1. A pure salt was found to have the composition by mass: 19.1% sodium, 0.84% hy
ID: 828543 • Letter: 1
Question
1. A pure salt was found to have the composition by mass: 19.1% sodium, 0.84% hydrogen, 26.7% sulfur and 53.3% oxygen. Find the empirical formula of the salt.
a. Another experiment determined the formula weight of the salt above to be near 120g/mol. Determine the chemical formula of the salt.
2. The molecule capsaicin gives hot peppers their heat. The composition by mass: 70.78% carbon, 0.84% hydrogen, 4.59% nitrogen, and 15.72% oxygen. Find the empirical formula of capsaicin.
Thank you for your time, can you please explain to me how you get it?
Explanation / Answer
a. We know the atomic weights of sodium, Hydrogen, sulfur and oxygen to be 23, 1, 32 and 16 respectively.
relative weights:
Sodium = 19.1/23 = 0.83
Hydrogen = 0.84/1 = 0.84
Sulfur = 26.7/32 = 0.83
Oxygen = 53.5/16 = 3.34
Therefore, ratios Na:H:S:O = 0.83:0.84:0.84:3.34 => 1:1:1:4
Thus compound is NaHSO4
b. mol weight of NaHSO4 = 23+1+32+64= 120g
1 mole weighs 120gram same as what we got above.
Thus the formula is NaHSO4
2. C:H:N:O have the weights 12:1:14:16
relative weights:
C:70.78/12 = 5.9
H;8.4/1 = 8.4 (Corrected 0.84% to 8.4% as it doesnt total to 100% otherwise)
N:4.59/14 = 0.32
O: 15.72/16 = 0.98
C:H:N:O = 5.9:8.4:0.32:0.98
divide by 0.32
=18.4:26:1:3.0
rounding to nearest integers gives : 18:26:1:3
formula is C18H26NO3
b. mol weight = 18*12+26+14+48 = 304 gm
Correct molecular weight = 305gm
Difference = 305-304 = 1gm = 1 Hydrogen atom
Thus, we have missed 1 H atom in our formula. Therefore, correct formula is C18H27NO3
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