Worksheet 1: REPRESENTATIVE PARTICLES Directions: For each substance below, state the representative particle. If the RP is a molecule, state the number of atoms that make up the molecule. If the RP is a formula unit, state the number of ions that make up the formula unit. 1. NaCl 2. H 2 SO 4 3. K + 4. CaCl 2 5. S 6. S 6 7. NH 4 Br 8. Ca 3 (PO 4 ) 2 9. C 6 H 12 O 11 10. Mg(NO 3 ) 2 11. Cl 2 12. KMnO 3 13. H 2 O 2 14. H 3 PO 3 + 15. NH 4 16. Fe 2 O 3 17. NaC 2 H 3 O 2 3-18. PO 4 19. Hg 20. O 2-
Worksheet 2: THE MOLE AND AVOGADRO S NUMBER One mole of a substance contains Avogadro s Number (6.02 X 10 23 ) of molecules. How many molecules are in the quantities below? 1. 2.0 moles 2. 1.5 moles 3. 0.75 mole 4. 15 moles 5. 0.35 mole How many moles are in the number of molecules below? 1. 6.02 x 10 23 2. 1.204 x 10 24 3. 1.5 x 10 20 4. 3.4 x 10 26 5. 7.5 x 10 19
Worksheet 3: MOLAR MASS Determine the molar mass (the mass of one mole) of each compound below. Remember to include units (either amu or g/mol). Hint: for hydrated compounds such as CuSO 4 5H 2 O, add the molar mass of the salt (CuSO 4 ) to the mass of the number of water molecules indicated by the coefficient (5H 2 O = 5 water molecules). 1. KMnO 4 2. KCl 3. Na 2 SO 4 4. Ca(NO 3 ) 2 5. Al 2 (SO 4 ) 3 6. (NH 4 ) 3 PO 4 7. CuSO 4 5H 2 O 8. Mg 3 (PO 4 ) 2 9. Zn(C 2 H 3 O 2 ) 2 2H 2 O 10. Zn 3 (PO 4 ) 2 4H 2 O 11. H 2 CO 3 12. Hg 2 Cr 2 O 7 13. Ba(ClO 3 ) 2 14. Fe 2 (SO 3 ) 3 15. NH 4 C 2 H 3 O 2
Worksheet 4: PERCENTAGE COMPOSITION Determine the percentage composition of each of the compounds below. Answers: Work: 1. KMnO 4 K = Mn = O = 2. HCl H = Cl = 3. Mg(NO 3 ) 2 Mg = N = O = 4. (NH 4 ) 3 PO 4 N = H = P = O = 5. Al 2 (SO 4 ) 3 Al = S = O = Solve the following problems. 6. How many grams of oxygen can be produced from the decomposition of 100 g of KClO 3? 7. How much iron can be recovered from 25.0 g Fe 2 O 3? 8. How much silver can be recovered from 125 g of Ag 2 S?
Worksheet 5: Determining Empirical Formulas What is the empirical formula (lowest whole number ratio) of the compounds below? 1. 75% carbon, 25% hydrogen 2. 52.5% potassium, 47.3% chlorine 3. 22.1% aluminum, 25.4% phosphorus, 52.5% oxygen 4. 13% magnesium, 87% bromine 5. 32.4% sodium, 22.5% sulfur, 45.1% oxygen 6. 25.3% copper, 12.9% sulfur, 25.7% oxygen, 36.1% water Worksheet 5 continues onto the next page
Worksheet 5 Continued: Determining Molecular Formulas (True Formulas) 1. The empirical formula of a compound is NO2. Its molecular mass is 92.0 g/mol. What is its molecular formula? 2. The empirical formula of a compound is CH2. Its molecular mass is 70 g/mol. What is its molecular formula? 3. A compound is found to be 40.0% carbon, 6.7% hydrogen and 53.5% oxygen. Its molecular mass is 60. g/mol. What is its molecular formula? 4. A compound is 64.9% carbon, 13.5% hydrogen and 21.6% oxygen. Its molecular mass is 74 g/mol. What is its molecular formula? 5. A compound is 54.5% carbon, 9.1% hydrogen and 36.4% oxygen. Its molecular mass is 88 g/mol. What is its molecular formula?
Worksheet 6: COMPOSITION OF HYDRATES A hydrate is an ionic compound with water molecules loosely bonded to its crystal structure. The water is in a specific ratio to each formula unit of the salt. For example, the formula Na 2 S 9H 2 O indicates that there are nine water molecules for every one formula unit of Na 2 S. Answer the questions below. 1. What percentage of water found in Na 2 S 9H 2 O? 2. A 5.0 g sample of a hydrate of BaCl 2 was heated, and only 4.3 g of the anhydrous salt remained. What percentage of water was in the hydrate? 3. A 2.5 g sample of a hydrate of Ca(NO 3 ) 2 was heated, and only 1.7 g of the anhydrous salt remained. What percentage of water was in the hydrate? 4. A 3.0 g sample of Na 2 CO 3 H 2 O is heated to constant mass. How much anhydrous salt remains? 5. A 5.0 g sample of Cu(NO 3 ) 2 nh 2 O is heated, and 3.9 g of the anhydrous salt remains. What is the value of n?
Worksheet 7: Chemical Quantities Review (CP) 1. Name the representative particle for the following substances: N N + N 2 CO 2 C 6 H 6 Na 2 SO 4 NaHCO 3 NaOH 2. Calculate the molar mass of each the following substances: C 6 H 6 Ca(NO 3 ) 2 MgSO 4 7H 2 O 3. How many moles are in 20.1 g of HC 2 H 3 O 2? 4. Calculate the mass of 15.6 moles of CuSO 4 5H 2 O. 5. How many molecules are in 100.5 g N 2 O? 6. Calculate the volume of 67.8 g of Cl 2 gas at STP. 7. How many oxygen atoms are in 6.50 molecules of HC 7 H 5 O 2? 8. Calculate the mass of 2.35 x 10 15 molecules of CH 4. 9. Calculate the percentage composition of Ca(OH) 2. 10. How many grams of zinc could be extracted from 1.00 kg (1000 g) of ZnCl 2?
HELPFUL TIPS FOR THE UPCOMING TEST! Know the four representative particles and be able to determine what the R.P. is for a given substance.! Know how to find the molar mass / molecular weight (MW) of a given substance.! Know how to determine the number of atoms / ions present in one molecule or formula unit of a given substance.! Know how to convert between units of mass, moles, volume, representative particles, and atoms or ions when appropriate.! Know the values of standard temperature and pressure.! Know how to calculate percent composition.! Know how to calculate the mass of some part of a compound that could be recovered. o For example, a typical bottle of fingernail polish contains 215.25 mg of tin (IV) oxide. What mass of tin is present in this amount?! Begin calculations with the given value.! PAY ATTENTION TO UNITS! Convert to the mole before converting to any other unit.! Round to the tenth s place when calculating molar mass.! Attach the appropriate units to all values.! Give your answer with the same number of significant digits as the given value when converting between units.! PAY ATTENTION TO UNITS! Use Avogadro s number (6.02 x 10 23 representative particles / mole) to convert to and from representative particles.! Use molar mass to convert to and from mass.! Use molar volume (22.4 L / mole) to convert to and from volume of a gas at STP.! PAY ATTENTION TO UNITS! Remember that density = mass (g) / volume (L) Remember: 1 mole = 6.02 x 10 23 R.P. s 1 mole = molar mass in grams 1 mole = 22.4 L of gas @STP