1. What do you notice about these formulae? C 2 H 4 C 3 H 6 C 4 H 8

2. 1.23 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation 1.24 calculate empirical and molecular formulae from experimental data

3. The molecular formula of a compound indicates how many moles of each element are in 1 mole of the compound. For example: Glucose is C 6 H 12 O 6. How many moles of carbon are in 1 mole of glucose?

4. There are 6 moles of carbon in 1 mole of glucose because of the subscript 6 after the C in the formula. Now look at the ratio of the atoms in glucose. Glucose is C 6 H 12 O 6. The ratio of atom is C 1 H 2 O 1. Therefore the empirical formula is CH 2 O.

5. What is the empirical formula of C 6 H 12 ? What is the empirical formula of C 6 H 6 ? Answers 1 - CH 2 2 - CH

6. Step 1: Write down the symbols for the elements in the compound Step 2: Underneath each element, write down the masses/percentages in the question Step 3: Divide each mass by the relative formula mass of the element Step 4: Divide all the answers by the smallest answer to give the ratio… C O 27.3 72.7 12 = 2.3 16 =4.5 2.3 = 1 4.5= 2 2.3

7. Compound X had the following percentage composition by mass: 10.8% magnesium, 31.8% chlorine and 57.4% oxygen. Relative atomic masses: Mg = 24; Cl = 35.5; O = 16 Calculate the empirical formula of compound X. Answer: MgCl 2 O 8 ! (Put the elements in the order given in the question) Hints: 1.Write the elements! 2. Write the masses/percentages under each element 3. Divide the number’s by the atomic masses of those elements 4.Divide by the smaller of the two numbers Write the formula!

8. A compound is called phosgenite. Analysis of this compound shows that it contains: 76.0% lead (Pb) 13.0% chlorine (Cl) 2.2% carbon (C) 8.8% oxygen (O) Calculate the empirical formula of this compound. Relative atomic masses: Pb = 207; Cl = 35.5; C = 12 ; O = 16 Answer: Pb 2 Cl 2 CO Hints: 1.Write the elements! 2. Write the masses/percentages under each element 3. Divide the number’s by the atomic masses of those elements 4.Divide by the smaller of the two numbers Write the formula!

9. A sample of the solvent used in one perfume contained 0.60 g of carbon, 0.15 g of hydrogen and 0.40 g of oxygen. Relative atomic masses: H = l; C = 12; O = 16. Calculate the empirical (simplest) formula of the solvent. Answer: C 2 H 6 O! Hints: 1.Write the elements! 2. Write the masses/percentages under each element 3. Divide the number’s by the atomic masses of those elements 4.Divide by the smaller of the two numbers Write the formula!

10. Calculate the simplest (empirical) formula of this substance: 70 % of iron (Fe) and 30 % of oxygen (O) Relative atomic masses: O = 16; Fe = 56. Hint: If the ratio is.5 (eg 2.5), don’t round up! Double both numbers Eg 2.5: 3 becomes 5: 6 Answer: Fe 2 O 3 !

11. Calculate the simplest (empirical) formula of this substance: 70 % of iron (Fe) and 30 % of oxygen (O) Relative atomic masses: O = 16; Fe = 56. Answer: Fe 2 O 3 !

12. Given a compound with an empirical formula of CH 2 and a molecular mass of 42, what is the Molecular Formula? C3H6C3H6

13. 1. Clean a 10–20 cm length of magnesium ribbon with emery cloth to remove the oxide layer. Loosely coil it. 2. Weigh a clean crucible and lid. Place the magnesium inside and reweigh. 3. Heat the crucible for 5–10 minutes, lifting the lid a little from time to time with tongs. Ensure that as little product as possible escapes. 4. Continue heating until glowing ceases. 5. Cool the crucible and reweigh. 6. Repeat steps 4 and 5 until there is no change in mass

14. 1.Whilst one person sets up the apparatus, the other should 2.Weigh an empty crucible, lid on, and record the mass. 3.Put 2 spatula-fulls of CuSO 4 ·xH 2 O into the crucible, put the lid back on and find and record the mass. 4.Place crucible on the pipe clay triangle and heat on blue flame for 5 mins. 5.Meanwhile calculate the mass of CuSO 4 ·xH 2 O which you started with. 6.Carefully remove the lid and check that the contents are no longer blue, indicating that the reaction has finished. They should be white, but may be a little brown. If this is not the case, heat for 2 mins more, then check again. 7.When the reaction has finished turn off the Bunsen and allow the apparatus to cool for 5 mins. 8.Once the crucible is cool weigh it (including lid) and record the mass. 9.Calculate the mass of CuSO 4 you were left with at the end. 10.Calculate x.