comp practice 2

Chemistry 2015-2016
Percent Composition Practice 2
Directions: The following questions are practical applications of percent composition. Round to two
decimal places and include proper units.
1. C8H10N4O2 is the chemical formula for a common substance found in coffee, tea, and most soda. What
do you think the substance is?
2. 96.08 g carbon, 10.08 g hydrogen, 56.04 g nitrogen and 32.00 g oxygen are the components of this
substance. What is the percent composition of each?
3. Ascorbic acid is commonly known as Vitamin C and has the formula C6H8O6. Calculate the percent
composition of each element in ascorbic acid.
4. A sample of sulfur mustard [(ClCH2CH2)2S] with a mass of 318.16 g has the following composition:
44.57 % Cl, 30.20 % C, 5.08 % H, and 20.16 % S. What is the mass of each element in the compound?
5. What is a more common name for sulfur mustard? Where have you heard of it? (Do a google search if
you don’t know!)
7. A pharmacist accidentally mixed two different capsules full of a white, powdery substance. Capsule A
had a total mass of 924.35 g. Capsule B had a total mass of 820.73 g. All she knows is that Drug X had a
higher percentage composition of carbon than Drug Y. The mass of carbon in Capsule A was 225.90. The
mass of carbon in Capsule B was 140.28. Which capsule contains Drug X?
8. A solution of salt and water is 33.0% salt by mass and has a density of 1.50 g/mL. What mass of the salt
in grams is in 5.00L of this solution?
6. A prominent issue for farmers recently has been the increase in the cost of fertilizers. The increase in
cost is a result of the increase in natural gas prices. The atmosphere is composed of 80% nitrogen.
Unfortunately for our wallets, it is not in a form plants can use. Small amounts of nitrogen are converted
to plant-available forms and sent to the earth in lightning strikes, with rainfall, by free-living blue-green
algae, and through bacteria in legumes' roots. However, of all these, only the legumes supply enough
plant-available nitrogen for high-yield agriculture. Here's where natural gas comes in. In 1910, scientists
discovered that they could combine natural gas and the atmosphere at very high temperature (about 900
ºF) and pressure (between 200 and 1,000 atmospheres) to create anhydrous ammonia gas. Therefore,
the more ammonia the fertilizer requires to make, the more expensive it is to produce.
Use the percent composition of nitrogen for each of the following fertilizers to determine which would be
more expensive to produce.
Ammonium Nitrate (NH4NO3)
Formula mass = 80.04 amu
Urea (CO(NH2)2)
Formula mass = 60.07 amu
9. Challenge: A solution of water and HCl contains 25% HCl by mass. The density of the solution is 1.05
g/mL. If you need 1.7g of HCl for a reaction, what volume of this solution will you use?
10. Challenge: A solution containing 42% NaOH by mass has a density of 1.30 g/mL. What mass, in
kilograms, of NaOH is in 6.00 L of this solution?