1. Suppose you had a buffer containing 0.5 moles of sodium monobasic phosphate a

Question

1. Suppose you had a buffer containing 0.5 moles of sodium monobasic phosphate and 0.5 moles of sodium dibasic phosphate. How many moles of hydrochloric acid would this phosphate buffer be able to accept before the pH of the solution began to change drastically?

Conclusions

2.Which chemical provides the conjugate base in the buffer containing NaH2PO4 and Na2HPO4?

3. Explain why phosphate buffer needs both Na2HPO4 and NaH2PO4 in order to resist changes in pH.   

4. Predict what might happen if you made up phosphate buffer with only half as much NaH2PO4 compared to Na2HPO4.   

5. Your lab mate attempts to use bromothymol blue to differentiate between two solutions – one that should be pH 7.3, and another that should be pH 6.7. What is your advice to your lab mate? Do you agree with his decision?   

Explanation / Answer

1.In order to change pH drastically atleast 5 moles of HCl would be needed to change pH by 1 point.

2.Na2HPO4 provides the conjugate base in the buffer containing NaH2PO4 and Na2HPO4

3. The phosphate buffer contains This buffer system consists of dihydrogen phosphate ions (HPO4-) as hydrogen-ion donor (acid) and hydrogen phosphate ions (HPO42-) as hydrogen-ion acceptor (base). These two ions are in equilibrium with each other as indicated by the chemical equation below.

H2PO4-(aq) +   H+(aq) + HPO42-(aq)

If additional hydrogen ions are added, they are consumed in the reaction with HPO42-, and the equilibrium shifts to the left. If additional hydroxide ions enter the added, they react with H2PO4-, producing HPO42-, and shifting the equilibrium to the right.

Thus we can say that phosphate buffer needs both the Na2HPO4 and NaH2PO4 in the solution to resist the change in pH.

4. When you made up phosphate buffer with only half as much NaH2PO4 compared to Na2HPO4 the buffering capacity of the solution will decrease and there will be residual acidic H(+) ions willbe free in the system. This will casue pH to become 6.30. (Slighltly acidic buffer).

5. I will diagree wiyh my lab mate. Because bromothymol blue is not a suitable indicator defferentiate between two solutions – one that should be pH 7.3, and another that should be pH 6.7. bromothymol blue will show yellow color below pH 6 and it bacame blue above 7.6.

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

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