A student combusted an amino acid to try and figure out what amino acid she had.

Question

A student combusted an amino acid to try and figure out what amino acid she had. She knew she had a sulfur containing amino acid and that there were 5 carbons, 11 hydrogens and 1 nitrogen. Hence for formula is C_5H_11NO_2S_x. Combustion of 22.85 mg sample of the amino acid produced 9.810 mg of sulfur dioxide and 3.371 mg of dinitrogen oxide. a. C_5H_11NO_2S_1 b. C_5H_11NO_2S_2 c. C_5H_11NO_2S_3 d. C_5H_11NO_2S_4 For questions 25 --- 30 consider a fixed number of moles of unknown gas at a constant 31 degree C. In order to double the pressure in the system the volume will have to a. Increase by a factor of 2 b. Increase by a factor of 1.414 c. Decrease by a factor of 2 d. Decreased by a factor of 1.414 The reason the pressure changes in the question above is because a. The gas particles begin to move more quickly. b. The average force of the collisions with the walls of the container changes c. The frequency of the collisions with the walls of the container changes d. Both the frequency and force of the collisions change If you allow the sample of unknown gas to expand to double its current volume, but the number of moles and temperature remain constant, the average velocity of the gas will: a. Increase b. Decrease c. Stay the same d. You need to know the pressure of the system to answer this question. If helium diffuses twice as fast as the unknown gas above, the identity of the unknown gas might be: a. Hydrogen (H2) b. Neon (Ne) c. Methane (CH4) d. Argon (Ar)

Explanation / Answer

25) PV = nRT
   since n is fixed and R ,T are constants
   P will be inversely proportional to V, hence V decreases by a factor of 2
   option c)

26) option d)

27) When you double the volume by keeping moles and temperature constant the pressure decreases
   and the average velocity should increase.
   Imagine if the velocity remains same volume won;t change
   option a)

28) mol wt of CH4 = 16 gm/mol ; He = 4 gm/mol
r1 / r2 = (M2 / M1)0.5 = (16/4)0.5 = 2
r1 = 2r2  
   Option c)

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