Titration burette clamp ring stand burette erlenmeyer flask (buret)

standard equivalence point end point titration OUTCOME QUESTION(S): C12-5-04: Write balanced neutralization reactions involving strong acids and bases. C12-5-10: Using a standardized acid or base, determine the concentration of an unknown acid or base. Vocabulary & Concepts  standard equivalence point end point titration

Neutralization reaction Acid and base reaction involving the combination of H+ ions and OH- ions to generate water and salt. (generally neutralizing the acid and base properties) Acid + Base H2O + salt Salt: ionic compound produced by reacting acid with base HCl + NaOH H2O + NaCl Neutralization is a (non-reversible) type of double replacement reaction

Ignore the H/OH and just write water – combine the other ions Write complete neutralization reactions: Acid + Base H2O + salt Ignore the H/OH and just write water – combine the other ions a) Sulfuric acid and potassium hydroxide b) Nitric acid and calcium hydroxide c) Phosphoric acid and lithium hydroxide H2SO4 + KOH 2 2 H2O + K2SO4 2 HNO3 + Ca(OH)2 2 H2O + Ca(NO3)2 Reactants (crisscross) 2) Products (re-crisscross) 3) Balance H3PO4 + LiOH 3 3 H2O + Li3PO4

Titration – quantitative chemical technique of reacting a standard solution to determine the concentration of an unknown. Standard: solution with known concentration. standard unknown HCl + KOH H2O + KCl 2.0 M ? Titration Apparatus: burette clamp ring stand burette Erlenmeyer flask (buret) We will be using titration to find the unknown in a neutralization reaction

Equivalence point is defined by the balanced equation If a titration can be stopped at the exact point of neutralization the unknown can be calculated. HCl + KOH standard unknown H2O + KCl 2.0 M ? Equivalence point Point where amount of standard added is enough to completely neutralize amount of unknown. moles H+ = moles OH- Equivalence point is defined by the balanced equation

End point: point where indicator turns colour. Graphing changes in pH during a neutralization reaction shows an associated spike in pH at the point of equivalence Since the equivalence point is not visible, an indicator is added to identify neutralization. End point: point where indicator turns colour. Goal is to pick an indicator with a end point (colour change) that occurs in same pH range as the equivalence point

How to Preform a Titration Reaction: Add a measured volume of unknown to an Erlenmeyer flask. Add the appropriate indicator to the unknown flask. Fill the burette with the known solution. Slowly titrate the known from the burette into the flask. Stop the titration at the exact point when a colour has changed. Endpoint - determined by the choice of indicator Record all values and calculate the unknown concentration. burette clamp ring stand burette Erlenmeyer flask (buret) Titration can also be preformed the other way - the standard in the flask, and the unknown in the burette

Titrations problems typically involve 3 basic steps: Determine the concentration of a 15.0 mL HCl solution neutralized by a 0.100 M NaOH solution. Titration data recorded below. unknown standard HCl + NaOH H2O + NaCl ? 0.100 M 15.0 mL 13.83 mL Indicator used: phenolphthalein (endpoint is pink) Titrations problems typically involve 3 basic steps: Find moles of standard used Use stoichiometry to determine moles of unknown Calculate the missing value Burette Base Initial Reading 0.62 mL Final Reading 14.45 mL Total Volume 13.83 mL

Volumes must be converted to litres (L) unknown standard 1 HCl + NaOH 1 H2O + NaCl ? 0.100 M 15.0 mL 0.0922 M 13.83 mL Volumes must be converted to litres (L) 1. Calculate the moles of standard used: 0.100 mol 0.01383 L = 0.001383 mol NaOH (used) 1 L 2. Use stoichiometry to determine moles of unknown: 1:1 ratio therefore: 0.001383 mol HCl (used) 3. Calculate missing value: 0.001383 moles used = 0.0922 M HCl 0.015 L

Calculate the concentration of hydrochloric acid, if 25 Calculate the concentration of hydrochloric acid, if 25.0 mL is just neutralized by 40.0 ml of a 0.15 mol/L magnesium hydroxide solution. unknown standard 2 HCl + Mg(OH)2 1 H2O + MgCl2 2 ? 0.15 M 25.0 mL 0.48 M 40.0 mL 1. Moles of standard: 2. Moles of unknown: 2:1 ratio 0.15 mol 0.0400 L 0.006 molS 2 HCl 1 L 1 Mg(OH)2 = 0.006 mol Mg(OH)2 = 0.012 mol HCl 3. Calculate missing value: 0.012 moles HCl used = 0.48 M HCl 0.025 L

What volume of a 0.250 mol/L solution of carbonic acid will neutralize 30.0 g of sodium hydroxide. unknown standard H2CO3 + NaOH 2 H2O + Na2CO3 2 0.250 M 30.0 g ? 1.5 L 1. Moles of standard: 2. Moles of unknown: 1:2 ratio Mol mass of NaOH = 40.0 g/mol 0.750 molS 1 H2CO3 30.0 g 1 mol 2 NaOH 40.0 g = 0.375 mol H2CO3 = 0.750 mol NaOH 3. Calculate missing value: 0.375 mol H2CO3 1 L = 1.5 L H2CO3 0.250 mol

Titration Curves 1. Strong titrant with a strong analyte. Plotting pH values during a titration gives a titration curve. Two classes of curve are produced by acid-base interactions: 1. Strong titrant with a strong analyte. 2. Weak titrant with strong analyte. Titrant – standard : Analyte – unknown

Strong - Strong S-S titrations produce well defined “s-curves” SA - SB SB - SA S-S titrations produce well defined “s-curves” Equivalence point is centre of the sharp rise of curve Equivalence point: pH = 7

Strong - Weak S-W titrations produce sloppy s-curves WA - SB WB - SA S-W titrations produce sloppy s-curves Equivalence point is centre of the rise of curve Equivalence point: pH ≠ 7 Due to secondary reactions with the acidic/basic salt produced

standard equivalence point end point titration CAN YOU / HAVE YOU? C12-5-04: Write balanced neutralization reactions involving strong acids and bases. C12-5-10: Using a standardized acid or base, determine the concentration of an unknown acid or base. Vocabulary & Concepts  standard equivalence point end point titration