RespirometerA classic acid-base indicator can also be used as a simply made respirometer

Written By: Vishal Bhatt

Respirometer Release: 2.2 - 2018-12-19

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INTRODUCTION

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

TOOLS:Scissor (1)Paper Cutter (1)Tape (1)Dropper (1)

PARTS:Calcium oxide (1)Water (1)Bromothymol blue (1)Filter Paper (1)Litmus paper (1)

RedPlastic bottle or (Plastic glass) (2)Fat Straw (1)Bendable Straw (1)

Respirometer Release: 2.2 - 2018-12-19

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— Precautions

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!

— Step 1 - Creating Units of Measure

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.

Respirometer Release: 2.2 - 2018-12-19

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— Step 2 - Unit of Measure

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

— Step 3 - Measuring 100 ml of Water

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.

Respirometer Release: 2.2 - 2018-12-19

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— Step 4 - Preparing Lime-water Solution

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.

— Step 5 - Cutting the Bottle

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.

Respirometer Release: 2.2 - 2018-12-19

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— Step 6 - Red Litmus Test

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.

— Step 7 - Preparing the Cap

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 thenumber of exhalations till the solution slowly turns pale green.

Respirometer Release: 2.2 - 2018-12-19

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— Play!

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.

— Troubleshooting

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.

Respirometer Release: 2.2 - 2018-12-19

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— Observations

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

After physical exertion, try the same experiment again. Note down the number of exhalationsrequired 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.

Respirometer Release: 2.2 - 2018-12-19

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— Observations

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 ofrespiration.

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.

Respirometer Release: 2.2 - 2018-12-19

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— Variations

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

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

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

— Variations

Perform the same experiment withdilute sodium hydroxide.

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

Respirometer Release: 2.2 - 2018-12-19

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