2. Would a dozen of each weigh the same amount? Give a reason for your answer.

5. Formulae

13. 1.How many moles are in 15 grams of lithium? 2. How many grams are in 2.4 moles of sulphur? 3. How many grams are in 4.5 moles of sodium fluoride, NaF? 4. How many moles are in 98.3 grams of aluminum hydroxide, Al(OH) 3 ?

20. Worksheet 1.How many moles are present in 2.45 x 10 23 molecules of CH 4 ? 2. How many grams are there in 7.4 x 10 23 molecules of AgNO 3 ? 3. Calculate the number of moles in 42.15g of magnesium carbonate. 4. Calculate the number of atoms in 1.5 mol HCl. 5. Calculate the mass of 1.5 x 10 23 formula units of MgSO 4.

26. Worksheet 1 Worksheet 2

30. Empirical Formula Molecular Formula Name CH 2 C2H4C2H4 ethene CH 2 OC 6 H 12 O 6 glucose NO 2 N2O4N2O4 dinitrogen tetroxide

32. KCrO mass (in grams) 6.524.345.34 molar mass (in gmol -1 ) 395216 number of moles 6.52 = 0.167 39 4.34 = 0.083 52 5.34 = 0.333 16 ÷ by smallest number to get whole number ratio, i.e. ÷ 0.083 214 The empirical formula is K 2 CrO 4

34. Answer CHO mass (in grams)406.753.3 molar mass (in gmol -1 ) 12116 number of moles 40 = 3.3 12 6.7 = 6.7 1 53.3 = 3.3 16 ÷ by smallest number to get whole number ratio, i.e. ÷ 0.083 121 The empirical formula is CH 2 O M(CH 2 O) = 12 + (2x1) + 16 = 30gmol -1 M(Glucose) = 180gmol -1 Ratio between glucose and CH 2 O = 180 = 6 30 So, molecular formula is C 6 H 12 O 6

35. Empirical & Molecular Formula Worksheet

36. Percentage purity of a substance can be calculated by dividing the mass of the pure chemical by the total mass of the sample, and then multiplying this number by 100.

37. A 12.00g sample of a crystallised pharmaceutical product was found to contain 11.57g of the active drug. Calculate the % purity of the sample of the drug. % purity = actual amount of desired material x 100 total amount of material % purity = 11.57 x 100 = 96.4% (to 1dp) 12