Download chapter 9: aqueous solutions

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CHAPTER 9: AQUEOUS SOLUTIONS
I. Dissociation Equations:
 Can be written for ionic compounds or strong acids dissolving in water.
 Show that the ions separate from each other in solution.
Steps:
1. write the separate aqueous ions (including their correct charges) on the right side
2. write the formula of the compound followed by an arrow
3. balance using coefficients
4. add state symbols
(state of pure substance on the left, ((s) usually), (aq) for ions on the right)
Example 1: Solid Sodium carbonate dissolves in water
Example 2: Iron (III) sulfate dissolves in water
II. Calculations involving Ion Concentrations
 Concentrations may be expressed as concentrations of entire compounds or
concentrations of individual ions.
 [Ca2+] = “concentration of calcium ions”
 Dissociation equations and simple ratios can be used to calculate ion concentrations from
compound concentrations or vise versa. (because there is ONE solution with a single
volume)
Steps:
1. Write the balanced dissociation equation
2. Write down the given information
2. Use a ratio to solve to the missing information
Example 3: What are the concentrations of sodium and phosphate ions in a 0.090 mol/L
sodium phosphate solution?
Example 4: How many grams of calcium hydroxide must be dissolved in 250.0 mL of solution in
order to produce a hydroxide concentration of 0.15 mol/L?
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DISSOCIATION & IONIC CONCENTRATIONS PRACTICE: for each of the following show the
dissociation equation for the salt and calculate the requested information, showing your work.
1. Write the dissociation equation for the following compounds dissolving:
a) iron (III) nitrate
b) sodium thiosulfate
c) barium hydroxide
2. Calculate the concentration of each ion in :
a) 1.30 mol/L ZnCl2 solution.
b) a solution formed by dissolving 15.0 mg of Al2 (SO4 )3 in 2.00 L of water.
3. What concentration of (NH4)2SO4 will give an ammonium concentration of 1.20 mol/L?
4. What mass of Calcium chloride is required to prepare 2.000 L of 0.120 mol/L of Cl-
Answers:
2a) Zn2+ 1.30 mol/L , 2.60 mol/L Cl- 2b) Al 3+ = 4.38 x 10-5M, SO4 2- = 6.58 x 10-5M
3. 0.600 M (NH4)2SO4
4. 133 g CaCl2
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LESSON ON NET IONIC EQUATIONS


Many chemical reactions take place in solutions
Reactions in solution can be written In 3 different forms:
Nonionic equation
Total ionic equation
Net ionic equation
1. eg. barium hydroxide solution mixes with nickel (III) chloride solution
NONIONIC EQUATION:
 Write formulas of reactants and products
 look up the solubility of the products on your solubility chart.
 Then, balance the whole reaction.
2. TOTAL IONIC EQUATION:
 all ionic substances and strong acids dissolved in solution exist as separate ions.
 Show ALL the DISSOLVED (aq) salts and strong acids in their dissociated form.
eg. Ba(OH)2 (aq) becomes
NiCl3(aq) becomes
This salt is NOT dissolved, so
it remains together and intact.
3. SPECTATOR IONS: substances that are EXACTLY the same before and after the reaction
4. NET IONIC EQUATION:
 Eliminate spectators
 Simplify
STRONG ACIDS: fully dissociate in water, (ie. strong electrolytes) write in ion form for total ionic & net
ionic equations
HCl, HBr, HI, H2 SO4 , HNO3, HClO4
(Show H2SO4 as forming H+ and HSO4 -)
REGARDING SOLUBILITY: There is no such thing as an ION that is insoluble. It is only COMBINATIONS
of ions that are either soluble or insoluble or sparingly soluble.
Use a solubility chart to predict the solubility of any salt that is formed in a reaction.
REGARDING METALS: metals are neutral substances unless they are part of salts. Do NOT add a charge
unless you are dealing with metal that is part of an ionic compound
Eg. Copper metal is Cu(s) (NOT Cu+ or Cu2+)
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NET IONIC EQUATIONS WORKSHEET.
The nonionic chemical equation is provided below.
Balance the equation, provide the missing state symbols.
Write the total ionic equation and then the net ionic equation for each of the following.
1. Zinc nitrate solution reacts with a sodium sulfide solution to form a precipitate.
____ ZnNO3 2 aq   ____ Na2 S aq  
 ____ NaNO3    ____ ZnS  
2. Hydrobromic acid is neutralized by a potassium hydroxide solution.
____ HBraq  ____ KOH aq 
 ____ HOH    ____ KBr 
3. Magnesium is placed in hydrochloric acid.
____ Mg  s   ____ HCl aq  
 ____ MgCl 2

 ____ H 2 g 
4. Aqueous solutions of cesium sulfate and barium chloride are mixed.
____ Cs2SO4aq  ____ BaCl2aq 
 ____ BaSO4   ____ CsCl 
5. An iron strip is placed in a solution of nickel II nitrate.
____ Fe s   ____ NiNO3 2 aq  
 ____ FeNO3 3    ____ Ni
6. Bromine is added to a magnesium iodide solution.
____ Br2 l   ____ MgI 2aq 
 ____ MgBr2   ____ I 2


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SOLUTION STOICHIOMETRY
Example: 20.0 mL of 0.0400 mol/L ferric nitrate
solution is mixed with 30.0 mL of 0.0500 mol/L
lithium sulfite.
a) which substance
reactant?
Fe(NO3)3is +the limiting
Li2SO
3 
FOR SOLUTION STOICHIOMETRY:
DO: Use n=CV to calculate moles
DO: Use moles in stoichiometry ratios
DO NOT: Use dilution formula (C1V1 = C2V2)
DO NOT: Use concentrations in stoichometry ratios…
Use moles! (two different solutions may have different
volumes… comparing concentrations doesn’t indicate total
number of moles of each)
Fe2( SO3)3 +
LiNO3
a) what mass of precipitate forms?
b) assuming that 75.0 mL of distilled water was added during the filtering process, what is the
concentration of leftover reactant in the filtrate.
c) what is the concentration of the soluble product in the filtrate?
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SOLUTION STOICHIOMETRY PRACTICE
1.
2Al(NO3)3
+
3 K2S 
6 KNO3
+
Al2S3
a) If 100.0 mL of 0.0300 mol/L aluminum nitrate mixes with 25.0 mL of potassium sulfide, what must
be the concentration of potassium sulfide if the reaction is complete (no leftover reactants)?
b) What will be the concentration of potassium ions in the reaction mixture at the end of the reaction?
2.
BaCl2 +
2AgNO3 
Ba(NO3)2 +
2 AgCl
An excess of barium chloride solution was added to 400.0 mL of silver nitrate solution and 5.10 g of
precipitate was formed.
a) What was the concentration of the silver nitrate solution?
b) If 0.500 mol/L BaCl2 solution was used the the reaction described above, what minimum volume
would be necessary to fully react the AgNO3 ?
3.
2 NaOH 
H2 SO4 +
Na2SO4 +
2 H2O
a) How many mL of 15.5 mol/L sulfuric acid solution is necessary to completely neutralize 150.0 mL of
2.00 mol/L sodium hydroxide solution.?
b) If only 3.00 mL of sulfuric acid is mixed with the NaOH, what concentration of NaOH will remain in
the mixture?
4.
Zn +
2HCl 
ZnCl2 +
H2
A 20.0 g zinc strip is put in 50.0 mL of 6.00 mol/L hydrochloric acid. After reaction is complete, the zinc
strip is taken out and weighed.
a) What is the final mass of the strip?
b) If a further 20.0 mL of water is added to the solution while rinsing the zinc strip and then the water is
evaporated from the solution. What will be the concentration of zinc chloride in the reaction mixture?
5.
AgNO3
+
NaCl 
AgCl +
NaNO3
a) 26.0 mL of 0.100 mol/L silver nitrate reacts completely with 0.600 mol/L sodium chloride. How
many mL of sodium chloride must be added?
b) what mass of precipitate will result?
c) suppose the reaction mixture is filtered to remove the precipitate. What will the concentration of
sodium nitrate be in the filtrate if 50.0 mL of distilled water is used for rinsing during the filtration?
ANSWERS:
1a) 0.180 mol/L K2S
3a) 9.68 mL H2SO4
5a) 4.33 mL NaCl
1b) 0.0720 mol/L K+
3b) 1.35 mol/L NaOH
5b) 0.373 g AgCl
2a) 0.0890 mol/L AgNO3
2b) 35.6 mL BaCl2
4a) 10.2 g Zn 4b) 2.14 mol/L ZnCl2
5c) 0.0324 mol/L NaNO3