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Abstract

Protocol

Representative Results

Materials

Chemistry

Acid and Base Concentrations

Published: Not Published

  1. Preparation of Reagents

    Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

    • Prepare 25 mL of 50% w/w NaOH solution. Weigh 25 g of NaOH pellets and add them to a 125-mL Erlenmeyer flask.
    • Measure 25 mL of deionized water and add it to the flask.
    • Add a magnetic stir bar and mix the solution on a stir plate until the solution appears homogeneous. After mixing, cover the opening of the flask with paraffin film. Note: The solution produces heat, so allow it to cool before handling.
    • Once cooled, use a powder funnel to pour the solution into a polyethylene bottle labeled ‘50% w/w NaOH’. Store the solution in a corrosive storage cabinet until it is needed.
    • Prepare 25 mL of 0.5 M phosphoric acid. Use a 1-mL volumetric pipette to measure 0.85 mL of stock 14.8 M phosphoric acid and add it to a 25-mL volumetric flask.
    • Fill the flask with deionized water to the volume marking. Add a magnetic stir bar and mix the solution until it is homogeneous.
    • Use a powder funnel to transfer the solution to a polyethylene bottle labeled ‘0.5 M H3PO4’. Store the solution in a corrosive storage cabinet until it is needed.
    • Prepare 5 mL of 1% phenolphthalein. Use a volumetric pipette to transfer 2.5 mL of ethanol into an Erlenmeyer flask.
    • Weigh 0.05 g of phenolphthalein and add it to the ethanol. Rinse the weigh boat with ethanol to transfer residual phenolphthalein.
    • Add a stir bar and mix the solution until the phenolphthalein dissolves and the solution appears homogeneous.
    • Add another 2.5 mL of deionized water to the flask and stir. Once the solution is well-mixed, transfer it to a labeled dropper bottle.
    • Prepare dry potassium hydrogen phthalate (KHP). Weigh approximately 20 g of stock KHP into a glass container with a lid.
    • Place the uncovered glass container in an oven at 125 °F to dry the KHP overnight.
    • When the KHP is dry, secure the lid and set it by the balance to cool.
    • Make sure there is a clean and dry spatula, several weigh boats, and a 150-mL beaker labeled, ‘Excess’.
  2. Preparation of Laboratory
    • Set out the following glassware and equipment at each lab station (we suggest that students work in pairs):
       1    50-mL glass burette
       1    60-mL plastic burette with 2-valve system
       3    250-mL Erlenmeyer flasks
       1    10-mL graduated cylinder
       1    50-mL graduated cylinder
       1    100-mL beaker
       1    250-mL beaker
       1    400-mL beaker
       1    Glass stirring rod
       1    Ring stand
       1    Medium 2-prong clamp
       1    Burette clamp
       1    1-mL pipette
       15    1-mL pipette tips
       1    500-mL polyethylene bottle with cap
       1    Drop counter
       1    pH sensor probe
       1    Stirplate
       1    Stir bar
       1    Data acquisition system
       1    Flash drive

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What are Arrhenius acids and bases?

An Arrhenius acid is an acid that dissociates and produces hydrogen ions when dissolved in water, whereas an Arrhenius base produces hydroxide ions when dissolved in water.

What is pH, and how is it calculated?

pH is a measure of the degree of acidity or alkalinity of a solution. It is calculated as the negative log base 10 of the concentration of hydrogen or hydronium ions.......

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  • 50-mL glass burette
    5
  • 60-mL plastic burette with two-valve system
    5
  • 250-mL Erlenmeyer flask
    15
  • 10-mL graduated cylinder
    5
  • 50-mL graduated cylinder
    5
  • 100-mL beaker
    5
  • 250-mL beaker
    5
  • 400-mL beaker
    5
  • Glass stirring rod
    5
  • Ring stand
    5
  • Medium 2-prong clamp
    5
  • Burette clamp
    5
  • 1-mL pipette
    5
  • 1-mL pipette tips
    75
  • 500-mL polyethylene bottle with a cap
    5
  • Drop counter
    5
  • pH sensor probe attachment
    5
  • pH 7.00 calibration buffer
    -1 Dependent on lab size
  • pH 10.00 calibration buffer
    -1 Dependent on lab size
  • Handheld data acquisition device
    5
  • Flash drive
    5
  • Stirplate
    5
  • Stir bar
    5
  • NaOH pellets
    30 g
  • 14.8 M Phosphoric acid
    1 mL
  • Phenolphthalein
    0.1 g
  • Ethanol
    5 mL
  • KHP
    20 g
  • Powder funnel
    3
  • 150-mL beaker
    1
  • 125-mL Erlenmeyer flask
    1
  • 25-mL graduated cylinder
    1
  • Paraffin film
    1 roll
  • 125-mL polyethylene bottle
    2
  • 1-mL volumetric pipette
    1
  • 25-mL volumetric flask
    1
  • 5-mL pipette
    2
  • 25-mL Erlenmeyer flask
    1
  • Spatula
    2
  • 100-mL beaker
    1
  • Plastic pipette/eyedropper
    1
  • Dropper bottle
    1
  • 200-mL glass jar with lid
    1
  • Oven
    1
  • Pipetter
    1
  • Weigh boats (at least 10)
    -1 Dependent on lab size
  • Balance (at least 1)
    -1 Dependent on lab size
  • Deionized water
    -1 Dependent on lab size

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