# Ba(OH) 2. 8H 2 O + 2NH 4 SCN  Ba(SCN) 2 + 2NH 3 + 10H 2 O What is the sign of  G in this reaction? What is the sign of  G in this reaction? What is.

## Presentation on theme: "Ba(OH) 2. 8H 2 O + 2NH 4 SCN  Ba(SCN) 2 + 2NH 3 + 10H 2 O What is the sign of  G in this reaction? What is the sign of  G in this reaction? What is."— Presentation transcript:

Ba(OH) 2. 8H 2 O + 2NH 4 SCN  Ba(SCN) 2 + 2NH 3 + 10H 2 O What is the sign of  G in this reaction? What is the sign of  G in this reaction? What is the sign of  H in this reaction? What is the sign of  H in this reaction? What is the driving force in this reaction? What is the driving force in this reaction? How does the reaction proceed even though both reactants are solids? How does the reaction proceed even though both reactants are solids?

LeChatlier’s Principle Any change to a system at equilibrium will alter so as to minimize the effects of the change. Any change to a system at equilibrium will alter so as to minimize the effects of the change. Reaction quotient: Ratio of concentration of products to reactants at any time (not just at equilibrium) Q Reaction quotient: Ratio of concentration of products to reactants at any time (not just at equilibrium) Q If Q > K reaction not at equil. & will go toward reactants If Q > K reaction not at equil. & will go toward reactants If Q < K reaction not at equil. & will go toward products If Q < K reaction not at equil. & will go toward products If Q = K reaction is at equilibrium If Q = K reaction is at equilibrium

Example problem For reaction: H 2 O (l) === H + + OH - K = 1.0 x 10 -14 @ 25 o C. The [ ] of the system out of equilibrium = [H + ] = 3.0 x 10 -5 M and [OH - ] = 2.0 x 10 -7 M will reaction go toward the reactants or products to reach equilibrium?

How will reaction be affected if you remove product? How will reaction be affected if you remove product? How will reaction be affected if you add product? How will reaction be affected if you add product? How will reaction be affected if you remove reactant? How will reaction be affected if you remove reactant? How will reaction be affected if you add reactant? How will reaction be affected if you add reactant?

Ba(OH) 2. 8H 2 O + 2NH 4 SCN  Ba(SCN) 2 + 2NH 3 + 10H 2 O If the temperature is raised, which direction will equilibrium shift toward? If the temperature is raised, which direction will equilibrium shift toward? If the temperature is lowered? If the temperature is lowered? If the temperature of an exothermic reaction is raised? If the temperature of an exothermic reaction is raised? If the temperature of an exothermic reaction is lowered? If the temperature of an exothermic reaction is lowered?

Remember! Just because a reaction is thermodynamically favored K is big does not mean it is fast. Kinetics and thermodynamics are distinct!

Resources to find methods Standard Methods for the Examination of Water and Wastewater Standard Methods for the Examination of Water and Wastewater Journal of Chemical Education Journal of Chemical Education ASTM Methods ASTM Methods Analytical Chemistry for Technicians Analytical Chemistry for Technicians Environmental Chemistry: Experiments and Demonstrations Environmental Chemistry: Experiments and Demonstrations Analytical Chemistry: Practice Analytical Chemistry: Practice Methods for environmental trace analysis Methods for environmental trace analysis Methods for environmental trace analysis Methods for environmental trace analysis NIOSH manual of analytical methods / NIOSH manual of analytical methods / NIOSH manual of analytical methods / NIOSH manual of analytical methods /

Steps in Experimental Design 1. Formulate the question 2. Develop the hypothesis Hypothesis must be testable 3. Make predictions What will the data look like if the hypothesis is supported? Not supported? 4. Plan methods for testing hypothesis What experimental methods will be used for testing the hypothesis?

Steps in Experimental Design 5. Collect data 6. Evaluate data Does it support the hypothesis? Do additional experiments need to be done?

Hypotheses Study of the effectiveness of laundry detergents Study of the effectiveness of laundry detergents Taking aspirin reduces the length of headache time versus taking Tylenol Taking aspirin reduces the length of headache time versus taking Tylenol Lightbulbs: longevity vs. cost Lightbulbs: longevity vs. cost Application of fertilizer increases the concentration of nitrate in nearby surface water Application of fertilizer increases the concentration of nitrate in nearby surface water Null hypothesis: Increasing the size of the buffer zone between a farm field and surface water does not result in reduced nutrient levels. Null hypothesis: Increasing the size of the buffer zone between a farm field and surface water does not result in reduced nutrient levels.

Why can we ignore the concentration ratio of solvent (usually water) in equilibrium expressions? (Hint: consider the case of the dissociation of 0.1M acetic acid if you would like a concrete example.) Why can we ignore the concentration ratio of solvent (usually water) in equilibrium expressions? (Hint: consider the case of the dissociation of 0.1M acetic acid if you would like a concrete example.) Why is it also permissible to omit the concentration of solids in equilibrium expressions? (If you want a concrete example use Mn, the density of Mn is 7.21g/mL.) Why is it also permissible to omit the concentration of solids in equilibrium expressions? (If you want a concrete example use Mn, the density of Mn is 7.21g/mL.)

Solubility Product

Solubility Product Example Calculate the solubility product of Ag 3 PO 4 if 500.mL of saturated solution contains 0.00325g of dissolved salt. Neglect any hydrolysis effects. Calculate the solubility product of Ag 3 PO 4 if 500.mL of saturated solution contains 0.00325g of dissolved salt. Neglect any hydrolysis effects.

Another Ksp example Calculate the solubility of Ag2CrO4 @ 25oC in moles/liter. Ksp = 2.4 x 10-12. Calculate the solubility of Ag2CrO4 @ 25oC in moles/liter. Ksp = 2.4 x 10-12.

Common ion effect Addition of a common ion displaces reaction toward reactants, less will dissolve. A salt will be less soluble if one of its constituent ions is already present in solution. Addition of a common ion displaces reaction toward reactants, less will dissolve. A salt will be less soluble if one of its constituent ions is already present in solution. Solubility, like any other equilibria expression is affected by addition of common ions Solubility, like any other equilibria expression is affected by addition of common ions

Common ion effect example Calculate the solubility of AgCl @ 25 o C in 0.010M AgNO 3 solution. Calculate the solubility of AgCl @ 25 o C in 0.010M AgNO 3 solution.

Common Ion Effect Demo The solubility of KCl at room temperature is 3.7M The solubility of KCl at room temperature is 3.7M Each test tube contains 20mL of saturated KCl initially Each test tube contains 20mL of saturated KCl initially To test tube #1 20mL of 6M HCl is added To test tube #1 20mL of 6M HCl is added To test tube #2 20mL of 12M HCl is added To test tube #2 20mL of 12M HCl is added Explain results which appear to contradict the principles of the common ion effect. (Hint: Calculate the concentrations of K + and Cl - after the addition of HCl and calculate Q for each system.)

A waste bottle contains 0.01M Cu +1 and Sn +2 ions. For waste disposal, it is considerably cheaper if these two metals were precipitated separately rather than co-precipitated. Is such a separation possible? What would you precipitate the solutions with? (Use the K sp values given at the back of your book.) A waste bottle contains 0.01M Cu +1 and Sn +2 ions. For waste disposal, it is considerably cheaper if these two metals were precipitated separately rather than co-precipitated. Is such a separation possible? What would you precipitate the solutions with? (Use the K sp values given at the back of your book.)

Solubility Rules When applying solubility rules focus mainly on the anion portion of your molecule When applying solubility rules focus mainly on the anion portion of your molecule Always soluble: Always soluble: Group I metals and ammonium salts are soluble Group I metals and ammonium salts are soluble Nitrates, acetates, and perchlorates are soluble Nitrates, acetates, and perchlorates are soluble Cl -, Br -, and I - are soluble except with Ag +, Pb 2+, Cu +, and Hg 2+ Cl -, Br -, and I - are soluble except with Ag +, Pb 2+, Cu +, and Hg 2+ Sulfates are soluble except with Ca 2+, Sr 2+, Ba 2+, and Pb 2+ Sulfates are soluble except with Ca 2+, Sr 2+, Ba 2+, and Pb 2+ Always insoluble: Always insoluble: CO 3 2- are insoluble except with Group I and NH 4 + CO 3 2- are insoluble except with Group I and NH 4 + PO 4 3- are insoluble except with Group I and NH 4 + PO 4 3- are insoluble except with Group I and NH 4 + S 2- except Group I, II, and NH 4 + S 2- except Group I, II, and NH 4 + OH - except with Group I, NH 4 +, Ca 2+, Sr 2+, and Ba 2+ OH - except with Group I, NH 4 +, Ca 2+, Sr 2+, and Ba 2+

Acids and Bases Review Bronsted – Lowry Acid: Proton donor Bronsted – Lowry Acid: Proton donor Bronsted – Lowry Base: Proton acceptor Bronsted – Lowry Base: Proton acceptor Lewis acid: e- pair acceptor Lewis acid: e- pair acceptor Lewis base: e- pair donor Lewis base: e- pair donor Salt: ionic solid can be thought of as the product of an acid base reaction Salt: ionic solid can be thought of as the product of an acid base reaction

Demonstration: pH of distilled water Why is the pH of distilled water acidic? Write it down in your notebook. Why is the pH of distilled water acidic? Write it down in your notebook. How can this be minimized? How can this be minimized? How can the CO 2 be removed? How can the CO 2 be removed?

Strong acids & bases completely dissociate Strong Acids: Strong Acids: Everything else is weak Strong Bases: Alkali earth metal OH R4NOH R are all organic groups Alkaline earth metal OH (but not always soluble) Everything else is weak

Explain why, if benzoic acid is a weak acid with a K a of 6.28 x 10 -5, sodium benzoate is basic. Use equilibria. Explain why, if benzoic acid is a weak acid with a K a of 6.28 x 10 -5, sodium benzoate is basic. Use equilibria. If you have a 0.100M solution of sodium benzoate, what will be the pH of the solution? If you have a 0.100M solution of sodium benzoate, what will be the pH of the solution?

Buffers Buffer resists changes in pH Buffer resists changes in pH How does a buffer work? How does a buffer work? It contains significant amounts of both an acid and its conjugate base at equilibrium such that with the common ion effect/ L’Chatlier’s Principle it is able to minimize the effects of additions of acid or base It contains significant amounts of both an acid and its conjugate base at equilibrium such that with the common ion effect/ L’Chatlier’s Principle it is able to minimize the effects of additions of acid or base

Buffer Example What is the pH of 0.180 mole of NaNO2 mixed with 0.230 moles of HNO2 in 1.0 liter of solution? What is the pH of 0.180 mole of NaNO2 mixed with 0.230 moles of HNO2 in 1.0 liter of solution?

Buffer capacity How well a buffer resists changes to pH when a strong acid or strong base is added. How well a buffer resists changes to pH when a strong acid or strong base is added. Buffers are most effective closer to their pKa Buffers are most effective closer to their pKa Do not want to generally make a buffer more than 1 pH unit from its pKa Do not want to generally make a buffer more than 1 pH unit from its pKa

Buffer example 2 How would you make a buffer at a pH of 7.80? (There is more than one correct answer.) How would you make a buffer at a pH of 7.80? (There is more than one correct answer.)

Buffer example 3 What would the pH be of a buffer solution containing 100.0mL of 0.15M NH3 and 4.25mL of 1.0M HCl? What would the pH be of a buffer solution containing 100.0mL of 0.15M NH3 and 4.25mL of 1.0M HCl?

Buffer example 4 How will the pH change when 10.0mL of 0.1M HCl is added to a buffer containing 0.15moles of Sodium acetate and 0.12 moles of acetic acid in 1.0 liter of solution?