Chemistry Chapter 7 PDF

## **Oxidation** - The addition of oxygen or any other electronegative radical. - The removal of hydrogen or any other electropositive radical. **Examples:** - **Addition of oxygen:** - $2Mg + O_2 \rightarrow 2MgO$ - **Addition of an electronegative radical:** - $4FeSO_4...

## **Oxidation** - The addition of oxygen or any other electronegative radical. - The removal of hydrogen or any other electropositive radical. **Examples:** - **Addition of oxygen:** - $2Mg + O_2 \rightarrow 2MgO$ - **Addition of an electronegative radical:** - $4FeSO_4 + 2H_2SO_4 + O_2 \rightarrow 2Fe_2(SO_4)_3 + 2H_2O$ - **Removal of hydrogen:** - $H_2S + Br_2 \rightarrow 2HBr + S$ - **Removal of an electropositive radical:** - $2KI + H_2O_2 \rightarrow 2KOH + I_2$ ## **Reduction** - The addition of hydrogen or any other electropositive radical. - The removal of oxygen or any other electronegative radical. **Examples:** - **Addition of hydrogen:** - $H_2S + Cl_2 \rightarrow 2HCl + S$ ## **Uses of Hydrogen** - Production of ammonia ($NH_3$) - Production of hydrochloric acid ($HCl$) - Production of methanol ($CH_3OH$) - Production of vegetable ghee - Filling balloons and airships. ## **Physical Properties of Hydrogen** - **Colour, odour and taste:** Colourless, tasteless and odourless. - **Density:** 0.098 g/L. The lightest element known. - **Solubility:** Almost insoluble in water. - **Inflammability:** Highly flammable. Burns in air with a blue flame, making a popping sound. ## **Chemical Properties of Hydrogen** - Hydrogen reacts with almost all elements except noble gases. - Hydrogen forms ionic and covalent compounds. ### **Reaction of Hydrogen with Non-metals** - **With oxygen or air:** Burns explosively in air or oxygen with a blue flame. - $ 2H_2(g) + O_2(g) \rightarrow 2H_2O(g) + Heat$ - **With halogens:** Hydrogen reacts with halogens to form hydrogen halides. - Fluorine and chlorine react explosively with hydrogen. - The reaction with iodine is reversible: - $H_2(g) + I_2 \rightleftharpoons 2HI(g)$ ### **Reaction of Hydrogen with Metals** - Highly electropositive metals (like sodium, lithium, calcium) react at high temperatures with hydrogen to form ionic hydrides. - $2Na(s) + H_2(g) \rightarrow 2NaH(s) $ ## **Laboratory Preparation of Hydrogen** - Zinc granules are reacted with dilute sulphuric acid ($H_2SO_4$) in a Woulfe's bottle. - $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g) $ - The hydrogen gas is collected by the downward displacement of water, as it is lighter than air and almost insoluble in water. This is because hydrogen is less dense than air and barely dissolves in water. ## **Preparation of Hydrogen from Water** - ***By the action of active metals on water:*** - Sodium and magnesium react vigorously with cold water. Calcium reacts with hot water. - $Na(s) + H_2O(l) \rightarrow NaOH(aq) + H_2(g)$ - $Mg(s) + H_2O(l) \rightarrow MgO(s) + H_2(g)$ - $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$ - ***By the action of acids on metals:*** - Metals like zinc, magnesium, etc., displace hydrogen from acids. - $Zn(s) + dil. H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g) $ - $Mg(s) + dil. H_2SO_4(aq) \rightarrow MgSO_4(aq) + H_2(g)$ - ***By the action of alkalis on metals:*** - Metals like zinc, aluminium, and tin react with boiling sodium hydroxide to produce hydrogen. - $Zn(s) + 2NaOH(aq) \rightarrow Na_2ZnO_2(aq) + H_2(g)$ ## **Electrolysis of Water** - The process of decomposition of an electrolyte with the help of electricity is called electrolysis. - Water is a poor conductor of electricity, so a small amount of acid (like $H_2SO_4$) or base (like $NaOH$) is added to make it conducting. - When electricity is passed through acidified water using platinum electrodes, water decomposes into hydrogen ($H_2$) and oxygen ($O_2$). - **Reactions:** - **At cathode:** $H^+ + e^- \rightarrow H$ followed by $H + H \rightarrow H_2(g)$ (Reduction) - **At anode:** $OH^- \rightarrow OH + e^-$ followed by $2OH \rightarrow H_2O + O + 2e^-$ (Oxidation) - **Overall reaction:** $2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$ ## **Bosch's Process** - It is a commercial process for producing hydrogen gas. It consists of three steps: 1. **Production of water gas:** - A mixture of CO and $H_2$ is produced by passing steam through red hot coke. 2. **Water gas shift reaction:** - $CO + H_2O \rightleftharpoons CO_2 + H_2$ - The mixture is passed over a heated catalyst ($Fe_2O_3$ and $Cr_2O_3$) at 450°C to oxidize CO to $CO_2$. This step is done to increase the yield of hydrogen gas. 3. **Separation of carbon dioxide:** - The mixture of $H_2$ and $CO_2$ is passed through water under pressure. Carbon dioxide dissolves in water, leaving hydrogen gas.