Lecture Problems
Jan 6, 2016
1. Silicon (Si) has three naturally occurring isotopes: 28Si, 29Si, and 30Si. Determine the number of
protons, neutrons, and electrons in each silicon isotope.
2. Silver has 46 known isotopes, but only two occur naturally, 107Ag and 109Ag. Given the following
data, calculate the atomic mass of Ag.
Isotope
Mass (amu)
Abundance (%)
107
Ag
106.90509
51.84
109
Ag
108.90476
48.16
3. Calculate the molecular mass of tetraphosphorus trisulfide
4. How many atoms are there in 5g of silver?
5. How many grams are there in 40 x 1015 atoms of gold?
6. What percent of each element is present in the fertilizer ammonium nitrate ?
7. What is the mass of nitrogen (grams) in 500 kilograms of ammonium nitrate?
8. Suppose you isolate an organic acid from clover leaves and know that it contains only the
elements C, H and O. Combustion of 0.513 g of the acid in pure oxygen produces 0.501g of CO2
gas and 0.103g of H2O. In a separate experiment the molecular mass of the acid was determined
to be 90.04 g/mol. Determine the empirical formula AND Molecular formula of the acid CxHyOz.
9. We react 280 grams of B2O3 with 100 grams of solid elemental Magnesium (Mg) to produce
magnesium oxide and elemental Boron (B)
Balanced reaction:
a. Calculate the theoretical yield for Boron and magnesium oxide.
b. The percentage yield of the reaction is 85%. Determine the actual yields of Boron and Magnesium
oxide.
c. Determine how much (in grams) of the excess reagent will be left over after the reaction is
complete.