Acids, Bases, and Salts

Properties of Acids Conduct electricity when in aqueous solution. Taste tart or sour Conduct electricity when in aqueous solution. Can be strong or weak electrolytes in aqueous solution React with metals to form H2 gas. React with bases (hydroxides) to form water and a salt. Ex: Vinegar (acetic acid), citric acid

Properties of Acids Blue litmus paper turns red in contact with an acid.

Properties of Acids Acids have a pH less than 7

Properties of Bases Taste bitter. Feel slippery Conduct electricity when in aqueous solution. -Can be strong or weak electrolytes in aqueous solution React with acids to form water and a salt Ex: Sodium hydroxide (lye or Drano), Magnesium hydroxide (Milk of Magnesia) Calcium hydroxide (lime water)

Properties of Bases Red litmus paper turns blue in contact with a base. Phenolphthalein turns pink in a base. Reference Table M

Bases have a pH greater than 7 Properties of Bases Bases have a pH greater than 7

Bases neutralize Acids Properties of Bases Bases neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2H2O Acid Base Notice – a salt and water

Hydrogen Ions from Water HOH ↔ H+ + OH- At room temperature the molar concentration: hydrogen ions = 1 x 10-7 M hydroxide ions = 1 x 10-7 M In pure water the concentration of H+ and OH- are equal An aqueous solution in which [H+] and [OH-] are equal is a neutral solution

Hydrogen Ions from Water HOH ↔ H+ + OH- Acidic solution [H+] is greater than [OH-] [H+] of an acidic solution is greater than 1 x 10-7 M Basic solution (AKA alkaline solution) [H+] is less than [OH-] [H+] of an alkaline solution is less than 1 x 10-7 M

pH means power of hydrogen The pH Scale The pH scale was devised to easily show how acidic or basic a solution is. Used to express the hydrogen ion concentration pH means power of hydrogen pH : [H+] : [OH-] : more acidic pH : [H+] : [OH-] : more basic or alkaline.

100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 [H+] 1 3 5 7 9 11 13 14 pH Acidic Neutral Basic 1 3 5 7 9 11 13 14 pOH Basic 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 [OH-]

The pH Scale In an acidic solution, pH < 7 In a basic solution, pH > 7 pH = -log[H+] pH = -log(1 x 10-7) pH = 7 pH = -log(1 x 10-9) pH = 9

Practice with the pH Scale What is the pH of a solution with [H+] = 1 x 10-2? What is the [H+] of a solution with a pH of 8? What is the [H+] of a solution with a pH of 9? The concentration of H+ in a solution with a pH of 8 is ___ times greater than the H+ concentration in a solution with a pH of 9? The [H+] in a solution with a pH of 2 is ___ times greater than the [H+] in a solution with a pH of 4? 2 1 x 10-8 1 x 10-9 10 100

Measuring pH Indicators Substances that change color Why measure pH? Maintaining proper acid-base balance in swimming pools, creating proper soil conditions for plant growth, and making medical diagnosis How do we measure pH? Sometimes we can use indicators, other times we might need a pH meter Indicators Substances that change color to show whether a substance is an acid or base See Reference Table M for a list of Indicators

Measuring pH 2. Compare the color to the chart on the vial – read the pH value. 1. Moisten indicator strip with a few drops of solution, by using a stirring rod.

Neutralization Reactions Remember, in a neutral solution [H+] = [OH-] So, if I mix a strong acid containing a certain number of H+ ions with strong base that has an equal number of OH- ions, a neutral solution results Strong Acid with: 1000 H+ ions Strong Base with: 1000 OH- ions [H+] = [OH-]: Neutral solution HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O (l)

Neutralization Reactions Neutralization reactions produce water and a salt. Acid + Base  Water + Salt The salt forms from an anion from the acid and a cation from the base. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O (l) water base salt acid base water acid salt

Applications of Neutralization Reactions Properties related to every day: Antacids depend on neutralization Farmers use these reactions to control soil pH Human body kidney stones from insoluble salts from neutralization reactions Acid + Base  Water + Salt

Titration We use neutralization reactions to determine the concentration of an acid (or base) in a solution. Remember that indicators indicate the pH by the color they turn. Often we use phenolphthalein It is colorless in neutral and acidic solutions Pink in basic solutions

How to Titrate an Unknown Acid A titration is a neutralization reactions. Here’s how it works: Notice it’s clear I have .2 liters of NaOH (base) but I don’t know how concentrated it is… …in other words I don’t know its molarity (moles/liter)

How to Titrate an Unknown Base Dropper with phenolphthalein I want to know the molarity of this base, so I do a titration… Step 1: Add a few drops of phenolphthalein This solution is basic, so it will turn pink when I add phenolphthalein Notice it’s pink

How to Titrate an Unknown Base Step 2: Using a burette filled with a acid, slowly add acid to the beaker I need to know the molarity of the acid. I need to know the volume of the acid. Lets use 1 molar HCl for this example Burette filled with a acid (1M HCl)

How to Titrate an Unknown Base Step 3: When the solution in the beaker just barely changes color – STOP you have just reached the equivalence point (moles of H+ = moles of OH-) What does the (just barely) color change mean? Solution has just barely reached the point where it is not longer basic, it is neutral, but not acidic Remember: phenolphthalein will change to colorless to indicate a neutral or acidic solution Burette filled with an acid (1M HCl)

How to Titrate an Unknown Acid Burette filled with a acid (1M HCl) Step 4: Record how much of the acid went from the burette into the beaker. For this example, let’s say I used .15 liters of HCl Step 5: Use the titration equation to determine the molarity of the unknown base

Titration Equation MAVA = MBVB MH+VH+ = MOHVOH This equation is found on Table T MAVA = MBVB MA = MAcid = molarity of H+ MB = MBase = molarity of OH- The equation is actually MH+VH+ = MOHVOH

Titration Equation MH+VH+ = MOHVOH In the above equation the M values are for [H+] & [OH-] not the molarity of the acids or bases

Using Titration Equation for our Example Remember: I used .15L of 1M HCl (acid) to neutralize .2L of ? M NaOH (base) MH+VH+ = MOHVOH (1M)(.15L) = (MOH)(.2L) (.15) = .2MOH .15 / .2 = MOH .75 moles of OH- per liter of solution The base is NaOH, there is: 1 “OH” in every 1 “NaOH” so… It is also .75 moles of NaOH per liter

moles of H+ vs moles of Acid moles of OH- vs moles of Base Some acids have two or more moles of H+ for every mole of acid. H2SO4 has 2 moles of H+ for every 1 mole H2SO4 Thus, 1.0M H2SO4 has 2.0M H+ The same is true for bases. Ba(OH)2 has 2 moles of OH- thus 1.0M Ba(OH)2 has 2.0M OH-

Titration Practice Problem If 15.0 ml of 2.00M H2SO4 titrates 3.00M NaOH, what was the volume of NaOH? MH+VH+ = MOHVOH (4)(15) = (3)(VOH) (60) = (3)(VOH) 60/3 = VOH 20mL = VOH 2.00M H2SO4 has 4.00 MH+ because every 1 mole H2SO4 has 2 moles H+. Likewise, every 1 mole NaOH has only 1 mole OH-. FOR THIS PROBLEM - Molarity of NaOH solution is same as Molarity of OH-

Titration Practice Problem If 25.0 ml of 2.00M HCl titrates 30.0ml of NaOH, what is the molar concentration of NaOH? 2.00M HCl has 2.00 MH+ because every 1 mole HCl has 1 mole H+. Likewise, every 1 mole NaOH has 1 mole OH-. FOR THIS PROBLEM - Molarity of solution is same as Molarity of H+ and OH- (25 ml)(2.00 M) = (30 ml)(x) x = 1.67M ANSWER: 1.67 MOH- = 1.67 moles OH-/ 1 Liter

Naming Acids Binary Acids Ternary Acids Hydro – anion name – ic acid ex: HF hydrofluoric acid Ternary Acids Named for the polyatomic anion -ate ending becomes –ic -ite ending becomes –ous ex: Sulfuric acid

Videos *Intro video (1:24 min): http://www.youtube.com/watch?v=S7CsO3p5t5M Acids & Bases with Hannah & Kelsie (~3 min): http://www.youtube.com/watch?v=6fZ2OJ-HNr0&feature=related Puppet Acid & base Video(6:56 min): http://www.youtube.com/watch?v=4cL1kmjASbY Richard Thorpe Acids & Bases: (~3:30 min): http://www.youtube.com/watch?v=JCcpWMW-SzY&feature=related *Rainbow Connection with the Muppets(~3:22 min): (man) http://www.youtube.com/watch?v=lCrMB8341rU (female) http://www.youtube.com/watch?v=IUAa0usLZeU&feature=related Acid / base Indicators: http://www.youtube.com/watch?v=6Y4Y-__ME60 (4:11 min) How to do a Titration Experiment(~2min): http://www.youtube.com/watch?v=r1uEXOOR2nU&feature=related World of Chemistry (the Proton in Chemistry (29:05 min): http://www.learner.org/resources/series61.html# *Neutralization reaction: http://www.youtube.com/watch?v=8IRI5gPR5EY (59 sec0 Acid / base Neutralization: http://www.youtube.com/watch?v=enPG0vkn4QA (3:23 min) Acid & Bases have two different Faces: http://www.youtube.com/watch?v=zTLiJE-j1-I (3:26 min) Titrating an Acid http://www.youtube.com/watch?v=6woC_HSVtmQ (3:22 min) *Titration of an Acid http://www.youtube.com/watch?v=yNSE_xa5lfA (1:22 min) How to Perform a titration: http://www.youtube.com/watch?v=YDzzMcrdyB4 (6:07 min) Cool Universal Indicator Video http://www.youtube.com/watch?v=TXA9NNLrQFc (1:52 min)