1. ACIDS AND BASES TOPIC 8 1

2. ARRHENIUS MODEL OF ACIDS AND BASES Acid is a substance that contains hydrogen and ionizes to produce a hydrogen ion in an aqueous solution. Base is a substance that contains a hydroxide group (OH) and dissociates to produce a hydroxide ion in aqueous solution. This model did not include all bases (some bases (ammonia) do not have a OH group)

3. 8.1.1-8.1.2 LEWIS MODEL OF ACIDS & BASES A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate an electron pair to form a covalent bond.

4. 8.1.1-8.1.2 BRØNSTED-LOWRY MODEL OF ACIDS AND BASES Acid is a substance that donates an H + ion (proton) to another substance. Base is a substance that accepts an H + ion (proton) from another substance.

5. 8.1.3 CONJUGATE ACIDS AND BASES After an acid donates an H +, it becomes a conjugate base. After a base accepts an H +, it becomes a conjugate acid. HCl + H 2 O  H 3 O + + Cl -

6. 8.2 PROPERTIES OF ACIDS AND BASES Acids and bases can be identified using indicators. Indicators change color according to concentration of H+ ions.

7. ACIDS REACT TO FORM SALTS A salt is a compound formed when the H of an acid is replaced by a metal or other positive ion. There are 3 main types: Acid + metal  salt + hydrogen 2HCl + Zn  ZnCl 2 + H 2 Acid + base  salt + water HCl + NaOH  NaCl + H 2 O Acid + carbonate  salt + water + carbon dioxide 2HCl + CaCO 3  CaCl 2 + H 2 O + CO 2 7

8. 8.3 STRONG AND WEAK ACIDS/BASES Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO 3 (aq) + H 2 O(liq)  H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water.

9. HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Strong and Weak Acids/Bases

10. Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

11. Strong Base: 100% dissociated in water. NaOH(aq)  Na + (aq) + OH - (aq) NaOH(aq)  Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O  Ca(OH) 2 (slaked lime) Ca(OH) 2 (slaked lime) CaO

12. Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O(liq)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

13. 8.4 THE PH SCALE A common way to express acidity and basicity is with pH pH =- log [H + ] In a neutral solution, [HO + ] = [OH - ] = 1.00 x 10 -7 at 25 o C In a neutral solution, [H 3 O + ] = [OH - ] = 1.00 x 10 -7 at 25 o C pH = -log (1.00 x 10 -7 ) = - (-7) = 7

14. If the pH of Diet Coke is 3.12, what is it’s H + concentration? Because pH = - log [H + ] then log [H + ] = - pH log [H + ] = - pH Take antilog and get [H + ] = 10 -pH [H + ] = 10 -3.12 = 7.6 x 10 -4 M

15. CONVENIENT FEATURES OF PH SCALE 1.pH numbers are usually positive and have no units 2.The pH number is inversely related to the [H + ] 3.A change in one pH unit represents a 10 fold change in [H + ] 15