ACIDS & BaseS

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

Importance of pH: pH of soil pH of tank pH of food

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.

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

*pH Scale pH is 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.

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

Common pH indicators: Universal Indicator Litmus paper Phenolphthalein Methyl orange Bromthmymol blue *Different colors are observed in solutions depending whether it is: acidic or alkaline

pH Indicators

Some everyday things that contain acids

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

*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”

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

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

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

H2SO4 HNO3 HSO4- & H+ SO42- & H+ NO3- & H+ Common strong acids: Formula: Ions produced: 1.Sulfuric acid H2SO4 HSO4- & H+ SO42- & H+ 2.Nitric acid HNO3 NO3- & H+

HClO4 HCl ClO4- & H+ Cl- & H+ Common strong acids: Formula: Ions produced: 3. Perchloric acid HClO4 ClO4- & H+ 4. Hydrochloric acid HCl Cl- & H+

HBr HI Br- & H+ I- & H+ Common strong acids: Formula: Ions produced: 5.Hydrobromic acid HBr Br- & H+ 6.Hydroiodic acid HI I- & H+

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

*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 –

*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

NaOH KOH LiOH Na+ & OH- K+ & OH- Li+ & OH- Common strong bases: Formula: Ions produced: 1. Sodium hydroxide NaOH Na+ & OH- 2. Potassium hydroxide KOH K+ & OH- 3. Lithium hydroxide LiOH Li+ & OH-

RbOH CsOH Rb+ & OH- Cs+ & OH- Common strong bases: Formula: Ions produced: 4. Rubidium hydroxide RbOH Rb+ & OH- 5. Cesium hydroxide CsOH Cs+ & OH-

Ca(OH)2 Ba(OH)2 Sr(OH)2 Ca2+ & 2OH- Ba2+ & 2OH- Sr2+ & 2OH- Common strong bases: Formula: Ions produced: 6. Calcium hydroxide Ca(OH)2 Ca2+ & 2OH- 7. Barium hydroxide Ba(OH)2 Ba2+ & 2OH- 8. Strontium hydroxide Sr(OH)2 Sr2+ & 2OH-

*A Brønsted-Lowry acid is a proton donor *A Brønsted-Lowry base is a proton acceptor conjugate acid conjugate base base acid

ACID-BASE THEORIES The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

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

Representative pH Values pH Scale 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 Representative pH Values Substance pH battery acid 0.5 gastric acid 1.5-2.0 lemon juice 2.4 cola 2.5 vinegar 2.9 orange juice 3.5 acid rain 4.5-5.0 tea 5.5 milk 6.5 pure water 7.0 saliva 7.0-7.4 blood 7.3-7.5 sea water 8.0 soap 9.0-10.0 ammonia 11.5 household bleach 12.5 lye (sodium hydroxide) 13.5

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

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!!!

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

*Given [OH-] and calculating pH formula: 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

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

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

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)

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

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)

Sample Problem 4 4.57g HCl 1 mol HCl = 0.125 mol HCl 36.46 g HCl 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 4.57g HCl 1 mol HCl = 0.125 mol HCl 36.46 g HCl

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

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

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

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

*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 MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base

*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.

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

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

Setup for titrating an acid with a base

Buret Stopcock Ring Stand

Titration Acid with Phenolpthalein End-Point

Titration problems MAVA = MBVB (MA)(34.57ml) = (0.1025M)(25.19ml) 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= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base (MA)(34.57ml) = (0.1025M)(25.19ml) MA= 0.0747M

Ex. 1 What is the concentration of HCl if 30.0 mL of 0.10 M NaOH neutralizes 50.0mL HCl? NaOH + HCl  H2O + NaCl Hint: Use MaVa=bMbVb Ma= How many moles of HCl were used? Hint: #moles= MaVa , but convert the volume to L( 50mL=0.05L).

Ex. 2 A 20.0 mL solution of Sr(OH)2 is neutralized after 25.0 mL of standard 0.05 M HCl is added. What is the concentration of Sr(OH)2? 2 HCl + Sr(OH)2  2 H2O + SrCl2

Ex. 3 How many mL of 0.20 M H3PO4 are needed to neutralize 55.0 mL of a 0.10 M solution of NaOH?

Ex. 4 What volume of 0.20M Ca(OH)2 will neutralize 45.0 mL of a 1M solution of HClO3?

Practice! Give two ways that acids are different from bases that does not include their pH.

Practice! Titration problems MAVA = MBVB (0.5M)(20.0ml) = MB(65.0ml) If 20.0ml of a 0.50M HCl solution is needed to neutralize 65.0ml of a NaOH solution. What was the concentration of the base? MAVA = MBVB MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base (0.5M)(20.0ml) = MB(65.0ml) MB= 0.154M

Practice! Titration problems 43.0ml of HCl was titrated with 32.0 ml of 0.100 M NaOH. What is the molarity of the hydrochloric acid solution? MAVA = MBVB MA= molarity of acid VA= volume of acid MB= molarity of base VB= volume of base MA(43.0ml)=(0.100M)(32.0ml) MA= 0.0744 M

Practice! What is the [H+] of an acid with a pH of 5.56? Determine the pH of a 0.0045 M HCl? Determine pOH of a solution with a pH of 8.7? What is the pH of a base with an [OH-] of 3.44X10-5 M? Answers: 1. [H+] is 2.75X 10-6 10-5.56 2. pH = -log[H+] = 2.3 3. pOH is 5.3 (14-8.7 = 5.3) 4. pH is 9.5 (because pOH= 4.5)