the composition of solutions copyright © houghton mifflin company. all rights reserved.4–24–2...

The Composition of Solutions

Copyright © Houghton Mifflin Company. All rights reserved. 4–2

Which of the following solutions contains the greatest number of ions? (Assume complete solubility for all salts.)– One mole of potassium chloride dissolved in 1.0 L of

water.– One mole of sodium phosphate dissolved in 1.0 L of

water.– One mole of iron(II) nitrate dissolved in 1.0 L of water.– One mole of sodium hydroxide dissolved in 1.0 L of water.– At least two of the above solutions have an equally great

number of ions.

React 2


Let’s Think About It

• Draw molecular level pictures showing each solution. Think about relative numbers of ions.

• How many moles of each ion are in each solution?

React 2


Molarity

• Molarity (M) = moles of solute per volume of solution in liters:

M

M

molaritymoles of soluteliters of solution

HClmoles of HClliters of solution

362


Which of the following solutions containsthe greatest number of ions?

a) 400.0 mL of 0.10 M NaCl.

b) 300.0 mL of 0.10 M CaCl2.

c) 200.0 mL of 0.10 M FeCl3.

d) 800.0 mL of 0.10 M sucrose.

React 3



• Draw molecular level pictures showing each solution. Think about relative numbers of ions.

• How many moles of each ion are in each solution?

React 3


Notice

The solution with the greatest number of ions is not necessarily the one in which:– the volume of the solution is the largest.– the formula unit has the greatest number of

ions.

Precipitation Reactions


The Reaction of K2CrO4(aq) and Ba(NO3)2(aq)


Simple Rules for Solubility

1. Most nitrate (NO3) salts are soluble.

2. Most alkali (group 1A) salts and NH4+ are soluble.

3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+,

Hg22+)

4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4)

5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble)

6. Most S2, CO32, CrO4

2, PO43 salts are only slightly

soluble.


Describing Reactions in Solution

1. Molecular equation (reactants and products as compounds)

– AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3 (aq)

2. Complete ionic equation (all strong electrolytes shown as ions)

• Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq)

AgCl(s) + Na+(aq) + NO3

(aq)


Describing Reactions in Solution (continued)

3. Net ionic equation (show only components that actually react)

Ag+(aq) + Cl(aq) AgCl(s)

Na+ and NO3 are spectator ions.


You have two separate beakers with aqueous solutions, one with 4 “units” of potassium sulfate and one with 3 “units” of barium nitrate.

a) Draw molecular level diagrams of both solutions.

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b) Draw a molecular level diagram of the mixture of the two solutions before a reaction has taken place.

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c) Draw a molecular level diagram of the product and solution formed after the reaction has taken place.

React 4

Stoichiometry of Precipitation Reactions


a) Draw two pictures, one of solution A and one of solution B. Make sure your pictures show the relative volumes of solutions and the relative numbers of ions.

Solution A:2.00 L2.00 M

AgNO3 (aq)

React 5

Solution B:3.00 L1.00 M

Na2CrO4 (aq)


b) Draw a picture of solution C (made by adding solution A to solution B) before any reaction has taken place. Make sure this picture shows the relative volume of solution C and the relative number of ions, as compared with solutions A and B.

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c) Draw a picture of solution C after the reaction has taken place. Make sure this picture shows the relative volume of solution C and the relative number of ions, as compared with solutions A and B.

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d) Calculate the concentrations (in M) of all ions in solution C.

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To solve this problem we need to know:– the initial concentration of all ions in

solution C before a reaction has taken place.

– the balanced equation for the reaction that has taken place. In this case, it makes sense to use the net ionic equation.

– which reactant, if either, is limiting.

React 5


Calculating an Answer

• How many moles of each ion are present in solution?

• What is the total volume of the solution?

• What is the definition of molarity?


You have two 500.0 mL aqueous solutions. Solution A is a solution of silver nitrate and solution B is a solution of potassium chromate (K2CrO4). The masses of the solutes in each of the solutions are the same. When the solutions are added together, a blood red precipitant is formed. After the reaction has gone to completion, you dry the solid and find that it has a mass of 331.8 grams.

a) Calculate the concentration (molarity) of the original potassium chromate solution.

React 6


You have two 500.0 mL aqueous solutions. Solution A is a solution of silver nitrate and solution B is a solution of potassium chromate (K2CrO4). The masses of the solutes in each of the solutions are the same. When the solutions are added together, a blood red precipitant is formed. After the reaction has gone to completion, you dry the solid

and find that it has a mass of 331.8 grams. b) Calculate the concentration (molarity) of the

chromate ions in the final solution.

React 6



• To solve this problem we need to know:– the initial concentrations of all ions in the

final solution before a reaction has taken place.

– the balanced equation for the reaction that has taken place. In this case, it makes sense to use the net ionic equation.

– which reactant, if either, is limiting.

React 6


Calculating an Answer

• How many moles of each ion is present in solution?

• What is the total volume of the solution?

• What is the definition of molarity?

Acid-Base Reactions


Key Titration Terms

• Titrant - solution of known concentration used in titration.

• Analyte - substance being analyzed.

• Equivalence point - enough titrant added to react exactly with the analyte.

• Endpoint - the indicator changes color so you can tell the equivalence point has been reached.


Performing Calculations for Acid-Base Reactions

1. List initial species and predict reaction.

2. Write balanced net ionic reaction.

3. Calculate moles of reactants.

4. Determine limiting reactant.

5. Calculate moles of required reactant or product.

6. Convert to grams or volume, as required.

Oxidation-Reduction Reactions


Reaction of Sodium and Chlorine


Rules for Assigning Oxidation States

1. Oxidation state of an atom in an element = 0

2. Oxidation state of monatomic element = charge

3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1)

4. H = +1 in covalent compounds

5. Fluorine = 1 in compounds

6. Sum of oxidation states = 0 in compounds

7. Sum of oxidation states = charge of the ion


React 7

Find the oxidation states for each of the elements in each of the following compounds:

• K2Cr2O7

• CO32-

• HClO4

• MnO2

• PCl5• SF4


Make a list of nitrogen compounds with as many different oxidation states for nitrogen as you can.

React 8


Which of the following are oxidation-reduction reactions? Identify the oxidizing agent, and the reducing agent.

• Zn (s) + 2HCl(aq) ZnCl2 (aq) + H2 (g)

• Cr2O72-(aq) + 2OH-(aq) 2CrO4

2-(aq) + H2O(l)

• O3 (g) + NO (g) O2 (g) + NO2 (g)

• 2CuCl (aq) CuCl2 (aq) + Cu (s)

React 9


Balancing Oxidation-Reduction Reactions

• Cr2O72-(aq) + SO3

-(aq) Cr3+(aq) + SO4

2-(aq)

• How can we balance this equation?


Method of Half Reactions

• Cr2O72-(aq) 2Cr3+(aq)

• SO3-(aq) + SO4

2-(aq)

• How many electrons are involved in each half reaction?


• 6e- + Cr2O72- (aq) 2Cr3+ (aq)

• SO3- (aq) + SO4

2- (aq) + 2e-

• How can we balance the oxygen atoms?

Method of Half Reactions (continued)


• 6e- + Cr2O72- (aq) Cr3+ (aq) + 7H2O

• H2O +SO3- (aq) + SO4

2- (aq) + 2e-

• How can we balance the hydrogen atoms?



• This reaction occurs in an acidic solution.

• 14H+ + 6e- + Cr2O72-(aq) Cr3+(aq) + 7H2O

• H2O +SO3- (aq) SO4

2- (aq) + 2e- + 2H+

• How can we balance the electrons?




• 14H+ + 6e- + Cr2O72- (aq) Cr3+

(aq) + 7H2O

• 3[H2O +SO3- (aq) SO4

2- (aq) + 2e- + 2H+]

• Cr2O72- (aq) + 3SO3

-(aq) + 8H+

(aq) 2Cr3+(aq) + 3SO42-(aq) +

4H2O(l)


Half-Reaction Method - Balancing in Base

1. Balance as in acid.

2. Add OH that equals H+ ions (both sides!)

3. Form water by combining H+, OH.

4. Check elements and charges for balance.


Balance the following oxidation-reduction reactions that occur in acidic solution.

• ClO- (aq) + I- (aq) Cl- (aq) + I3- (aq)

• Br- (aq) + MnO4- (aq) Br2 (l)+ Mn2+ (aq)

• CH3OH(aq) + Cr2O72-(aq) CH2O(aq) + Cr3+(aq)

React 10

the composition of solutions copyright © houghton mifflin company. all rights reserved.4–24–2...

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noticethe solution

relative number of ions

picture of solution

relative volume of solution

greatest number of ions

aqueous solutions

relative numbers of