Concentration units, converting between

It is important to be able to convert among the different concentration units. Conversions between molality and mole fraction are performed by considering a solution containing 1 kg of solvent ... 

The units of concentration most frequently encountered in analytical chemistry are molarity, weight percent, volume percent, weight-to-volume percent, parts per million, and parts per billion. By recognizing the general definition of concentration given in equation 2.1, it is easy to convert between concentration units. 

The inhalation RfD is derived from the NOAEL by applying uncertainty factors similar to those listed above for oral RfDs. A UF of 10 is used when e.Ktrapolating from animals to humans in addition to the calculation of the human equivalent dose, to account for interspecific variability in sensitivity to the to. icant. The resulting RfD value for inhalation c. posure is generally reported as a concentration in air in mg/m for continuous, 24 hour/day c. posurc, although it may be reported as a corresponding inhaled intake (in mg/kg-day). A human body weight of 70 kg and an inhalation rate of 20 nv /day are used to convert between an inhaled intake e.xprcsscd in units of mg/kg-day and a concentration in air e. pressed in mg/m. ... 

We see that the experimentally determined concentration range converts into a pH range of 1. That is, the buffer acts most effectively within a range of 1 units of p/v, (Fig. 11.3). For instance, because the pKa of H2P04 is 7.21, a KH2P04/K2HP04 buffer can be expected to be most effective between about pH = 6.2 and pH = 8.2. 

The expression of results is in basic SI units. Analytical chemistry is used to express results of the measurement process as concentrations expressed in different units according to the specific problem addressed. As long as these concentration units are properly defined there cannot be a problem in converting results. Neither can there be any real problem with the subtle difference between mass and amount of substance. 

To decide which value of R to use when you convert between and K, you can reason as follows. involves molar concentrations, for which the units are mol/L involves pressures expressed in atm. Thus the appropriate value of R to use for these conversions... 

To convert between units of radon-222 radioactivity (Ci or Bq) and the potential alpha energy concentration (WL or J/m the equilibrium between radon gas and radon daughters must be known (See Chapter 9 for conversion formula). When radon is in equilibrium with its progeny, that is, when each of the short-lived radon daughters is present at the same activity concentration in air as radon-222, then 1 WL equals 100 pCi radon-222/L of air. However, when removal processes other than radioactive decay are operative, such as with ventilation, the concentration of short- lived daughters will be less than the equilibrium amount. In such cases an equilibrium factor (F) is applied. For example, if the equilibrium factor is 0.5, then 200 pCi radon-222/L of air is equivalent to 1.0 WL if the equilibrium factor is 0.3, then 1 WL corresponds to 333 pCi radon-222/L of air. 

The easiest way to convert between concentrations is to take a careful look at the units of both what you want and what you have, and ask what physical properties (i.e. molar mass, density) you could use to interchange them. In this example, we want to convert a molarity into a mass fraction. We have from the definitions that ... 

If you follow the dimensional analysis techniques you learned in Chapter 1, you can convert between concentration units, as shown in Sample Exercise 13.5. To convert between molality and molarity, the density of the solution will be needed, as in Sample Exercise 13.6. 

We have referred to the solubility of silver salts regularly in this chapter. In Chapter 3, we defined solubility in terms of the mass of solute that dissolves in 100 g of solute, but this was just one possible choice of concentration units. Molar solubility is the concentration of a dissolved solid present in a saturated solution, expressed in molarity. Based on the units for concentration presented in Chapter 4, we can convert between these two different expressions for solubility. Molar solubility is easily determined from K p, as you can see in Example Problem 12.11. 

Solution Concentration Solution concentration is useful in converting between amounts of solute and solution. Mass percent and molarity are the most common concentration units. Molality is used to quantify colligative properties such as freezing point depression and boiling point elevation. 

Molal units are used predominately by engineers and scientists studying electrolytes because the concentration calculation is independent of density and, hence, temperature. Molal concentration is the number of gm-moles per 1000 gm of solvent. Equations 2-lc and 2-ld show how to convert between molal and molar concentrations. Note that as the acid or base weight fraction approaches one (the grams of solvent approaches zero), the molal concentration approaches infinity. 

Any property of a reacting system that changes regularly as the reaction proceeds can be formulated as a rate equation which should be convertible to the fundamental form in terms of concentration, Eq. (7-4). Examples are the rates of change of electrical conductivity, of pH, or of optical rotation. The most common other variables are partial pressure p and mole fraction Ni. The relations between these units... 

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