2007 ada free sample test chem section, need help. LETS GOOO

[yankeefan86]

Hey guys these questions are from the 2007 ADA free sample test. Im basically stumped on these three questions. They look like easy problems and maybe im a little exhausted but I need some help! So if someone could explain them to me, that would be awesome

41. A 49 gram sample of sulfuric acid, H2SO4 (98 G mol-1) contains
A) 1mol of S atoms
B) 16 grams of O
C) 2.0 grams of H
D) 2 moles of O atoms
E) 1mole of molecules

the answer is D.

43. A flask weighs 95g when empty. When filled with 200 ml of a certain liquid, the weight is 328g. What volume(in milliliters) would 1,000g of the liquid occupy?

A) 200/[ (1000)(328-95)]
B) [(200)(1000)]/(328-95)
C) (200)(1000)(328-95)
D) (328-95)/ [(200)(1000)]
E) [(200)(1000)]/328

the answer is B

51. During a titration it was determined that 30ml of a .100M Ce+4 solution was required to react completely with 20 ml of a .150 M Fe+2 solution. Which reaction occured?
A) Ce+4 + 3Fe+2 + H2O---->3Fe+3 + CeO- + 2H+
B) 2 Ce+4 + Fe+2 ------> Fe+4 + 2Ce+3
C) Ce+4 + Fe+2-------> Fe+3 + Ce+3
D) Ce+4 + 2Fe+2------> 2Fe+3 + Ce+2
E) Ce+4 + 2Fe+2 ------>2Fe+4 + Cs+2 + 2e-

The answer is C.

---

Members don't see this ad.

 

[bharat008]

Hey guys these questions are from the 2007 ADA free sample test. Im basically stumped on these three questions. They look like easy problems and maybe im a little exhausted but I need some help! So if someone could explain them to me, that would be awesome

41. A 49 gram sample of sulfuric acid, H2SO4 (98 G mol-1) contains
A) 1mol of S atoms
B) 16 grams of O
C) 2.0 grams of H
D) 2 moles of O atoms
E) 1mole of molecules

the answer is D.

43. A flask weighs 95g when empty. When filled with 200 ml of a certain liquid, the weight is 328g. What volume(in milliliters) would 1,000g of the liquid occupy?

A) 200/[ (1000)(328-95)]
B) [(200)(1000)]/(328-95)
C) (200)(1000)(328-95)
D) (328-95)/ [(200)(1000)]
E) [(200)(1000)]/328

the answer is B

51. During a titration it was determined that 30ml of a .100M Ce+4 solution was required to react completely with 20 ml of a .150 M Fe+2 solution. Which reaction occured?
A) Ce+4 + 3Fe+2 + H2O---->3Fe+3 + CeO- + 2H+
B) 2 Ce+4 + Fe+2 ------> Fe+4 + 2Ce+3
C) Ce+4 + Fe+2-------> Fe+3 + Ce+3
D) Ce+4 + 2Fe+2------> 2Fe+3 + Ce+2
E) Ce+4 + 2Fe+2 ------>2Fe+4 + Cs+2 + 2e-

The answer is C.

The first one should be "D".
(49g H2S04) (1mol H2SO4/98g H2SO4) (4mol O/1mol H2SO4) = 2mol O

Not sure about the second one..

Last one think of it in terms of which one will be able to lose an electron out of Ce+4 and Fe+2... Fe+2 is less positive so it will be able to lose more electron easily compared to Ce+4 (already lost so many electrons).. Therefore, Fe+2 would lose 1 more electron and become Fe+3 while the Ce+4 would gain that electron and become Ce+3..

Fe+2 is oxidized
Ce+4 is reduced

HOpe this helps..

 

[reely989]

For the second one, I would just step back a moment and analyze the information given and what they want. You can obviously figure out the weight of the compound by the difference of the weight of the flask with and without it. You also know the volume of the material is 200 mL. Now, it wants the volume of 1000g, so you need to find a way to eliminate grams and get your answer in volume. To do this, simply find mL/g, and multiply it by the desired amount of grams (in this case 1000). So, you end up with 200mL/(328-95g) x 1000g. It seems to me that they are testing your ability to work with unit conversions.

 

[Bis-GMA111]

for the second one, i set up a proportion...

200ml/(328-95)=X/1000g

solving for X gives us...

(328-95)X=200(1000)

X=200(1000)/(328-95) which is answer choice B.

hope this helps.

 

[bigndog525]

for number 43, how come we have to set it up like a proportion? I thought you use M1V1 = M2V2.... I saw a similar problem dealing with pressure and moles in kaplan and the answer key had it set up as a proportional.... can anyone explain how you know which one to use? Im so confused.... thanks.

 

[toothhornet88]

for number 43, how come we have to set it up like a proportion? I thought you use M1V1 = M2V2.... I saw a similar problem dealing with pressure and moles in kaplan and the answer key had it set up as a proportional.... can anyone explain how you know which one to use? Im so confused.... thanks.

for number 43, how come we have to set it up like a proportion? I thought you use M1V1 = M2V2.... I saw a similar problem dealing with pressure and moles in kaplan and the answer key had it set up as a proportional.... can anyone explain how you know which one to use? Im so confused.... thanks.

M1V1=M2V2 Is used with titrations of acids and bases. For example, 20 mL of 5M NaOh is titrated with 3M HCl. How much mL of HCl is needed to reach the equivalence point. So It's used when you have Molarity and Volume given for all but one variable.

For #43 you actually have to set it up as a ratio:
(Final Grams given)/(x volume needed) = (Grams in 200ml of volume)/(volume that is given)

hope it helps

 

[bigndog525]

M1V1=M2V2 Is used with titrations of acids and bases. For example, 20 mL of 5M NaOh is titrated with 3M HCl. How much mL of HCl is needed to reach the equivalence point. So It's used when you have Molarity and Volume given for all but one variable.

For #43 you actually have to set it up as a ratio:
(Final Grams given)/(x volume needed) = (Grams in 200ml of volume)/(volume that is given)

hope it helps

so basically if it doesn't confine with charles law, boyles law, avagadros law, gay-lussacs law, or a titration then set it up as a ratio?

ex. if it contains pressure, temp, M, L then do the non-ratio route?

 

[toothhornet88]

so basically if it doesn't confine with charles law, boyles law, avagadros law, gay-lussacs law, or a titration then set it up as a ratio?

ex. if it contains pressure, temp, M, L then do the non-ratio route?

I mean you have to look at what the problem is asking but with simple set ups like these Yes, if it doesn't deal with any laws but is just a simple conversion type where they don't give you any reagents then you use a ratio!