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2.3

Minor Versionm

by Procheta Mallik

Introduction

Chemical reactions often create a change in colour. Here, we use one such reaction to also measure our rate of respiration and metabolism

Video Overview

    • Do not ingest any material.

    • Do not suck from the straw by mistake; only blow, and blow gently!

    • Scissors/Cutters have sharp functional edges. Contact with body may harm.

  1. Make a mark on a fat straw at 1 cm from one end.
    • Make a mark on a fat straw at 1 cm from one end.

    • Seal the end using a tape. Make sure the tape does not cross the 1 cm mark.

    • Add another piece of tape to make a tight seal.

    • Cut the straw at the 1 cm mark. This is our unit of measure. This piece can hold approximately 0.2 g of lime.

    • The given test tube has a capacity of about 17 ml.

    • Add 6 test tubes full of water to a plastic bottle/container.

    • This volume of water will be equal to approximately 100 ml.

    • Use the 100 ml of water we prepared in the previous step.

    • Take one measure of 0.2 g of the calcium oxide (lime).

    • Add it to the 100 ml of water and stir well.

    • Remove the bottle cap and cut the bottle in half using a cutter/scissors.

    • Place the upper half of the bottle inverted over the lower part. This acts like a funnel.

    • Place a filter paper in the upper part of the bottle.

    • Transfer the calcium hydroxide solution into the bottle through your bottle-funnel.

    • Wait for all the liquid to filter down.

    • Dip a red litmus paper into it and observe if there's a colour change.

    • Transfer 5 ml of the filtered Calcium Hydroxide solution into a test tube with the help of a dropper.

    • Add 5 drops of Bromothymol blue indicator.

    • Insert a straw into the test tube and start to blow after taking a deep breath. Count and record the number of exhalations till the solution slowly turns pale green.

    • Continue blowing till the colour of the liquid changes to a shade of green.

    • Dip a red litmus paper into the solution and observe if the litmus paper changes its colour.

    • Patiently blow until the colour changes.

    • If it is taking too many blows it is also possible that, Lime is not mixed well with water.

    • If it is taking too many blows it is also possible that, not enough indicator is used.

    • Run, jog or exercise to increase your rate of respiration.

    • After physical exertion, try the same experiment again. Note down the number of exhalations required to change the colour to pale green.

    • Tabulate your observations in the given table.

    • Make sure to always use the same amount and concentration of the lime solution.

    • Count the number of breaths required to change the colour of the solution to pale green.

    • Record this in a table similar to that shown here.

    • Repeat the experiment 5 times; the mean will give you a statistically better estimate of your rate of respiration.

    • Test the solution before exhaling and after, using red and blue litmus paper.

    • Add 3 to 5 drops of lime to the pale green solution. Predict, observe and record the colour change, if any.

    • Change the volume of the solution and see how that affects the number of exhalations required to cause the colour change.

    • Change the concentration of Calcium Hydroxide and see how that affects the number of exhalations required to cause the colour change.

    • Try obtaining Carbondioxide from vinegar + Baking soda or Coke + Mentos and pass it through the respirometer to observe the colour change.

    • Perform the same experiment with dilute sodium hydroxide.

    • To learn variations of Respirometer. Please visit this link Respirometer (Variations).

Finish Line

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Vishal Bhatt

Member since: 04/26/2017

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