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# Acids and Bases

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### Transcript of "Acids and Bases"

1. 1. Acids and Bases By: Clarissa
2. 2. THE PH SCALE #
3. 3. pH scale• pH is equal to -log10 of the hydrogen ion concentration – Equal to the power of ten of the hydrogen ion concentration• pH 7 is neutral – If solution is acidic, the H+ will be >10-7 mol dm-3  pH decrease – Basic solutions will have a pH >7 H+ will be <10-7 mol dm-3 #
4. 4. • pH scale runs from 0 to 14• A change in one unite in the pH – Corresponds to a tenfold change H+• 0.1 mol dm-3 solution of a strong monoprotic acid will have pH of 1• 0.001 mol dm-3 solution of the same acid will have a pH of 3 #
5. 5. Determination of pH• Using pH meter “universal” indicator #
6. 6. Question• pH value of a solution rises from 4 to 7. What is the change in concentration of hydrogen ions in it? – Increase by factor 3 – Increase by factor 1000 – Decrease by factor 3 – Decrease by factor 1000• Decrease by factor 1000 #
7. 7. Question• 10cm3 of an HCl solution with a pH value of 2 was mixed with 90cm3 of water. What will be the pH of the resulting solution?• Ratio 1:10 – pH 3 #
8. 8. THEORIES OF ACIDS ANDBASES AND SALTHYDROLYSIS #
9. 9. The Ionic Theory• Acid: oxide of a non-metal combined with water• Substance which produces hydrogen ions, H+ (aq)• HCl  H+(aq) + Cl-(aq)• Base: substance that can neutralize acid• Alkali is a base that is soluble in water #
10. 10. Bronsted-Lowry Acid and Bases• Bronsted-Lowry Acid can donate a proton• Bronsted-Lowry Base can accept a proton – Must contain a non-bonding pair of electrons• Conjugate base of an acid is the species remaining after the acid has lost a proton• Conjugate acid is the species formed after the base has accepted a proton• HCl + H2O ↔ H3O+ + Cl- – Water is conjugate base of H3O+ and Cl- is conjugate base of HCl #
11. 11. Bronsted-Lowry Acid and Bases• Water can act both as acid and base  amphiprotic• Strong acids have weak conjugate base• Weak acids have strong conjugate base – ACID: Ethanol (C2H5OH) weak – CONJUGATE BASE: Ethoxide ion (C2H5O-)  strong #
12. 12. Lewis Acids and Bases• Bases can donate a pair of electrons• Acids can accept a pair of electrons – Covalent bond is formed• Many Lewis Acids don’t contain hydrogen – BF3: Lewis acid, only six electrons so leaves room for two more – Pair up with NH3 #
13. 13. PROPERTIES OF ACIDS ANDBASES #
14. 14. Properties of Acids and Bases• Neutralization reaction with bases – With hydroxides to form salt and water • CH3COOH + NaOH  NaCH3COO + H2O – With metal oxides to form a salt and water • H2SO4 + CuO  CuSO4 + H2O – With ammonia to form salt • HCl + NH3  NH4Cl #
15. 15. Properties of Acids and Bases• With reactive metals to form salt and hydrogen – 2HCl + Mg  MgCl2 + H2• With carbonates to form salt, CO2, water – 2HCl + CaCO3  CaCl2 + CO2 + H2O• With hydrogencarbonates to form salt, CO2, water – HCl + NaHCO3  NaCl + CO2 + H2O #
16. 16. Strong Acids and Bases• Strong acid and base is completely dissociated (ionized) into its ions in aqueous solutions• Strong acids – HCl (Hydrochloric acid) – HNO3 (Nitric Acid) – H2SO4 (Sulfuric Acid)• Strong bases – NaOH (Sodium Hydroxide) – KOH (Potassium Hydroxide) – Ba(OH)2 (Barium Hydroxide) #
17. 17. Strong Acids and Bases• Monoprotic acid – One mole of HCl produces one mole of Hydrogen ions• Diprotic acid – One mole of H2SO4 produces two moles of Hydrogen ions #
18. 18. Weak Acids and Bases• Weak acids and bases is slightly dissociated into their ions in aqueous solution• Weak acids – CH3COOH (Ethanoic Acid) – H2CO3(Carbonic acid)• Weak bases – NH3 (Ammonia) – C2H5NH2 (Aminoethane) #
19. 19. The Differences• Can be seen in the reaction with water: – Strong Acid • HCl + H2O  H3O+ + Cl- (strong) – Reaction goes to completion – Weak Acid • CH3COOH + H2O ↔ CH3COO- + H3O+ (weak) – Equilibrium lies on left  A solution of HCl consist only of hydrogen ions and chloride ions in water  Solution of Ethanoic Acid contains mainly undissociated ethanoic acid with only very few hydrogen and ethanoate ions #
20. 20. The Differences– Strong Base • KOH  K+ + OH (strong)– Weak Base • NH3 + H2O ↔ NH4+ + OH- (weak) – Equilibrium lies on the left #
21. 21. Distinguish Between Strong & Weak Acid & Bases • Strong acids has lower pH • Strong base has higher pH • Strong: more positively charged • Strong: larger atomic radius • Strong: higher electronegativity • Strong: have much higher conductivity #
22. 22. Question• Which of the following statements about aqueous solutions of most weak acids is correct? a. They react with carbonates to produce CO2 b. They conduct electricity better than strong acid• A. Because strong acid conducts electricity better #
23. 23. Question• Ammonia (weak base) + water = alkaline Why?• H2O + NH3  NH4OH Dissociation of ammonia to produce hydroxide This will have smaller pH because hydroxide is stronger #
24. 24. Question• What mass of ethanoic acid would you use to prepare 0.5dm3 of a 0.5mol dm-3 ethanoic acid solution? (Mt ethanoic acid = 60.0)• 0.5 x 0.5 x 60 = 15 grams #
25. 25. Question• Which will be the same for separate 1mol dm-3 solutions of a strong acid and a weak acid? – Electrical conductivity – Concentration of H+ ions• Neither #
26. 26. BUFFER SOLUTION #
27. 27. Buffer Solution• Resist change in pH – When small amounts of acid or base are added to it #
28. 28. Buffer Solution• Acidic buffer solution – Made by mixing a strong base and excess of weak acid so the solution contains salt and unreacted weak acid – Example: • NaOH + CH3COOH  NaCH3COOH + H2O + CH3COOH #
29. 29. Buffer Solution• Basic buffer solution – Made from a weak base with the salt of the base with a strong acid – Example: • NH4Cl  NH4+ + Cl- • NH3 + H2O  NH4+ + OH- #
30. 30. Question• Will these solutions form a buffer solution? – 1.0dm3 solution containing 0.1mol NH3 and 0.2mol HCl• No – After reaction: 0.1 mol NH4Cl + 0.1 mol HCl – Weak acid and strong acid  strongly acidic solution – Not a weak acid-conjugate base combination #
31. 31. Question• Will these solutions form a buffer solution? – 1.0dm3 solution containing 0.2mol NH3 and 0.1mol HCl• Yes – After reaction: 0.1mol NH3 + 0.1mol NH4Cl – Weak acid and conjugate base #
32. 32. THANK YOU  #
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