1. How much does the pH change when a strong acid is added to an equal mixture o

Question

1. How much does the pH change when a strong acid is added to an equal mixture of H2PO4- and HPO4 -2 ?

2. How much does the pH change when a strong base is added to an equal mixture of H2PO4- and HPO4 -2 ?

256 Activity 51 l What Are Buffer systems in Your Body that Keep You Alive phos Consider a beaker the dilhydrogen phosphate and hydrogen containing equal amounts of strong base is added phate to which either a strong acid i added 1.0 mL 1.0 mL 1.0 M NaOH 1.0 M HCI 1.0 L 1.0 L [H2PO4 LH2PO41 0.010 M 0.010 M UHPO42 0.010 M 0.010 M Beaker D Beaker C 9. Calculate the pH of the contents of Beaker C

Explanation / Answer

1. pH of the solution can be calculated easily by calculating total Hydronium ion concentration. Dihydrogren phosphate and hydrogen phosphate both are very week acids and are also conjugate acid base pairs. Also the Hydronium ions coming from HCl ( 1ml*1M= 1 millimoles) is significantly large as compared to concentration of both the phosphate acids present. Having said that, the total hydronium ions are approximately equal to that coming from HCL, neglecting the H+ from H2PO4- and HPO42-

Therefore, [H+] = moles of H+ from HCl/ total volume of final solution after mixing

= 1 millimole/ 2L = 5*10^(-4)

pH=-log(5*10^(-4))= 4- 0.6989= 3.3 =Ans

2 Similarly, the OH- coming from NaOH (1ml*1M= 1millimole) brings significantly large no. of OH-ion in the solution and OH- coming from hydrolysis of HPO4^2-

Total [OH-]= 1 millimoles/ 2L= 5*10^(-4)

pOH= 3.3

pH= 14-pOH= 14-3.3= 10.7=Ans

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.