Mass/volume percent concentrations

Chemists often express the concentration of an unsaturated solution as the mass of solute dissolved per volume of the solution. This is different from solubility. It is usually expressed as a percent relationship. A mass/volume percent gives the mass of solute dissolved in a volume of solution, expressed as a percent. The mass/volume percent is also referred to as the percent (m/v). 

You need to calculate the concentration of the solution, in grams of solute dissolved in 100 mL of solution. Then you need to express this concentration as a mass/volume percent. 

You have learned about several different ways in which chemists express concentration mass/volume, mass/mass, and volume/volume percent parts per million and parts per billion and molar concentration. The Concept Organizer above summarizes what you have learned in this chapter so far. 

Three ways of quantitatively expressing the concentration of a solution will be presented here Mass/mass percent, %(m/m), mass/volume percent, %(m/v), and molarity, M. A fourth, molality, will appear later in this chapter. You should know an interesting fact about concentrations. No matter what size sample of a solution you have, be it a teaspoonful or a bucketful, the concentration is the same for both. This is because concentrations are stated in terms of the amount of solute in a fixed amount of solvent 100 g, 100 mL, or 1.00 L. It s like density. The density of mercury is 13.6 g/mL. If I have 100 mL or three drops of mercury, the density of mercury is still 13.6 g/mL. Neither density nor concentration depends on the size of the sample. 

The mass/volume percent, %(m/v), states the mass of solute dissolved in a given volume of solution. Almost always, mass is in grams and volume in milliliters. Mass/volume percent is widely used in medicine for injectable medications and IV solutions. If a solution has a concentration of 2.5%(m/v), it contains 2.5 g of solute in 100 mL of solution. The units of g and mL do not appear in the concentration term, you must remember that with %(m/v), mass is in grams and volume in milliliters. 

What is the mass/volume percent concentration of a solution prepared by dissolving 72.5 g of sodium hydroxide, NaOH, in enough water to produce 850.0 mL of solution ... 

Because the cell membranes in biological systems are semipermeable, osmosis is an ongoing process. The solutes in body solutions such as blood, tissue fluids, lymph, and plasma all exert osmotic pressure. Most intravenous (FV) solutions used in a hospital are isotonic solutions, which exert the same osmotic pressure as body fluids such as blood. The percent concentration typically used in IV solutions is similar to the types of percent concentrations we have already discussed, except that the concentration of IV solutions is mass/volume percent m/v). The most typical isotonic solutions are 0.9% (m/v)... 

An ethanol-water solution is prepared by dissolving 10.00 mL of ethanol, CH3CH2OH d = 0.789 g/mL), in a sufficient volume of water to produce 100.0 mL of a solution with a density of 0.982 g/mL (Fig. 14-1). What is the concentration of ethanol in this solution expressed as (a) volume percent (b) mass percent (c) mass/volume percent (d) mole fraction (e) mole percent (f) molarity (g) molality ... 

Each part of this problem uses an equation presented in the text. Expressing concentrations in these different units will illustrate the similarities and differences among volume percent, mass percent, mass/volume percent, mole fraction, mole percent, molarity, and molality. 

Solution Concentration—Any description of the composition of a solution must indicate the quantities of solute and solvent (or solution) present. Solution concentrations expressed as mass percent, volume percent, and mass/volume percent all have practical importance, as do the units, parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt). However, the more fundamental concentration units are mole fraction, molarity, and molality. Molarity (moles of solute per liter of solution) is temperature dependent, but mole fraction and molality (moles of solute per kilogram of solvent) are not. 

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. 

Clearly, paying attention to units is important when working with concentration. Only by observing which units are attached to a measurement can you determine whether you re working with molarity, with mass percent, or with a mass-mass, mass-volume, or volume-volume percent solution. 

When mixing two liquids to form a solution, it is easier to measure their volumes than their masses. A volume/volume percent gives the volume of solute divided by the volume of solution, expressed as a percent. The volume/volume percent is also referred to as the volume percent concentration, volume percent, percent (v/v), or the percent by volume. You can see this type of concentration on a bottle of rubbing alcohol from a drugstore. (See Figure 8.17.)... 

Uniformity of lower limits on a mass basis. Concentrations of vapors and gases usually are reported in volume percent. As molecular weight increases, the lower limit usually decreases. On a mass basis, the lower limits for hydrocarbons are fairly uniform at about 45 mg/L at 0°C and 1 atm. Many alcohols and oxygen-containing compounds have higher values for example, on a mass basis, ethyl alcohol in air has a lower limit of 70 mg/L.27... 

The concentration units, indicated in the 3rd column, are molarity (c) molality (m) mass (w), volume (v) or mole (x) fiactions volume percent (V%). 

Intravenous solutions—those that are administered directly into a patient s veins— must have osmotic pressure equal to that of bodily fluids. These solutions are called isoosmotic. When a patient is given an IV in a hospital, the majority of the fluid is usually an isoosmotic saline solution—a solution containing 0.9 g NaCl per 100 mL of solution. In medicine and in other health-related fields, solution concentrations are often reported in units that indicate the mass of the solute in a given volume of solution. Also common is percent mass to volume—which is the mass of the solute in grams divided by volume of the solution in milliliters times 100%. In these units, the concentration of an isoosmotic saline solution is 0.9% mass/volume. 

The concentration of a solution is expressed through different concentration terms, including molarity, molality, mass percent, volume percent, and mole fraction. These terms are interconvertible. Section 13.4)... 

An important property of a solution is its oomcentratioii, the amount of solute relative to the amount of solvent. Two common ways to express concentration are percent by mass or percent by volume. For example, a 5% sugar solution by mass contains 5 g of sugar for every 100 g of solution. A 3% acetic acid solution by volume contains 3 ml of acetic acid for every 100 mL of solution. 

Concentrations of medicinal solutions are sometimes given in terms of weight/volume percent, the mass of solute per 100 ml of solution. The density of dilute solutions is very close to 1 g/mt, so the mass of 100 ml of solution is very close to 100 g. Thus, for solutions of 5% or less, mass percent and weight/volume percent are essentially equal. 

Concentration Mass Percent Volume Percent Mass/Volume Molarity... 

Percent concentration can also be expressed as a volume/volume (v/v) ratio or mass/volume (m/v) ratio. 

In addition, it sometimes becomes necessary to convert concentration from weight percent to mass of one component per unit volume of material (i.e., from units of wt% to kg/m ) this latter composition scheme is often used in diffusion computations (Section 5.3). Concentrations in terms of this basis are denoted using a double prime (i.e., Cf and Q), and the relevant equations are as follows ... 

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