ACID and Bases.pdf

ACIDS AND BASES  ▪ Explain the pH scale in terms of I Can … hydrogen ion concentration ▪ Explain the pH scale in terms of hydroxide ion concentration ▪ Explain the pH scale in terms of acidity ▪ Explain the pH scale in terms of...

ACIDS AND BASES  ▪ Explain the pH scale in terms of I Can … hydrogen ion concentration ▪ Explain the pH scale in terms of hydroxide ion concentration ▪ Explain the pH scale in terms of acidity ▪ Explain the pH scale in terms of basicity 2  An acid is… ▪ An aqueous solution that has H+ ions. ▪ The more H+ ions, the more acidic the solution. ▪ Examples of acids: HCl (H+ and Cl-), HNO3 (H+ and NO3-) 3  Properties of an Acid ▪ Tastes Sour ▪ Corrosive ▪ Turns blue litmus paper red Picture from BBC Revision Bites http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_b ases_1.shtml 4  Some Common Acids ▪ Vinegar ▪ Citrus fruits (lemons, limes, & oranges ▪ Ascorbic acid = Vitamin C which your body needs to function. ▪ Car batteries 5  A Base is.. ▪ An aqueous solution that has OH- ions. ▪ Base = alkaline ▪ Examples of Bases: NaOH (Na+ and OH-), Ca(OH)2 (Ca+2 and OH-) 6  Properties of Bases ▪ Feel Slippery ▪ Taste Bitter ▪ Corrosive ▪ Turns red litmus paper blue. 7  pH Scale ▪ pH is a measure of how acidic or basic a solution is. Ranges from 0 to 14. ▪ Acidic solutions - pH below 7 ▪ pH of 7 is neutral. Pure water has a pH of 7 Basic solutions - pH above 7. 8  pH scale P= power of H = Hydrogen Ranges from 0-14 measures H+ concentration [H+] the more H+, the more acidic the solution  Every Acidic/Basic solution contains + - H and OH For acids H+1 > OH-1 For bases OH-1 > H+1 when [H+] = [OH-] the substance is neutral so we can actually measure pH and pOH pH + pOH =14  Logarithmic scale (based on powers of 10) each decrease of one unit of pH represents a 10x increase in H+ concentration – Ex: pH 4 is ten times more acidic then pH 5 – Ex: pH 10 is ten times more basic then pH 9 Try to remember: The lower the pH, the higher the concentration of H+ ions  + Calculating pH pH=-log [H ] – [H+] = concentration – Ex. 0.01M HCl has a pH of? This means you have.01 moles of H+ and.01 moles of Cl- per every 1 L pH = -log(0.01) pH=2 We are going to learn an easier way!  Because it’s based on powers of 10 there is a trick -x 10 where x = pH If molarity of acid is.001M =10-3 pH = 3 If molarity of acid is.00001M = 10-5 pH = 5  Now you are looking at OH- ions instead of H+ – ONLY CAN CALC pOH pOH=-log [OH-] or our trick 10-x where x = pOH pH + pOH = 14 pH of a base – So 14 – pOH = pH – Ex. 0.01M NaOH has a pH of? This means you have.01 moles of OH- and.01 moles of Na+ per every 1 L – pOH=2 pH = 14-2 = 12 Because it’s based on powers of 10 there is a trick If molarity of base is.001M = 10-3 pOH = 3 pH 14-3 = 11 If molarity of base is.00001M = 10-5 pOH = 5 pH 14-5 = 9  If pH = 4 +1 [H ] = ? 1 x 10-4 M pH + pOH = 14 pOH = ? 4 + X = 14 X =10 -1 -10 -1 [OH ] = ? 1x10 M = [OH ]  -1 -3 If the [OH ] = 1 X 10 M pOH = ? pOH = 3 pH = ? pH + pOH = 14 X + 3 = 14 X = 11 +1 [H ] = ? 1x10-11 M  +1 -5 If the [H ] = 1 x 10 M The pH = ? =5 The pOH = ? pH + pOH =14 5+x =14 X=9 - The [OH ] = ? 1x10 M -9  Calc pH for.01M HCl -2 10 = 2 so pH = 2.01M NaOH 10-2 = 2 so pOH = 2 14-2 – 12 pH=12 Using a scientific calculator (The brackets [ ] mean concentration or Molarity) Example: If [H+] = 1.00 X 10-10 M, what is the pH? pH = - log (1 X 10-10) pH = 10.0 Example: If [OH-] = 1.80 X 10-5 M ,what is the pOH? pOH = - log 1.80 X 10-5 pOH = 4.74 For simplicity you will use 3 significant figures for pH, pOH, [H+] and [OH-] calculations (watch the video below)  Item pH H+ OH- pOH Acidic or basic 1-3. 3 Acidic 4-7. 1x10-10 8-11. 5x10-11 12-15. 11.5 Asynchronous pH, pOH, [H+] and [OH-] calculations activity Brønsted–Lowry Acids and Bases According to the Brønsted–Lowry theory, an acid is a substance that donates H+. a base is a substance that accepts H+. Learning Goal Identify conjugate acid–base pairs for NH3, a Brønsted–Lowry Base In the reaction of ammonia and water, NH3 acts as the base that accepts H+. H2O acts as the acid that donates H+. Because the nitrogen atom of NH3 has a stronger attraction Study Check In each of the following equations, identify the Brønsted–Lowry acid and base in the reactants: A. HNO3(aq) + H2O(l) H3O+(aq) + NO3−(aq) B. HF(aq) + H2O(l) H3O+ (aq) + F−(aq) Solution In each of the following equations, identify the Brønsted–Lowry acid and base in the reactants: A. HNO3(aq) + H2O(l) H3O+(aq) + NO3−(aq) Acid Base B. HF(aq) + H2O(l) H3O+ (aq) + F−(aq) Acid Base Study Check Identify each as a characteristic of A. an acid or B. a base. ____ 1. has a sour taste ____ 2. produces OH− in aqueous solutions ____ 3. has a chalky taste ____ 4. is an electrolyte ____ 5. produces H+ in aqueous solutions Solution Identify each as a characteristic of A. an acid or B. a base. A 1. has a sour taste B 2. produces OH− in aqueous solutions B 3. has a chalky taste A, B 4. is an electrolyte A 5. produces H+ in aqueous solutions Conjugate Acid–Base Pairs In any acid–base reaction, there are two conjugate acid–base pairs. Each pair is related by the loss and gain of H+. One pair occurs in the forward direction. One pair occurs in the reverse direction. Acid and conjugate base pair 1 HA + B A− + BH+ Base and conjugate acid pair 2 Conjugate Acid–Base Pairs In this acid–base reaction, the first conjugate acid–base pair is HF, which donates H+ to form its conjugate base, F−. the other conjugate acid–base pair is H2O, which accepts H+ to form its conjugate acid, H3O+. each pair is related by a loss and gain of H+. Conjugate Acid–Base Pairs In the reaction of NH3 and H2O, one conjugate acid–base pair is NH3/NH4+. the other conjugate acid–base pair is H2O/H3O+. Core Chemistry Skill Identifying Conjugate Acid–Base Pairs Study Check 1. Write the conjugate base for each of the following acids: A. HBr B. H2S C. H2CO3 2. Write the conjugate acid of each of the following bases: A. NO2− B. NH3 C. OH− Solution 1. Write the conjugate base for each of the following acids: A. HBr H+ + Br− B. H2S H+ + HS− C. H2CO3 H+ + HCO3− 2. Write the conjugate acid of each of the following bases: (Add an H+ to each base to get the conjugate acid.) A. NO2− + H+ HNO2 B. NH3 + H+ NH4+ C. OH− + H+ H 2O Study Check Identify the sets that contain acid–base conjugate pairs. 1. HNO2, NO2− 2. H2CO3, CO32− 3. HCl, ClO4− 4. HS−, H2S 5. NH3, NH4+ Amphoteric Substances Substances that can act as both acids and bases are amphoteric or amphiprotic. For water, the most common amphoteric substance, the acidic or basic behavior depends on the other reactant. Water donates H+ when it reacts with a stronger base. Water accepts H+ when it reacts with a stronger acid. Guide to Writing Conjugate Acid–Base Pairs Study Check Identify the conjugate acid–base pairs in the following reaction: HNO3(aq) + NH3(aq) NO3−(aq) + NH4+(aq) Solution Identify the conjugate acid–base pairs in the following reaction: HNO3(aq) + NH3(aq) NO3−(aq) + NH4+(aq) STEP 1 Identify the reactant that loses H+ as the acid. In the reaction, HNO3 donates H+ to NH3. STEP 2 Identify the reactant that gains H+ as the base. In the reaction, NH3 gains H+ to form NH4+. Thus, NH3 is the base and NH4+ is its conjugate acid. HNO3 is the acid and NO3− is its conjugate base Solution Identify the conjugate acid–base pairs in the following reaction: HNO3(aq) + NH3(aq) NO3−(aq) + NH4+(aq) STEP 3 Write the conjugate acid–base pairs. HNO3 / NO3 is the acid and conjugate base pair. NH3/NH4+ is the base and conjugate acid pair.