Chemical Reactions & Equations

Cheatsheet Content

### Introduction - Acids and bases are present in food, giving sour and bitter tastes respectively. - **Remedy for acidity:** Baking soda solution (neutralizes excess acid). - Acids turn blue litmus red; bases turn red litmus blue. - **Indicators:** Substances that change color in acidic or basic solutions. - **Natural:** Litmus (purple dye from lichen), turmeric, red cabbage leaves, colored petals (Hydrangea, Petunia, Geranium). - **Synthetic:** Methyl orange, phenolphthalein. - **Olfactory indicators:** Substances whose odor changes in acidic or basic media (e.g., onion, vanilla essence, clove oil). ### Chemical Properties of Acids and Bases #### Acids and Bases in the Laboratory - Acids (e.g., HCl, H₂SO₄, HNO₃, CH₃COOH) and Bases (e.g., NaOH, Ca(OH)₂, KOH, Mg(OH)₂, NH₄OH) show distinct color changes with indicators: - **Red Litmus:** Acids (no change), Bases (blue) - **Blue Litmus:** Acids (red), Bases (no change) - **Phenolphthalein:** Acids (colorless), Bases (pink) - **Methyl Orange:** Acids (red), Bases (yellow) #### Reaction with Metals - **Acid + Metal → Salt + Hydrogen gas** - **Example:** $\text{Zn(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{(g)}$ - Hydrogen gas can be tested by bringing a burning candle near it; it extinguishes with a "pop" sound. - **Base + Metal → Salt + Hydrogen gas** (not all metals react) - **Example:** $2\text{NaOH(aq)} + \text{Zn(s)} \rightarrow \text{Na}_2\text{ZnO}_2\text{(s)} + \text{H}_2\text{(g)}$ (Sodium zincate) #### Reaction of Metal Carbonates and Bicarbonates with Acids - **Metal Carbonate/Bicarbonate + Acid → Salt + Carbon dioxide + Water** - **Example (Sodium Carbonate):** $\text{Na}_2\text{CO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ - **Example (Sodium Bicarbonate):** $\text{NaHCO}_3\text{(s)} + \text{HCl(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ - **Testing $\text{CO}_2$ gas:** Pass through lime water ($\text{Ca(OH)}_2$). - $\text{Ca(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{CaCO}_3\text{(s)} \downarrow + \text{H}_2\text{O(l)}$ (white precipitate) - If excess $\text{CO}_2$ is passed: $\text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)} \rightarrow \text{Ca(HCO}_3)_2\text{(aq)}$ (soluble) - Limestone, chalk, and marble are forms of calcium carbonate. #### How Acids and Bases React with each other (Neutralisation) - **Acid + Base → Salt + Water** - **Example:** $\text{NaOH(aq)} + \text{HCl(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}$ - This is a **neutralisation reaction**, where the effect of an acid is nullified by a base and vice-versa. - In general: $\text{H}^+\text{(aq)} + \text{OH}^-\text{(aq)} \rightarrow \text{H}_2\text{O(l)}$ #### Reaction of Metallic Oxides with Acids - **Metallic Oxide + Acid → Salt + Water** - **Example:** $\text{CuO(s)} + 2\text{HCl(aq)} \rightarrow \text{CuCl}_2\text{(aq)} + \text{H}_2\text{O(l)}$ - Metallic oxides are **basic oxides** because they react with acids to form salt and water, similar to bases. #### Reaction of Non-metallic Oxides with Bases - **Non-metallic Oxide + Base → Salt + Water** - **Example:** $\text{Ca(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)}$ - Non-metallic oxides are **acidic in nature** because they react with bases to form salt and water, similar to acids. ### What do All Acids and Bases Have in Common? #### Acids in Water Solution - Acids produce $\text{H}^+\text{(aq)}$ ions in water, responsible for their acidic properties. - $\text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^-$ ($\text{H}^+$ ions cannot exist alone, they combine with water to form hydronium ions, $\text{H}_3\text{O}^+$). - Acidic solutions conduct electricity due to the presence of ions. - Glucose and alcohol solutions, though containing hydrogen, do not produce $\text{H}^+$ ions and thus do not conduct electricity. - Dry $\text{HCl}$ gas does not change litmus color as $\text{H}^+$ ions are not formed without water. #### Bases in Water Solution - Bases produce $\text{OH}^-\text{(aq)}$ ions in water. - **Example:** $\text{NaOH(s)} \xrightarrow{\text{H}_2\text{O}} \text{Na}^+\text{(aq)} + \text{OH}^-\text{(aq)}$ - **Alkalis:** Bases that are soluble in water. They are soapy, bitter, and corrosive. - All bases do not dissolve in water; all alkalis are bases. #### Dilution of Acids and Bases - Dissolving an acid or base in water is a highly **exothermic process**. - Always add acid slowly to water with constant stirring (never water to acid!) to prevent splashing and burns. - **Dilution:** Mixing acid/base with water decreases the concentration of $\text{H}_3\text{O}^+$/$\text{OH}^-$ ions per unit volume. ### How Strong are Acid or Base Solutions? - **Universal Indicator:** A mixture of several indicators showing different colors at different concentrations of hydrogen ions. - **pH Scale:** A scale (0-14) for measuring hydrogen ion concentration ($\text{H}^+$) in a solution. - 'p' in pH stands for 'potenz' (power in German). - Higher $\text{H}^+$ concentration $\rightarrow$ lower pH value (more acidic). - **Neutral solution:** pH = 7. - **Acidic solution:** pH 7. - **Strength of acids/bases:** Depends on the number of $\text{H}^+$/$\text{OH}^-$ ions produced. - **Strong acids:** Produce more $\text{H}^+$ ions (e.g., HCl). - **Weak acids:** Produce less $\text{H}^+$ ions (e.g., $\text{CH}_3\text{COOH}$). #### Importance of pH in Everyday Life - **Living organisms:** Work within a narrow pH range (7.0-7.8). - **Acid Rain:** Rainwater with pH ### More About Salts #### Family of Salts - Salts are formed from the reaction of acids and bases. - Salts with common positive or negative radicals belong to the same family (e.g., $\text{NaCl}$ and $\text{Na}_2\text{SO}_4$ are sodium salts; $\text{NaCl}$ and $\text{KCl}$ are chloride salts). #### pH of Salts - **Strong Acid + Strong Base:** Neutral salt (pH = 7). - **Strong Acid + Weak Base:** Acidic salt (pH 7). #### Chemicals from Common Salt (NaCl) - Common salt is a vital raw material for sodium hydroxide, baking soda, washing soda, and bleaching powder. ##### Sodium Hydroxide ($\text{NaOH}$) - Produced by **chlor-alkali process**: Electrolysis of aqueous sodium chloride (brine). - $2\text{NaCl(aq)} + 2\text{H}_2\text{O(l)} \rightarrow 2\text{NaOH(aq)} + \text{Cl}_2\text{(g)} + \text{H}_2\text{(g)}$ - **Products:** - Chlorine ($\text{Cl}_2$): Water treatment, PVC, disinfectants, pesticides. - Hydrogen ($\text{H}_2$): Fuels, margarine, ammonia for fertilizers. - Sodium Hydroxide ($\text{NaOH}$): Degreasing metals, soaps, detergents, paper making, artificial fibers. ##### Bleaching Powder ($\text{Ca(ClO)}_2$) - Produced by the action of chlorine on dry slaked lime ($\text{Ca(OH)}_2$). - $2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(ClO)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O}$ - **Uses:** - Bleaching cotton, linen, wood pulp. - Oxidizing agent in chemical industries. - Making drinking water free from germs. ##### Baking Soda (Sodium Hydrogencarbonate, $\text{NaHCO}_3$) - Produced using NaCl as a raw material: $\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl} + \text{NaHCO}_3$ - Mild non-corrosive basic salt. - When heated: $2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$ - **Uses:** - **Baking powder:** Mixture of baking soda and a mild edible acid (e.g., tartaric acid). Produces $\text{CO}_2$ when heated or mixed with water, making cakes/bread soft and spongy. - **Antacid:** Neutralizes excess acid in the stomach. - **Soda-acid fire extinguisher.** ##### Washing Soda (Sodium Carbonate Decahydrate, $\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$) - Obtained by heating baking soda to get sodium carbonate, then recrystallizing with water: $\text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$ - Basic salt. - **Uses:** - Glass, soap, and paper industries. - Manufacture of sodium compounds like borax. - Cleaning agent for domestic purposes. - Removing permanent hardness of water. #### Are the Crystals of Salts Really Dry? - Many salts contain **water of crystallisation**: A fixed number of water molecules present in one formula unit of a salt. - **Hydrated Copper Sulphate ($\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$):** Blue crystals. When heated, it loses water and turns white (anhydrous $\text{CuSO}_4$). Adding water restores blue color. - **Gypsum ($\text{CaSO}_4 \cdot 2\text{H}_2\text{O}$):** - On heating to 373 K, it loses water to form **Plaster of Paris (Calcium Sulphate Hemihydrate, $\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}$)**. - Plaster of Paris is a white powder that, when mixed with water, changes back to gypsum, forming a hard solid mass. - **Uses of Plaster of Paris:** Supporting fractured bones, making toys, decorative materials, smoothing surfaces.