Equation for weak base

The equation for weak base calculator calculates the unknown concentration of the dissociated weak base in a water solution. 

INSTRUCTIONS: Choose the preferred units and enter the following:

• (K_b) This is the base equilibrium constant
• (F) This is the formal concentration in units of (mol/L)

Concentration of Dissociated Base: Thee concentration of the dissociated base [BH⁺] in units of (mol/L)

The Math / Science

The common weak-base reaction is 

for which the equilibrium equation is 

since we are usually given the formal concentration , the [BH⁺]=x is unknown and we must solve for it. First we assume that x is going to be much smaller than the formal concentration, thus the equilibrium equation becomes

Multiplying both sides by the formal concentration we get

Taking a square root of both sides we get 

Description

The equation is 

where 

• K_b is the base equilibrium constant
• F is the formal concentration in units of (mol/L)
• x is the concentration of the dissociated base [BH⁺] in units of (mol/L)

References

Harris, 9th Edition.  Pp.195