Acids and Bases

1. Acids and Bases What are Acids and Bases???

2. Acids • Acids have a very tart, sour taste to them. • Many acids are highly caustic and should not be put to a taste test. • Acids are electrolytes (they dissociate in water) • They break down into H3O+ ions which have a positive charge and is just passed from water molecule to water molecule. • Electricity can be passed through an acidic solution and is able to light a light bulb.

3. Acids and Metals • Acids react with many metals • In these reactions, the hydronium reacts with the metal to produce hydrogen gas as one of the products. 2 H3O+(aq) + Zn(s) 2 H2O(l) + H2(g) + Zn2+(aq) • Notice that the HCl have been replaced with _____________. • HCl will break down into _________ ions and _________ ions. • The chlorine ions cancel out and do not appear in the net ionic equation. Why is this??

4. Strong Vs. Weak • Some electrolytes are strong and others are weak, depending on whether they dissociate completely or partially. • Acids are electrolytes and therefore can be classified as strong or weak acids. • Strong acid will dissociate COMPLETELY in water. HNO3(l) + H2O(l) H3O+(aq) + NO3-(aq) • The strong acids are:

5. Weak Acids • When a weak acid is dissolved in water, only a small fraction of its molecules are ionized at any given time. • These reactions are usually reversible • Example: HOCl(l) + H2O H3O+(aq) + ClO-(aq) • Which acids are weak acids?

6. Polyprotic Acids • What do you think the term “polyprotic” means? • A single molecule can react to form more than one hydronium ion. This occurs with stronger acids containing more than one hydrogen atom (hydronium ion). • Consider sulfuric acid: H2SO4(l) + H2O(l) H3O+(aq) + HSO4-(aq) Now, it can go one more step (it has one more H): HSO4-(aq) + H2O(l) H3O+(aq) + SO42-(aq)

7. Bases • Solutions of bases are slippery to the touch. • If you are working with a strong base and your fingers feel slippery like soap, wash them immediately! • This slippery feeling comes from the base reacting with the oils in your skin, converting them to soaps. • This property is why bases are often used as cleaning agents (ammonia) • Alkali metals react with water VIOLENTLY to produce bases. They are very reactive and will actually react with the water in the air to form hydroxides. • These solutions are said to be basic or alkaline.

8. Strong Vs. Weak Bases • Acids generate the ___________ ion, bases generate the hydroxide, or OH- ion. • A strong base is a base that ionizes completely in a solvent. This solvent can be water or, if the base is insoluble in water, a ____________ solvent may be used. • A weak base is a base that releases few hydroxide ions in aqueous solution. • Example: Ammonia

9. Weak Bases • Weak bases, like ammonia, also DO NOT completely dissociate: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) • A few of the ammonia molecules react with water to reach equilibrium. • The vast majority of ammonia molecules, however, remain un-ionized at any given time.

10. BrØnsted-Lowry Classification • BrØnsted-Lowry acids donate protons • Any species that donates a proton can be called an acid by this definition. HCl + H2O  H3O+ + Cl- • This can also be thought of as: HCl H+ + Cl- Followed by H+ + H2O  H3O+

11. BrØnsted-Lowry Classification • BrØnsted-Lowry bases accept protons • Any species that accepts a proton can be called a base by this definition. • Ammonia serves as the proton acceptor and is therefore the BrØnsted-Lowry base. NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

12. Conjugate Acids and Bases • When considering BrØnsted-Lowry acids and bases, an acid-base reaction is very simple: One molecule or ion passes a proton to another molecule or ion. • Whatever loses the proton in the ____________ and whatever gains the proton is the ____________ . NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) • The water donates the proton to ammonia so it is an acid. The ammonia then is going to be the ___________ because it _____________ the proton.

13. Conjugate Acids and Bases • The conjugate acid is the acid that forms when a base gains a proton. • The conjugate baseis the base that is formed when an acid loses a proton. NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) • The ammonia is the base, the water is the acid. • The Ammonium ion is the __________________ and the hydroxide ion is the __________________ . Conj Acid Conj Base Base Acid

14. Amphoteric Substances • The term amphoteric describes a substance, such as water, that has the properties of an acid and the properties of a base. • Usually just depends on who it is with and what role needs to be played. • These species can donate AND accept a proton when needed. • The hydrogen carbonate ion, HCO3-, is amphoteric in aqueous solution.

15. Amphoteric Substances HCO3-(aq) + NH3(aq) CO32-(aq) + NH4+(aq) • Hydrogen carbonate acts as an acid here with ammonia (a base). Donates a proton to the NH3 HCO3-(aq) + H3O+(aq) H2CO3(aq) + H2O(l) • Hydrogen carbonate acts as a base here with hydronium (an acid). Accepts a proton to the H3O+ ion Conjugate Acid Base Conjugate Base Acid Conjugate Base Conjugate Acid Base Acid

16. Water • Water itself is amphoteric. • A water molecule can donate a proton and become a hydroxide ion in the process. • It can also accept a proton to become a hydronium ion. • This is why water is the product of the N.I.E. of an acid-base neutralization reactions (DBL displacements with an acid and a base).

17. Continue looking over the notes and tests for the EXAM coming up. • Vocab sheet due Monday!!