Neutralizations and Titrations

pOH, Neutralizations and Titrations

By Abby Fancsali

pOH

• ​pH measure the amount of Hydronium ions, pOH measures the amount of Hydroxide ions in a solution

  • Not used as much outside of labs to make calculations easier

  • Equation for pOH is virtually the same​ as pOH

    • ​pOH= -log [OH]

  • pH + pOH = 14

    • once you know the pH, you can find the pOH

Neutralizations

• Neutralization Reaction: a reaction between the hydronium [H₃O⁺] ions in an acid and the hydroxide [OH^-] ions in a base that forms water and a salt

  • An acid + A Base = A salt + Water

  • All Neutralizations are the same reaction between ions regardless of the type or strength of the acid or the base

    • H₃O⁺ + OH^- → 2 H₂O

    ​

Titrations

• Titration: The General addition of one solution to another to reach an equivalence point

  • Uses an acid or a bas of a known concentration to determine the concentration of an unknown

  • As a strong base is added to a strong acid, the two react until they are in amounts that use each other up, neutralizing the substance

    • Equivalence Point: the point at which a neutralization reaction is complete and the pH is equal to 7

Parts of a Titration

• Buret: a graduated glass tube with a tap at the end

• Titrand: a solution with an unknown concentration

• Titrant: a solution with a known concentration used in a titration of an unknown concentration

  • Can be either an acid or a base​

• Standard solution: a solution of known concentration

• Indicator Solution: a chemical that changes color in the presence of an acid or base

Reading a Buret

• When a liquid is added to any measuring tube, the water tends to form a dip within the container

  • Meniscus: the curved upper surface of a liquid in a tube

    • When reading from a graduated container, it is important to look at the measurement at the curve, not the edge

Reading a Buret

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Multiple Choice

This is the solution you know the concentration of in a titration

• Titrand

• Titrant

• Indicator Solution

• Buret

Multiple Choice

This is the solution you don't know the concentration of in a titration

• Titrand

• Titrant

• Indicator Solution

• Buret

Setting up a Titration

• Setting up Burets: Set up two clean burets

  • One is for your acid, one is for your Base

    • Rinse your acid buret with the acid and the base buret with the base three time each

  • Fill the acid buret to a point above the 0mL mark with the acid of unknown concentration

    • release some acid from the buret into the waste beaker to release air bubbles

    • Record the volume of the acid in the buret as the initial volume

  • Allow approximately the volume of acid deemed needed by the lab procedure to flow into a clean flask

    • record the amount of acid in the flask as close to the nearest 0.01 mL​

  • Add three drops of the indicator solution to the flask

Setting up a Titration

• Fill the Base Buret to the calibration point, and release a small amount into a waste beaker

  • Record the initial volume of your base to the closest 0.01 mL

• Place your Flask with the acid under the buret so that the tip of the buret rests inside the flask

• SLOWLY release base into the flask while gently swirling the Flask

  • The equivalence point is reached when a very light color remains after 30 seconds of swirling

• Subtract the initial volume reading on the buret from the final volume to find the exact amount of base added​

Multiple Choice

Which of the following results shows the equivalence point in a titration

• The solution is colorless

• The Solution is a dark color

• The Solution has a light/faint Color

Multiple Choice

The first time you do a titration on a solution, at what speed should you release your titrant?

• Dripping

• Fast

• It doesn't matter

Titration Calculations

• Once you have the volume of your solution, you can solve for the concentration of the unknown

  • Concentration would be measured Using Molarity

• Steps

  • ​Identify Balanced Chemical Equation of the reaction taking place

  • Determine the moles of your known concentration substance used

  • Convert your Moles of your known substance to Moles of your unknown substance

  • Use Your moles of unknown and amount used to determine the Molarity of the unknown

Titration Calculation Sample Problem

In a titration, 27.4 mL of 0.0154 M Ba(OH)₂ is added to a 20.0 mL sample of a HCl solution​ whose concentration is unknown until the equivalence point is reached. What is the molarity of the acid solution?

• Step 1: Identify the Balanced Equation​

Titration Calculation Sample Problem

In a titration, 27.4 mL of 0.0154 M Ba(OH)₂ is added to a 20.0 mL sample of a HCl solution​ whose concentration is unknown until the equivalence point is reached. What is the molarity of the acid solution?

• Step 1: Identify the Balanced Equation​

  • Ba(OH)₂ + 2HCl →​ BaCl₂ + 2H₂O

• Step 2: Convert the volume of your known solution into moles

  ​

Titration Calculation Sample Problem

In a titration, 27.4 mL of 0.0154 M Ba(OH)₂ is added to a 20.0 mL sample of a HCl solution​ whose concentration is unknown until the equivalence point is reached. What is the molarity of the acid solution?

• Step 1: Identify the Balanced Equation​

  • Ba(OH)₂ + 2HCl →​ BaCl₂ + 2H₂O

• Step 2: Convert the volume of your known solution into moles=4.22E-4 mol Ba(OH)₂

• Step Three: Use the mole ration to convert from Ba(OH)​

  ​

Titration Calculation Sample Problem

In a titration, 27.4 mL of 0.0154 M Ba(OH)₂ is added to a 20.0 mL sample of a HCl solution​ whose concentration is unknown until the equivalence point is reached. What is the molarity of the acid solution?

• Step 1: Identify the Balanced Equation​

  • Ba(OH)₂ + 2HCl →​ BaCl₂ + 2H₂O

• Step 2: Convert the volume of your known solution into moles=4.22E-4 mol Ba(OH)₂

• Step 3: Use the mole ration to convert from Ba(OH)​ to HCl= 8.44E-4 mol HCl

• Step 4: Solve for your molarity​

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