Chemistry Chapter 2 & 3 test prep
1. Fill in the following table
Isotope name
atomic #
mass #
# of protons
# of neutrons
# of electrons
Potassium-37
Oxygen-17
uranium-235
uranium-238
boron-10
boron-11
2. The two naturally occurring isotopes of chlorine are 35Cl with a mass of 34.9689 amu and 37Cl with a
mass of 36.9659 amu. The atomic mass of elemental chlorine on earth is found to be 35.46 amu.
Calculate the percent abundance of each of the two chlorine isotopes.
3. Magnesium has three of it's own isotopes. 78.7% is Magnesium-24. 10.13% is Magnesium-25. 11.17% is
Magnesium-26. Calculate the relative atomic mass of Magnesium, to two decimal places.
4. How many H2O molecules are there in a snowflake weighing 1 mg?
5. Borax is the common name of sodium tetraborate, Na2B4O7. In 20.0 g of borax,
(a) how many moles of boron are present?
(b) how many grams of boron are present?
6. The plant photosynthetic pigment chlorophyll contains 2.68 percent magnesium by weight. How many
atoms of Mg will there be in 1.00 g of chlorophyll?
7. Calculate the grams present in:
1) 0.200 moles of H2S
2) 0.100 moles of KI
3) 1.500 moles of KClO
4) 0.750 moles of NaOH
5) 3.40 x 10¯5 moles of Na2CO3
8. Calculate the moles present in:
1) 2.00 grams of H2O
2) 75.57 grams of KBr
3) 100. grams of KClO4
4) 8.76 grams of NaOH
5) 0.750 grams of Na2CO3
9. You have 2.00 mol of H2 at STP. How many liters is this?
10. Calculate the volume occupied by 0.82g of SO2(g) at STP
11. What is the mass of 17.0L of methane (CH4 at STP)
12. Calculate the percent composition of carbon in each of the following:
1) CO2
2) C6H12O6
13. A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the
empirical formula of the compound?
14. NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O. Calculate the empirical formula of
NutraSweet and find the molecular formula. (The molar mass of NutraSweet is 294.30 g/mol)
15. Find the empirical formula for a compound which contains 32.8% chromium and 67.2% chlorine.
16. What is the empirical formula for a compound which contains 67.1% zinc and the rest is oxygen?
17. Barry Um has a sample of a compound which weighs 200 grams and contains only carbon, hydrogen,
oxygen and nitrogen. By analysis, he finds that it contains 97.56 grams of carbon, 4.878 g of hydrogen,
52.03 g of oxygen and 45.53 g of nitrogen. Find its empirical formula.
18. A compound with an empirical formula of C2OH4 and a molar mass of 88 grams per mole. What is the
molecular formula of this compound?
19. A 1.50 g sample of hydrocarbon undergoes complete combustion to produce 4.40 g of CO 2 and 2.70 g of
H2O. What is the empirical formula of this compound?
20. A 0.2500 g sample of a compound known to contain carbon, hydrogen and oxygen undergoes complete
combustion to produce 0.3664 g of CO2 and 0.1500 g of H2O. What is the empirical formula of this
compound?
21. Caffeine, a stimulant found in coffee, tea, and certain soft drinks, contains C, H, O, and N. Combustion of
1.000 mg of caffeine produces 1.813 mg CO2, 0.4639 mg H2O, and 0.2885 mg N2. Estimate the molar
mass of caffeine, which lies between 150 and 200 g/mol.
22. When 5.00 g of FeCl3 · xH2O are heated, 2.00 g of H2O are driven off. Find the chemical formula and the
name of the hydrate.
23. A student heated a sample of hydrated magnesium iodide (MgI2 ) in a crucible and recorded the data
shown in the table below. What was the complete formula of the compound before heating? What was
the name of the compound before heating? Show your work.
Mass of empty crucible 19.21 g
Mass of crucible + sample before heating 34.74 g
Mass of crucible + sample after heating 29.44 g