Acids Bases Chapter 16 Electrolyte substance which conducts

Acids & Bases Chapter 16

� Electrolyte - substance which conducts electricity when dissolved in water � examples › strong: HCl(hydrochloric acid), Na. Cl(salt) › weak: HC 2 H 3 O 2(vinegar), NH 3(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. Na. Cl(s) Na+1(aq) + Cl-1(aq) › 2. Na 2 SO 4(s) 2 Na+1(aq) + SO 4 -2(aq) �*Note the sulfate does not split

Try It On Your Own � (NH 4)3 PO 4(s) � Pb(NO 3)2(s)

� Ionization - formation of ions caused by the reaction of a molecular compound with water › Example: › HC 2 H 3 O 2(aq) + H 2 O(l) C 2 H 3 O 2 -1(aq) + H 3 O+1(aq) - hydronium ion = H 3 O+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 H 3 O+) ions when it reacts with water › HCl(g) H+ + Cl-1 › H 2 CO 3(aq) H+ + HCO 3 -1 �Note only one hydrogen (H+) comes off in this process › HCO 3 -1(aq) H+ + CO 3 -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) + H 2 O(l) H 3 O+1(aq) + Cl-1(aq) 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 H 3 O+1, H 2 O NH 4+1, NH 3 H 2 O, OH-1 HNO 3, NO 3 -1 H 3 O+1, H 2 O HC 2 H 3 O 2, C 2 H 3 O 2 -1 H 2 O, OH-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 (H 2 O) 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-] equal to 1. 0 x 10 ^-14 must always be

Determining the Acidity of a Solution Section 16. 2

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

p. H � p. H = -log[H+] � Steps for calculating p. H › 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.

p. OH � p. OH = -log [OH-] � Once you have taken the –log[OH-] then you must find the p. H. › p. H + p. OH = 14. 00 › p. OH = 14. 00 - p. H

Steps for Calculating [H+] from p. H Take the inverse log (antilog) by using 2 nd log keys in that order. 2. Enter (-) 3. Enter the p. H 1.

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