volumetric flask inverted several times
How should burette readings be recorded?
Two dp
Last value is 0 or 5
When calculating the error interval, which apparatus needs to be doubled
Burette
both final and initial reading
How do you do an acid-base titration?
1) Add measured volume of solution to conical flask using pipette
2) Add other solution to burette and record initial reading
3) add few drops of indicator to solution in conical flask
4) run solution in burette into solution in conical flask, swirling conical flask, until indicator changes colour at end point of titration
5) Record final burette reading
6) Quick trial titration is carried out and then it’s repeated more accurately until two concordant results
What is concordant titre
Agreeing within 0.10 cm^3
Why is an oxidation number?
Measure of the number of electrons that an atom uses to bond with atoms of another element
Oxidation number of O
-2
Oxidation number of H
+1
Oxidation number of F
-1
Oxidation number of Na, K
+1
Oxidation number of Mg, Ca
+2
Oxidation number of Cl, Br, I
-1
Oxidation number of H in metal hydrides
-1
Oxidation number of O in peroxides
-1
Oxidation number of O bonded to F
+2
What are oxidation number rules for elements?
Always 0
Eg, Na, H2
Oxidation number rules for compounds
-oxidation number has sign that’s placed before
-each atom in a compound has a charge that sums to 1
How do you use Roman numbers in naming
Oxidation number in brackets
Oxidation in terms of oxidation number
Increase in oxidation number
Reduction in terms of oxidation numbers
Decrease in oxidation number
Formula of hydrochloric acid
HCl
Formula of sulfuric acid
H2SO4
Formula of nitric acid
HNO3
Formula of ethanoic acid
CH3COOH
Formula of sodium hydroxide
NaOH
Formula of potassium hydroxide
KOH
Formula of ammonia
NH3
What is neutralisation
Chemical reaction in which an acid and a base react to form a salt
H+ (aq) + OH- (aq) –> H2O (l)
What is a redox reaction?
Reaction involving both reduction and oxidisation
Oxidation in terms of oxygen and electrons?
Gain of oxygen
Loss of electrons
What is an oxidising agent?
Reagent that accepts electrons from another species
Reduction in terms of oxygen and electrons?
Loss of oxygen
Gain of electrons
What is a reducing agent?
Reagent that donates electrons to another species