Compounds In Water 07

Compounds in Water • Dissociation – a compound made of ions falls apart in water (ex. NaCl)

– When a substance dissociates, the amount of ions in the solution can be found by looking at the formula of the compound. – Ex. If 1 mole of NaCl dissociates, making 2 moles of ions in solution. – Ex. If 1 mole of MgCl2 dissociates, making 3 moles of ions in solution.

• Solubility – some substances dissolve better than others in certain solvents (“Like dissolves like”.) • Solubility guidelines are on p. 427.

Definitions • Ionization: Some compounds are pulled apart by water (or other solvents) in solution. When pulled apart, the pieces form ions. If H+ forms, it reacts quickly. – Ex: in H2O, H+ makes hydronium ion, H3O+.

• Electrolytes: Strong electrolytes conduct electricity well.

– They form when virtually all of the dissolved solute forms ions.

• Weak electrolytes occur when not many of the dissolved solute molecules form ions. – Strong & weak electrolytes differ in their“degree of ionization/dissociation”.

Precipitation Reactions • What is a precipitate? – Precipitate – an insoluble salt (solid) produced from mixing two ionic solutions. – Precipitates are denoted by (s) solid – Soluble Compounds are denoted with (aq) aqueous or in water solution.

How do you know when a precipitate will form? • You can predict the formation of a precipitate by using the solubility rules. • Soluble = aqueous (solution). • Insoluble = Solid

Solubility Rules • 1.) All common compounds of Group I and ammonium ions • • • • •

are soluble. 2.) All nitrates, acetates, and chlorates are soluble. 3.) All binary compounds of the halogens (other than F) with metals are soluble, except those of Ag, Hg(I), and Pb. 4.) All sulfates are soluble, except those of barium, strontium, calcium, lead, silver, and mercury (I). The latter three are slightly soluble. 5.) Except for rule 1, carbonates, hydroxides, oxides, silicates, and phosphates are insoluble. 6.) Sulfides are insoluble except for calcium, barium, strontium, magnesium, sodium, potassium, and ammonium.

Protocol For Using Solubility Rules • The rule that is the first to apply is the rule that you use to determine solubility. • Even if another rule applies to the equation, the one with the lower number is the rule you go by.

• 2AgNO3(aq) + CaCl2(aq) ->

2AgCl(s)+ Ca(NO3)2(aq

• 2NaOH(aq) + PbCl2(aq)

2NaCl(aq)+ Pb(OH)2(s)

->

• K2CO3(aq) + CaS(aq) ->

K2S(aq)+ CaCO3(s)

• Complete Ionic Equation – an

equation that shows dissolved ionic compounds as their free ions. • Net Ionic Equation – an equation that indicates only those particles that actually take part in the reaction. • Spectator Ions – Ions that are not directly involved in the reaction.

Dating Analogy • Four people go out on a blind date.

At the end of the evening, only one couple decides to continue dating. • The couple that decides to continue dating can be one of three things: – – –

(s) In a Solid Relationship (l) in Love (g) Going out together

Example • Skeleton Equation: 2HCl(aq) + ZnS(aq) -> H2S(g) + ZnCl2(aq)

• Complete Ionic Equation: 2H+(aq) + 2Cl-(aq) + Zn2+(aq) + S2-(aq) -> H2S(g) + 2Cl-(aq) + Zn2+(aq)

• Net Ionic Equation: 2H+(aq) + S2-(aq) -> H2S(g)

Your Turn! • Skeleton Equation: 2KF(aq) + Ca(NO3)2(aq) -> CaF2(s) + 2KNO3(aq)

Complete Ionic Equation: 2K+(aq) + 2F-(aq) + Ca2+(aq) + 2NO3-(aq) -> CaF2(s) + 2NO3-(aq) + 2K+(aq)

• Net Ionic Equation: 2F-(aq) + Ca2+(aq) -> CaF2(s)

Last One! • Skeleton Equation: 2LiBr(aq) + Pb(ClO3)2(aq) -> PbBr2 (s) + 2LiClO3(aq)

Complete Ionic Equation:

2Li+(aq) + 2Br1-(aq) + Pb2+(aq) + 2ClO3-(aq) -> PbBr2(s) + 2ClO3-(aq) + 2Li

• Net Ionic Equation: 2Br1-(aq) + Pb2+(aq) -> PbBr2(s)

Do you know what time it is?

What weapon can you make from the metals Potassium, Nickel and Iron? (more a riddle than trivia)

A KNiFe