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Acids and Bases
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Properties of Acids and Bases
Water soluble Electrolyte Sour Bitter Corrosive Feels like water Feels slippery, like soap/wax Turns litmus paper red Turns litmus paper blue Neutralizes bases Neutralizes acids Reacts with active metals to form H2(g)
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Svante Arrhenius Developed the Arrhenius acid-base theory
Acids produce H+ ions in solution Must have at least 1 hydrogen Ex. HCl, H2S, CH3COOH Bases produce OH- ions in solution Have OH-, ex. NaOH, or react with water to form OH-, ex. NH3
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Svante Arrhenius When acids or bases are dissolved in solution they undergo ionization and separate into their ions NaOH Na+ + OH- HCl H+ + Cl-
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Hydronium H+ ions in solution react with water to form H3O+, an ion called Hydronium Small amounts of hydronium are also formed by water reacting with itself: 2 H2O ↔ H3O+ + OH-
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Hydronium Hydronium in solution is the source of acid- base chemistry.
The amount present in water is pH-neutral Higher concentrations of hydronium leads to acidity Lower concentrations of hydronium leads to being a base
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Strong Acids and Bases When ionic acids and bases are dissolved in water they dissociate completely. Virtually every molecule will split into ions(99+%). H2S 2 H+ + S2- 1 mol of H2S dissociates into 2 mol of H+ and 1 mol of S2- These solutions are called strong acids and strong bases
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Weak Acids and Bases When covalent acids and bases are dissolved in water they only dissociate partially. Only some molecules will split into ions. CH3COOH ↔ CH3COO- + H+ 1 mol of CH3COOH dissociates into mol of CH3COO- and H, with mol of CH3COOH remaining These solutions are called weak acids and weak bases 1.3%
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Weak Acids and Bases STRONG ACID/BASE WEAK ACID/BASE Ionic Covalent
Complete dissociation Partial dissociation Better electrolytes (more ions) Worse electrolytes (less ions)
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Strength Vs. Concentration
H+ or OH- concentrations are affected by Acid/Base Concentration: “How much acid/base is in this solution?” Acid/Base strength: “How much of it split into ions?”
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pH A simple measure of acidity, usually ranging from 0- 14
7 is neutral (pure water) 0 is very acidic 14 is very basic
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pH So why 0-14? Most acids and bases have a hydronium concentration from 1.0x100 to 1.0x mol/L They just used the exponents and dropped the negative sign! 1 pH difference is a 10x change in concentration of H3O+. 2 pH = 100x, 3 pH =1000x, etc.
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pH pH = - log[H3O+] [H3O+] = 10-pH
Reminder: [Chemical] means concentration in mol/L
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Measuring pH Indicators are chemicals that change colour under certain pH Phenolphthalein; colourless in acid, hot pink in base
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Measuring pH Digital pH meters have a glass electrode that changes in conductivity when it interacts with Hydronium. This lets it measure pH.
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