KH2PO4 vs K2HPO4: Key Differences Every Lab Must Know
KH2PO4 is monopotassium phosphate, delivering one H+ ion and used to lower pH; K2HPO4 is dipotassium phosphate, accepting one H+ and used to raise pH. Both are potassium salts of phosphoric acid, yet their proton count flips buffering direction.
Technicians grab the wrong jar because the labels differ by only one digit. In cell culture, using K2HPO4 when the recipe calls for KH2PO4 can swing pH past 8, stressing cells and ruining weeks of work.
Key Differences
KH2PO4 adds acid, K2HPO4 adds base. Their molar masses differ by ~18 g/mol, so recipes calibrated for one will drift if the other is substituted. Check the bottle: “mono” vs “di” decides your buffer’s fate.
Which One Should You Choose?
Need acidic pH (5.8–6.5) for plant media or yeast? Pick KH2PO4. Preparing neutral to slightly alkaline mammalian cell media? Choose K2HPO4. Always verify the pKa curve before you weigh anything.
Can I mix both?
Yes; blending gives a precise pH, but calculate molar ratios with a Henderson-Hasselbalch calculator first.
Storage tips?
Keep both powders in airtight bottles with desiccant; they’re hygroscopic and clump quickly in humid labs.