10.1. The Mole Concept http://www.ck12.org
12.01 g/mol + 2(16.00 g/mol) = 44.01 g/molOne mole of carbon dioxide molecules would have a mass of 44.01 grams. What about for an ionic compound? The
molar mass of sodium sulfide (Na 2 S) can be calculated as follows:
2(22.99 g/mol) + 32.06 g/mol = 78.04 g/molBecause Na 2 S is the empirical formula for this substance, the representative particle consists of two sodium atoms
and one sulfur atom.
Example 10.4
What is the molar mass of hydrogen peroxide (H 2 O 2 ).
Answer:
H - 2×1.0 g/mol = 2.0 g/mol
O - 2×16.0 g/mol = 32.0 g/mol
H 2 O 2 = 34.0 g/mol
Example 10.5
How many moles of carbon are present in a 10.00 gram sample?
Answer:
10 .00 g C×(^6.^022 ×^10
(^23) atoms C
1 mol C ) =^6.^022 ×^10
(^24) atoms C
Lesson Summary
- One mole of any chemical substance contains 6.022 x 10^23 representative particles.
- The masses on the periodic table can be read as average atomic masses or as molar masses.
- Molar mass is the mass of one mole of any given substance.
Lesson Review Questions
- Imagine that you have 1 mole of coins, each of which is 1.5 mm thick. If they were placed in a single stack,
how tall would the stack be (in km)? If the closest distance between the earth and the moon is 356,400 km,
would the coins reach the moon? (Hint: Use the technique of dimensional analysis.) - Calculate the number of moles of N that must be present in 3 moles of NH 3.
- Calculate the number of moles of oxygen that must be present in 2 moles of C 6 H 12 O 6.
- How many moles of gold are present in a sample containing 1.81 x 10^24 gold atoms?
- How many atoms are in 0.065 moles of Hg?
- Calculate the number of Br−ions in 0.0038 moles of CaBr 2.
- Calculate the molar mass of K 2 Cr 2 O 7.
- Calculate the molar mass of dinitrogen tetroxide (N 2 O 4 ).
Further Reading / Supplemental Links
- Avogadro biography: http://www.bulldog.u-net.com/avogadro/avoga.html