CHE 1302 Study Guide - Midterm Guide: Stoichiometry, Ionic Compound, Dynamic Equilibrium

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2 : [2 ag+][cro4, [ag+][cro4, 2[ag+]2[cro4, [ag+]2[cr3+][o2 ]4, [ag+]2[cro4. Explanation: as usual, we can write a balanced equation for the dissociation of the sparingly soluble ionic compound, and then write an equilibrium constant expression (ksp) involving concentrations of products / concentrations of reactants. Each concentration term is raised to a power equal to the stoichiometric coefficient for the species in the balanced equation. We do not include pure solids or liquids in the expression. Explanation: the solution above a solid in a heterogeneous mixture is called the. It is saturated with ions from the solid, and we know this because solid. Crf3 remains in the mixture (no more can dissolve up, because a dynamic equilibrium has been reached). We can write an equation describing the equilibrium for the dissolution, and hence a ksp expression. We are given the value of ksp and the [cr3+], so we just plug in the numbers to find [f ] .

Related Questions

write the equilibrium expression (k) for the following reactions: a. CH4

Silver bromide, AgBr (s), is an essential reagent in black and white film developing. It is,

however, only sparingly soluble in water. AgBr (s) has K = 5.0 Ã 10-13, making it difficult to

rinse AgBr from the film negative with water.

Instead, excess AgBr is removed by an aqueous solution of sodium thiosulfate (Na2S2O3), which forms the complex ion Ag(S2O3)23-:

Ag+ (aq) + 2 S2O32- (aq) Ag(S2O3)23- (aq) Kf = 4.7 Ã 10+13 a) To see how this helps, first determine the molar solubility of AgBr (s) in water.

b) The large formation constant of Ag(S2O3)23- (aq) means that almost all of the silver is complexed with the thiosulfate. To determine how much, calculate the [Ag+] at equilibrium in a 1.0 L solution that initially contains 0.001 M silver ions and 0.200 M sodium thiosulfate. Do so by setting up an ICE table and assuming that x is small compared to 0.200 (but not 0.001). Show that this results in a value of x = [Ag(S2O3)23-] = 0.001. In other words, all of the Ag+ complexes.

c) Your result from part b suggests that no Ag+ remains in solution. This obviously canât be correct, since it would result in an infinitely large reaction quotient that wouldnât be equal to an admittedly large equilibrium constant. To determine the correct [Ag+], use the equilibrium concentrations determined in part b as your initial concentrations in a new ICE table. Then use Kf to determine [Ag+]. [This approach is called a stoichiometric shift and is useful when a reaction starts with only reactants but goes almost to completion. Is essence, we are approaching the equilibrium from the direction of all Ag(S2O3)23- and no Ag+ as opposed to the direction of all Ag+ and no Ag(S2O3)23-.]

d) Before we determine the solubility of AgBr (s) in a thiosulfate solution, we need to know the appropriate equilibrium constant. To find it, determine the value of the equilibrium constant for the reaction:

AgBr (s) + 2 S2O32- (aq) <-->Ag(S2O3)23- (aq) + Br - (aq) Kc = ??

e) Finally, calculate the molar solubility of AgBr (s) in 1.0 M sodium thiosulfate. In other words, what is [Ag(S2O3)23-] for the reaction given in part d when the initial concentration of thiosulfate is 1.0 M?

The following data were collected at 20 ^oC for the reaction of bromophenol blue (HBPB^2-) and hydroxide ions (OH^-):

HBPB^2- (aq) + OH^- (aq) ---> BPB^3- (aq) + H₂O (l)

The times required to form a constant [BPB^3-] at varying initial concentrations of reactants were determined and tabulated. From the rate data, determine the rate law for the reaction.

trial	[OH^-]	[HBPB^2-]	reaction time (sec)	rate (1/sec)
1	1.00	7.22 x 10^-6	75
2	0.25	7.22 x 10^-6	290
3	1.00	3.63 x 10^-6	152

		rate = k[HBPB^2-]²[OH^-]
		rate = k[HBPB^2-]²[OH^-]²
		rate = k[HBPB^2-][OH^-]
		rate = k[HBPB^2-][OH^-]²

QUESTION 2

Which of the following balanced molecular equations represent reactions for which the rate law expression could likely be determined via time to turbidity determinations? Select all that apply.

	a.	2 KI (aq) + Pb(NO₃)₂ (aq) ---> PbI₂ (s) + 2 KNO₃ (aq)
	b.	2 HBr (aq) + Ca(OH)₂ (aq) ---> 2 H₂O (l) + CaBr₂ (aq)
	c.	2 NO (g) + 5 H₂ (g) ---> 2 NH₃ (g) + 2 H₂O (g)
	d.	FeS (s) + HCl (aq) ---> FeCl₂ (aq) + H₂S (g)
	e.	3 SrCl₂ (aq) + 2 Li₃PO₄ (aq) ---> Sr₃(PO₄)₂ (s) + 6 LiCl (aq)

QUESTION 3

When working in the laboratory a small amount of 0.30 M sodium thiosulfate accidentally splashes on your exposed forearm. What should you do? Select all that apply.

	a.	Inform your lab instructor.
	b.	Proceed immediately to the sink in the laboratory and flush the area with copious amounts of water. Then wash the area with mild hand soap.
	c.	Leave the laboratory immediately. All lab work is over for you today.
	d.	Do nothing.
	e.	Stop, drop, and roll.

QUESTION 4

	volume of 1.0 M HCl	volume of water	volume of 0.3 M Na₂S₂O₃
well 1	2.0 mL	0	3.0 mL
well 2	2.0 mL	1.5 mL	1.5 mL
well 3	2.0 mL	2.0 mL	1.0 mL

The above table summarizes the amounts and concentrations of the reactants that will be used in each trial in Parts II. Use the dilution equation, M₁V₁ = M₂V₂, to calculate the concentration M_f (molarity_final) of Na₂S₂O₃ in each well after mixing but before any reaction occurs. The [HCl] has been worked for you as an example.

M_1(HCl)V₁ = M_2(HCl)V₂ where V₂ = final total volume V_f

(1.0 M)(2.0 mL) = M_2(HCl)(5.0 mL)

M_2(HCl) = 0.40 M = M_f(HCl)

- a. b. c. d. e. f.	well 1 M_f
- a. b. c. d. e. f.	well 2 M_f
- a. b. c. d. e. f.	well 3 M

a.	0.090 M
b.	0.18 M
c.	0.60 M
d.	0.20 M
e.	0.060
f.	0.30 M

CHE 1302 Study Guide - Midterm Guide: Stoichiometry, Ionic Compound, Dynamic Equilibrium

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