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Acids, bases, and pH

Acids, bases, and pH. Objectives. Describe the ionization of strong acids in water and the DISSOCIATION of strong BASES in water Distinguish between solutions of weak acids or bases and strong acids or bases Relate pH to the concentration of HYDRONIUM ions in a solution. What are acids.

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Acids, bases, and pH

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  1. Acids, bases, and pH

  2. Objectives • Describe the ionization of strong acids in water and the DISSOCIATION of strong BASES in water • Distinguish between solutions of weak acids or bases and strong acids or bases • Relate pH to the concentration of HYDRONIUM ions in a solution

  3. What are acids

  4. ACIDS • Acid – any compound that INCREASES the number of HYDRONIUM ions when dissolved in water • Example : H2O + HCl  H3O+ + Cl- • Acids will IONIZE in water = form ions see above example • Acids will turn BLUE litmus paper RED

  5. Common acids • Common examples of acids – • citrus fruits • Formic acid – an acid found in stinging ants HCOOH • Vinegar = acetic acid CH3COOH • Hydrochloric acid – HCl • Nitric acid HNO3

  6. Acids IONIZE • When an acid is dissolved in water the Hydrogen from the acid forms a bond with a water molecule to form a HYDRONIUM ION and the anion from the acid • Example : H2O + HCL  H3O+ + Cl- • H2O + CH3COOH  H3O+ + CH3COO- •  • A double arrow in an equation indicates that the reaction goes in both directions

  7. Weak acids DO NOT ionize completely • A double arrow indicates that the ions quickly go back to the original acid and water • Weak acids are POOR ELECTROLYTES • A STRONG acid DOES ionize completely indicated by a single arrow • Strong acids are GREAT ELECTROLYTES

  8. STRONG ACIDS conduct electricty = Electrolyte – a light bulb will glow brightly

  9. Weak Acids are POOR Electrolytes • A light bulb will BARELY glow http://www.youtube.com/watch?v=a21kuzQW7AE

  10. Indicators • A compound that can reversibly change color depending on the pH of the solution • Litmus paper – Identifies if a solution is an acid or a base • An acid turns blue litmus paper RED • A base turns red litmus paper blue • pH paper – will determine the pH of the solution from a range of pH1(strong acid) red through pH14 (strong base) blue

  11. Acids are dangerous in concentrated form • Concentrated acids damage human tissue • Acetic acid = vinegar sold in 5% solution b/c concentrated acetic acid(glacial) damages tissue and the vapors damage tissues of the eyes, mouth, lungs • Stomach acid = pH 2 which damages tissue outside of the stomach – when a person “throwsup” the mucus lining of their throat and nose is “burned”

  12. BASES • Any compound that increases the number of HYDROXIDE ions when dissolved in water • Example: Strong bases • NaOH + H2O Na+ + OH- + H2O • KOH + H2O  K+ +OH- + H2O • Strong ELECTROLYTES

  13. WEAK BASES • Do minimally increase the OH- • Do not dissociate completely in water • The water acts like an ACID by donating the hydrogen ion • NH3 + H2O  NH4+ + OH- •  • Ammonia becomes ammonium ion

  14. CH3NH2 + H2O  CH3NH3+ + OH- •  • Just as in the weak acid the “double arrow” in the equation means the reaction is going in both directions • Weak Electrolyte – since the ions form and then reform into noncharged molecules again

  15. pH scale • http://www.alternativemedicinedirect.com/NewSiteImages2011/phscalergb.jpg

  16. pH power of hydronium • A value used to express the acidity or alkalinity(base) of a solution • Negative logarithm • Logarithm = exponent • Example: • If the concentration of H3O+ = 1x10-2 • The exponent = -2 • The “NEGATIVE” of -2 = 2 • The pH then =2

  17. WATER

  18. Because water dissociates the concentration of H3O+ equals the concentration of OH- • The total concentration of H3O+ and OH- ions = 1x10-14 • H3O+ = 1x10-7 • OH- = 1x10-7

  19. How pH tells us acidity • If the pH of a solution = 1x10-1 then the amount of H3O+ = .1 • If .1 was money = 10 cents • I

  20. If the pH of a solution was 1x10-2 then the H3O+ concentration = .01 • If .01 was money = one penny

  21. Which value is MORE acidic – pH1 or pH2 • Which is more money a dime or a penny

  22. If the concentration of H3O+ = .0000000000001 then the pH = 1x10-13 • You would need a WHOLE lot of these to just equal ONE PENNY! • There are VERY little H3O+ ions in solution! • How many OH- ions will be in this solution?

  23. Calculating OH- ions via pH • H3O+ + OH- = 1x10-14 • If H3O+ = 1x10-13 then • 1x10-13 + OH- = 1x10-14 then • OH- = 1x10-1 • 1x10-1(OH-) = .1 (a dime) • 1x10-13(H3O+) = very very very very little • So there are MUCH more OH- • pH13 solution is a very strong BASE

  24. 8-2 Reactions with acids and bases • Objectives: • Write ionic equations for neutralization reactions • Identify the products of neutralization reactions • Describe the composition of a salt

  25. Neutralization Reactions • Reactions with Acids and Bases

  26. Examples • AB + CD  AD + BC • The cation of the first compound will form a new bond with the anion of the second compound • The cation of the second compound will form a bond with the anion of the first compound

  27. HCl + NaOH  HOH + NaCL • Notice HOH = H2O • A strong acid (HCl) reacts with a strong Base (NaOH) to form water and a salt • ALWAYS!!!!! Any strong acid any strong base reacts to from water and a salt • WATER is NEUTRAL pH =7 • Thus “Neutralization” reaction

  28. WHAT ARE SPECTATOR IONS • Spectator = a bystander of an event • Wouldn’t we all love to be a spectator in LONDON this summer for the olympics?

  29. Spectator ions are the ions that will eventually form the salt • HCl + NaOH  Na+ + Cl- + H2O • H2SO4 + KOH  K+ + SO4- + H2O • In both reactions, once the water evaporates the salts will form NaCl and K2SO4

  30. NOT all Neutralization reactions form salts. • Weak acid + Strong base  weak base no water still too many OH- ions in solution • Strong acid + Weak Base  weak acid no water still too many H3O+ ions in solution • Our body has Natural “buffers” to prevent our blood from being TOO acidic or TOO basic

  31. H+aq + HCO-3aq H2CO3aq H2OL+ CO2g

  32. 8-3 Acids, Bases, Salts in the home

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