Answer to Question #110722 in Molecular Biology for FRIDAY

Question

Question 2: Based on the equation below, which ion plays the role of hydrogen-ion donor (acid) and which ion plays the role of hydrogen-ion acceptor (base) in PBS?
H2PO4-(aq) ⇆ H+(aq) + HPO42-(

The composition of PBS is 0.137M NaCl, 0.012M Phosphate, 0.0027M KCl, pH 7.4. Below is the protocol to make 1 liter of 10x concentrate PBS.
Combine the following:
• 80g NaCl
• 2g KCl
• 14.4g Na2HPO4 (dibasic anhydrous)
• 2.4g KH2PO4 (monobasic anhydrous)
• 800mL distilled H2O

1. Adjust pH to 7.4 with HCl
2. Add H2O to 1L
3. Autoclave for 20 minutes on liquid cycle. Store at room temperature.

Answer 1

The reaction given:

H₂PO₄^-_(aq) ⇆ H⁺_(aq) + HPO₄^2-_( aq)

Here, H₂PO₄^- ion serves as a proton donor, while HPO₄^2- ion is a proton acceptor. In a PBS solution, Na₂HPO₄ dissociates into Na⁺ and HPO₄^2-. As a result, this molecule serves as a proton acceptor. In contrast, KH₂PO₄ dissociates into K⁺ and H₂PO₄^-. As H₂PO₄^- is a proton donor, KH₂PO₄ serves as a proton donor in a PBS solution.