Chapter 6 Acids and Bases

2 Stomach Acid & Heartburn the cells that line your stomach produce hydrochloric acid to kill unwanted bacteria to help break down food to activate enzymes that break down food if the stomach acid backs up into your esophagus, it irritates those tissues, resulting in heartburn acid reflux GERD = gastroesophageal reflux disease = chronic leaking of stomach acid into the esophagus

3 Curing Heartburn mild cases of heartburn can be cured by neutralizing the acid in the esophagus swallowing saliva which contains bicarbonate ion taking antacids that contain hydroxide ions and/or carbonate ions

4 Properties of Acids sour taste react with “active” metals i.e., Al, Zn, Fe, but not Cu, Ag, or Au 2 Al + 6 HCl  AlCl H 2 corrosive react with carbonates, producing CO 2 marble, baking soda, chalk, limestone CaCO HCl  CaCl 2 + CO 2 + H 2 O change color of vegetable dyes blue litmus turns red react with bases to form ionic salts

5 Common Acids

6 Structures of Acids binary acids have acid hydrogens attached to a nonmetal atom HCl, HF

7 Structure of Acids oxy acids have acid hydrogens attached to an oxygen atom H 2 SO 4, HNO 3

8 Structure of Acids carboxylic acids have COOH group HC 2 H 3 O 2, H 3 C 6 H 5 O 7 only the first H in the formula is acidic the H is on the COOH

9 Properties of Bases also known as alkalis taste bitter alkaloids = plant product that is alkaline  often poisonous solutions feel slippery change color of vegetable dyes different color than acid red litmus turns blue react with acids to form ionic salts neutralization

10 Common Bases

11 Structure of Bases most ionic bases contain OH ions NaOH, Ca(OH) 2 some contain CO 3 2- ions CaCO 3 NaHCO 3 molecular bases contain structures that react with H + mostly amine groups

12 Indicators chemicals which change color depending on the acidity/basicity many vegetable dyes are indicators anthocyanins litmus from Spanish moss red in acid, blue in base phenolphthalein found in laxatives red in base, colorless in acid

13 Arrhenius Theory bases dissociate in water to produce OH - ions and cations ionic substances dissociate in water NaOH(aq) → Na + (aq) + OH – (aq) acids ionize in water to produce H + ions and anions because molecular acids are not made of ions, they cannot dissociate they must be pulled apart, or ionized, by the water HCl(aq) → H + (aq) + Cl – (aq) in formula, ionizable H written in front HC 2 H 3 O 2 (aq) → H + (aq) + C 2 H 3 O 2 – (aq)

14 Arrhenius Theory HCl ionizes in water, producing H + and Cl – ions NaOH dissociates in water, producing Na + and OH – ions

15 Hydronium Ion the H + ions produced by the acid are so reactive they cannot exist in water H + ions are protons!! instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H 3 O + H + + H 2 O  H 3 O + there are also minor amounts of H + with multiple water molecules, H(H 2 O) n +

16 Arrhenius Acid-Base Reactions the H + from the acid combines with the OH - from the base to make a molecule of H 2 O it is often helpful to think of H 2 O as H-OH the cation from the base combines with the anion from the acid to make a salt acid + base → salt + water HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l)

17 Problems with Arrhenius Theory does not explain why molecular substances, like NH 3, dissolve in water to form basic solutions – even though they do not contain OH – ions does not explain how some ionic compounds, like Na 2 CO 3 or Na 2 O, dissolve in water to form basic solutions – even though they do not contain OH – ions does not explain why molecular substances, like CO 2, dissolve in water to form acidic solutions – even though they do not contain H + ions does not explain acid-base reactions that take place outside aqueous solution

18 Brønsted-Lowry Theory in a Brønsted-Lowry Acid-Base reaction, an H + is transferred does not have to take place in aqueous solution broader definition than Arrhenius acid is H donor, base is H acceptor base structure must contain an atom with an unshared pair of electrons in an acid-base reaction, the acid molecule gives an H + to the base molecule H–A + :B  :A – + H–B +

19 Brønsted-Lowry Acids Brønsted-Lowry acids are H + donors any material that has H can potentially be a Brønsted-Lowry acid because of the molecular structure, often one H in the molecule is easier to transfer than others HCl(aq) is acidic because HCl transfers an H + to H 2 O, forming H 3 O + ions water acts as base, accepting H + HCl(aq) + H 2 O(l) → Cl – (aq) + H 3 O + (aq) acidbase

20 Brønsted-Lowry Bases Brønsted-Lowry bases are H + acceptors any material that has atoms with lone pairs can potentially be a Brønsted-Lowry base because of the molecular structure, often one atom in the molecule is more willing to accept H + transfer than others NH 3 (aq) is basic because NH 3 accepts an H + from H 2 O, forming OH – (aq) water acts as acid, donating H + NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH – (aq) base acid