Redox Reactions metals generally form ions by losing electrons with an increase in oxidation number to form positive ions: Zn Zn2+ + 2enon-metals generally react by gaining electrons with a decrease in oxidation number to form negative ions Cl2 + 2e- 2Cl- 4Li + O2 2Li2O 0 0 +1 -2 Lithium is oxidising because its oxidation number is increasing from 0 to +1 Oxygen is reducing because its oxidation number is decreasing from 0 to -2 WO3 + 3H2 W + 3H2O 0 0 +1 +6 Hydrogen is oxidising because its oxidation number is increasing from 0 to +1 Tungsten is reducing because its oxidation number is decreasing from +6 to 0 2Sr(NO3 )2 2SrO + 4NO2 + O2 -2 +4 0 +5 Oxygen is oxidising because its oxidation number is increasing from -2 to 0 Nitrogen is reducing because its oxidation number is decreasing from +5 to+4 Redox Reactions of Metals and acid 2HCl + Mg MgCl2 +H2 ACID + METAL SALT + HYDROGEN 0 0 +2 +1 Magnesium is oxidising because its oxidation number is increasing from 0 to +2 Hydrogen is reducing because its oxidation number is decreasing from +1 to 0 Fe + H2 SO4 FeSO4 +H2 Be able to write equations for reactions of metals with hydrochloric acid and sulphuric acid Observations: These reaction will effervesce because H2 gas is evolved and the metal will dissolve Note that not all the oxygen atoms are changing oxidation number in this reaction 2 NH3 + NaClO N2H4 + NaCl + H2O +1 -2 -1 -3 Nitrogen is oxidising because its oxidation number is increasing from -3 to -2 Chlorine is reducing because its oxidation number is decreasing from +1 to -1
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2.1.5 Redox
Redox reactions
(d) oxidation and reduction in terms of:
(i) electron transfer
(ii) changes in oxidation number
Should include examples of s-, p- and d-block elements.
(e) redox reactions of metals with acids to form salts, including full equations (see also 2.1.4 c) Metals should be from s-, p- and d-blocks e.g. Mg, Al, Fe, Zn. Ionic equations not required. In (e), reactions with acids will be limited to those producing a salt and hydrogen. Reactions involving nitric acid or concentrated sulfuric acid could be assessed in the context of (f).
(f) interpretation of redox equations in (e), and unfamiliar redox reactions, to make predictions in terms of oxidation numbers and electron loss/ gain.
2.1.5 redox Page 2
Oxford Textbook Pages : 50 - 51
CGP Revision Guide Pages : 38 - 39
