Pka weak acid

A 1:1 equilibrium mixture of HIn and In^-

Orange

An equilibrium mixture of HIn and In^-  where [In^- ]/[HIn] = 100/1:

Yellow

An equilibrium mixture of HIn and In^-  where [In^- ]/[HIn] = 1/100:

Red

A buffer contains a weak acid, HA, and its conjugate base A*.

a. In a buffer containing a mixture of potassium dihydrogen phosphate and sodium hydrogen phosphate, identify the weak acid and the conjugate base. Write the reaction for the equilibrium between the weak acid and its conjugate base in this buffer.

H₂PO₄⁻ (aq)⇌HPO₄²⁻ (aq) + H⁺ (aq)

If HCL is added to the buffer above, show the reaction that would occur. (write a net ionic equation). How would the ratio [A^- ]/[H⁺] change?

net ionic: A^- + H⁺ —> HA.

This decreases the concentration of A- (numerator)

And increases the concentration of HA (denominator)

Therefore, the ratio [A-]/[HA] becomes smaller

In this experiment, potassium nitrite is added for

2l^- + 2NO₂ + 4H⁺ → I₂ + 2NO + 2H₂O

Why is the nitrite necessary when it is the (l) at equilibrium that we want to measure?

Nitrite is necessary to convert I⁻ into I₂, which is what the spectrophotometer actually measures