ADA sample chem questions

[livehard]

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Hi,
I find their chem questions are pretty okay but don't know why I got these questions wrong! If anyone can explain to me, it would be much appreciated!

41. A 49-gram sample of sulfuric acid, H2SO4 (98g/mol) contains
A. 1 mol of S atoms
B. 16.0 grams of O
C. 2.0 grams of H
D. 2 moles of O atoms
E. 1 mole of molecules

The answer is D, but I don't know why I chose C?! 😕

51. During a titration it was determined that 30.00 mL of a 0.100 M Ce4+ solution was required to react completely with 20.00 mL of a 0.150 M Fe2+ solution. Which one of the following reactions occured?

Answer C. Ce4+ + Fe2+ ---> Fe 3+ + Ce3+
(I'm not sure how to approach this question at all )

My cDAT is in 2 days! so help me out guys 😀
Thanks

 

[UCB05]

Hi,
I find their chem questions are pretty okay but don't know why I got these questions wrong! If anyone can explain to me, it would be much appreciated!

41. A 49-gram sample of sulfuric acid, H2SO4 (98g/mol) contains
A. 1 mol of S atoms
B. 16.0 grams of O
C. 2.0 grams of H
D. 2 moles of O atoms
E. 1 mole of molecules

The answer is D, but I don't know why I chose C?! 😕

51. During a titration it was determined that 30.00 mL of a 0.100 M Ce4+ solution was required to react completely with 20.00 mL of a 0.150 M Fe2+ solution. Which one of the following reactions occured?

Answer C. Ce4+ + Fe2+ ---> Fe 3+ + Ce3+
(I'm not sure how to approach this question at all )

My cDAT is in 2 days! so help me out guys 😀
Thanks

49g of sulfuric acid is half a mol (49/98). Therefore half a mol of H2SO4 will contain:
0.5 mol of molecules
(0.5)(2) = 1 mol H = 1g H
(0.5)(1) = 0.5 mol S = 16g S
(0.5)(4) = 2 mol O = 32g O

D is the only answer that matches any of these properties.


51. You are given that 30.00 mL of a 0.100 M Ce4+ solution reacts with 20.00 mL of a 0.150 M Fe2+ solution. convert that into mols:
(0.1M)(.03) = .003 mol Ce4+
(0.15M)(.02) = .003 mol Fe2+

The correct answer will be the one that represents the Fe+2 and Ce4+ in a 1:1 reaction ratio. I don't know what your other answer choices were, but C seems like a logical choice in which the redox reaction involves equivalent transfer of 1 electron. An incorrect example might have been:
Ce4+ + 2 Fe2+ ---> Fe 3+ + Ce2+
where the reactants won't be titrated in a 1:1 ratio