Some H 2 CO 3 and HCO 3 – are added to water such that both concentrations are 1

Question

Some H2CO3 and HCO3– are added to water such that both concentrations are 12.0 mmol L-1 (pKa = 6.3, 10.3). The water was initially at pH 7.00 and 25 °C. How does the pH of the solution change as the reaction approaches equilibrium?

The pH will decrease

The pH will increase

The pH will remain unchanged

There is insufficient information to answer this question

1 points   

QUESTION 2

Calculate the average charge of H3A2+ at pH 7.40 (pKa = 3.5, 6.0, 9.3). (Hint: remember that the answer must be ± 0.5 of the dominant charge.)

1 points   

QUESTION 3

Some H2CO3 and HCO3– are added to water such that both concentrations are 12.0 mmol L-1 (pKa = 6.3, 10.3). The water was initially at pH 7.00 and 25 °C. Calculate Grxn in kJ mol-1. (R = 8.3145 J mol-1 K-1)

The pH will decrease

The pH will increase

The pH will remain unchanged

There is insufficient information to answer this question

Explanation / Answer

Q1.

pH= pKa + log(HCO3-/H2CO3)

pH = 6.3 + log(12/12)

pH = 6.3

the pH should drop to acidic pH = 6.3 due to buffer formation

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