Percent composition of a compound

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   A lab analysis of 10 g of table sugar finds 4.21 g of carbon. What percent carbon is that, to 0.1%, Esme?

   42.1 %
2. 2.

   A lab analysis of 9 g of water finds 1.01 g of hydrogen. What percent hydrogen is that, to 0.1%, Jun?

   11.2 %
3. 3.

   A lab analysis of 12 g of table salt finds 4.72 g of sodium. What percent sodium is that, to 0.1%, Kira?

   39.3 %
4. 4.

   Bo says water is 66.7% hydrogen because 2 of its 3 atoms are hydrogen. Which reply fits, Luz?

   • Disagree: by mass, hydrogen is just 11.2%
   • Agree, for small samples of water
   • Agree: percent composition counts atoms, not their masses
5. 5.

   Zee says the element percents in a compound add to 100%. Which reply fits, Noah?

   • Agree: glucose's 40.0% + 6.7% + 53.3% = 100%
   • Disagree: they add to the molar mass, 180.18
   • Disagree: each element is 100% of itself, so they add to 300%
6. 6.

   Glucose has 6 C atoms at 12.01 g/mol in 180.18 g/mol. What percent of its mass is carbon, Pia?

   • 6.7%
   • 25.0%
   • 40.0%
7. 7.

   Glucose has 12 H atoms at 1.01 g/mol in 180.18 g/mol. What percent of its mass is hydrogen, Ren?

   • 6.7%
   • 50.0%
   • 0.6%
8. 8.

   Glucose has 6 O atoms at 16.00 g/mol in 180.18 g/mol. What percent of its mass is oxygen, Tala?

   • 25.0%
   • 53.3%
   • 8.9%
9. 9.

   Two labs test pure water from two cities. What percent hydrogen should both find, Zee?

   • 11.2%, since pure water is always H₂O
   • 66.7%, since 2 of 3 atoms are H
   • Different values, since each city's water is different
10. 10.

    A sample sold as pure salt tests at 45.0% sodium. What does that suggest, Ari?

    • It is pure salt, since salt's percent can vary
    • It is pure salt from a larger sample
    • It is not pure salt, which is 39.3% sodium