Creatinine, , is a by-product of muscle metabolism, and creatinine levels in the body are known to be a fairly reliable indicator of kidney function. The normal level of creatinine in the blood for adults is approximately 1.0 mg per deciliter (dl) of blood. If the density of blood is 1.025 g/ml, calculate the molality of a normal creatinine level in a 10.0-ml blood sample.

Molality = 0.0862 mole/kg

Explanation:

Molality = (number of moles of solute)/(mass of solvent in kg)

Number of moles of solute = (mass of Creatinine in the blood sample)/(Molar mass of Creatinine)

To obtain the mass of creatinine in 10 mL of blood. We're told that 1 mg of Creatinine is contained in 1 decilitre of blood.

1 decilitre = 100 mL

1 mg of Creatinine is contained in 100 mL of blood

x mg of Creatinine is contained in 10 mL of blood.

x = (1×10/100) = 0.1 mg = 0.0001 g

Molar mass of Creatinine (C₄H₇N₃O) = 113.12 g/mol

Number of moles of Creatinine in the 10 mL blood sample = (0.0001/113.12) = 0.000000884 moles

Mass of 10 mL of blood = density × volume = 1.025 × 10 = 10.25 mg = 0.01025 g = 0.00001025 kg

Molality of normal creatinine level in a 10.0-ml blood sample = (0.000000884/0.00001025)

Molality = 0.0862 moles of Creatinine per kg of blood.

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