Apply Your Percentage Skills!
Complete all problems showing your work. Remember to:
Problem 1
A quarter from 1964 is made of 90% silver and has a mass of 5.670 g. What is the mass of silver in the quarter?
Problem 2
A sample of brass contains 65% copper. If the brass sample has a mass of 250.0 g, how many grams of copper does it contain?
Problem 3
Pure gold is 24 karat. If you have an 18-karat gold ring (75% gold) with a mass of 8.50 g, what is the mass of pure gold in the ring?
Problem 4
A 500.0 mL sample of seawater contains 3.5% dissolved salts by mass. If the density of seawater is 1.025 g/mL, what mass of salt is present?
Problem 5
The atmosphere is 20.95% oxygen. If you breathe in 0.5 L of air, what volume of oxygen did you breathe?
Problem 6
Earth's atmosphere is 78.08% nitrogen by volume. A room contains 450 m³ of air. What volume of nitrogen is in the room?
Problem 7
Carbon dioxide makes up 0.04% of the atmosphere. If you breathe 12 L of air, how many liters of CO₂ did you inhale?
Problem 8
A helium-oxygen mixture used in deep-sea diving contains 96% helium and 4% oxygen. If a diver's tank holds 3.5 L of this mixture, how many liters of oxygen are in the tank?
Problem 9
Your body contains about 16 kg of carbon, and 18% of that carbon is carbon-12. If you have \(3.0 \times 10^{27}\) carbon atoms total, how many are carbon-12?
Problem 10
A sample of chlorine gas contains 75.78% Cl-35 and 24.22% Cl-37. If the sample contains \(1.5 \times 10^{24}\) total chlorine atoms, how many Cl-35 atoms are present?
Problem 11
A bronze statue is made of 88% copper and 12% tin. If the statue contains \(2.5 \times 10^{26}\) total metal atoms, how many are copper atoms?
Problem 12
Natural boron consists of 19.9% B-10 and 80.1% B-11. A sample contains \(6.02 \times 10^{23}\) boron atoms (1 mole). How many B-11 atoms are in the sample?
Problem 13
If silver is worth $31.02 per troy ounce, and there are 31.1 g in 1 troy ounce, what is the value of silver in all 1964 quarters ever minted (1,950,000,000 quarters)?
Hint: Each quarter has a mass of 5.670 g and is 90% silver.
Problem 14
A copper mine produces ore that is 0.75% copper by mass. If copper sells for $4.50 per pound and there are 453.6 g in 1 pound, what is the value of copper in 1000 kg of ore?
Problem 15
A sterling silver necklace is 92.5% silver and has a mass of 45.0 g. If silver is worth $0.85 per gram, what is the silver value of the necklace?
Problem 16
A compound is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. If you have 250.0 g of the compound, how many grams of each element are present?
Problem 17
Ammonia (NH₃) is 82.35% nitrogen by mass. How many grams of nitrogen are in 150.0 g of ammonia?
Problem 18
A fertilizer contains 15% nitrogen, 30% phosphorus, and 15% potassium (15-30-15 fertilizer). A bag contains 25.0 kg of fertilizer.
Problem 19
A sample of air in Los Angeles contains 0.15% carbon monoxide by volume (a dangerously high level!). If you breathe 8.5 L of this air, what volume of toxic CO did you inhale?
Problem 20
The human body is approximately 65% oxygen by mass. If a person weighs 70.0 kg, what mass of oxygen is in their body? How does this compare to the 16 kg of carbon in a typical human body?