How much 1.0 mol/L HCL would you need to add to 1 L of an imaginary buffer of 0.10 mol/L to change the pH from 6.8 to 6.0. (Neglect volumes and remember that HCL disassociates completely)
(About the buffer= triprotonic weak acid with pK1= 2.0, pK2 7.5, pK3= 12)