Some Basic Concepts Of Chemistry Question 143
Question: The empirical formula of a compound composed of 38.4% potassium, 36.3% oxygen, 23.7% carbon and 1.66% hydrogen is determined to be
Options:
A) $ ~KC _2H _5O _4 $
B) $ K _3C _6H _5O _7 $
C) $ K _2CHO _3 $
D) $ K _6C _4H _5O _7 $
Show Answer
Answer:
Correct Answer: B
Solution:
[b] Element %by mass Atomic mass Rel.no.of moles of element Simplest molar ratio K 38.4 39.10 $ \frac{38.4}{39.10}=0.982 $ $ \frac{0.982}{0.982}=1 $ O 36.3 16.00 $ \frac{36.3}{16.00}=2.27 $ $ \frac{2.27}{0.982}=2.3 $ C 23.7 12.01 $ \frac{23.7}{12.01}=1.97 $ $ \frac{1.97}{0.982}=2.00 $ H 1.66 1 1.01 $ \frac{1.66}{1.01}=1.64 $ $ \frac{1.64}{0.982}=1.67 $ In this case fractions are in thirds so a factor of 3 will change Simple molar ratio Fraction nearest decimal value Nearest factor Whole no. mole ratio 1.00 mol K 1 mol K $ \times 3 $ 3 mol K 2.31 mol O 2 1/3 mol O $ \times 3 $ 7 mol O 2.01 mol C 2 mol C $ \times 3 $ 6 mol C 1.67 mol 4 1 2/3 mol H $ \times 3 $ 5 mol H Hence empirical formula is $ K _3C _6H _5O _7 $ which is formula of potassium citrate.
