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Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases.

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Presentation on theme: "Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases."— Presentation transcript:

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2 Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases

3 Bitter! Some foods have a “bite” of their own because they’re somewhat bitter. WHY?

4 Acidic/Basic There is a scientific reason for this: These foods are either acidic or basic. Other substances besides foods have these characteristics.

5 Acids and Bases Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral. pH measures how acidic or basic a solution is.

6 Acids Often taste sour Strong acids can burn skin & eyes Strong acids can dissolve metals Examples: Lemon juice Vinegar Car battery acid (dangerous!)

7 Bases Can taste bitter, sweetish, or salty Strong bases can burn skin & eyes Bases react more easily with protein than with metal; they are often used for cleaning Examples: Milk Baking soda Soap Drain cleaner (dangerous!)

8 Some substances are not really an acid or a base: For example, pure water

9 Acids are easy to recognize as compounds as they begin with the element hydrogen. As with other ionic bonds, acids fall into 2 categories, binary and ternary. The Nomenclature of ACIDS

10 Examples of binary acids would include things like: HF, HI, H 2 S and HCl Examples of ternary acids would include things like: H 2 SO 4 and HNO 3 The Nomenclature of ACIDS

11 Naming of binary acids Step 1:Name the anion, changing the ending to “-ic” Step 2: Add the prefix “hydro-” Step 3: Slap acid on the end The Nomenclature of ACIDS

12 Example #1: HF Example #1: HF The Nomenclature of ACIDS “fluorine” becomes “fluoric” becomes “fluoric” becomes “hydrofluoric” becomes “hydroflouric acid”

13 Naming of ternary acids Step 1:Name the polyatomic Step 2: Change “-ate” to “-ic” or “-ite” to “-ous” Step 3: Slap acid on the end The Nomenclature of ACIDS

14 “sulfuric acid” “sulfuric” becomes “sulfuric” becomes “sulfate” becomes Example #1: H 2 SO 4 Example #1: H 2 SO 4 The Nomenclature of ACIDS

15 Rules for Writing Formulas for binary acids Step 1: Does the name begin with “hydro-”? If yes, then… Step 2:Write the symbol for the hydrogen ion followed by the symbol for the second element Step 3: Crisscross the charges and write them as subscripts. The Nomenclature of ACIDS

16 Rules for Writing Formulas for binary acids Example: hydrosulfuric acid The Nomenclature of ACIDS

17 Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H +1 S -2 The Nomenclature of ACIDS

18 Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H +1 S -2 The Nomenclature of ACIDS

19 Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H +1 S -2 H2SH2S The Nomenclature of ACIDS

20 Rules for Writing Formulas for ternary acids Step 1: Does the name begin with “hydro-”? If no, then… Step 2:Write the symbol for the hydrogen ion followed by the appropriate polyatomic ion Step 3: Crisscross the charges and write them as subscripts. The Nomenclature of ACIDS

21 Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature of ACIDS

22 Rules for Writing Formulas for binary acids Example: sulfuric acid H +1 SO 4 -2 The Nomenclature of ACIDS

23 Rules for Writing Formulas for binary acids Example: sulfuric acid H +1 SO 4 -2 The Nomenclature of ACIDS

24 Rules for Writing Formulas for binary acids Example: sulfuric acid H +1 SO 4 -2 H 2 SO 4 The Nomenclature of ACIDS

25 1. HI 2. phosphoric acid 3. hydrobromic acid 4. H 2 SO 3 Name the chemical or write the symbol The Nomenclature of ACIDS

26 hydroiodic acid phosphoric acid 3. hydrobromic acid 4. H 2 SO 3 Name the chemical or write the symbol The Nomenclature of ACIDS

27 H 3 PO 4 hydroiodic acid hydrobromic acid 4. H 2 SO 3 Name the chemical or write the symbol The Nomenclature of ACIDS

28 HBr H 3 PO 4 hydroiodic acid H 2 SO 3 Name the chemical or write the symbol The Nomenclature of ACIDS

29 sulfurous acid HBr H 3 PO 4 hydroiodic acid Name the chemical or write the symbol The Nomenclature of ACIDS

30 pH Scale We use this scale to measure the strength of an acid or base. pH is defined as the –log[H+] pH can use the concentration of hydronium ions or hydrogen ions.

31 pH Scale Acid Base Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 515

32 pH of Common Substances Timberlake, Chemistry 7 th Edition, page 335

33 The pH Scale pH scale ranges from pH 7 is neutral; neither acid nor base Pure water is pH 7 Low pH (0-6.9) = acid High pH (7.1-14) = base The closer to the ends of the scale, the stronger the solution is

34 Acid Any substance which has a pH of value of less than 7 is considered an acid Acid Neutral Base

35 Base Any substance which has pH value greater than 7 is a base Acid Neutral Base

36 pH 7 A pH of 7 is called neutral—neither acid nor base Acid Neutral Base

37 The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10x100

38 The pH Scale Careful measurement is important A mistake of one pH unit means 10 times too much or too little! x10x100

39 How Do We Measure pH? One way to measure pH is by using special strips of paper called pH paper

40 How Does It Work? The paper is treated with chemicals (indicators) that change color to show the pH. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.

41 To Use pH Paper Place the edge of the pH paper into the mixture. Observe the color change of the pH paper Match the resulting color to the colors listed on the outside of the pH paper package. The colors match with a correlated pH number. The number is the pH value of the sample.

42 A)The Oldest Theory is the Arrhenius Theory Historical views on acids

43 Arrhenius looked at the substances which were called acids. Some of these substances were known from even before the days of alchemy. They taste sour, turn blue litmus to red, neutralize bases, release hydrogen gas when added to an active metal and release carbon dioxide when added to a carbonate. Arrhenius said these properties were due to the production of H + ions when acids dissolve in water.

44 He looked at the properties of bases. They taste bitter, feel slippery (soapy), turn red litmus blue and neutralize acids. Arrhenius said these properties were due to the production of OH- ions when bases are dissolved in water.

45 Historical views on acids Ionization + ClH H H O + H H HO + O 2 found in oxyacids (e.g. H 2 SO 4 ) was originally thought to cause acidic properties. Later, H 2 was implicated, but it was still not clear why CH 4 was neutral. Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H 2 + ions in solution.

46 Historical views on acids The more recent Bronsted-Lowry concept is that acids are H + (proton) donors and bases are proton acceptors + ClH H H O + H H HO +

47 The Bronsted-Lowry concept In this idea, the ionization of an acid by water is just one example of an acid-base reaction. Acids and bases are identified based on whether they donate or accept H +. “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H +. + ClH H H O + H H HO + acidbase conjugate acidconjugate base conjugate acid-base pairs

48 Today we know that a bare proton does not exist in water, it forms a chemical bond with a water molecule forming the H 3 O +. This ion is called the hydronium ion. The Bronsted-Lowry concept H 2 O   H 3 O + + OH - “Pure” water is always a dynamic mixture of these three substances in equilibrium

49 1) A B/L acid is the species which donates a proton in a proton transfer reaction. What is meant by a proton here? 2) A B/L base is the species which _________. 3) A B/L acid is the species which _________ The Bronsted-Lowry concept

50 4) A specific strong acid - base reaction: HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) HCl (aq) is the ___________________. H 2 O (l) is the ________________. H 3 O + (aq) is the ________________________. Cl - (aq) is the _________________________.

51 CH 3 COOH is the _____________________. H 2 O is the _________________________. H 3 O + is the ____________________. CH 3 COO - is the _____________________.

52 Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 – (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH – (aq) + HCO 3 – (aq)  CO 3 2– (aq) + H 2 O (l) conjugate acid-base pairs

53 1. HF (aq) + SO 3 2– (aq) 2.CO 3 2– (aq) + HC 2 H 3 O 2 (aq) 3. H 3 PO 4 (aq) + OCl – (aq) OYO Practice

54 acidbase conjugate acidconjugate base HF (aq) + SO 3 2– (aq)  F – (aq) + HSO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2– (aq) + HC 2 H 3 O 2 (aq)  C 2 H 3 O 2 – (aq) + HCO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl – (aq)  H 2 PO 4 – (aq) + HOCl (aq) conjugate acid-base pairs Answers: OYO Practice

55 Reaction Types Neutralization Reaction – a special double replacement reaction in which an acid is combined with a base and yields water and a salt. HCl + NaOH  NaCl + H 2 O HCl + NaOH  NaCl + H2O

56 Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is neutral Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color 4.7 End point – the point at which the reaction becomes complete

57 What volume of a M NaOH solution is Required to titrate mL of a 4.50 M H 2 SO 4 solution? WRITE THE CHEMICAL EQUATION! H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 M a x V a = M b x V b


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