Oxidation and Reduction Reactions - High School Chemistry PDF

# OXIDATION & REDUCTION ## TERM * **OXIDATION REACTION:** A chemical reaction involving: * Addition of oxygen - to a substance * Removal of hydrogen - from a substance * Loss of electrons - from an atom or ion * **REDUCTION REACTION:** A chemical reaction involving: * Removal of ox...

# OXIDATION & REDUCTION ## TERM * **OXIDATION REACTION:** A chemical reaction involving: * Addition of oxygen - to a substance * Removal of hydrogen - from a substance * Loss of electrons - from an atom or ion * **REDUCTION REACTION:** A chemical reaction involving: * Removal of oxygen - from a substance * Addition of hydrogen - to a substance * Gain of electrons - by an atom or ion ## EXAMPLE * **Oxidation - reaction involving** * Addition of oxygen - to a substance * 2 Cu + O2 → 2 Cu O * Removal of hydrogen - from a substance * H₂ S + Cl2 → 2 HCl + S * Loss of electrons from an atom * 2FeCl2+ Cl2 → 2FeCl3 * Fe²⁺ + e^- → Fe³⁺ * [ferrous] [ferric] * **Reduction - reaction involving** * Removal of oxygen - from a substance * CuO + H₂ → Cu + H₂O * Addition of hydrogen - to a substance * Cl2 + H2S → 2HCl + S * Gain of electrons - by an atom * 2FeCl3+SO2+2H2O→2FeCl2+2HCl+H2SO4 * Fe³⁺ + e^- → Fe²⁺ * [ferric] [ferrous] ## REDOX REACTION * It is a chemical reaction involving- Oxidation of one substance & reduction of the other. * They are reactions in which - oxidation & reduction takes place simultaneously. * All chemical reactions involving - loss or gain of electrons are considered redox reactions. * Cl₂ is reduced to HCl [gain - of hydrogen] * Cl₂ + H₂S → 2HCl + S * H₂S oxidised to S [removal - of hydrogen] ## OXIDIZING AGENTS * They are substances which - lose oxygen or gain hydrogen or accept electrons. * e.g. O2, Cl2, H2O2, conc. H2SO4, conc. HNO3, MnO2, PbO2, Pb3O4 ΚΝΟ3 ## REDUCING AGENTS * They are substances which - gain oxygen or lose hydrogen or donate electrons. * e.g. H₂, CO, SO2, H2S, NH3, HCl, C, metals [K, Na]. * The substance that gets reduced acts as an - oxidizing agent & * The substance which gets oxidised acts as a - reducing agent. # HYDROGEN - Chemical properties ## 1. EXPERIMENT TO PROVE THAT HYDROGEN IS * **COMBUSTIBLE** - i.e. itself burns & * **NON-SUPPORTER OF COMBUSTION** - i.e. does not allow other substances to burn in it. **Conclusion:** * Hydrogen - * is combustible - & hence burns at the mouth of the jar. * does not support combustion - extinguishes a burning candle when pushed inside. ## 2. EXPERIMENT TO PROVE THAT HYDROGEN IS * **A STRONG - REDUCING AGENT** **Conclusion:** Hydrogen - * Reduces - copper oxide to copper * is a strong reducing agent - reduces heated copper [II] oxide to copper. ## 3. EXPERIMENT TO **PROVE THAT - COMBUSTION OF HYDROGEN IN AIR - Forms Water** **Conclusion:** Hydrogen - * on combustion or burning in air - produces water. # HYDROGEN - Preparation ## 3. LABORATORY METHOD **a) REACTION** * Laboratory preparation of hydrogen * Zinc + Hydrochloric acid [dil.] → Zinc chloride + Hydrogen gas * Zn + 2HCl → ZnCl2 + H2 [g] **b) PROCEDURE** * The apparatus is arranged as shown in the figure above. * Zinc granules are added to the Flask 'A' - fitted with a two holed stopper. * Granulated zinc - is commercial zinc obtained from molten zinc. * It may contain traces of impurities, which have a slight catalysing effect on the reaction. * [Traces of copper [II] sulphate added to the reaction medium - also enhances the speed of the reaction] * Dilute hydrochloric acid - is added through the thistle Funnel 'B'. * The preferred acid in the above preparation is - dil. HCl or dil. H2SO4 * Dilute nitric acid is not used since - being a strong oxidizing agent, it would oxidise the hydrogen formed - to water. * The reaction between zinc & dilute hydrochloric acid results in formation of - hydrogen gas. **c) COLLECTION** * The hydrogen gas formed above is collected by - **downward displacement of water**. * **Reason:** Hydrogen - is very slightly soluble in water. * Even though it is lighter than air - it is not collected by the * downward displacement of air, since hydrogen-air mixture is highly explosive. **d) PRECAUTIONS** * No leakage of gas - should take place & no flame must be near the apparatus. * Hydrogen is collected - after all the air in the apparatus is allowed to escape. * The end of the thistle funnel - should dip below the level of the dil. acid in the flask 'A' or * the hydrogen gas may escape out - through the thistle funneb'