Acids & Bases Chapter 16

Electrolyte - substance which conducts electricity when dissolved in water examples strong: HCl(hydrochloric acid), NaCl(salt) weak: HC2H3O2(vinegar), NH3(ammonia) Nonelectrolyte - substance which does not conduct electricity when dissolved in water

Why do electrolytes do this? When an ionic compound dissolves in water, the ions dissociate. As a result, you get free-flowing ions in the aqueous solution

Dissociation - process through which ionic solids separate into free flowing ions in water solution 1. NaCl(s) Na+1(aq) + Cl-1(aq) 2. Na2SO4(s) 2 Na+1(aq) + SO4-2(aq) *Note the sulfate does not split

Try It On Your Own (NH4)3PO4(s)  Pb(NO3)2(s) 

Ionization - formation of ions caused by the reaction of a molecular compound with water Example: HC2H3O2(aq) + H2O(l) C2H3O2-1(aq) + H3O+1(aq) - hydronium ion = H3O+1

Properties of Acids & Bases Section 16.1

Acids were first recognized as substances that taste sour. Bases, sometimes called alkalis, are characterized by their bitter taste and slippery feel.

The Arrhenius Model Svante Arrhenius On the basis of his experiments with electrolytes He postulated that acids produce hydrogen ion in aqueous solution, whereas bases produce hydroxide ions.

Arrhenius Acid - molecular substance which produces H+ (or H3O+) ions when it reacts with water HCl(g)  H+ + Cl-1 H2CO3(aq)  H+ + HCO3-1 Note only one hydrogen (H+) comes off in this process HCO3-1(aq)  H+ + CO3-2 Note that no (aq) is required; all ions by definition can only exist in aqueous solution

The Bronsted-Lowry Model Danish chemist Johannes Bronsted & English chemist Thomas Lowry. In the Bronsted-Lowry model, an acid is a proton (H+) donor, and a base is a proton acceptor.

Label the Lowry-Bronsted acids and bases: HCl(aq) + H2O(l)  H3O+1(aq) + Cl-1(aq) A B A B Note that HCl is the acid because it donates a proton to become Cl-1. Similarly, Cl-1 accepts a proton to become HCl, so it is the base.

Conjugate Acid-Base Pairs - pairs within a Lowry-Bronsted acid/base reaction that differ by one proton HCl, Cl-1 H3O+1, H2O NH4+1, NH3 H2O, OH-1 HNO3, NO3-1 HC2H3O2, C2H3O2-1

The general reaction that occurs when an acid is dissolved in water can best be represented as an acid (HA) donating a proton to a water molecules to from a new acid (conjugate acid ) and a new base (conjugate base)

Amphoteric substance - acts as both an acid and a base in different situations; examples from above? Water (H2O) is an amphoteric substance because it acts as a base in T#1, and an acid in T#2

Acid Strength Strong Acid – An acid that completely dissociates to produce H+ ions in solution. Weak Acid – An acid that dissociates to a slight extent in aqueous solution.

A strong acid contains a relatively weak conjugate base – one that has a low attraction for protons.

Strong Acid

Weak Acid

Kw – The Ion –Product Constant for water [H+][OH-] = 1.0 x 10 ^-14 = Kw at 25 ⁰C The product of [H+][OH-] must always be equal to1.0 x 10 ^-14

Determining the Acidity of a Solution Section 16.2

The pH Scale Because the pH scale is a log scale based on 10, the pH changes by 1 for every power of 10 change in the [H+]

pH pH = -log[H+] Steps for calculating pH 1. Enter (-) 2. Press the log key 3. Enter the [H+] The number of decimal places for a log must be equal to the number of significant figures in the original number.

pOH pOH = -log [OH-] Once you have taken the –log[OH-] then you must find the pH. pH + pOH = 14.00 pOH = 14.00 - pH

Steps for Calculating [H+] from pH Take the inverse log (antilog) by using 2nd log keys in that order. Enter (-) Enter the pH

Measuring pH Indicators – A chemical that changes color depending on the pH of solution. Indicator Paper – A strip of paper coated with a combination of acid-base indicators. pH meter – A device used to measure the pH of a solution.