Reading Focus Questions

September 11

3.1

1.    What is the carbon-12 standard?  How are masses of atoms determined? (These two questions are related.)

2.    There is no such thing as a silver atom with an atomic mass of 107.9, and yet we use this number to determine the mass of 6.022 x 10²³ atoms of  silver.  Explain why this number gives accurate results.

3.2

3.    You should memorize Avogadro's number as 6.022 x 10²³ atoms of 'x' per one mole of 'x'.  This is the number of particles in one mole of a substance.  The numerical value of Avogadro's number is determined by counting the number of carbon atoms in exactly 12 grams of carbon.   So it must be true that 12 grams of carbon has 6.022 x 10²³ atoms.  How many grams does one carbon atom weigh?  Why do we not put this number on the periodic table?

3.3

4.    What is the definition of the terms molar mass, molecular weight,  and formula weight?

3.4

5.    What role do the subscripts of a chemical formula play when determining the molecular weight of a compound?

3.5

6.    When using percent composition of elements to determine the formula of a compound, the relative numbers of moles of each element are converted to their smallest whole number ratio.  Why is it necessary to do this?

7.    What is the empirical formula?  Is it the same thing as the molecular formula for covalent compounds?  Is it the same thing as the ionic formula for ionic compounds?