Acids, Bases, and Indicators

• Acids and bases influence the sour and bitter tastes of food respectively.
• Acidity due to overeating can be remedied by baking soda solution.
• Acids neutralize bases.
• Acids are sour and turn blue litmus red, while bases are bitter and turn red litmus blue.
• Litmus and turmeric are natural indicators.
• Curry stains turn reddish-brown with soap (basic) but become yellow again when washed with water.
• Methyl orange and phenolphthalein are synthetic indicators for acids and bases.

Indicators

• Litmus solution, a purple dye, comes from lichen (Thallophyta division).
• Litmus is purple when neither acidic nor basic,
• Other natural indicators include red cabbage leaves, turmeric, and colored flower petals (Hydrangea, Petunia, Geranium).
• Acid-base indicators detect acids or bases usually with a solution.

Understanding Chemical Properties

• Solutions for lab experiments include hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2], potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)2], ammonium hydroxide (NH4OH).
• Indicators reveal whether a substance is acidic or basic through color changes.
• Olfactory indicators are substances that change odor in acidic or basic media.
• Finely chopped onions' odor changes can be used as olfactory indicators with cloth strips.
• Vanilla essence and clove oil can also serve as olfactory indicators.

Reactions with Metals

• Metals react with acids to produce hydrogen gas and a salt. Acid+Metal→Salt+Hydrogen gasAcid + Metal \rightarrow Salt + Hydrogen\ gasAcid+Metal→Salt+Hydrogen gas
• Hydrogen gas can be tested by bringing a burning candle near gas-filled bubble; it burns with a 'pop' sound.
• Not all metals react with acids.
• Zinc reacts with sodium hydroxide to produce hydrogen. 2NaOH(aq)+Zn(s)→Na2ZnO2(s)+H2(g)2NaOH(aq) + Zn(s) \rightarrow Na_2ZnO_2(s) + H_2(g)2NaOH(aq)+Zn(s)→Na2​ZnO2​(s)+H2​(g)
• These reactions may not occur with all metals.

Metal Carbonates and Hydrogencarbonates

• Metal carbonates/hydrogencarbonates react with acids to produce salt, carbon dioxide, and water. Metal carbonate/Metal hydrogencarbonate+Acid→Salt+Carbon dioxide+WaterMetal\ carbonate/Metal\ hydrogencarbonate + Acid \rightarrow Salt + Carbon\ dioxide + WaterMetal carbonate/Metal hydrogencarbonate+Acid→Salt+Carbon dioxide+Water
• The reaction of metal carbonates with hydrochloric acid produces carbon dioxide. Na2CO3(s)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g)Na_2CO_3(s) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_2O(l) + CO_2(g)Na2​CO3​(s)+2HCl(aq)→2NaCl(aq)+H2​O(l)+CO2​(g)
• CO2 gas turns lime water milky: Ca(OH)2(aq)+CO2(g)→CaCO3(s)+H2O(l)Ca(OH)_2 (aq) + CO_2(g) \rightarrow CaCO_3(s) + H_2O(l)Ca(OH)2​(aq)+CO2​(g)→CaCO3​(s)+H2​O(l)
• Excess CO2 causes the reaction: CaCO3(s)+H2O(l)+CO2(g)→Ca(HCO3)2(aq)CaCO_3(s) + H_2O(l) + CO_2(g) \rightarrow Ca(HCO_3)_2(aq)CaCO3​(s)+H2​O(l)+CO2​(g)→Ca(HCO3​)2​(aq)
• Limestone, chalk, and marble are calcium carbonate forms.

Acid-Base Reactions

• Acids and bases neutralize each other, NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)NaOH(aq) + HCl(aq) \rightarrow NaCl(aq) + H_2O(l)NaOH(aq)+HCl(aq)→NaCl(aq)+H2​O(l). This is Base+Acid→Salt+WaterBase + Acid \rightarrow Salt + WaterBase+Acid→Salt+Water

Metallic Oxides Reactions

• Metal oxides react with acids to form salt and water. Metal oxide+Acid→Salt+WaterMetal\ oxide + Acid \rightarrow Salt + WaterMetal oxide+Acid→Salt+Water
• Metallic oxides are considered basic oxides.

Non-Metallic Oxide Reactions

• Non-metallic oxides react with bases.
• Non-metallic oxides are acidic in nature

Acids and Bases

• Acids in aqueous solutions show acidic behavior versus alcohol and glucose solutions.
• Acids produce hydrogen gas when reacting with metals.
• Acids increase hydrogen ion concentration, thus are acidic.
• Diluting acids should involve adding acid to water.
• As acids are diluted, hydronium ion concentration decreases.
• Excess base dissolves in sodium hydroxide, decreasing hydroxide ions.

Common Properties

• Acids share chemical properties due to hydrogen.
• Acids containing solutions conduct electricity

Aqueous Acids and Base Reactions

• Acids form ions in water: HCl+H2O→H3O++Cl−HCl + H_2O \rightarrow H_3O^+ + Cl^-HCl+H2​O→H3​O++Cl−
• Hydrogen ions combine with water molecules to form hydronium ions H++H2O→H3O+H^+ + H_2O \rightarrow H_3O^+H++H2​O→H3​O+
• Bases containing solutions generate hydroxide ions: NaOH(s)→Na+(aq)+OH−(aq)NaOH(s) \rightarrow Na^+ (aq) + OH^- (aq)NaOH(s)→Na+(aq)+OH−(aq)
• Bases which are soluble in water are called alkalis.

Neutralization

• Neutralization is when acids and bases can react to form salt and water Acid+Base→Salt+WaterAcid + Base \rightarrow Salt + Water Acid+Base→Salt+Water or H+(aq)+OH−(aq)→H2O(l)H^+ (aq) + OH^- (aq) \rightarrow H_2O(l)H+(aq)+OH−(aq)→H2​O(l)
• Dissolving acids or bases can be highly exothermic and acids must be added to water slowly while stirring.
• Dilution decreases H3O+/OH- ion concentration,

Solution Strength

• Universal indicators distinguish acids/bases.
• pH scale is for measuring hydrogen ion concentration; 'p' stands for 'potenz' (power).
• pH ranges from 0 (acidic) to 14 (alkaline); pH indicates the nature of a solution.
• Hydronium ion concentration dictates pH, inverse relationship.
• Neutral solution's pH is 7 while pH values below 7 are acidic, and above 7 are basic.

pH Testing

• pH paper with universal indicator measures pH.
• Acids' and bases' strength relies on H+ and OH- ions.
• Strong acids produce more H+ ions; weak acids produce fewer

Daily life pH

• The body functions at pH 7.0-7.8, and living organisms require a narrow pH range.
• Rainwater pH below 5.6 is acid rain which lowers river pH, threatening aquatic life.
• Venus has sulfuric acid clouds.

Soil pH

• Certain pH is needed for healthy growing plants, can be tested with soil samples and pH indicator paper.

Digestive Systems pH

• The stomach uses hydrochloric acid to digest food.
• Antacids, like magnesium hydroxide (milk of magnesia), neutralize excess acid during indigestion.

Neutralization and Tooth Decay pH

• Tooth decay happens when mouth pH drops below 5.5,
• Tooth enamel corrodes.
• Bacteria degrades sugars forming acids.
• Toothpaste neutralizes excess acid.

Chemical Self-Defense

• Honeybee sting creates acid that can be neutralized with baking soda.
• Nettle leaves sting with methanoic acid.

Acid examples

• Naturally occurring acids include acetic (vinegar), citric (orange, lemon), lactic (sour milk), tartaric (tamarind), oxalic (tomato), and methanoic (ant/nettle sting).

Family of Salts

• Salts share positive/negative radicals.
• Sodium salts are NaCl and Na2SO4 and chloride salts are NaCl and KCl.
• pH of salts: Strong acid/base salts are neutral (pH 7). Salts of strong acid/weak base are acidic (pH < 7), while a strong base/weak acid are basic (pH > 7).

Chemicals and Salts

• Sodium chloride (common salt) forms with hydrochloric acid and sodium hydroxide.

Sea Water

• Seawater contains dissolved salts, including sodium chloride.
• Rock salt are solid salt deposits.
• Mahatma Gandhi's Dandi March was to fight salt laws in india.

Common salt

• Common salt makes the chemicals sodium hydroxide, baking soda, washing soda, bleaching powder.

Sodium hydroxide Properties

• Electrolysis of brine (aqueous NaCl) forms sodium hydroxide, chlorine gas, and hydrogen gas, called the chlor-alkali process 2NaCl(aq)+2H2O(l)→2NaOH(aq)+Cl2(g)+H2(g)2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)2NaCl(aq)+2H2​O(l)→2NaOH(aq)+Cl2​(g)+H2​(g).
• Chlorine produced at occurs at the anode, and hydrogen forms at the cathode.
• Sodium hydroxide accumulates near the cathode.

Powdered Bleach

• Chlorine from the electrolysis of brine is used to manufacture bleaching powder by the action of chlorine on dry slaked lime Ca(OH)2+Cl2→CaOCl2+H2OCa(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2OCa(OH)2​+Cl2​→CaOCl2​+H2​O

Baking Soda properties

• Sodium Chloride plus other raw materials makes baking soda. NaCl+H2O+CO2+NH3→NH4Cl+NaHCO3NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3NaCl+H2​O+CO2​+NH3​→NH4​Cl+NaHCO3​
• Baking soda is sodium hydrogencarbonate (NaHCO3), and is a mild, non-corrosive base.
• Heating sodium hydrogencarbonate produces sodium carbonate. 2NaHCO3→Na2CO3+H2O+CO22NaHCO_3 \rightarrow Na_2CO_3 + H_2O + CO_22NaHCO3​→Na2​CO3​+H2​O+CO2​
• Mixing baking soda with mild acid makes baking powder by producing carbon dioxide NaHCO3+H+→CO2+H2O+Sodium salt of acidNaHCO_3 + H^+ \rightarrow CO_2 + H_2O + Sodium\ salt\ of\ acidNaHCO3​+H+→CO2​+H2​O+Sodium salt of acid
• CO2 makes mixtures rise

Washing Soda

• Sodium chloride makes washing soda (Na2CO3.10H2O)
• Recrystallization of sodium carbonate forms washing soda Na2CO3+10H2O→Na2CO3.10H2ONa_2CO_3 + 10H_2O \rightarrow Na_2CO_3.10H_2ONa2​CO3​+10H2​O→Na2​CO3​.10H2​O
• Washing soda is used for glass, soap, paper, and sodium industries.

Crystallization

• Copper sulphate crystals have water molecules
• When heated the crystals turn white.
• Adding water restores the crystal color.
• Water of crystallization is waters in one formula unit of a salt (e.g., CuSO4.5H2OCuSO_4.5H_2OCuSO4​.5H2​O).

Gypsum Reactions

• Gypsum also has water CaSO4.2H2OCaSO_4.2H_2OCaSO4​.2H2​O
• Heating gypsum at 373 K makes Plaster of Paris CaSO4.(1/2)H2OCaSO_4.(1/2)H_2OCaSO4​.(1/2)H2​O. This is calcium sulphate hemihydrate.

Plaster of Paris use

• Plaster of Paris is a white powder that reforms gypsum with water. CaSO4.(1/2)H2O+1(1/2)H2O→CaSO4.2H2OCaSO_4.(1/2)H_2O + 1(1/2)H_2O \rightarrow CaSO_4.2H_2OCaSO4​.(1/2)H2​O+1(1/2)H2​O→CaSO4​.2H2​O
• Plaster of Paris makes toys, decorations, and smooth surfaces.