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Strong vs Weak Acids 4-28-14. Strong acids ionize completely. HCl H + + Cl - HNO 3 H + + NO 3 - H 2 SO 4 2H + + SO 4 -. Weak Acids ionize partially. H 2 CO 3 2H + + CO 3 - CH 3 COOH H + + CH 3 COO - H 3 PO 4 3H + + PO 4 -.
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Strong acids ionize completely HCl H+ + Cl- HNO3 H+ + NO3- H2SO4 2H+ + SO4-
Weak Acids ionize partially H2CO3 2H+ + CO3- CH3COOH H+ + CH3COO- H3PO4 3H+ + PO4-
Ka is the acid dissociation constant • Large Ka value means more ionization, means stronger acid. • Smaller ka value means less ionization, means weaker acid.
1.Which acid is stronger? • Methanoic acid ka= 1.8 x 10-4 • Carbonic acid ka= 4.3 x 10-7
2.Which acid is weaker? • Ethanoic acid ka = 1.8 x 10-3 • Oxalic acid ka = 5.6 x 10-2
Neutralization Reactions When an acid reacts with a base, the product is always a SALT and WATER. HCl + NaOH NaCl + H2O HNO3 + KOH KNO3 + H2O CH3COOH + NaOH NaCH3COO + H2O
Write the reaction ratio under the equation Example: HCl + NaOH NaCl + H2O 1 mol 1 mol 1 mol 1 mol
Your turn 3. H2SO4+ 2NaOH Na2SO4 + 2 H2O 4. 2HCl + Ca(OH)2 CaCl2 + 2 H2O
Titration • to find concentration of an unknown acid or base • Use the balanced equation to set up a mole ratio • Use the volume of titrant to calculate concentration of unknown
Comparing strong acid vs weak acid titration with strong base
How does a titration work? 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 while the flask is gently swirled 3. Measured volumes of a base of known concentration (standard solution) are added until the indicator just barely changes color. 4. Neutralization occurs at the equivalence point = end point of the titration (color change)
Calculations A 25ml of H2SO4 is neutralized by 18ml of 1.0M NaOH. What is the concentration of the H2SO4 solution? H2 SO4 + 2 NaOH Na2 SO4 + 2H2O Known: Stoich: Final equation: Molarity = mol / L
How to • Convert ml to L (divide by 1000) • Find moles of base (moles = M x L) • Use balanced equation to set up mole ratio (place unknown at the top) • Multiply answer from 2. (moles) with the ratio from 3. (mole ratio) • Find concentration of acid M =moles L (answer of 4. divided by L of acid from 1.)
Practice A 50 ml of H2SO4 is neutralized by 25ml of 1.0M NaOH. What is the concentration of the H2SO4 solution? H2 SO4 + 2 NaOH Na2 SO4 + 2H2O
Practice/exit slip A 25ml of H2SO4 is neutralized by 50ml of 1.0M NaOH. What is the concentration of the H2SO4 solution? H2 SO4 + 2 NaOH Na2 SO4 + 2H2O
Bellwork 25ml of HCl are titrated with 30 ml of 0.5M NaOH. What is the concentration of the acid. HCl + NaOH NaCl + H2O
Work due by end of class today: Lab report with completed calculations Vocab foldable
Put on your goggles andSet up your burettesTitration strong acid with strong base • Fill burette with NaOH solution. Record your starting volume . • Measure 20 ml of HCl into a small Erlenmeyer flask (using a measuring cylinder) • Add 5 drops of Bromothymol blue indicator. • Swirl flask gently as you add NaOH from the burette to the flask until you get a slight color change to green/blue • Record volume used from the burette Work in groups of 3
Calculate the molarity (M) of the acid (HCl) HCl + NaOH NaCl + H2O ___ml ____ml ? M 0.1M
Vocab foldable (grade for color/quality/completeness) Equivalence point End point Titration Weak acid Strong acid Base Alkaline Buffer Indicator Phenolphtalein Bromothymol blue Neutralization Molarity Standard solution