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ACIDS & BaseS

Learn about the pH scale, importance in agriculture, common substances, acid-base theories, properties of acids and bases, pH calculations, and how pH and pOH relate. Discover the significance of [H+] in solutions.

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ACIDS & BaseS

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  1. ACIDS & BaseS

  2. What is the pH Scale? • A scale which measures the degree of acidity or alkalinity of an aqueous solution. • Ranges from 0 – 14.

  3. Importance of pH: • pH of soil • pH of tank • pH of food

  4. pH & Agriculture • pH of soil • Excess acid in the soil can be neutralised by adding calcium hydroxide (slaked lime). • Farmers spread calcium hydroxide powder over their fields to neutralize acids.

  5. pH = 0 1 2 Increasing Acidity 3 Orange Juice 4 Acid Rain 5 Soft drink, Black Coffee 6 Urine Neutral 7 8 Sea water 9 Baking Soda Increasing Alkalinity 10 Soap 11 Ammonia 12 Detergent 13 pH = 14 Sodium hydroxide pH of some common substances: HCL Lemon Juice , Vinegar “Pure water”

  6. *pH Scale • pHis a measure of how acidic or basic a solution is. • The pH scale ranges from 0 to 14. • Acidic solutions have pH values below 7 • A solution with a pH of 0 is very acidic. • A solution with a pH of 7 is neutral. • Pure water has a pH of 7. • Basic solutions have pH values above 7.

  7. Universal Indicator pH Indicators Chemicals which change colors when they are put into acids or bases. These indicators change colors in response to the [H+] Table M

  8. Common pH indicators: • Universal Indicator • Litmus paper • Phenolphthalein • Methyl orange • Bromthmymol blue • *Different colors are observed in solutions depending whether it is: • acidicoralkaline

  9. pH Indicators

  10. Some everyday things that contain acids

  11. In fact, we even have acid in our stomach!!!

  12. *Some Properties of Acids • Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) • Taste sour • Corrode metals • Are electrolytes • React with bases to form a salt and water • pH is less than 7 • Turns blue litmus paper to red “Blue to Red A-CID”

  13. What is the meaning of acids? • An acid is a substance that donates ___________ when it dissolves in water. hydrogen ions,H+

  14. without water water • *Acids produce hydrogen ions in water. • *Acids only show the properties of acids when they are dissolved in water.

  15. *Acids ionize in water. add water • It is the hydrogen ions which are responsible for acidic properties.

  16. Name ‘Em! • HI (aq) • HCl(aq) • H2SO4 (aq) • HNO3 (aq) • HClO4 (aq) • HBr(aq)

  17. *What is the meaning of bases? • solution of hydroxide ions,OH-are produced when bases dissolve in water. NaOH  Na+ + OH- Ca(OH)2 Ca2+ + 2OH –

  18. *Some Properties of Bases • Produce OH- ions in water (accepts H+ acceptor) • Taste bitter • Slippery texture • Are electrolytes (strength depends on concentration of hydroxide, OH-, ions) • React with acids to form a salt and water • pH is greater than 7 • Turns red litmus paper to blue

  19. *A Brønsted-Lowryacidis a proton donor *A Brønsted-Lowrybaseis a proton acceptor conjugatebase conjugateacid base acid

  20. ACID-BASE THEORIES The Brønsted definition means NH3 is aBASEin water — and water is itself anACID

  21. conjugate acid-base pairs Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2 + H2O  C2H3O2– + H3O+ conjugate base conjugate acid acid base conjugate acid-base pairs OH–+ HCO3–  CO32– + H2O acid conjugate base conjugate acid base conjugate acid-base pairs

  22. The pH scale ranges from 0 to 14. 0 being the most acidic and 14 being the most basic. So what does the pH tell us about [H+] of a solution? If something has a pH of: pH 1 = [H+] = 0.1 M pH 2 = [H+] = 0.01 M pH 3 = [H+] = 0.001M pH 4 = [H+] = 0.0001M pH 5 = [H+] = 0.00001M pH 6 = [H+] = 1X 10-6M pH 7 = [H+] = 1X 10-7M pH 8 = [H+] = 1X 10-8M pH 9 = [H+] = 1X 10-9M pH 10=[H+] = 1X 10-10M pH 11=[H+] = 1X 10-11M pH 12=[H+] = 1X 10-12M pH 13=[H+] = 1X 10-13M pH 14=[H+] = 1X 10-14M pH Scale

  23. *Given: H+Calculating for pHFormula: pH = - log [H+]*Remember that the [ ] means Concentration (Molarity) Example: If [H+] = 1 X 10-10pH = - log 1.0 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5pH = - log 1.8 X 10-5 pH = - (- 4.7) pH = 4.7

  24. How to Figure it out? • If you were given HCl with a concentration of 0.003M, what would be the pH? • pH = -log [H+] • pH = -log[0.003M] • pH = 2.5 • pH will not have a unit!!!

  25. How do pH and pOH relate? • pH and pOH relate in the following way: • pH + pOH = 14 • pOH is the measure of the [OH-], in a solution. • What would be the pOH of an solution with a pH of 5.8? • pOH = 14 – 5.8 • pOH = 8.2

  26. *Given [OH-] and calculating pHformula: pH=14-(-log [OH-]) What is the pH of the 0.0010 M NaOH solution? [OH-]= 0.0010 pH = 14- (-log 0.0010) pH = 14 - (3) pH = 11

  27. pH calculations: Solving for [H+] If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Take antilog (10x) of both sides and get 10-pH =[H+] or [H+] =antilog -pH [H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

  28. *Given-pHCalculating-H+ or H3O+Formula: [H+] = antilog(-pH) • [H+] = antilog(-pH) • What is the [H+] of a solution with a pH of 12.05? • [H+] = antilog(-pH) • [H+] = antilog (-12.05) [H+] = 10 (-12.05) • [H+] = 8.91 X 10 -13 M *Antilog (2nd button of log): usually is 10x

  29. Sample Problem 1 • What is the pH and pOH of a solution with [H+] of 3.33 X 10-9 M? • 1st solve for pH pH = -log [H+] • pH = - log[3.33 X 10-9 M] • pH = 8.48 • 2nd  solve for pOH • pOH = 14 – pH • pOH = 14 - 8.48 • pOH = 5.52 (acidic)

  30. Sample Problem 2 • What is the [H+] of a solution with a pOH of 4.14? • 1st determine pH pH = 14 – pOH • pH = 14 – 4.14 • pH = 9.86 (basic) • 2nd determine [H+] • [H+] = antilog (-pH) • [H+] = antilog (-9.86) • [H+] = 1.38 X 10 -10 M

  31. Sample Problem 3 • What is the pH of a solution with a [OH-] = 2.35 X 10-9? • OH = 14-(-log [OH-]) • pH = 14-(-log[2.35X10-9 M]) • pH = 5.37 (acidic)

  32. Sample Problem 4 • What is the pH of a solution that was made from 4.57g of HCl dissolved in 750 mL of water? • 1st determine moles of HCl 1 mol HCl 4.57g HCl = 0.125 mol HCl 36.46 g HCl

  33. Sample 4 …. • 2nddetermine concentration of [H+], since this is an acid the [H+] would be the same as the concentration(molarity “M”) of the whole molecule of HCl. We will get [H+] & [Cl-], both with the total of 0.125 moles each. • So concentration “M” will be moles / volume (L) • [H+] = 0.125 moles/ 0.750 L • [H+] = 0.333M

  34. Problem 4… • Next determine pH • pH = -log [H+] • pH = -log [0.333M] • pH = 0.48 (very acidic)

  35. Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid

  36. Neutralization reaction Bases reacts with an acid to produce a salt and water ACID + BASE --> SALT + WATER HCl + NaOH -----> NaCl + H2O

  37. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base *Neutralization reactions - Products are always water and salt • Perform titrations to determine an unknown volume or concentration of an acid/base • ENDPOINT = when indicator changes color • Moles of H+ = Moles of OH- MAVA = MBVB

  38. *Titration: • A laboratory method for determining the concentration of an unknown acid or base using a neutralization reaction. • A standard solution,(a solution of known concentration), is used.

  39. *Equivalence Point • The point at which there are stoichiometrically equivalent amounts of acid and base. • [H+] = [OH-]

  40. Methods of Solving Titration Problems: a) using stoichiometry b) using the titration formula MaVa=bMbVb.

  41. Setup for titrating an acid with a base

  42. Buret Stopcock Ring Stand

  43. Titration Acid with Phenolpthalein End-Point

  44. MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base Titration problems Calculate the molarity of an acetic acid solution if 34.57 mL of this solution are needed to neutralize 2.519 cL of 0.1025 M sodium hydroxide MAVA = MBVB (MA)(34.57ml) = (0.1025M)(25.19ml) MA= 0.0747M

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