Respirometer A classic acid-base indicator can also be used as a simply made respirometer Written By: Vishal Bhatt 2018 Page 1 of 13
INTRODUCTION Chemical reactions often create a change in colour. Here, we use one such reaction to also measure our 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) Red Plastic bottle or (Plastic glass) (2) 2018 Page 2 of 13
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. 2018 Page 3 of 13
Step 2 - Unit of Measure Cut the straw at the 1 cm mark. This is our unit of measure. This piece can hold approximately 0.2 g 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. 2018 Page 4 of 13
Step 4 - Preparing Lime-water Solution 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. 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. 2018 Page 5 of 13
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 the number of exhalations till the solution slowly turns pale green. 2018 Page 6 of 13
Step 8 - 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. Step 9 - 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 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 2018 Page 7 of 13
Troubleshooting Patiently blow until the colour changes. Lime is not mixed well with water. Not enough indicator Observation 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. 2018 Page 8 of 13
Variations 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. Variation 1 - Step 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 of exhalations required to cause the colour change. 2018 Page 9 of 13
Variation 1 - Step 2 - Changing the Volume Tabulate your results in the given table. 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 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. 2018 Page 10 of 13
Variation 3 - Step 1 - 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. Variation 3 - Step 2 - Use Dilute NaOH Count the number of exhalations required to change the colour. Watch the solution slowly turn to pale green. 2018 Page 11 of 13
Variation 4 - Step 1 - Using Vinegar + Baking Soda for CO2 Make a hole in the bottle cap with the help of scissors. Pass the capillary tube into the hole in the bottle cap. Variation 4 - Step 2 - Using Vinegar + Baking Soda for CO2 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. 2018 Page 12 of 13
Variation 4 - Step 3 - Using Vinegar + Baking Soda for CO2 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. 2018 Page 13 of 13