Unknown Solution Determination
Unknown Solution Determination
1) Most chemical reactions are placed in three categories:
i. Two ionic solutions are mixed and produce an ionic solid.
ii. The most common type of precipitation reaction is a double displacement reaction or metathesis reaction.
1. This reaction can also be referred to as an exchange reaction.
2. Example: 2KBr(aq) + Pb(NO3)2(aq) ( PbBr2(s) + 2KNO3(aq)
iii. To predict precipitation reactions, the solubilities of reactants and products must be assessed.
1. If all reactants and products are soluble in water, no product results.
b. Acid–base neutralization reactions
i. An acid and base are combined to form an ionic compound (i.e. salt) and possibly water (if the base is a hydroxide).
ii. A Brønsted–Lowry acid is defined as a proton donor.
1. Example: HBr or H2SO4
iii. A Brønsted–Lowry base is defined as a proton acceptor.
1. Example: LiOH or NH3
iv. An example reaction: LiOH(aq) + HBr(aq) ( LiBr(aq) + H2O(l)
v. Some ionic salts, when reacted with acid, form gases.
1. The most common gases produced are CO2, SO2, and H2S.
2. Example: K2CO3(aq) + 2HBr(aq) ( 2KBr(aq) + H2O(l) + CO2(g)
a. The H2O(l) + CO2(g) result from the spontaneous decomposition of H2CO3(aq).
c. Oxidation–reduction reactions
i. These reactions involve electron transfer where one species is oxidized and another species is reduced.
1. Oxidation: loss of electrons or an increase in the oxidation number.
2. Reduction: gain of electrons or a decrease in the oxidation number.
ii. The most common types of oxidation–reduction reactions are:
1. Combination (or synthesis) reactions
2. Decomposition reactions
3. Single displacement reactions
4. Combustion reactions
2) There are a number of driving forces for reactions to occur:
a. Formation of molecular compounds
i. Example: H2O
b. Formation of a gas
i. Examples: H2S, CO2, SO2
c. Formation of an insoluble precipitate
3) You will be given seven aqueous solutions to identify.
a. You will identify the acids and bases using pH paper.
b. Next, you will mix each solution with another unknown and determine if a reaction has taken place.
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