Chapter 10 Study Guide Answers

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1. Atomic masses are expressed on a scale based on the mass of what? Carbon-12
2. Name the unit used to express atomic masses of individual atoms. Grams or molar mass, gmm
3. Define formula mass.
Sum of the atomic masses of all atoms in a compound
4. What do we call the number of atoms of an element equal to the number of atoms in exactly 12.0 grams of carbon-12? Mole or Avogadro’s number
5. How many atoms are in a sample of an element whose mass is numerically equal to the atomic mass of that element? 6.02x1023
6. For what substance do we use formula units?
Ionic compound
7. At STP, equal volumes of different gases contain what?
Same number of particles = 1 mole
8. Identify the value for standard temperature. 25C
9. Identify the value for standard pressure. 1 atm
10. Identify the number used to express molar volume of a gas at STP. 22.4 L 11. What does the sum of the percentages in the percentage composition of a substance equal? 100% 12. Define empirical formula. Identify the empirical formula of a compound with molecular formula of C2Cl6 EF = smallest whole number ratio of the atoms in a compound CCl3

13. Define molecular formula. Identify the molecular formula of a compound with empirical formula of CH MF = formula that gives you the actual number of atoms in the compound Need more information

14. Calculate the masses of the following molecules
a. carbon tetrachloride (CCl4) 153.82 g/mol
b. sulfuric acid (H2SO4) 98.1 g/mol
c. phosphorus pentoxide (P2O5) 141.89 g/mol
15. A sample of ammonia (NH3) contains 7.22 moles of ammonia. How many molecules of ammonia are in the sample? 7.22 x 6.02x1023 = 4.35x 1024
16. Find the molar masses of the following substances:
a. sodium sulfate (Na2SO4) 142.04 g/mol
b. dinitrogen tetroxide (N2O4). 92.011 g/mol
17. Suppose that a pure copper coin has a mass of 3.22 g. How many moles of copper (Cu) are in the coin? 3.22 g /63.55 = 0.051 mol Cu...
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