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- Concepts:
- solution, colloid, suspension, solute, solvent
- coefficient, balanced chemical reaction, ion exchange (precipitation or
double displacement) reaction, molecular equation, full ionic equation,
net ionic equation (reaction), spectator ion(s)
- solubility rules, soluble, insoluble
- Skills:
- Predict the products of ion-exchange reaction and write net ionic
reaction
- Know and apply solubility rules
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- 1. Combination/Synthesis
- Combination reactions are ones where the reactants are two different
elements or an element and a compound or two compounds which combine to
produce a single compound.
- Element A + Element B à
Single Compound containing A and B
- A metal and a non-metal can combine to form an ionic compound or two
non-metals can combine to form a covalent compound.
- Two metals cannot combine to form compounds however. (They do mix to
give alloys, which is a mixture and not a compound however.)
- Or
- Element A + Compound BC à
Single Compound containing A, B & C elements
- Or
- Compound AB + Compound CD à Single Compound containing A, B, C & D elements
- Sometimes this type of reaction is also referred to as a synthesis
reaction.
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- 2. Combustion
- Combustion reaction is reaction between a substance (element or
compound) and oxygen.
- This is essentially the reaction that takes place when a substance burns
in air.
- Combustion reaction is the source of most of the energy we use.
- Combustion of natural gas (methane) is the reaction that release heat
energy used in cooking food.
- Combustion of petrol is the reaction that take place in the engine of a
motor vehicle the energy evolved driving it.
- The product(s) of combustion of an element is always the oxide of the
element.
- Mg(s) + O2(g) à MgO(s)
- S(s) + O2(g) à
SO2(g)
- C(s) + O2(g) à
CO2(g)
- N2(g) + O2(g) à NO(g)
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- H2(g) + O2(g) à H2O(l) (the oxide of hydrogen)
- Notice that the reaction between an element and oxygen can be classified
as both combination and combustion.
- When a compound burns the oxides of the elements that make up the
compound are formed.
- When you burned methane in the lab, for instance, the products formed
are carbon dioxide and water.
- The reason those to oxides are formed is because methane is made up of
carbon and hydrogen.
- CH4(g) + O2(g) à CO2 + H2O(l)
- We have also looked at some reaction invloving acids and bases but we´ll
return to that later.
- Next we will look at ion-exchange reactions.
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- 3. Ion-exchange/double displacement
(replacement)/metathesis/precipitation reaction
- Salt solution 1 + salt solution 2 à precipitate of insoluble salt + solution of other salt
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- We´ll start with ion’exchange reactions.
- In these reactions solutions of two compounds exchange ions.
- For example, if the following reaction did occur as written, then the
reaction would be classified as ion-exchange reaction
- 2 NaCl (aq) + Pb(NO3)2
(aq) ®
PbCl2 + 2 NaNO3
- Since both the reactants are in solution, they contain free aqueous
ions, namely Na+ (aq), Cl- (aq), Pb2+ (aq)
and NO3- (aq).
- What has basically appeared to have taken place is the exchange of the
ions; sodium and lead have swapped their anions, hence the name ion-exchange
reaction.
- Such reactions may also be referred to as double-displacement reaction
or metathesis reaction or precipitation reaction.
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- Swap partners to determine the cross-products!
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- Similarly the following molecular equations as written could represent
equations for ion-exchange reactions:
- CaCl2 + AgNO3
® AgCl + Ca(NO3)2
- NaCH3COO + Mg(NO3)2
® Mg(CH3COO)2
+ 2NaNO3
- Li2SO4 + Ba(NO3)2 ® BaSO4 + LiNO3
- KOH + CuCl2 ® KCl
+ Cu(OH)2
- Na3PO4 + Zn(NO3)2 ® Zn3(PO4)2
+ NaNO3
- Mg3(PO4)2 + Sr(NO3)2 ® Sr3(PO4)2
+ Mg(NO3)2
- ZnCl2 + Fe(NO3)2 ® Zn (NO3)2 + FeCl2
- (NH4)2CO3 +
Ca(NO3)2 ® NH4NO3 + CaCO3
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- What determines whether an ion-exchange (precipitation) reaction will
take place?
- If one of the products is insoluble then ion-exchange reaction will
occur.
- How does one know if a product is insoluble?
- Solubility rules.
- An insoluble salt will precipitate out from a solution.
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- All Group I and NH4+ compounds are soluble
- All nitrates are soluble
- All acetates (ethanoates) are soluble
- All acids are soluble
- All chlorides, bromides, and iodides are soluble except those of Pb(II),
mercury(I) (Hg22+) and Ag
- All sulfates are soluble except those of Pb(II), mercury(I), Ag, Group
II Ca and below
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- All Hydroxides are insoluble except those of Group I, Group II Ca and
below
- All metal oxides are insoluble except those of Group I
- All carbonates are insoluble except those of Group I and NH4+
- All sulfides are insoluble except Group I and NH4+
- All phosphates are insoluble except those of Group I and NH4+
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- What does it mean for a compound to be soluble in water?
- The substance will dissociate into ions.
- Example 1: AB (s) ( + water) ® AB (aq) ® A+ (aq) + B-(aq)
- AB (aq) represents an aqueous solution of AB containing
hydrated ions, A+ (aq) and B-(aq).
- Each formula unit in the above example produces one each of the ions.
Or, a mole of the formula unit produces a mole each of the cations and
anions, a total of 2 moles of aqueous ions.
- Example 2: AB2 (s) ( + water) ® AB2 (aq) ® A+ (aq) + 2 B-(aq)
- In example 2, 1 mole of the compound produces 1 mol of hydrated cations
and 2 moles of hydrated anions, a total of 3 moles of aqueous ions.
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- What does it mean for a substance to be insoluble in water?
- It will not dissolve in water, that it will precipitate out of a
solution if it is one of the products in a reaction.
- That is, PbCl2 (s) + H2O(l) ® No change!
- And therefore,
- 2NaCl(aq) + Pb(NO3)2
(aq) ® PbCl2
(s) + 2NaNO3 (aq)
- ppt.
- PbCl2 precipitates out of the solution since it is an
insoluble compound (check solubility rules).
- Similarly, Ba(NO3)2 (aq) + K2CrO4
(aq) ® BaCrO4
(s) + 2 KNO3 (aq)
- ppt.
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- Reactant Solutions to the left:
(a) Ba(NO3)2(aq) and (b) K2CrO4(aq)
- Bottom left, on mixing, (a) before reaction, (b) at the end of reaction.
- Bottom right, appearance of reaction mixture at the end of reaction.
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- Precipitation of (white) silver chloride by mixing solutions of silver
nitrate and potassium chloride.
- The K+ and NO3- ions remain in
solution.
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- The reaction of KCl(aq) with AgNO3 to form AgCl(s).
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- Conversely, if a solution of sodium chloride and magnesium nitrate were
to be mixed, no change would be observed since both sodium nitrate and
magnesium chloride (potential products) are soluble.
- That is,
- Na+(aq) + Cl-(aq) + Mg2+(aq) + 2NO3-(aq) ® Na+(aq) +
Cl-(aq)
+ Mg2+ (aq) + 2NO3-(aq)
- (NaCl(aq) + Mg(NO3)2
(aq)) which is essentially no reaction.
- For an ion-exchange reaction to occur, one of the products must be
insoluble.
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- Solutions of the reactants depicted below are mixed.
- Assign state symbols to the equations and using the solubility rules
state whether the reactions as depicted occur. (See next several slides
for solutions.)
- 2 NaCH3COO + Mg(NO3)2
® Mg(CH3COO)2
+ 2 NaNO3
- Li2SO4 + Ba(NO3)2 ® BaSO4 + 2 LiNO3
- 2 KOH + CuCl2 ® 2
KCl + Cu(OH)2
- Na3PO4 + Zn(NO3)2 ® Zn3(PO4)2
+ 2 NaNO3
- Mg3(PO4)2 + Sr(NO3)2 ® Sr3(PO4)2
+ Mg(NO3)2
- ZnCl2 + Fe(NO3)2 ® Zn(NO3)2 + FeCl2
- (NH4)2CO3 +
Ca(NO3)2 ® 2 NH4NO3 +
CaCO3
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- 2 NaCH3COO(aq) +
Mg(NO3)2(aq) ® No change (no reaction), all soluble
- Li2SO4 (aq) + Ba(NO3)2 (aq)
® BaSO4 (s)
+ 2 LiNO3 (aq)
- Ion-exchange reaction does take place; barium sulfate is insoluble.
- 2 KOH (aq) + CuCl2 (aq) ® 2 KCl (aq) + Cu(OH)2(s)
- Na3PO4 (aq) + Zn(NO3)2 (aq)
® No reaction.
- Mg3(PO4)2 (aq) + Sr(NO3)2
(aq) ® Sr3(PO4)2 (s)
+ Mg(NO3)2 (aq)
- ZnCl2 (aq) + Fe(NO3)2 (aq)
® No reaction.
- (NH4)2CO3 (aq) + Ca(NO3)2 (aq)
® 2 NH4NO3
(aq) + CaCO3 (s)
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- The molecular equation for the reaction between solutions of NaCl and
Pb(NO3)2 is
- 2NaCl(aq) + Pb(NO3)2
(aq) ® PbCl2 (s)
+ 2NaNO3 (aq)
- When the soluble salts are represented in the aqueous ionic form you get
the full ionic equation
- 2Na+ (aq) + 2Cl-(aq) + Pb2+
(aq) + 2 NO3 -(aq) ® PbCl2
(s) + 2Na+
(aq) + 2 NO3 -(aq)
- Notice hydrated sodium and nitrate ions do not undergo any change (and
are referred to as spectator ions); they remain in solution (in aqueous
ionic form) from start to finish, and as such can be eliminated from the
equation giving us
- 2Cl-(aq) + Pb2+ (aq) ®
PbCl2 (s)
- The above equation showing only the species that undergo change, showing
only the species that are involved in the reaction, is referred to as a
(net) ionic equation.
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- Molecular equation: AB(aq) + CD(aq) ® AD(s) + CB (aq)
- Full ionic equation: A+ (aq) + B- (aq) + C+ (aq)
+ D- (aq)
® AD (s) +
C+ (aq) + B- (aq)
- So, the difference between molecular and full ionic equation in the case
of an ion-exchange reaction is that the aqueous salts are represented in
their aqueous ionic form in the full ionic equation.
- Net ionic equation: A+ (aq) + D- (aq) ® AD(s)
- The difference between a full ionic equation and net ionic equation in
the case of ion-exchange reaction (and all other reactions as we shall
see later) is that the spectator ions are not included in the net ionic
equation.
- A (net) ionic equation shows only the species that undergo chemical
transformation in the reaction.
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- A solution of calcium chloride and silver nitrate is mixed in a beaker.
- Write balanced molecular, full ionic and net ionic equations for the
reaction that takes place including state symbols.
- Molecular: CaCl2 (aq) + 2AgNO3 (aq) ® 2 AgCl (s)
+ Ca(NO3)2 (aq)
- [Silver chloride precipitates out because it is an insoluble compound.]
- Full Ionic: Ca2+(aq) + 2Cl-(aq) + 2Ag+(aq) + 2NO3-(aq) ® 2AgCl(s) + Ca2+(aq)
+ 2NO3-(aq)
- [Calcium and the nitrate ions are spectator ions.]
- Net Ionic: Ag+ (aq) + Cl-(aq) ® AgCl(s)
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- Write balanced net ionic equations for the following molecular
equations:
- Li2SO4 (aq) + Ba(NO3)2 (aq)
® BaSO4 (s)
+ 2 LiNO3 (aq)
- 2 KOH (aq) + CuCl2 (aq) ® 2 KCl (aq) + Cu(OH)2(s)
- Mg3(PO4)2 (aq) + Sr(NO3)2
(aq) ® Sr3(PO4)2 (s)
+ Mg(NO3)2 (aq)
- (NH4)2CO3 (aq) + Ca(NO3)2 (aq)
® 2 NH4NO3
(aq) + CaCO3 (s)
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- For an ion-exchange reaction to occur, one of the products must be
insoluble.
- The difference between molecular and full ionic equations for a
precipitation reaction:
- Soluble salts appear in their
dissociated or ionized (aqueous ionic) form in the full ionic equation.
All other reagents are the same in both equations.
- The difference between full ionic and net ionic equations for a
precipitation reaction:
- Spectator ions—the aqueous ions that remain aqueous at the end of the
reaction— appear in the full ionic equation but do not appear in the
net ionic equation.
- Note again that a spectator ion(s) is(are) always an aqueous ion(s).
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- 1. Write full ionic and net ionic equations for the following reactions.
- NaCl(aq) + Pb(NO3)2
(aq) ® PbCl2(s) + NaNO3(aq)
- Full ionic:
- Net ionic:
- CaCl2(aq) + AgNO3(aq) ® AgCl(s) + Ca(NO3)2(aq)
- Full ionic:
- Net ionic:
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- 2. Determine if the following reaction can take place, and if they do,
give the products and write balanced net ionic equation for it.
- NaCH3COO(aq) + Mg(NO3)2(aq) ®
- Ionic Equation:
- Li2SO4(aq)
+ Ba(NO3)2(aq) ®
- Ionic Equation:
- KOH(aq) + CuCl2(aq) ®
- Ionic Equation:
- Na3PO4(aq) +
Zn(NO3)2(aq) ®
- Ionic Equation:
- Mg3(PO4)2(aq) + Sr(NO3)2(aq) ®
- Ionic Equation:
- ZnCl2(aq) + Fe(NO3)2(aq) ®
- Ionic Equation:
- (NH4)2CO3(aq) +
Ca(NO3)2(aq) ®
- Ionic Equation:
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- 3. Determine whether a reaction takes place when the following reagent
are mixed. If a reaction takes place, write a net ionic equation to
represent it:
- a) Aqueous solution of iron(III) sulfate and sodium hydroxide
- b) Aqueous solution of silver nitrate and potassium carbonate.
- c) Aqueous solution of lead(II) nitrate and sodium acetate.
- d) Magnesium carbonate and sulfuric acid
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- e) Sodium hydrogen carbonate and hydroiodic acid.
- f) Sodium hydroxide and ethanoic acid.
- g) Aqueous ammonia and hydrobromic acid.
- h) Magnesium oxide and hydrochloric acid.
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- 4. Write balanced equations (with state symbols and all) for reactions
between solutions of compound in column A and every compound in column
B. If there is no reaction, then indicate so on the product side. For
every pair of mixture that undergoes a reaction, include also full ionic
and balanced net ionic equations for the reaction.
- Column A Column B
- 1. Sodium sulfide magnesium nitrate
- 2. Potassium phosphate calcium nitrate
- 3. Potassium sulfate strontium nitrate
- 4. Sodium carbonate barium nitrate
- 5. Sodium chloride lead(II) nitrate
- 6. Sodium hydroxide iron(II) nitrate
- zinc nitrate
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Notes