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TITRATION

TITRATION. © Mr. D. Scott; CHS. In a titration a solution of accurately known concentration is gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete.

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TITRATION

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  1. TITRATION © Mr. D. Scott; CHS In a titration a solution of accurately known concentration is gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at (or near) the equivalence point

  2. © Mr. D. Scott; CHS TITRATION The standard solution (known concentration) is placed into the burette and is called either the reagent, or the titrant. The analyte or titrand (unknown concentration), is placed in the container located beneath the burette. The calibrated burette enables the exact amount needed to reach the endpoint to be measured as it is mixed with the analyte. The endpoint is the point at which the titration is complete, as determined by an indicator. This is ideally the same volume as the equivalence point—the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte.

  3. © Mr. D. Scott; CHS TITRATION Read the burette scale downward. 15.75 mL The meniscus can be easier to see if a paper card with a straight dark line is held in the line of sight behind the burette. The card can be moved up and down to help establish the exact location of the meniscus.

  4. © Mr. D. Scott; CHS TITRATION Stoichiometric Method • Collect data: • Write a balanced equation for the reaction. • Calculate moles of titrant • Use mole ratio from balanced equation • Calculate analyte concentration. Performing Titration Calculations

  5. © Mr. D. Scott; CHS TITRATION Example Problem 1 15.0 ml of Ca(OH)2 solution were titrated with 0.25 M HCl. The volumes used were recorded in the data table below. Calculate the concentration of the Ca(OH)2. Performing Titration Calculations (1) Find volume used 22.57 - 0.15 22.42 (2) Balanced Equation: (3) Moles titrant: (5) Concentration analyte: (4) Moles analyte:

  6. © Mr. D. Scott; CHS TITRATION Ratio Method Using Normality Performing Titration Calculations acids bases

  7. TITRATION Performing Titration Calculations © Mr. D. Scott; CHS Ratio Method • Collect data: • Convert molarities to normalities • Use Ratio Formula: Nacid Vacid = Nbase Vbase • Convert back to molarity if necessary

  8. TITRATION Performing Titration Calculations © Mr. D. Scott; CHS Example Problem 2 Ratio Method 25.0 ml of NaOH solution were titrated with 0.30 M H2SO4. The volumes used were recorded in the data table below. Calculate the concentration of the NaOH. (1) Find volume used 32.55 - 0.75 31.80 (2) Convert to Normality (3) Use Ratio Formula (4) Convert back to Molarity

  9. Strong Acid-Strong Base Titrations NaOH (aq) + HCl (aq) H2O (l) + NaCl (aq) OH-(aq) + H+(aq) H2O (l)

  10. CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l) CH3COOH (aq) + OH-(aq) CH3COO-(aq) + H2O (l) CH3COO-(aq) + H2O (l) OH-(aq) + CH3COOH (aq) Weak Acid-Strong Base Titrations At equivalence point (pH > 7):

  11. HCl (aq) + NH3(aq) NH4Cl (aq) H+(aq) + NH3(aq) NH4Cl (aq) NH4+(aq) + H2O (l) NH3(aq) + H+(aq) Strong Acid-Weak Base Titrations At equivalence point (pH < 7):

  12. Acid-Base Indicators HIn (aq) H+(aq) + In-(aq) [HIn] [HIn]  10  10 [In-] [In-] Indicators themselves are weak acids and bases. They generally have one color as an acid and another color as a base. Color of acid (HIn) predominates Color of conjugate base (In-) predominates Transition Interval

  13. Acid-Base Indicators

  14. Choosing An Indicator The proper indicator will change color in the vertical section of the pH curve. Ideally, the equivalence point will be within the transition interval of the indicator.

  15. The titration curve of a strong acid with a strong base.

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