The document discusses chemical formulae including molecular, empirical and structural formulae. It provides examples of formulae for different types of compounds such as ionic compounds, molecular compounds and covalent compounds. It also gives examples of how to calculate empirical formulae from experimental data including mass of elements and relative atomic masses.

1. Chemical Formulae

2. CHEMICAL FORMULAE The chemical formula of an element shows the symbol representing that element and the number of atoms making up that element. H 2 O 2 N 2 CH 4 CH 3 CH 2 OH CuCO 3 CuSO 4 .5H 2 O

3. 1. Moleculer formula 2. Empirical formula 3. Structural formula Chemical formulae for molecular elements and molecular/covalent compounds Chemical formulae for covalent and ionic componds Chemical formulae for molecular elements and covalent compounds that show the relative arrangement of atoms in a molecule. The chemical formula of a chemical compound shows the symbols of all elements and the number of atoms of each element in one molecule of the compound.

4. The molecular formula of a compound is the chemical formula which shows the actual number of atoms of each combining element in one molecule of a compound 1. Molecular formula Oxygen Gas O 2 One molecule of oxygen contains two oxygen atoms that combined together Ammonia NH 3 In one molecule of ammonia three hydrogen atoms combined with one nitrogen atom Trichloromethane CHCl 3 One molecule of trichloromethane contains one carbon atom, one hydrogen atom and three chlorine atoms

5. 2. EMPIRICAL FORMULA Ethane C 2 H 6 CH 3 Glucose C 6 H 12 O 6 CH 2 O Water H 2 O H 2 O Oxalic Acid H 2 C 2 O 4 HCO 2 The empirical formula of a compound is the chemical formula which shows the smallest ratio of atom of each element that made up a compound. Molecular formula Molecular formula Emphirical formula Molecular formula Emphirical formula Emphirical formula Molecular formula Emphirical formula

6. Chemical formula for an ionic compound is stated in term of its empirical formula. Ionic compounds do not exist in the form of simple molecules. At room conditions all ionic compounds are crystalline solid that consists of positively and negatively charged ions that are held together by a network of electrostatic attractive forces of attraction (ionic bond). “The whole crystalline solid is a molecule” Na + ions Cl - ions Sodium chloride

7. (NH 4 ) 2 SO 4 Ammonium sulphate ZnSO 4 Zinc sulphate Li 2 CO 3 Lithium carbonate Al 2( SO 4 ) 3 Aluminium sulphate Ca(OH) 2 Calcium hydroxide Empirical formula Compound

8. 3. Structural formula Ethanol C 2 H 6 O The chemical formulae for molecular elements and covalent compounds that show the relative arrangement of atoms in a molecule. The formula also shows the actual number of atoms of each element present in one molecule. Molecular formula Structural formula

9. Cyclohexane C 6 H 12 3-methyl-2-pentane C 6 H 12 Structural formula Molecular formula Structural formula Molecular formula

10. Calculating the Empirical Formula In general, the empirical formula of a compound can be determine from the masses of the elements that combine together. Determination of the empirical formula of magnesium oxide: Mass of the crucible + the lid = 21.02 g Mass of the crucible + the lid + Mg ribbon = 21.50 g Mass of the crucible + the lid + magnesium oxide = 21.82 g

11. Mass of the crucible + the lid = 21.02 g Mass of the crucible + the lid + Mg ribbon = 21.50 g Mass of the crucible + the lid + magnesium oxide = 21.82 g Mass of magnesium burnt = (21.50 – 21.02)g = 0.48 g Mass of oxygen used = ( 21.82 – 21.50) = 0.32 g The empirical formula = MgO 0.02/0.02 = 1 0.02/0.02 = 1 The simplest ratio 0.32/16 = 0.02 0.48/24 = 0.02 mol Number of moles of atom 0.32 g 0.48 g Mass O Mg elements

12. Example 1 : 3.12 g metal X reacts with oxygen to form 4.56 g X oxide. Determine the empirical formula of X oxide.(Relatif atomic mass: O = 16, X = 52) Empirical formula = X 2 O 3 3 2 0.09/0.06 = 1.5 0.06/0.06 = 1 Simplest ratio of the number of moles 1.44/16 = 0.09 mol 3.12/52 = 0.06 mol Number of moles of atom (4.56-3.12) = 1.44 g 3.12 Mass (g) O X Element

13. Empirical Formula : Fe 2 O 3 A sample of ferum oxide consists of 1.12 g ferum and 0.48g oxygen.Find the empirical formula of this compound. [Relative atomic mass : Fe, 56 ; O,16 ] 3 2 Ratio of atom 0.03 = 1.5 0.02 0.02 = 1 0.02 Divide by the smallest number 0.48 = 0.03 16 1.12 = 0.02 56 Number of moles 0.48 1.12 Mass, g O Fe Elements

14. Example 2: A compound of zinc bromide contains 28.89% zinc. What is the empirical formula of the compound? (R.A.M : Zn, 65 ; Br,80 )

15. Empirical formula : ZnBr 2 2 1 Ratio of atom 0.89 = 2 0.44 0.44 = 1 0.44 Divide by the smallest number 71.11 = 0.89 80 28.89 = 0.44 65 Number of moles of atoms 100 – 28.89 = 71.11 28.89 Mass per 100g compound Br Zn Elements

16. Example 3 The empirical formula of a compound is given as CH 2 . If the RMM of the compound is 56, what is the molecular formula? [ RAM C,12 ; H , 1 ]. ( Empirical formula ) n = RMM ( CH 2 ) n = 56 ( 1x 12 + 2 x 1 ) n = 56 14 n = 56 n = 4 Molecular formula (CH 2 ) 4 = C 4 H 8

17. Example 2 A compound CxHyOz contains 40% carbon and 53.3% oxygen. If the relative molecular mass of the compound is 180, finds it molecular formula [ RAM : H , 1 : C , 12 ; O , 16 ] Empirical Formula : CH 2 O 3.33 = 1 3.33 6.7 = 2 3.33 3.33 = 1 3.33 Simplest ratio 53.3 = 3.33 16 6.7 = 6.7 1 40 =3.33 12 Number of moles 53.3 40-53.3 = 6.7 40 Mass in 100g O H C Element

18. (Empirical formula ) n = RMM (CH 2 O)n = 180 (12 + 2 + 16 ) n = 180 30n = 180 n = 180/30 = 6 Molecular formula = (CH 2 O) 6 = C 6 H 12 O 6

19. Nama dan formula beberapa anion(ion -ve) dan kation(ion +ve) C 2 O 4 2- Oksalat Ti 4+ Titanium(IV) S 2 O 3 2- Tiosulfat Na + Natrium SCN - Tiosianat Zn 2+ Zink S 2- Sulfida V 5+ Vanadium(V) SO 3 2- Sulfit Pb 2+ Plumbum(IV) SO 4 2- Sulfat Pb 2+ Plumbum(II) PO 4­­ 3- Fosfat Sn 4+ Stanum(IV) O 2 2- Peroksida Sn 2+ Tin(II) MnO 4 - Manganate(VII) K + Pottasium O 2- Oxide Mg 2+ Magnesium N 3- Nitride Mn 2+ Manganate (II) NO 2 - Nitrite Mn 4+ Manganate(IV) NO 3 - Nitrate Li + Lihtium I - Iodide Fe 3+ Iron(III) OH - Hidroxide Fe 2+ Iron(II) HSO 4 - Hidrogen sulphate Cu + Copper(I) HCO 3 - Hidrogen carbonate Cu 2+ Copper(II) H - Hidride Co 2+ Cobalt(II) F - Fluoride Cr 3+ Cromium(III) Cr 2 O 7 2- Dichromate(VI) Ca 2+ Calsium CrO 4 2- Chromate(VI) Ba 2+ Barium Cl - Chloride Ag + Silver CO 3 2- Carbonate NH 4 + Ammonium Br - Bromide Al 3+ Aluminium FORMULA NAME FORMULA NAME ANION CATION