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# Nota kimia t5 no pengoksidaan

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NOTA KIMIA SPM

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### Nota kimia t5 no pengoksidaan

1. 1. Azlee Chemistry 2009 Oxidation number (NOMBOR PENGOKSIDAAN) Definition: The oxidation number of an element is the charge that the atom of the element would have if complete transfer of electron occurs Nombor pengoksidaan unsur adalah cas atom unsur itu sendiri jika pemindahan elektron berlaku dengan lengkap Tips from the rules:  the oxidation number for atom and molecule is zero =0 Atom or molecule Zn C Mg Ag H2 O2 Cl2 Oxidation number 0 0 0 0 0 0 0  the oxidation number for monoatomic ion is equal to its charge Monoatomic ion H+ Fe2+ Mn2+ Fe3+ Cr3- O2- N3- Oxidation number +1 +2 +2 +3 -1 -2 -3
2. 2. Azlee Chemistry 2009  the sum of oxidation numbers of all elements in the compound is zero Compound H2SO4 KMnO4 SO2 Na2SO4 K2Cr2O7 Oxidation number 0 0 0 0 0  the sum of oxidation number of all elements in polyatomic ions is equal to the charge of the ions Polyatomic ion NH4 + SO4 2- MnO4 - Cr2O7 2- S2O3 2- Fe(CN)6 3- Oxidation number +1 -2 -1 -2 -2 -3
3. 3. Azlee Chemistry 2009 Calculate the oxidation numbers for the underlined elements. (i) SO2 [compound] [refer to rules above] Element S O Sum of oxidation numbers Number of element 1 2 0 Oxidation number x -2 [let the unknown oxidation number is equal to x] 1(x) + 2(-2) = 0 x - 4 = 0 x = +4 Thus; Oxidation number of S in SO2 = +4 Latihan Dapatkan nombor pengoksidaan bagi  H2SO4  Na2S2O3
4. 4. Azlee Chemistry 2009  NH3  S2O3 2-
5. 5. Azlee Chemistry 2009 (ii) H2SO4 Element H S O Sum of oxidation numbers Number of element 2 1 4 0 Oxidation number +1 x -2 2(+1) + 1(x) + 4(-2) = 0 2 + x - 8 = 0 x = +6 Thus; Oxidation number of S in H2SO4 = +6
6. 6. Azlee Chemistry 2009 (iii) Na2S2O3 Element Na S O Sum of oxidation numbers Number of element 2 2 3 0 Oxidation number +1 x -2 2(+1) + 2(x) + 3(-2) = 0 2 + 2x - 6 = 0 x = 4 2 = +2 Thus; Oxidation number of S in Na2S2O3 = +2
7. 7. Azlee Chemistry 2009 (iv) NH3 Element N H Sum of oxidation numbers Number of element 1 3 0 Oxidation number x +1 1(x) + 3(+1) = 0 x = -3 Thus; Oxidation number of N in NH3 = -3
8. 8. Azlee Chemistry 2009 (v) S2O3 2- [polyatomic ion] [refer to rules above] Element S O Sum of oxidation numbers Number of element 2 3 -2 Oxidation number x -2 2(x) + 3(-2) = -2 2x - 6 = -2 x = (6 – 2) /2 x = +2 Thus; Oxidation number of S in S2O3 2- = +2 (vi) NH4 + : ammonium ion [polyatomic ion] Element N H Sum of oxidation numbers Number of element 1 4 +1 Oxidation number x +1 x(1) + 4(+1) = +1 x + 4 = +1 x = 1 - 4 x = -3 Thus; Oxidation number of N in NH4 + = -3
9. 9. Azlee Chemistry 2009 Exercises; Calculate the oxidation numbers for the underlined elements. i. KMnO4 potassium manganate(VII) ii. MnO4 - iii. K2Cr2O7 Potassium dichromate(VI) iv. Cr2O7 2-
10. 10. Azlee Chemistry 2009 Answer: i. KMnO4 Element K Mn O Sum of oxidation numbers Number of element 1 1 4 0 Oxidation number +1 x -2 1(+1) + 1(x) + 4(-2) = 0 1 + x – 8 = 0 x = +7 Thus; Oxidation number of Mn in KMnO4 = +7
11. 11. Azlee Chemistry 2009 ii. MnO4 - Element Mn O Sum of oxidation numbers Number of element 1 4 -1 Oxidation number x -2 1(x) + 4(-2) = -1 x – 8 = -1 x = +7 Thus; Oxidation number of Mn in KMnO4 = +7
12. 12. Azlee Chemistry 2009 iii. K2Cr2O7 Element K Cr O Sum of oxidation numbers Number of element 2 2 7 0 Oxidation number +1 x -2 2(+1) + 2(x) + 7(-2) = 0 2 + 2x – 14 = 0 2x = 12 2 x = 12 / 2 x = +6 Thus; Oxidation number of Cr in Cr2O7 2- = +6
13. 13. Azlee Chemistry 2009 iv. Cr2O7 2- Element Cr O Sum of oxidation numbers Number of element 2 7 -2 Oxidation number x -2 2(+1) + 2(x) + 7(-2) = 0 2 + 2x – 14 = 0 2x = 12 2 x = 12 / 2 x = +6 Thus; Oxidation number of Cr in Cr2O7 2- = +6