3.1 Relative Atomic Mass and Relative Molecular Mass

Short Answer Questions

1. What is the standard used to determine relative atomic mass?
   Answer
   Carbon-12 isotope.
2. Is RAM an absolute or relative value?
   Answer
   Relative value.
3. What does RAM stand for?
   Answer
   Relative Atomic Mass.
4. Does RAM have units?
   Answer
   No, it is a ratio and has no units.
5. What is the RAM of carbon?
   Answer
   12.
6. What is the RAM of oxygen?
   Answer
   16.
7. What is the difference between relative atomic mass and relative molecular mass?
   Answer
   Relative atomic mass (RAM) refers to single atoms, while relative molecular mass (RMM) refers to molecules, calculated by summing the RAMs of all atoms in a molecule.
8. What does RMM stand for?
   Answer
   Relative Molecular Mass.
9. How is the relative molecular mass of a molecule calculated?
   Answer
   By adding the relative atomic masses of all atoms in the molecule.
10. What is the relative molecular mass of water (H₂O)?
    Answer
    18 (H: 1 × 2 + O: 16).
11. What is the relative formula mass of sodium chloride (NaCl)?
    Answer
    58.5 (Na: 23 + Cl: 35.5).
12. What is the relative formula mass?
    Answer
    The sum of the relative atomic masses of all atoms in a formula unit of an ionic compound.
13. What type of compounds use RFM?
    Answer
    Ionic compounds.
14. Is RFM an absolute or relative value?
    Answer
    Relative value.
15. What is the relationship between RFM and RMM in terms of calculation?
    Answer
    Both are calculated by summing the relative atomic masses of all atoms in a compound, but RMM is for molecules and RFM is for ionic compounds.
16. What is the relative atomic mass of hydrogen?
    Answer
    1.
17. If the RAM of nitrogen is 14, what is the RMM of nitrogen gas (N₂)?
    Answer
    28 (14 × 2).
18. Give an example of a molecule whose mass is determined by RMM.
    Answer
    Water (H₂O).
19. Give an example of a compound whose mass is determined by RFM.
    Answer
    Sodium chloride (NaCl).
20. What is the formula used to calculate the relative atomic mass?
    Answer
    **RAM = (Σ (isotope mass × % abundance)) / 100**

Explanation Questions

1. Explain why relative atomic mass is a more useful concept than absolute atomic mass.
   Answer
   Absolute atomic mass is too small to be practical, so RAM provides a convenient way to compare atoms on a scale based on carbon-12.
2. Explain how the existence of isotopes affects the calculation of relative atomic mass.
   Answer
   The RAM is a weighted average of all isotopes of an element, considering their relative abundances.
3. Why is carbon-12 used as the standard for relative atomic mass?
   Answer
   Carbon-12 is stable, abundant, and provides a consistent reference for comparing atomic masses.
4. Explain the difference between RMM and RFM.
   Answer
   RMM applies to molecular compounds, while RFM applies to ionic compounds, though both are calculated similarly.
5. Explain why the term “relative formula mass” is used instead of “relative molecular mass” for ionic compounds.
   Answer
   Ionic compounds do not exist as discrete molecules but as lattice structures, so “formula mass” is used instead of “molecular mass.”
6. Describe the steps to calculate the RMM of a given molecule.
   Answer
   Identify all elements, find their RAM values, multiply by the number of atoms, then sum the values.
7. Describe the steps to calculate the RFM of a given ionic compound.
   Answer
   Identify all elements, find their RAM values, multiply by the number of atoms, then sum the values for the formula unit.
8. Explain the relationship between RAM, RMM, and RFM.
   Answer
   RAM applies to single atoms, RMM to molecules, and RFM to ionic compounds, but all are based on relative atomic masses.
9. Explain why RAM, RMM, and RFM do not have units.
   Answer
   They are ratios relative to carbon-12, so they have no physical units.
10. How would you determine the RMM of a hydrate such as copper(II) sulfate pentahydrate, CuSO₄·5H₂O?
    Answer
    Add the RAMs of CuSO₄ and 5H₂O separately, then sum the values.