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2.1

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

    • Avoid contact with lime (calcium oxide).

    • Be careful while handling calcium hydroxide (when lime is added to water).

    • Do not ingest any material.

    • Handle the scissors/cutter with care.

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

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  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.

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

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    • 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.

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

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

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

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    • 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.

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    • 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.

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    • 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.

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    • 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.

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    • 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

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    • Patiently blow until the colour changes.

    • Lime is not mixed well with water.

    • Not enough indicator

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    • 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.

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    • 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.

    • Perform the same experiment with dilute sodium hydroxide.

    • Try obtaining CO2 from vinegar + Baking soda, or Coke + Mentos and pass it through the respirometer to observe the colour change.

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    • In the main experiment, we took 5 ml of the filtered Calcium Hydroxide solution into the test tube.

    • Try performing the same experiment with 3 ml , 5 ml and 7 ml and compare the number of exhalations required to cause the colour change.

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    • Tabulate your results in the given table.

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    • In the initial experiment, we dissolved 1 measure (0.2 g) of lime in 100 ml of water.

    • Try the same experiment with half a measure (0.1 g), 1 measure (0.2 g) and 1.5 measures (0.3 g).

    • Compare the number of exhalations required to change the colour in each case.

    • The first picture shows half a measure (0.1 g) and the second one shows 1 measure (0.2 g).

    • Tabulate your observation with the help of the given table.

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    • Take 1 ml of NaOH given in the bottle and add it to the test tube with the help of the dropper.

    • Add 4 ml of water to it. This is to ensure that we obtain a very weak NaOH solution.

    • Now, add 5 drops of bromothymol blue and blow into the solution with the help of a straw.

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    • Count the number of exhalations required to change the colour.

    • Watch the solution slowly turn to pale green.

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    • Make a hole in the bottle cap with the help of scissors.

    • Pass the capillary tube into the hole in the bottle cap.

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    • Put 5g of baking soda in a tissue paper and wrap it.

    • Fill a bottle with 30 ml vinegar.

    • Place the tissue paper, which contains the baking soda, in the mouth of the bottle.

    • Put the other end of the capillary tube into the test tube. Push the tissue paper into the bottle and close the cap quickly and tightly.

    • Shake the bottle to increase the rate of reaction.

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    • Wait for the solution in the test tube to bubble.

    • Shake the bottle vigorously.

    • In a few seconds, the blue solution will turn pale green and then to yellow.

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Finish Line

Vishal Bhatt

Member since: 04/26/2017

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