General Chem please help!

[ATX04UT]

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Hey Guys--
Can ya'll help me on these few questions. It is from the ADA booklet. I totally suck in General Chemistry and I feel like a ****** because I don't understand some stuff. Only two more weeks! 😱

I figured these out using common sense but I wanted to know if there were specific formulas to figure these out incase they get complicated on the exam.

1. A flask weighs 95 g empty. When filled with 200mL of liquid, the weight is 328 g. What volume in mL would 1000g of the liquid occupy?

2. If one mole of N2 and 1 mole of H2 are mixed and allowed to react according to N2 + 3H2-----> 2NH3. What is the maximum number of moles of NH3 that could be produced?

3. During a titration it was determined that 30 mL of a 0.100 M Ce4+ solution was required to react completely with 20 mL of a 0.150 M Fe2+ solution. Which one of the reactions occurred?
A. Ce4+ +3Fe2+ + H2O --> 3Fe3+ + CeO- + 2H+
b. 2Ce4+ + Fe2+ --> Fe4+ + 2Ce3+
c. Ce4+ + fe2+ --> Fe3+ + Ce3+
d. Ce4+ + 2Fe2+ --> 2Fe3+ + Ce2+
e. ce4+ + 2Fe2+ --> 2Fe4+ + Cs2+ + 2e-

4. If a solution which is .5M in compound X decomposes for 5.0 minutes at an average rated of .04 M/min, what is the new concentration of X?

THANK YOU !!!!!!!!!!!!!!!! 😕

 

[toony]

let me give it a try..

1. you might wanna find the density of the liquid first. density = mass/volume. the weight of the liquid = 328g - 95g = 233g. thus the d = 233g/200ml = 1.165. so the unknown volume = 1000g / density = 858ml.

2. ratio N2: H2: NH3 = 1:3:2. H2 is the limiting reagent, which means it consumes all 1 mole.
1:3:2 = N2: (1 mole): NH3.

N2 = approx 0.11 mole
NH3 = approx 0.22 mole

3. the answer is c, b/c.. the statement hints at the fact that there're 3 moles of Ce4+ and 3 moles of Fe2+, which means they react w/ each other in 1:1 ratio. only the answer (c) shows such a relationship.

4. after 5 minutes the solution will be decayed by 0.2M (.04 times 5). so, the answer is 0.5M - 0.2M = 0.3M

Hope that helps!

 

[sailinx]

let me give it a try..


2. ratio N2: H2: NH3 = 1:3:2. H2 is the limiting reagent, which means it consumes all 1 mole.
1:3:2 = N2: (1 mole): NH3.

N2 = approx 0.11 mole
NH3 = approx 0.22 mole

I don't think this is the correct solution, as H2 is the limiting reagent, and from the equation,

N2 + 3H2-----> 2NH3

3moles of H2 are required to produce 2 moles of NH3, now if you have only 1 mole of H2, it will produce maximum of 2/3 moles of NH3 i.e. 0.667 moles of NH3 not 0.22 as suggested by your solution.

And also if some one ask how much N2 is consumed, it should be 1/3 i.e. 0.33 moles.

 

[toony]

oh yeah.. whoops, my bad. i was real tired last night..you're right! thax, sailinx-