Acids and Bases Unit 13

Transcription

1 Acids and Bases Unit 13

2 Chemistry of Acids and Bases 1. Watch video and complete worksheet Standard Deviants Teaching Systems: Chemistry: Module 05: Acids and Bases Guid/DBD191DB-A10E-43C2-8DDE-A73858F12FE2 2. Gallery walk to complete notes on pages 3-5 in packet 3. Homework is on page 6 in packet

3 Unit 13 Acids and Bases Notes #1: Intro Acids: Something that produces a hydrogen ion (H + ) in solution

4 Unit 13 Acids and Bases Notes #1: Intro Properties of Acids: Tart or sour taste (lemon juice) Electrolytic Both strong and weak Will cause indicators to change colors A metal + an acid will produce hydrogen gas Single replacement reaction Acid + metal hydrogen gas + a salt Double replacement reaction Acid + Base water + a salt

5 Single replacement reaction Acid + Metal Hydrogen gas_ + a _salt_ Double replacement reaction Acid + Base _water + a _salt_

6 Remembering Acid Naming Rules Handle acids carefully so you don t get a case of ate-icite-ous. ION Polys TYPEending ION in ENDING -ate are changed ACID NAME to -ic BEGINNING ACID ENDING Polys ending in -ite -ite are charged NO hydroto -ous beginning -ous Polyatomic -ate NO hydro- beginning -ic Monatomic -ide hydro- beginning -ic Hydro- prefix is not used with poly containing acids!!!!!

7 Examples of Naming Binary Acids HCl Hydrochloric acid HF HBr Hydrofluoric acid Hydrobromic acid

8 Examples of Naming Ternary Acids H 2 SO 4 H 2 CO 3 Sulfate is the poly, so sulfuric acid H 2 NO 2 carbonate is the poly, so carbonic acid Nitrite is the poly, so nitrous acid

9 Base: Something that produces a hydroxide ion (OH - ) in solution

10 Unit 13 Acids and Bases Properties of Bases: bitter slippery (soap) electrolytic Both strong and weak Will cause an indicator to change colors

11

12 Naming Bases The easiest are the bases, since most of these are _metal hydroxides, compounds you already know how to name. Metal hydroxides are named in the same way any other ionic compound is named. First give the name of the _metal_ ion. Follow this with the name of the anion, which, in the case of bases, is hydroxide. KOH Potassium Hydroxide Mg(OH) 2 Magnesium Hydroxide

13 Other definitions of Acids and Bases Arrhenius Acids and Bases: Acid: Hydrogen containing compound that ionize to yield a hydrogen ion in solution. Base: Compounds that ionize to yield a hydroxide ion in solution.

14 Brønsted Lowry Acids and Bases They felt the Arrhenius definition was too limiting. Acids: Hydrogen ion donor (Proton donor) Bases: Hydrogen ion acceptor (Proton acceptor)

15 Brønsted Lowry Acids and Bases Examples: NH 3 + H 2 O NH 4+ + OH - H 2 O donated the H + - Acid NH3 accepted the H + - Base HCl + H 2 O H 3 O + + Cl - HCl donated the H + - Acid H 2 O accepted the H + - Base

16 Amphoteric: Substance that can act as both an acid or a base. o Background Theory: The oxides of metals are basic in nature. For example, the oxides of the alkali metals (Group I) form alkali or basic solutions. Sodium oxide + water Sodium hydroxide solution Na 2 O(s) + H 2 O(l) NaOH(aq) o o The soluble oxides of non-metals are acidic in nature. Examples include, carbon dioxide, sulfur dioxide and nitrogen dioxide. Sulfur dioxide + water Sulfurous acid SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) Insoluble non-metallic oxides like carbon monoxide do not form acidic solutions. This is often the cause of acid rain. Compounds such as the amino acids, which contain both acidic and basic groups in their molecules, can also be described as amphoteric.

17 Strong Acids and Bases Strong Acids/Bases: Those that ionize completely in solution. Ex: HCl, NaOH Weak Acids/Bases: Those that only slightly ionize in solution. Ex: NH 3, Acetic Acid (vinegar) Tooth decay is caused by the weak acid lactic acid: C 3 H 6 O 3

18

19

20 Homework: pg 6

21 The ph Scale pg 7-

22 ph Scale

23 MEASURING ph Scientists use a ph scale to measure the strength of an acid or base. The term ph stands for potential for hydrogen. The amount of hydrogen in a substance determines its acidity or alkalinity. Alkaline is another term for base. A number on the ph scale is used to describe the strength of acidity or alkalinity. The most commonly used ph scale goes from 1 (very acidic) to 14 ( very basic). The number 7 on a ph scale means neutral neither acid nor base. Acids play important roles in the chemistry of living things. Many of the foods you eat are acids in vitamins like ascorbic acid or vitamin C, and folic acid. Other acids help the body such as stomach acids and others are waste products of cell processes like lactic acid in working muscles. Acids also are used to make valuable products for homes, farms and industries. People often use dilute solutions of acids to clean brick and other surfaces. Hardware stores sell muriatic (hydrochloric ) acid, which is used to clean bricks and metals. Industry uses sulfuric acid in car batteries, to refine petroleum and to treat iron and steel. Farmers depend on the nitric acid and phosphoric acid to make fertilizers for crops, lawns, and gardens.

24 The concentration of hydrogen ions in a solution is described by its number on the ph scale. A low ph tells you that the concentration of hydrogen ion is high. EX: ph 2 By comparison, a high ph tells you that the concentration of hydrogen ion is low. EX: ph 12

25 Self-ionization of water Self-ionization of water: Reaction in which 2 water molecules produce ions H 2 O + H 2 O OH - + H 3 O + Also written as: H 2 O H + + OH - The H 3 O + and H + represent hydrogen ions in solution.

26 Neutral Solutions In pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions 1 x 10-7 M or ph of 7 Remember M represents Molarity [H + ] = [OH - ] (brackets represent concentration) This represents a neutral solution.

27 Solutions In a solution, if the [H + ] increases, the [OH - ] decreases and vice versa. Think back to a see-saw. As one person went up the other went down. Ion-product constant of water, Kw: Kw = [H + ] x [OH - ] = 1 x M Acidic Solution: The [H + ] will be greater than the [OH - ]. Therefore, the [H + ] is greater than 1 x 10-7 M. Think about the # line. -5 is GREATER than -7 Basic Solution: The [H + ] will be less than [OH - ]. Therefore, the [H + ] is less than 1 x 10-7 M. A.k.a. alkaline solutions

28 NUMBER LINE and ph Remember the number line Increasing -7 Which is greater? 0 or Which is greater? -7 or -4-4 Which is less? -2 or

29 Acids Bases

30 Homework pg. 9

31 ph Calculations The ph scale ranges from = very acidic 7 = neutral 14 = very basic ph = -log [H + ] What is the ph of a neutral solution? Calculate using the Logarithmic function on the calculator (see at right)

32 Sample Problems As long as you have a 1 x 10 to some power, the ph is the exponent. 1. What is the ph of the following concentrations? a. [H + ] = 1 x 10-2 M b. [H + ] = 1 x 10-9 M c. [H + ] = 1 x 10-5 M ph = 2 acidic ph = 9 basic ph = 5 acidic

33 Sample Problems If you do not have 1 to the power then you MUST use our formulas. 2. What is the ph of the following? a. [H + ] = 2x10-2 ph = -log(2x10-2 ) = 1.7 ph b. [H + ] = 6x10-9 ph = -log(6x10-9 ) = 8.2 ph c. [H + ] = 3x10-5 ph = -log(3x10-5 ) = 4.5 ph

34 Other Formulas and Problems ph 14 = ph + poh (See example 1 in Example Problems)) Equilibrium constant labeled as Kw Kw is 1x10-14 K w = [OH - ] x [H + ] = 1x10-14

35 Other Formulas and Problems EX: What is the ph of a solution with a [OH - ] of 4.0 x M? o Use K w to find [H + ] then find ph using log function. Step1: Kw = [OH - ] x [H + ] = 1x10-14 [H+] = 1x10-14 /4x10-11 = 2.5x10-4 Step 2: ph = -log [H+] ph= -log(2.5x10-4 ) = 3.6

36 1. If ph = 5, poh = ph 14 = ph + poh 14 = 5 + poh 14 5 = 9 poh Acid because ph = 5

37 2. What is the ph of a solution that has a hydrogen ion concentration of 1.0 x 10-5 M? Is this solution acidic, basic or neutral? Given: [H + ] Solving for: ph ph = - log [H + ] ph = - log(1.0 x 10-5 M) ph = 5 ph < 7 ACIDIC

38 3. What is the hydrogen ion concentration of a solution with a ph of 11? Which has a greater concentration: H + or OH -? [H + ] = 1 x M more OH -, So basic

39 4. What is the ph of a solution that has a hydrogen ion concentration of 1.2 x 10-8 M? Is this solution acidic, basic or neutral? Given: [H + ]Solving for: ph ph = - log [H + ] ph = - log(1.2 x 10-8 M) ph = 7.92 ph > 7 BASIC

40 5. Assuming Kw = 1x10-14, calculate the molarity of OH - in solutions at 25ºC when the H + concentration is 0.2M At 25ºC, Kw = [OH - ] [H + ] = 1x x10-14 = [OH - ] 0.2M = 1x10-14 /.2 [OH - ] = 5x10-14 M

41 HOMEWORK: pg 12

42 Neutralization Notes Acid-Base reactions will produce salt water when completely neutralized. Salts are compounds consisting of a(n) anion from an acid and a(n) cation from a base. In general, reactions in which an acid and a base react in an aqueous solution to produce a salt and water is called Neutralization Reactions.

43 Neutralization Reactions Neutralization occurs when an Acid + Base water + salt Salt: Anion from acid and the cation from the base join together to form a salt. Where do we see this process? Antacids Farmers controlling the ph of soil Formation of caves

44 A strong acid + a strong base = neutral solution Examples: HCl + NaOH H 2 O + NaCl HCl + KOH H 2 O + KCl

45 Practice: Don t forget to balance them after you write them. HCl + LiOH HOH + LiCl HNO 3 + CsOH CsNO 3 + H 2 O HBr + KOH H 2 O + KBr

46 Titrations Titration: The process of adding a known amount of solution of known concentration to determine the concentration of the other solution. If you don t know the concentration of one solution, you can figure it out by performing a neutralization reaction, or titration, with a standard solution. A standard solution is one of known concentration.

47 Performing Titrations Steps in a neutralization reaction: 1. A measured volume of an acid solution of unknown concentration is added to a flask. 2. Several drops of indicator are added to the solution. 3. Measured volumes of a base with a known concentration are mixed into the acid until it barely changes color.

48 Performing Titrations, cont. End Point: The point at which the indicator changes color. Once you have reached the end point, you can perform calculations to find the unknown solution. Let s show a video! Ntt=titration## DJ730

49 Performing Titrations, cont. Example: A 25 ml solution of H 2 SO 4 is completely neutralized by 18 ml of 1.0 M NaOH. What is the concentration of H 2 SO 4 solution? Step 1: Balanced equation 2 2 H 2 SO 4 + NaOH Na 2 SO 4 + H 2 O Step 2: Use formula to solve for unknown. M a V a n a = M b V b n b n a = Number of moles of your Acid (coefficient) n b = Number of moles of your Base (coefficient) M = Molarity of acid or base V = Volume of acid or base (in Liters)

50 M a V a n a = M b V b n b Ma ( 25 ml) = (1.0 M)( 18 ml) 1 mol 2 mol Molarity = 0.36 M

51 1. How many moles of HCl are needed to neutralize 6 mols of KOH? 1 st ask, what is the mol ratio and then set it up as a proportion. HCl + KOH KCl + H 2 O This equation is balanced so 1 mole HCl = 1 mole KOH So 6 mols KOH will neutralize 6 moles HCl

52 2. H 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O a. One mole of sulfuric acid is needed to neutralize 2 moles of NaOH. b. How many moles of NaOH are needed to neutralize 4 moles of H 2 SO 4? Given that 1 H 2 SO 4 = 2NaOH So if you have 4 mols H 2 SO 4 you will need 8 moles NaOH

53 Homework pg 17 Also begin working on your Review on pages: 18-21