Blood & Sea Buffer LabHASPI Medical Chemistry Lab 8a

Background – Buffers in Blood & Sea There are many substances that have an effect on the pH of a solution. Of course directly adding an acid or a base to the solution will change its pH, but there are other chemicals that can react with the solution itself to make changes. One of these chemicals is Carbon Dioxide, or CO2. You might not have realized that a bit of CO2 can make a change because it’s so prevalent.

CO2 is all around us in the atmosphere, and you even breathe CO2 out with every breath, but if you didn’t have buffers in your blood stream you’d quickly die as your cells can’t handle a pH change. Your blood’s pH is maintained at 7.4. Anything above 7.8 is known as alkalosis, a pH below 6.8 is acidosis. Either of these problems can quickly lead to seizures, coma and ultimately death.

A buffer is a chemical that resists changes in pH because it’s a combination of a weak acid and its conjugate base, or a weak base and its conjugate acid. This combination means that the acid can neutralize any bases that enter the solution and the base can neutralize any acids that enter the solution, thereby keeping the pH from changing.

In order to keep this reaction at equilibrium, your body pulls out any CO2 by breathing it out and pulls out any HCO3

− through the urine. This means that you continually have a balance where the H2CO3

− is available to buffer the blood.

The CO2 in the air around us can also have an effect on the pH of solutions. In recent years the CO2 levels of our atmosphere has increased, and at one point the scientists realized that there was a bit less CO2 in the atmosphere than had been expected. Ultimately they found out that a portion of the CO2 emitted by cars and factories was being absorbed by the ocean.

Sadly, the ocean can only handle so much CO2. The dissolved CO2 particles react with the water in the ocean to create carbonic acid. As the ocean becomes more acidic the shells of certain organisms begin to dissolve, leaving them weak and the offspring is unable to grow shells properly. The carbonic acid leaves free hydrogen ions in the ocean which react to bind with carbonate ions in the shells of many sea organisms.

These shells, made of calcium carbonate and magnesium calcite, are found in corals, mussels, clams, sea urchins and sea stars. As these organisms are the food source for many other sea creatures, their decline could cause significant issues throughout the ocean food chain.

HASPI Medical Chemistry Unit 8: Solutions & Acids

The blood buffer system

at work

https://leukocyteerythrocyte.wordpress.com/2012/05/10/acidosis-and-alkalosis/

http://www.reefresilience.org/coral-reefs/stressors/ocean-acidification/ocean-carbon-chemistry/

Lab 8a, Page 1

Review Questions1. What are the effects of CO2 on the human body?

2. What is the safe pH range for human blood?

3. What are the effects of CO2 on the ocean?

4. What organisms are most affected by ocean acidification?

5. What can we do to stop or slow ocean acidification?

HASPI Medical Chemistry Unit 8: Solutions & AcidsLab 8a, Page 2

Blood & Sea Buffer LabHASPI Medical Chemistry Lab 8a

Objectives

By the end of this activity students will be able to Describe what happens to an aqueous solution when exposed to CO2

Explain the effect of a buffer on a solution Connect the ideas of buffers to equilibrium Better understand the reason that our blood maintains one pH Describe the relationship between CO2 levels and ocean acidification

Materials

1 Clear plastic cup 1 straws per group Universal IndicatorUniversal Indicator color chart pH strips NaHCO3

Procedure

Bag A:1. Add 20mL of water and 4 drops of universal indicators to two clear plastic cups. 2. Add 1 tsp of NaHCO3 to one cup. This will act as the buffer.3. Take the pH of each cup, using a pH strip, discard after each reading. Record in the table below.4. Blow through the straws for 15 second intervals, recording the pH after each interval.

Bag B:1. Add 20mL of water and 4 drops of universal indicators to two clear plastic cups. 2. Add 1 tsp of NaHCO3 to one cup. This will act as the buffer.3. Take the pH of each cup, using a pH strip, discard after each reading. Record in the table below.4. Blow into the cup for 15 second intervals, so the CO2 is only added at the surface, recording the pH after

each interval.

Data CollectionBag A: CO2 addition through a straw

Water color Water pH Buffered water color Buffered water pHBefore experimentAfter 15 secAfter 30 secAfter 45 secAfter 1 minuteAfter 2 minutes

Bag B: CO2 addition through surface exposureWater color Water pH Buffered water color Buffered water pH

Before experimentAfter 15 secAfter 30 secAfter 45 secAfter 1 minuteAfter 2 minutes

Conclusion

HASPI Medical Chemistry Unit 8: Solutions & AcidsLab 8a, Page 3

1. Consider the pH of your buffered solutions. Why is this buffer a good buffer for your blood?

Consider the following reaction as you answer the following equilibrium questions:3. When CO2 is added to the blood, what direction would the reaction shift?

4. When free hydrogen ions are added to the water (H+ aq) which direction would the reaction shift?

5. What is H2CO3 called?

HASPI Medical Chemistry Unit 8: Solutions & AcidsLab 8a, Page 4