Concentration units molarity

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. 

Whereas the Bjerrum length is a property of the solvent, the Debye length is a property of the solution. The dependence of on the electrolyte concentration can be written in terms of the experimentally convenient concentration unit (molarity, i.e., number of moles per liter, with liter being dm ). The number density tiao of ions of a-type is... 

Several different methods are used to express relative amounts of solute and solvent in a solution. Two concentration units, molarity and mole fraction, were referred to in previous chapters. Two others, mass percent and molality, are considered for the first time. 

Experiments on sufficiently dilute solutions of non-electrolytes yield Henry s laM>, that the vapour pressure of a volatile solute, i.e. its partial pressure in a gas mixture in equilibrium with the solution, is directly proportional to its concentration, expressed in any units (molar concentrations, molality, mole fraction, weight fraction, etc.) because in sufficiently dilute solution these are all proportional to each other. 

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. 

A stock solution is prepared by weighing out an appropriate portion of a pure solid or by measuring out an appropriate volume of a pure liquid and diluting to a known volume. Exactly how this is done depends on the required concentration units. For example, to prepare a solution with a desired molarity you would weigh out an appropriate mass of the reagent, dissolve it in a portion of solvent, and bring to the desired volume. To prepare a solution where the solute s concentration is given as a volume percent, you would measure out an appropriate volume of solute and add sufficient solvent to obtain the desired total volume. 

The solubihty coefficient must have units that are consistent with equation 3. In the hterature S has units cc(STP)/(cm atm), where cc(STP) is a molar unit for absorbed permeant (nominally cubic centimeters of gas at standard temperature and pressure) and cm is a volume of polymer. When these units are multiphed by an equihbrium pressure of permeant, concentration units result. In preferred SI units, S has units of nmol /(m GPa). 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

In solution k metics we commonly work with systems at constant volume, and we find it convenient to employ molar concentration units. Dividing both sides of Eq. (1-9) by volume V gives... 

To carry out these calculations for solution reactions, you need to be familiar with a concentration unit called molarity, which tells you how many moles of a species are in a given volume of solution. ... 

In Chapter 4, molarity was the concentration unit of choice in dealing with solution stoichiometry. You will recall that molarity is defined as... 

Molality and molarity are concentration units morality is something else. 

It is frequently necessary to convert from one concentration unit to another This problem arises, for example, in making up solutions of hydrochloric acid. Typically, the analysis or assay that appears on the label (Figure 10.2, p. 263) does not give the molarity or molality of the add. Instead, it lists the mass percent of solute and the density of the solution. 

Molal boiling point constant, 269,270t Molal freezing point constant, 269,270t Molality (m) A concentration unit defined as the number of moles of solute per kilogram of solvent, 259,261-262 Molar mass The mass of one mole of a substance, 55,68-68q alcohol, 591 alkane, 591... 

The molality, m = moles per kilogram of solvent, as a temperature-independent concentration unit instead of the molarity, C = moles per litre of solution this means that the amount of solvent and hence its number of moles is fixed. 

Equivalents are measures of the quantity of a substance present, analogous to moles. Normality is a concentration unit, analogous to molarity. The similarities are so great that these two units should be very easy to learn to use, but many students have difficulty with them. Be sure that you understand the underlying definitions before you proceed. 

In contrast to the other reaction orders, the velocity of a zero-order reaction does not change with the concentration of the substrate or with time (Fig. 24-6). The velocity (slope) is a constant and k has the units molar per minute (M/min, or M min ). Reactions that are zero-order in absolutely everything are rare. However, it is common to have reactions that may be zero-order in the reactant that you happen to be watching. Let s think of a two-step reaction. 

In this chapter, you learned about solutions. A solution is a homogeneous mixture composed of a solvent and one or more solutes. Solutions may be unsaturated, saturated, or supersaturated. Solution concentration units include percentage, molarity, molality, and mole fraction. The solubility of solids in liquids normally increases with increasing temperature, but the reverse is true of gases dissolving in liquids. The solubility of gases in liquids increases with increasing pressure. 

One important aspect of solutions is their concentration, the amount of solute dissolved in the solvent. In the chapter on solutions and colligative properties we will cover several concentration units, but for the purpose of stoichiometry, the only concentration unit we will use at this time is molarity. Molarity (M) is defined as the moles of solute per liter of solution ... 

There are many ways of expressing the relative amounts of solute(s) and solvent in a solution. The terms saturated, unsaturated, and supersaturated give a qualitative measure, as do the terms dilute and concentrated. The term dilute refers to a solution that has a relatively small amount of solute in comparison to the amount of solvent. Concentrated, on the other hand, refers to a solution that has a relatively large amount of solute in comparison to the solvent. However, these terms are very subjective. If you dissolve 0.1 g of sucrose per liter of water, that solution would probably be considered dilute 100 g of sucrose per liter would probably be considered concentrated. But what about 25 g per liter—dilute or concentrated In order to communicate effectively, chemists use quantitative ways of expressing the concentration of solutions. Several concentration units are useful, including percentage, molarity, and molality. 

Notice that this equation uses kilograms of solvent, not solution. The other concentration units use mass or volume of the entire solution. Molal solutions use only the mass of the solvent. For dilute aqueous solutions, the molarity and the molality will be close to the same numerical value. 

For the chemist the most useful unit of concentration is molarity (M), which is the moles of solute per liter of solution. Know how to work molarity problems. 

In working rate law problems, be sure to use molarity for your concentration unit. 

Consequently, a more rigorous treatment particularly specifies Kp as the ratio of the activities of the substance (A) in the two solvents instead of their concentrations. Hence, for dilute solutions, at a specified constant pressure and temperature, the mole fraction of a solute is directly proportional to its concentration in molarity or mass per unit volume which implies that these may be employed instead of mole-fraction in Eq. 

The phase rule is often used in the form t = c - p + 2 to ascertain the number of degrees of freedom of a system even when the concentration units in the aqueous phase are molal (m) or molar. This is not correct because the phase rule is derived 1n terms of mole fractions (X). Thus, an additional quantity, the total number of moles, is required to convert X into m. This is illustrated by equations below which we shall find useful later on. 

A = latm. The units of are (mL gas)/(LSWatm), giving [A(aq)] units of (mL gas)/G. SW). In this concentration unit, the gas abundance is expressed as the volume it would occupy if extracted from the seawater and subjected to STE Under these conditions, the gas s molar volume is 22,414 mL (assuming ideal gas behavior). Thus, gas concentrations expressed in units of can be converted to molarity and molinity (mol/kg) using the following ... 

Solubility concentratiorrs can be expressed many ways, including molarity (mol/L), molality (mol/kg), mole fraction, weight percent, mass per unit volume (e g., g/L), etc. The conversion formttlas for solutiotts having different concentration units are presented in Table 1. 

The standard enthalpy difference between reactant(s) of a reaction and the activated complex in the transition state at the same temperature and pressure. It is symbolized by AH and is equal to (E - RT), where E is the energy of activation, R is the molar gas constant, and T is the absolute temperature (provided that all non-first-order rate constants are expressed in temperature-independent concentration units, such as molarity, and are measured at a fixed temperature and pressure). Formally, this quantity is the enthalpy of activation at constant pressure. See Transition-State Theory (Thermodynamics) Transition-State Theory Gibbs Free Energy of Activation Entropy of Activation Volume of Activation... 

Pj), mole fraction (xj), and concentration (Cj). For these units the standard state is defined as unit activity Oj, which is typically Pj = 1 atm and 298 K, or Xj = 1 for pure liquid at 1 atm and 298 K, or C = 1 mole/liter at 298 K, respectively. Students have seen the first two of these for gases and liquids in thermodynamics. We wiU use concentration units wherever possible in this course, and the natural standard state would be a 1 molar solution. However, data are usually not available in this standard state, and therefore to calculate equilibrium composition at any temperature and pressure, one usually does the calculation with Pj or Xj and then converts to Cj ... 

---