CHM 50 Class Activity – Chapter 3 – Part 2 – Molar mass and % Composition

Name/……………………

1.  What are the molar mass of the following compounds?

a. NaOH b. Cu(ClO4)2•6H2O

c. Mn2Se7 d. (NH4)2SO4

2.  Borax is the common name of sodium tetraborate, Na2B4O7. In 20.0 g of borax,
i. How many moles of sodium tetraborate are there?

ii. How many moles of boron are present?


iii. How many grams of boron are present?

3.  Complete the following table

Mass of compound / Molar mass of compound / # moles of compounds / Mol:mol ratio of 1st element to the formula unit / # mol of 1st element / # grams of 1st element
2.50g Ca3(PO3)2
15.3 g N2O5

4.  Calculate the mass percent of carbon, nitrogen and oxygen in acetamide, C2H5NO

5.  What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0% oxygen?

6.  If the molar mass of the compound in problem 5 is 110 grams/mole, what’s the molecular formula?

7.  What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0% oxygen?

8.  If the molar mass of the compound in problem 7 is 73.8 grams/mole, what’s the molecular formula?

9.  A hydrocarbon fuel is fully combusted with 18.214 g of oxygen to yield 23.118 g of carbon dioxide and 4.729 g of water. Find the empirical formula for the hydrocarbon.

10.  After combustion with excess oxygen, a 12.501 g of a petroleum compound produced 38.196 g of carbon dioxide and 18.752 of water. A previous analysis determined that the compound does not contain oxygen. Determine the empirical formula of the compound.

11.  Balance the following chemical reaction

a.  ____ MgF2 + ____ Li2CO3 à ____ MgCO3 + ____ LiF

b.  ____ P4 + ____ O2 à ____ P2O3

c.  ____ RbNO3 + ____ BeF2 à ____ Be(NO3)2 + ____ RbF

d.  ____ CF4 + ____ Br2 à ____ CBr4 + ____ F2

e.  ____ HCN + ____ CuSO4 à ____ H2SO4 + ____ Cu(CN)2

12.  In your own words, describe the chemical reactions below. Don’t forget to include all states of matters.

1.  CuSO4(aq) + NaBr(aq) à Na2SO4(aq) + CuBr2(s)

2.  2 Mg(s) + O2(g) à 2 MgO(s)

13.  Write the word equations below as chemical equations and balance:

1) Zinc and lead (II) nitrate react to form zinc nitrate and lead.

2) Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas.

7) Copper and sulfuric acid react to form copper (II) sulfate and water and sulfur dioxide.

8) Hydrogen gas and nitrogen monoxide react to form water and nitrogen gas.

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