Respirometer · — 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

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

Written By: Vishal Bhatt

Respirometer Release: 1.3 - 2018-07-24

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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)

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

RedPlastic bottle or (Plastic glass) (2)


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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!

— 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.


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— Step 2 - Creating units 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 can hold 17 ml of water.

Add 6 volumes of the water with the test tube to a plastic bottle/container.

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


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— Step 4 - Preparing lime-water solution

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

Use one measure (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 onto the lower part. This acts like a funnel.

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


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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 6 -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. Count the number of exhalations. The solutionwill slowly turn pale green.


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— Step 6 - The Colour Change

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.

— After physical exertion

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.

— Troubleshooting

Patiently blow untill the colour changes.

Lime is not mixed well with water.


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— Observation

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

Record this in a table similar to shown here.

Repeat above 5 times to average out any error in measurements.

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.

— 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.

Perform the same experiment with dilute sodium hydroxide.

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


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— Variation 1: Changing the Volume

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 ofexhalations required to cause the colour change.

— Variation 1: Changing the Volume

Tabulate your results in the giventable.


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— Variation 2 : Changing the Concentration

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

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

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

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

Tabulate your observation with the help of the given table.

— Variation 3 : Use Dilute NaOH

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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— Variation 3 : Use Dilute NaOH

Count the number of exhalations required to change the colour.

Watch the solution slowly turn to pale green.

— Variation 4 : Using Vinegar + Baking Soda for CO2

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

Be careful while handling the scissors.

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


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Put 5 g 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 andclose the cap tightly.

Shake the bottle to increase the rate of reaction.


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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Documents

Respirometer · — 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