Question

Blood plasma has the following composition (milliequivalents per litre). Calculate its osmotic pressure at $37^{\circ}C$
$Na^{+}=138, Ca^{2+}=5.2, K^{+}=4.5, Mg^{2+}=2.0, Cl^{-}=105, HCO^{-}_{3}=25, PO^{3-}_{4}=2.2, SO^{2-}_{4}=0.5$, Proteins = 16, Others = 1.0

• A. $7.47\,atm$
• B. $7.30 \,atm$
• C. $7.29\,atm$
• D. $7.40 \,atm$

Answer 1

Answer: (A)

Since for calculating osmotic pressure we require millimoles/litre therefore
$Na^{+}=138$,
$Ca^{2+}=\frac{5.2}{2}$
$=2.6, K^{+} \ = 4.5$,
$Mg^{2+}=\frac{2.0}{2}$
$=1.0$,
$Cl^{-}=105$,
$HCO^{-}_{3}=25$,
$PO^{3-}_{4}=\frac{2.2}{3}=0.73$,
$SO^{2-}_{4}=\frac{0.5}{2}=0.25$, Proteins = 16,
others = 1.0
Total = 294.18 millimoles/litre
$=\frac{294.18}{1000}=0.294$ moles/litre
Now since $\pi=CST$
$=0.294 \times 0.0821 \times .310=7.47$ atm