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

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SUMMARY

The discussion focuses on calculating the bicarbonate ion (HCO3-) concentration in a blood sample with a dissolved CO2 concentration of 2.6 X 10^-2 mol/L and a pH of 7.43. The Henderson-Hasselbalch equation is utilized, with the pKa of carbonic acid (H2CO3) set at 6.1. The calculation leads to the equation 21.4 = x / ((2.6 X 10^-2) - x), where x represents the concentration of HCO3-. The subtraction of x from the denominator accounts for the equilibrium between H2CO3 and HCO3-, reflecting the total carbonate species in solution.

PREREQUISITES
  • Understanding of the Henderson-Hasselbalch equation
  • Knowledge of acid-base equilibria
  • Familiarity with pKa values and their significance
  • Basic concepts of buffer solutions and carbonate chemistry
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  • Study the Henderson-Hasselbalch equation in detail
  • Learn about carbonate chemistry and its role in biological systems
  • Explore the relationship between pH and bicarbonate concentration in blood
  • Investigate the implications of pKa values in buffer solutions
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This discussion is beneficial for chemistry students, biochemists, and healthcare professionals involved in understanding blood chemistry and acid-base balance.

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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)


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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?
 
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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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