Question

1. 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. 3 SrCl2 (aq) + 2 Li3PO4 (aq) ---> Sr3(PO4)2 (s) + 6 LiCl (aq)

b. 2 HBr (aq) + Ca(OH)2 (aq) ---> 2 H2O (l) + CaBr2 (aq)

c. FeS (s) + HCl (aq) ---> FeCl2 (aq) + H2S (g)

d. 2 NO (g) + 5 H2 (g) ---> 2 NH3 (g) + 2 H2O (g)

e. 2 KI (aq) + Pb(NO3)2 (aq) ---> PbI2 (s) + 2 KNO3 (aq)

2.

	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)

	well 1 Mf
	well 2 Mf
	well 3 M

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

Answer 1

1. Of the following balanced molecular equations, the ones which represent reactions for which the rate law expression could likely be determined via time to turbidity determinations are,

a. 3 SrCl2 (aq) + 2 Li3PO4 (aq) ---> Sr3(PO4)2 (s) + 6 LiCl (aq)

e. 2 KI (aq) + Pb(NO3)2 (aq) ---> PbI2 (s) + 2 KNO3 (aq)

2. Using Mf (final molarity of Na2S2O3) = initial molarity x initial volume/total volume

we get,

well 1 Mf = 0.3 x 3/5 = 0.18 M [b. 0.18]

well 2 Mf = 0.3 x 1.5/5 = 0.09 M [d. 0.18]

well 3 Mf = 0.3 x 1.0/5 = 0.06 M [f. 0.18]