Chapter 4 - Acids and bases Flashcards
What is an acid?
An acid releases hydrogen ions (H+) into the solution, in water
What is a strong acid?
A strong acid releases all of its hydrogen atoms into solution as H+ ions and completely dissociates.
e.g. Hcl(aq) -> H+(aq) + Cl-(aq)
What is a weak acid?
A weak acid only releases a small proportion of its hydrogen atoms into solution as H+ ions and partially dissociates in aqueous solution.
e.g. CH3COOH(aq) H+(aq) + CH3COO- (aq)
What is a base?
A base is a compound that neutralises an acid by accepting a hydrogen ion to form a salt.
What kind of compounds are bases?
Metal oxides (CuO, MgO, Na2O), metal hydroxides, metal carbonates, and ammonia (NH3) are classified as bases.
What is an alkali?
An alkali is a base that dissociates in water (soluble) forming hydroxide ions (OH-).
e.g. NaOH(s) + aq -> Na+(aq) + OH-(aq)
What is a salt?
Product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions.
Give the definition of neutralisation.
H+(ions) react with a base to form a salt and neutral water. H+ ions replaced by metal or ammonium ions from the base, in the acid.
Write ionic equation for neutralisation.
H+(aq) + OH-(aq) -> H2O(l)
Acid + alkali -> salt + water
What are the products of neutralisation of an acid with carbonates?
Salt, water and CO2
What is titration used for?
Used to accurately measure the volume of one solution that reacts exactly with another solution.
Other than finding the concentration of a solution, what can titrations be used for?
- Identification of unknown chemicals
- Finding purity of a substance
What piece of equipment is used to make standard solution?
Volumetric flask
How do you prepare a standard solution?
- ) Dissolve weighed solid in beaker using distilled water
- ) Transfer solution into volumetric flask and fill to graduation line by adding distilled water.
- ) Invert volumetric flask to mix solution
Describe acid-base titration procedure.
- ) Add measured volume of one solution to conical flask using a pipette.
- ) Add other solution to a burette, and record initial burette reading.
- ) Add indicator to solution in conical flask
- ) Run solution in burette into conical flask and swirl to make sure solutions mix. When the indicator changes colour this marks end of titration.
- ) Record final burette reading - volume added by burette called titre.
- ) Run trial titration
- ) Repeat until two concordant results occur (within 0.10cm^3)
What is the titre?
Volume added from the burette in a titration.
How do you determine unknown concentration of a solution from a titration?
results: pipette: 25.00cm^3of 0.100moldm^-3 KOH
titre: 25.70cm^3 of H2SO4
- find amount of standard solution: n = c x v v = 0.025dm^3 n = 0.1 x 0.0025 n = 0.0025 mol - find molar ratio from equation: 2KOH + H2SO4 - find moles of unknown, then concentration n = 0.00125mol c = 0.00125/0.02457 = 0.0486moldm^-3
What is oxidation number?
Measure of the number of electrons involved in bonding to a different element
What is the oxidation number for elements?
oxidation number is always 0.
Why is oxidation number 0 for pure elements?
Any bonding is to atoms of the same element.
What does the sum of the oxidation numbers equal?
Overall charge
What is the oxidation state/number of Iron (III)?
+3
What is reduction in terms of electrons?
Reduction is the gain of electrons
What is oxidation in terms of electrons?
oxidation is the loss of electrons
OILRIG
What is oxidised and reduced in:
2Fe + 3Cl2 -> 2FeCl3
Fe -> Fe3+ 3e-
Iron loses electrons, so is oxidised
Cl2 +2e- -> 2Cl-
Chlorine gains electrons, so is reduced
What is reduction in terms of oxidation number?
Reduction is a decrease in oxidation number.
What is oxidation in terms of oxidation number?
Oxidation is an increase in oxidation number
What is oxidised and reduced in: Cu + 2AgNO3 -> 2Ag + Cu(NO3)2
oxidation state:
Cu: 0 -> +2
Ag: +1 -> 0
Cu oxidation number increases by 2, so is oxidised
Ag oxidation number decreases by 1, so is reduced
