How Do You Calculate pH for a NaCN and HCN Solution?

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Homework Help Overview

The discussion revolves around calculating the pH of a solution formed by mixing sodium cyanide (NaCN) with hydrocyanic acid (HCN). The context involves understanding the behavior of weak acids and their salts in solution.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the Henderson-Hasselbalch Equation and the concept of buffer solutions. There are questions about how to determine ion concentrations and the implications of mixing a weak acid with its salt.

Discussion Status

Some participants have provided guidance on using the Henderson-Hasselbalch Equation and calculating concentrations, while others are exploring the implications of the solution being buffered and basic. Multiple interpretations of the approach are being considered.

Contextual Notes

There is a mention of the acid's ionization being minimal and the need to calculate molarity based on moles and volume. The specific values for concentrations and the dissociation constant (Ka) are provided, but further details on assumptions or constraints are not discussed.

Giuseppe
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I am stuck on this question...can anyone help?

What is the pH after .10 mol NaCN is added to 100 mL of .050 M of HCN?
(Ka=6.0x10^-19)

I think I have to use the Henderson-Hasselbalch Equation. Is this the right way to take. And if so, how should I go about getting the ion concentration?
 
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Apply the derived equation for the Weak Acid and strong base...I guess there is one dervied from that, applying the fact that the HCN will be very less ionized, whereas the NaCN will go and create a strong base thing...NaOH
 
Giuseppe,

As you are adding an Acid to its salt, the solution form a buffer which will be basic and can be calculate by using:

pH=pK+log [Salt]/[Acid]

Where [Salt]=Concentration Of NaCN

and [Acid]=Concentration of Acid


Calculate the concentration of salt By using the formula for calculation of molarity if you know the moles and the volume of the solution.
 
concentration of HCN will remain the same, for NaCN, .100moles/.1L
 

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