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JoVE Lab Manual
Lab: Chemistry

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Concentration Dependence

Concentration Dependence

Learning Objectives

At the end of this lab, students should know...

What is chemical kinetics?

Chemical kinetics describes the mechanisms of chemical reactions and the rates associated with them.

What factors affect the reaction rate?

The reaction rate is affected by the concentration of the reactants, the temperature of the reaction, the pressure at which the reaction is taking place, and the state of matter of the reactants.

What units describe the reaction rate?

The reaction rate describes the change in concentration of the product with time. The reaction rate is defined in units of M/s.

What is the reaction order?

The reaction order describes the dependence of the reaction rate on the concentration of each reactant. It is not related to stoichiometry.

What influences the reaction rate constant, and what are the units?

The reaction rate constant varies depending on the reaction, but it is influenced by reaction temperature. The units of the reaction rate constant depend on the order of the reaction. The units of rate constant are M/s for zero-order reactions, 1/s for first-order reactions, and 1/M⋅s for second-order reactions.

List of Materials

  • Glass test tube (25 mm x 150 mm)
  • Test tube cleaning brush
  • Small stir bar
  • pH paper
    5 packages
  • Long HCl-tolerant forceps
  • Lab tape
    5 rolls
  • Stir plate (+1 for instructor)
  • Lab stand
  • Medium 3-prong or test tube clamp
  • Glass thermometer
  • Thermometer clamp
  • 100-mL glass beaker
  • 50-mL glass beaker
  • 600-mL glass beaker
  • 50-mm watch glass
  • 10-mL glass volumetric pipette
  • 5-mL glass volumetric pipette
  • Pipette controller
  • 20-mL volumetric flask
  • 10-mL glass graduated cylinder
  • Stopwatch/Timer
  • 250-mL plastic wash bottle of deionized water (+1 for central hood)
  • Paper labels marked with 'X'
  • Plastic paraffin film
    1 roll
  • Scissors (+1 for central area)
  • 12.1 M HCl
    175 mL
  • Na2S2O3·5H2O
    40 g
  • Powder funnel
  • Glass funnel
  • 500-mL glass Erlenmeyer flask
  • 1-L glass graduated cylinder
  • 250-mL glass graduated cylinder
  • Magnetic wand
  • Large stir bar
  • 750-mL bottle
  • 500-mL bottle with acid resistant cap
  • 1-L glass volumetric flask
  • Weighing boats
  • Spatula
  • Top-loading balance
  • Baking soda
    1 box
  • Deionized water
    Dependent on lab size
  • Disposable plastic pipettes (minimum 3 per group)
    Dependent on lab size

Lab Prep

Source: Smaa Koraym at Johns Hopkins University, MD, USA

  1. Preparation of Solutions

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

    • Put on a lab coat, splash-proof safety glasses, and nitrile gloves. Obtain a waste container for aqueous sodium thiosulfate in advance. Note: HCl is toxic and highly corrosive, and sodium thiosulfate is an irritant, so the solutions for this lab must be prepared in a fume hood.
    • Prepare 750 mL of 0.2 M sodium thiosulfate. Weigh 37.227 g of sodium thiosulfate pentahydrate (Na2S2O3·5H2O) on a top-loading balance and pour it into a 1-L Erlenmeyer or volumetric flask through a powder funnel.
    • Rinse with water to transfer residual material into the flask. Then, use a graduated cylinder to measure out and add 600 mL of deionized water to the flask.
    • Place a magnetic stir bar in the flask and stir the solution on a large stir plate until the solution appears homogeneous.
    • Use a graduated cylinder to add another 150 mL of deionized water to the flask and continue stirring.
    • While the solution stirs, label a 750-mL bottle as ‘0.2 M sodium thiosulfate’.
    • Once the solution again appears homogeneous, turn off the stir motor. Retrieve the stir bar and transfer the solution to the bottle. Cap the bottle and store it in a central fume hood.
    • Prepare 350 mL of 6 M HCl. Measure 174 mL of 12.1 M HCl using a graduated cylinder and pour it into a 500-mL Erlenmeyer flask via a funnel.
    • Use a different graduated cylinder to measure 176 mL of deionized water and slowly add the water to the flask. Place another large magnetic stir bar in the flask and stir the solution until it appears homogeneous.
    • While the mixture stirs, label a 500-mL bottle as ‘6 M HCl’. Once the solution appears well mixed, turn off the stir motor and retrieve the stir bar.
    • Carefully pour the 6 M HCl solution into the bottle via a funnel, cap the bottle, and store it in the instructor's hood. Put away the concentrated HCl and the sodium thiosulfate.
    • Neutralize any acid waste and clean your glassware according to your lab's standard policies.
  2. Preparation of the Laboratory
    • Fill a 250-mL wash bottle with deionized water and place it near the sodium thiosulfate waste container.
    • Laser print X's on paper and apply one 'X' label to the lower half of a test tube for each group. Tape the labels so that the ‘X’ is facing inward.
    • Set out the following glassware and equipment at each fume hood (we suggest that students work in pairs):
       1    Stir plate with support stand
       1    Medium 3-prong clamp (or test-tube clamp)
       1    Thermometer clamp
       1    Labeled test tube
       1    Small magnetic stir bar
       1    50-mL beaker
       1    100-mL beaker
       1    600-mL beaker
       2    50-mm watch glasses
       1    10-mL graduated cylinder
       1    20-mL volumetric flask
       1    10-mL volumetric pipette
       1    5-mL volumetric pipette
       1    Volumetric pipette dispenser
       1    Test tube brush
       1    Glass thermometer
       1    Timer or stopwatch
       1    Pair of long forceps
       1    Roll of lab tape with pen
       1    Package of pH paper
       1    Pair of scissors
    • Put a roll of plastic paraffin film and a pair of scissors in a central location. Distribute baking soda and disposable plastic pipettes so that all students have access to them.
    • Just before the lab, place the bottle of 6 M HCl in the central fume hood. Note: Sulfur dioxide gas will still be evolving from the collected product mixtures at the end of the lab. The students will leave the neutralized waste in the fume hoods overnight.
    • The next day, at least 12 hours later, flush the liquid from the waste down the drain and put the solid sulfur and baking soda in the lab trash.

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