Consequently, a glucose concentration of 180 mg/l (or 18 mg/dl) is equal to 1 mmol/l. The molecular weight (mol wt) of glucose is 180. However, elsewhere, they are more commonly measured in the clinical laboratory as milligrams per deciliter (mg/dl or mg%). The concentration of uncharged molecules, e.g., glucose and urea, also can be measured in millimoles per liter and this is commonly the case where the Systeme International (SI units) is used. However, 1 mmol of NaCl (58.5 mg) largely dissociates into Na+ and Cl- ions and therefore contains almost twice as many particles. Thus, 1 mmol of Na+ contains the same number of atoms as 1 mmol of Cl- even though the former weighs 23 mg and the latter weighs 35.5 mg. Avogadro’s LawĪvogadro’s Law states that 1 mole of any non-dissociable substance (a substance than cannot be further reduced to component units) contains the same number of particles (approximately 6.02 x 10 23 = Avogadro’s number). Therefore, for Na+,Ģ3 mg of Na + in 1 liter of water = Na + concentration () of 1 mmol/l. The atomic weight of sodium (Na+ ) is 23. Similarly, one millimole (mmol) is equal to one-thousandth of a mole or the molecular (or atomic) weight in milligrams. One mole (mol) of any substance is defined as the molecular (or atomic) weight of that substance in grams. Also, important in this field is Avogadros number (NA) or Avogadros constant. For example, the molecular weight of water (H2O) is 18 ( + 16). A few things to consider when finding the molar mass for CuSO4 Jan 29. In a molecule, i.e., a substance containing two or more different atoms, the molecular weight is equal to the sum of the atomic weights of the individual atoms. By definition, one atom of oxygen is assigned a “weight” of 16, and the atomic weights of the other elements are determined in relation to that of oxygen. The atomic weight of a substance is an assigned number which allows comparison of the relative masses (weights) of the different elements. Total mass/total volume = concentration Atomic weight and molarity Total mass/concentration (mass/volume) = total volumeĪnd, given total mass and total volume provides a result for concentration as Similarly, knowing total mass and concentration gives total volume of solvent as So, Molar mass of Sodium oxalate (Na2C2O4) Molar mass of 2 Sodium (Na) atoms + Molar mass of 2 Carbon (C) atoms + Molar mass of 4 Oxygen (O) atoms. If we know the concentration of a substance (mass/volume) and we know the total volume of solvent in which the substance (solute) is dissolved (volume), it follows that the total mass of solute is given byĬoncentration (mass/volume) x total volume = total mass The unit of volume chosen is usually one appropriate to the expected concentration of the substance or to a volume that makes physiological sense – gram / liter (g/l), millimole / liter (mmol/l), milligram / milliliter (mg/ml). The units of measurement of an amount of substance are conveniently reported as concentration which is mass per unit of volume. a The notation for sodium chloride, NaCl, stands for one (a) formula unit.
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