[Sis290025]

1. Which reagent could be used to separate Br- from NO3- when added to an aqueous solution containg both?

a. CuSO4
b. AgNO3
c. NaI
d. Ba(OH)2

All choices are aqueous.

I don't understand what the problem is asking. Is it saying that these anions are combined together in a solution as in BrNO3? But is this not possible because both have the same sign in charge? Do I set up an hypothetical equation with reactants and products?

2. Using the following sequence of reactions, determine the order of oxidizing agents (strongest to weakest).

Q + U+ --> Q(+) + U  (1)
U + W+ --> U(+) + W  (2)
Q + W+ --> Q(+) + W  (3)

a. W+ > U+ > Q+
b. W > U > Q
c. Q > U > W
d. Q+ > U+ > W+

Is it W+ > U+ > Q+ ?
Here is my reasoning (without charges, which were looked at later):
(1) U = oxidizing agent  Q =reducing agent
(2) W is oxidizing agent U = reducing
(3) W = oxidizing Q=reducing

(Hopefully, I'm not confusing with W > U > Q!)

3. Ammonia reacts with hypobromite, OBr-, to form nitrogen gas and Br- anion. Find M of OBr- if 2.83 mL of solution reacts with 4.11 mg (.00411g) of NH3 (molar mass = 17.03). Balance equation by half reaction method in acid medium.

NH3 + OBr- --> Br- + N2

NH3 --> N2
OBr-  --> Br-

Now
2NH3 --> N2 + 6H+
2H+ + OBr- --> Br- + H2O

Then
2e- + 2H+ + OBr- --> Br- + H2O
2NH3 --> N2 + 6H+ + 6e-

So
3(2e- + 2H+ + OBr- --> Br- + H2O) = 6e- + 6H+ + 3OBr- -->3Br- + 3H2O
2NH3 --> N2 + 6H+ + 6e-

Finally,
3OBr- + 2NH3 --> N2 + 3Br- + 3H2O

M = mol OBr-/.00283 L OBr-

0.00411 g NH3 * (1 mol NH3 / 17.03 g) * (3 mol OBr- / 2 mol NH3) = 0.0003620 mol OBr-

so 0.0003620 mol OBr- / .00283 L OBr- = 0.1279 M??

Please reply. Thanks.




 

[Borek]

I don't understand what the problem is asking. Is it saying that these anions are combined together in a solution as in BrNO3? But is this not possible because both have the same sign in charge?

All it is saying is that both anions are present in the solution. Solution prepared using KBr and KNO₃ have both anions. K⁺ will be just a spectator.

[Borek]

OBr- = 0.1279 M??

Seems OK.

First, you enter substances and known mass of the NH₃ in the upper (input) part of the window:



Balancing and calculation of OBr^- mass is done automagically while-you-enter and displayed in the middle (balanced equation) and in the bottom (output pane). But it is still mass, not a cocentration - so you have to click on the small n=CV button to open concentration calculator and enter known volume:



0.1279 it is

[Sis290025]

Did I do #2 incorrectly?

Please reply. Thanks.

[Borek]

I am like a goldfish - I am dying after third wish. I have helped twice - you don't want me to die, don't you?