# Calculating HCO3- in Blood Sample w/ 2.6 X 10^-2 mol/L CO2

• lha08
In summary, a sample of arterial blood with a pH of 7.43 and a dissolved CO2 concentration of 2.6 X 10-2 mol/L can be used to determine the HCO3- concentration using the Henderson-Hasselbalch equation. However, to account for all forms of carbonate present, the concentration of HCO3- is represented as x and the concentration of dissolved CO2 is subtracted from it in the equation.
lha08

## Homework Statement

A sample of arterial blood was found to contain 2.6 X 10-2 mol/L dissolved CO2. The pH of the sample was 7.43. If it is assumed that in solution the CO2 forms H2CO3, what is the HCO3- concentration in this blood sample? (pKa for H2CO3 is 6.1)

## The Attempt at a Solution

so i first used the henderson hasselbalch equation for the equilibrium H2CO3 <-> HCO3- and then 7.43= 6.1 +log (A-)/(HA) and i got to 21.4= (HCO3-)/(H2CO3). Everything up to here i got, but then in the answer is said to let x= [HCO3-] and therefore 21.4= x / ((2.6X 10^-2)-x)...why do we have to subtract the x from the bottom?

Seems like dissolved CO2 means in this context all forms of carbonate present. But I agree wording is ambiguous.

When referring to buffers we commonly say things like "1M acetate buffer" and we mean sum of concentrations of acetic acid and acetate is 1M.

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## 1. How do you calculate the concentration of HCO3- in a blood sample with 2.6 X 10^-2 mol/L CO2?

The concentration of HCO3- can be calculated using the Henderson-Hasselbalch equation, which is pH = pKa + log([HCO3-]/[CO2]). First, determine the pKa value for HCO3-, which is 6.1. Then, plug in the values for pH (usually around 7.4 for blood), CO2 (2.6 X 10^-2 mol/L), and solve for [HCO3-]. This will give you the concentration of HCO3- in the blood sample.

## 2. What is the relationship between CO2 and HCO3- in blood?

CO2 and HCO3- are both important components of the bicarbonate buffer system in the blood. CO2 is converted into carbonic acid (H2CO3) by the enzyme carbonic anhydrase, which then dissociates into H+ and HCO3-. This process helps to maintain the pH of the blood within a narrow range.

## 3. How does the concentration of HCO3- affect blood pH?

HCO3- is a weak base and helps to buffer the blood against changes in pH. An increase in HCO3- concentration will cause the blood to become more basic (higher pH), while a decrease in HCO3- concentration will make the blood more acidic (lower pH).

## 4. What can cause an imbalance in HCO3- levels in the blood?

An imbalance in HCO3- levels can be caused by various factors, such as kidney or respiratory diseases, metabolic disorders, or medications. Certain lifestyle factors like diet and exercise can also affect HCO3- levels in the blood.

## 5. Why is it important to measure HCO3- levels in a blood sample?

HCO3- levels are important indicators of the body's acid-base balance. An abnormal level of HCO3- can be a sign of an underlying health issue or metabolic imbalances. Monitoring HCO3- levels can help healthcare professionals diagnose and manage various medical conditions.

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