Question

1)

The average cup of coffee contains about 125 mg of caffeine, C₈H₁₀N₄O₂. Caffeine is also found in tea, colas, and headache remedies.

How many moles of caffeine molecules are present in 250 mg caffeine?
moles

2)

Alexander Fleming discovered penicillin, C₁₆H₁₈N₂O₄S, in 1928 at the University of London. He isolated the compounds from a mold which had contaminated some of his experiments. Since then penicillin has been used as a general antibiotic since it destroys bacterial cells without harming animal cells.

What is the molar mass of penicillin to two decimal places?
g/mol

3)

How many atoms of nitrogen are present in 25.0 g of NH₄NO₃?

atoms N

Answer 1

1)

Molar mass of C8H10N4O2 = 8*MM(C) + 10*MM(H) + 4*MM(N) + 2*MM(O)

= 8*12.01 + 10*1.008 + 4*14.01 + 2*16.0

= 194.2 g/mol

mass of C8H10N4O2 = 250 mg

= 0.25 g [using conversion 1 g = 1000 mg]

we have below equation to be used:

number of mol of C8H10N4O2,

n = mass of C8H10N4O2/molar mass of C8H10N4O2

=(0.25 g)/(194.2 g/mol)

= 1.29*10^-3 mol

Answer: 1.29*10^-3 mol

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