Chemistry
Concentration
Concentration refers to the amount of a substance present in a given volume of a solution. It is typically expressed as the mass of the solute per unit volume of the solvent. Concentration is an important factor in chemical reactions and plays a crucial role in determining the properties and behavior of a solution.
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12 Key excerpts on "Concentration"
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2015(Publication Date)
- Openstax(Publisher)
The relative amount of a given solution component is known as its Concentration. Often, though not always, a solution contains one component with a Concentration that is significantly greater than that of all other components. This component is called the solvent and may be viewed as the medium in which the other components are dispersed, or dissolved. Solutions in which water is the solvent are, of course, very common on our planet. A solution in which water is the solvent is called an aqueous solution. A solute is a component of a solution that is typically present at a much lower Concentration than the solvent. Solute Concentrations are often described with qualitative terms such as dilute (of relatively low Concentration) and concentrated (of relatively high Concentration). Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful Concentration unit for many applications in chemistry. Molarity is defined as the number of moles of solute in exactly 1 liter (1 L) of the solution: M = mol solute L solution 150 Chapter 3 | Composition of Substances and Solutions This OpenStax book is available for free at http://cnx.org/content/col11760/1.9 Example 3.14 Calculating Molar Concentrations A 355-mL soft drink sample contains 0.133 mol of sucrose (table sugar). What is the molar Concentration of sucrose in the beverage? Solution Since the molar amount of solute and the volume of solution are both given, the molarity can be calculated using the definition of molarity. Per this definition, the solution volume must be converted from mL to L: M = mol solute L solution = 0.133 mol 355 mL × 1 L 1000 mL = 0.375 M Check Your Learning A teaspoon of table sugar contains about 0.01 mol sucrose.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
A solution in which water is the solvent is called an aqueous solution. A solute is a component of a solution that is typically present at a much lower Concentration than the solvent. Solute Concentrations are often described with qualitative terms such as dilute (of relatively low Concentration) and concentrated (of relatively high Concentration). Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful Concentration unit for many applications in chemistry. Molarity is defined as the number of moles of solute in exactly 1 liter (1 L) of the solution: EXAMPLE 3.14 Calculating Molar Concentrations A 355-mL soft drink sample contains 0.133 mol of sucrose (table sugar). What is the molar Concentration of sucrose in the beverage? 3.3 • Molarity 137 Solution Since the molar amount of solute and the volume of solution are both given, the molarity can be calculated using the definition of molarity. Per this definition, the solution volume must be converted from mL to L: Check Your Learning A teaspoon of table sugar contains about 0.01 mol sucrose. What is the molarity of sucrose if a teaspoon of sugar has been dissolved in a cup of tea with a volume of 200 mL? Answer: 0.05 M EXAMPLE 3.15 Deriving Moles and Volumes from Molar Concentrations How much sugar (mol) is contained in a modest sip (~10 mL) of the soft drink from Example 3.14? Solution Rearrange the definition of molarity to isolate the quantity sought, moles of sugar, then substitute the value for molarity derived in Example 3.14, 0.375 M: Check Your Learning What volume (mL) of the sweetened tea described in Example 3.14 contains the same amount of sugar (mol) as 10 mL of the soft drink in this example? Answer: 80 mL EXAMPLE 3.16 Calculating Molar Concentrations from the Mass of Solute Distilled white vinegar ( Figure 3.15) is a solution of acetic acid, CH 3 CO 2 H, in water.
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
This section describes the various ways in which the Concentration of a solu-tion can be expressed and the procedures and calculations involved in preparing solutions of a specific Concentration by dilution. 3.4.1 Measuring and expressing Concentrations When a substance is dissolved in a solvent such as water, a solution is formed. The Concentration of the solution is a measure of how much of the substance is dissolved per unit volume of solvent (Figure 3.2). There are many different ways of expressing the Concentration of a solution, but chemists prefer to work in mol dm -3 . One dm 3 (cubic decimetre) is the same volume as a litre or 1000 cm 3 . Therefore the unit of Concentration is mol per dm 3 , written as mol dm -3 , and a Concentration of 1 mol dm -3 is obtained when one mole of a substance is dissolved in 1 dm 3 of water. When a substance such as sugar dis-solves in water, a solution is formed. The substance that is being dissolved is called the solute, and the liquid it is dissolving in is called the solvent . For a reminder on units of volume, see Chapter 0 It is always safer to convert volumes to dm 3 to ensure the resulting con-centration is obtained in mol dm -3 . A volume in cm 3 or mL should be converted to dm 3 by multiplying by 10 -3 . A volume in litres can be chan-ged directly to dm 3 as 1 L is the same as 1 dm 3 . 86 Amount of Substance Concentration mol dm -3 = number of moles mol volume dm 3 or c = n V Using this equation, we can calculate Concentrations of solutions but also work out the number of moles of a solute dissolved in a certain volume of solu-tion, if we know its Concentration. Because solutions are normally made up in the laboratory by weighing out a certain amount of solid, it ’ s usually necessary to convert the mass of solute to an amount in moles to calculate the concentra-tion.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
We will use moles and molarity throughout most of this text so there will be no ambiguity about what the Concentration represents. Molarity calculations require a knowledge of the stoichiometry of reactions, that is, the ratio in which substances react. The journal Analytical Chemistry does not allow normality in articles it publishes, but other publications do. The unit eq/L is the same as normality and is accepted by most publications. FORMALITY——INSTEAD OF MOLARITY Chemists sometimes use the term formality for solutions of ionic salts that do not exist as molecules in the solid or in solution. The Concentration is given as formal (F). Formality is numerically the same as molarity. Operationally, formality is identical to molarity: The former is sometimes reserved for describing makeup Concentrations of solutions (i.e., total analytical Concentration), and the latter for equilibrium Concentrations. For convenience, we shall use molarity exclusively, a common practice. MOLALITY——THE TEMPERATURE-INDEPENDENT Concentration In addition to molarity and normality, another useful Concentration unit is molality, Molality does not change with temperature. m. A one-molal solution contains one mole per 1000 g of solvent. The molal Concentration is convenient in physicochemical measurements of the colligative properties of substances, such as freezing point depression, vapor pressure lowering, and osmotic pressure because colligative properties depend solely on the number of solute particles present in solution per mole of solvent. Molal Concentrations are not temperature dependent as molar and normal Concentrations are (since the solution volume in molar and normal Concentrations is temperature dependent). DENSITY CALCULATIONS——HOW DO WE CONVERT TO MOLARITY? The Concentrations of many fairly concentrated commercial acids and bases are usually given in terms of percent by weight.
- James N. Jensen(Author)
- 2022(Publication Date)
- Wiley(Publisher)
In equilibrium calculations, molar units (mol/L, or M) are useful because they capture the combining proportions inherent in chemical reactions. In other cases, you may wish to express mass concen- trations in the same units so they can be added. Thus, Concentrations sometimes are expressed as some other species. In expressing the Concentration of species X as Y, use the molar mass of Y as the molar mass of X and consider the number of moles of Y per mole of X. Dimensionless Concentration units (mole fraction; parts per million, billion, or trillion; and percentages) also are in common use. For aqueous system with a density near 1 kg/L, 1 part per million (l ppm) is very close to 1 mg/L. Another way to use the same units (or currency) when writing Concentrations is to use units of normality (or equivalents/L). In this case, always ask yourself: Equivalent to what? In other words, the basis of the equivalence (i.e., the number of equivalents per mole) must be established clearly. Common equivalences are the number of H + or electrons accepted or donated. Gas phase and solid phase Concentration units also were reviewed in this chapter. Mass or molar Concentration units may not be the most appropriate way to describe the behavior of chemical species in solution. In particular, temperature, pressure, and the presence of other chemical species are known to affect the behavior of dissolved chemicals. This observation necessitates a new look at Concentration and has led to the development of an idealized Concentration called activity. Activity is the most appro- priate choice of expressing the quantity of material in thermodynamic calculations. In this text, the effects of other inert chemicals, temperature, and pressure on the behavior of selected chemical species will be ignored until Chapter 21.
eBook - PDF- William R. Robinson, Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The empirical formula mass of a covalent compound may be compared to the compound’s molecular or molar mass to derive a molecular formula. 6.3 Molarity Solutions are homogeneous mixtures. Many solutions contain one component, called the solvent, in which other components, called solutes, are dissolved. An aqueous solution is one for which the solvent is water. The Concentration of a solution is a measure of the relative amount of solute in a given amount of solution. Concentrations may be measured using various units, with one very useful unit being molarity, defined as the number of moles of solute per liter of solution. The solute Concentration of a solution may be decreased by adding solvent, a process referred to as dilution. The dilution equation is a simple relation between Concentrations and volumes of a solution before and after dilution. 6.4 Other Units for Solution Concentrations In addition to molarity, a number of other solution Concentration units are used in various applications. Percentage Concentrations based on the solution components’ masses, volumes, or both are useful for expressing relatively high Concentrations, whereas lower Concentrations are conveniently expressed using ppm or ppb units. These units are popular in environmental, medical, and other fields where mole-based units such as molarity are not as commonly used. Exercises 6.1 Formula Mass and the Mole Concept 1. What is the total mass (amu) of carbon in each of the following molecules? (a) CH 4 (b) CHCl 3 (c) C 12 H 10 O 6 (d) CH 3 CH 2 CH 2 CH 2 CH 3 Chapter 6 | Composition of Substances and Solutions 333 2. What is the total mass of hydrogen in each of the molecules? (a) CH 4 (b) CHCl 3 (c) C 12 H 10 O 6 (d) CH 3 CH 2 CH 2 CH 2 CH 3 3. Calculate the molecular or formula mass of each of the following: (a) P 4 (b) H 2 O (c) Ca(NO 3 ) 2 (d) CH 3 CO 2 H (acetic acid) (e) C 12 H 22 O 11 (sucrose, cane sugar).
- Chavan, U D(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
It is one way of expressing the composition of a mixture in a dimensionless size ; mole fraction (percentage by moles, mol%) and volume fraction (percentage by volume, vol%) are others. This ebook is exclusively for this university only. Cannot be resold/distributed. 110 Laboratory Techniques with Reagents and Solutions For elemental analysis, mass fraction (or “mass percent composition”) can also refer to the ratio of the mass of one element to the total mass of a compound. It can be calculated for any compound using its empirical formula or its chemical formula. TERMINOLOGY “Percent Concentration” does not refer to this quantity. This improper name persists, especially in elementary textbooks. In biology, the unit “%” is sometimes (incorrectly) used to denote mass Concentration, also called “mass/volume percentage.” A solution with 1 g of solute dissolved in a final volume of 100 mL of solution would be labeled as “1 %” or “1 % m/v” (mass/volume). This is incorrect because the unit “%” can only be used for dimensionless quantities. Instead, the Concentration should simply be given in units of g/mL. “Percent solution” or “percentage solution” are thus terms best reserved for “mass percent solutions” (m/m = m% = mass solute/mass total solution after mixing), or “volume percent solutions” (v/v = v% = volume solute per volume of total solution after mixing). The very ambiguous terms “percent solution” and “percentage solutions” with no other qualifiers continue to occasionally be encountered. In thermal engineering vapor quality is used for the mass fraction of vapor in the steam. In alloys, especially those of noble metals, the term fineness is used for the mass fraction of the noble metal in the alloy. In chemistry, the mass Concentration ρ i (or g i ) is defined as the mass of a constituent m i divided by the volume of the mixture V : ρ i = V m i .
eBook - PDFEnvironmental Process Analysis
Principles and Modeling
- Henry V. Mott(Author)
- 2013(Publication Date)
- Wiley(Publisher)
16 Concentration Units for Gases, Liquids, and Solids Chapter 3 3.1 SELECTED Concentration UNITS With the exception of pure substances for which volume, density, and mass have a unique relation depending upon the nature of pure substances, in order to express the quantity (abundance) of a substance present in a solution or in a volume of soil, for example, we need to have a parameter termed Concentration. Concentration is an analog of density. For a substance dissolved in a liquid, inti- mately mixed in a gas, or comingled with a solid or soil, the Concentration and density would be identical if we held volume constant and simply removed all components other than the constituent of interest. Engineers tend to express their Concentrations using mass units, scientists (here predominantly the chemists) tend to desire use of molar units, and various groups within each major area have their own pet sets of units used in their particular subdiscipline. In Table 3.1, various units are listed and defined. These are divided into gas- phase, liquid-phase, and special categories. Further subdivisions are included for mass and molar units. Following the table, a number of examples of application/ interconversion are presented. In Table 3.2, several values of the universal gas constant (R) are presented. The first six are of course the most useful and the remainder are included in case the reader might encounter a situation in which alternative units of measure are employed. Environmental Process Analysis: Principles and Modeling, First Edition. Henry V. Mott. © 2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc. SELECTED Concentration UNITS 17 TABLE 3.1 Commonly Used Units of Concentration Unit Description Gas phase units atm i Partial pressure of component i—the pressure exerted in a gas phase by the component of interest, component i. Dalton’s law informs us that the total pressure of a gas is the sum of the partial pressures of each of the components.
eBook - PDFThermodynamics of Natural Systems
Theory and Applications in Geochemistry and Environmental Science
- Greg Anderson(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
In the former case, if we thought about it at all, we would probably expect that the properties of the mixture or solution would be some kind of average of the properties of the two separate substances. This is more or less true for some properties, but decidedly not true for the most important one, Gibbs energy. After making sure we understand how to express the composition of solutions, we begin by considering properties of ideal solutions , which are, as you might expect, the simplest possible properties that solutions might have. As you might also expect, no real solutions are in fact ideal, although some come fairly close. 7.2 Measures of Concentration ............................................................................... A number of Concentration terms are used in describing solutions, and it is naturally important to be able to change from one to another. 151 7.2 Measures of Concentration Mole Fraction Consider a solution containing a number of components, n 1 moles of component 1, n 2 moles of component 2, and so on. If it is an aqueous solution, then water is one of the components, normally the major component. The mole fraction of any one component i is defined as x i = n i ∑ i n i (7.1) where ∑ i n i is the total number of moles of components, n 1 + n 2 + n 3 + · · · . The mole fraction is very commonly used, especially in theoretical discussions, because it is perfectly general, and it can cover the entire range of compositions from dilute solutions to pure components. It is inconvenient for aqueous solutions because these are usually quite dilute on the mole fraction scale; that is, water is by far the dominant component, and the mole fractions of the solutes are numerically very small. The mole fraction is a simple concept, but there is one important thing to note. In any mole fraction the question is, n 1 , n 2 , etc., are moles of what ? This is not as simple as it might seem.
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
p. 400 12-2.1 Solubility is maximum amount of a solute that dissolves at a specific temperature. p. 401 12-2.1 Depending on the amount of solute dissolved and its solubility, the solution may be unsaturated, saturated, or, in certain circumstances, supersaturated. p. 401 12-2.1 The Concentration of a solute refers to the amount present in a certain amount of solvent or solution. p. 401 12-2.2 Recrystallization takes advantage of the difference in solubility of a substance at dif- ferent temperatures. p. 402 416 CHAPTER 12 Aqueous Solutions 12-2.4 According to Henry’s law, the solubility of gases in a liquid relates to the pressure above the liquid. p. 403 12-3 Concentration may be measured as percent by mass. p. 404 12-3.1 Parts per million (ppm) or parts per billion (ppb) are used for small Concentrations. p. 405 12-4.1 Molarity (M) is a Concentration unit that emphasizes the volume of the solution. p. 407 12-5.2 During a titration, an indicator can be used to determine the end point of the experiment. p. 414 Concentration Units Concentration Unit Name Relationship of solute Use g solute 100 g solvent ——— Mass of solvent Solubility tables g solute g solution * 100, Percent by mass Mass of solution High Concentrations (above 0.01%) g solute g solution * 10 6 ppm Parts per million (ppm) Mass of solution Low Concentrations (710 -4 %) g solute g solution * 10 9 ppb Parts per billion ppb Mass of solution Extremely low Concentrations (710 -7 %) mole solute L solution Molarity (M) Volume of solution Measuring molar amount with volume and in stoichiometry problems SUMMARY CHART OBJECTIVES 12-6 Explain the differences between nonelectrolytes, strong electrolytes, and weak electrolytes. 12-7 Calculate the boiling and melting points of aqueous solutions of electrolytes and nonelectrolytes. SETTING A GOAL ■ n You will learn how the physical properties of aqueous solutions differ from those of pure water.
eBook - PDFIntroductory Chemistry
An Active Learning Approach
- Mark Cracolice, Edward Peters, Mark Cracolice(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
The mole ratio from the balanced chemical equation is then used to change to the amount in moles of another species involved in the chemical change. Finally, the amount in moles is changed to a macroscopic measurable quantity. For solution stoichiometry, volume of solution and Concentration, typically molarity, can be used to convert to amount in moles. Goal 15 Given the volume of a solution that reacts with a known mass of a pri- mary standard and the equation for the reaction, calculate the molarity of the solution. Titration is the controlled and measured addition of one solution into another. Titration prob- lems are solution stoichiometry problems. A buret is a device that measures delivered vol- umes precisely. An indicator is a substance that exhibits different color in solution at different solution acidities. A solution is standardized when its Concentration is determined by reaction with a substance that can be weighed accurately, which is called a primary standard. Goal 16 Given the volumes of two solu- tions that react with each other in a titra- tion, the molarity of one solution, and the equation for the reaction or information from which it can be written, calculate the molarity of the second solution. Once a solution is standardized, we may use it to find the Concentration of another solution. Volume times molarity for the solution of known Concentration yields amount in moles for that solute. A balanced chemical equation is used to convert to amount in moles of the other spe- cies. The definition of molarity, moles per liter, is used to calculate the molarity of the second solution. Goal 17 Given the volume of a solution that reacts with a known mass of a pri- mary standard and the equation for the reaction, calculate the normality of the solution. In a reaction, the numbers of equivalents of acid and base that react with each other are equal. This idea of equal numbers of equivalents is the basis of the normality system.
eBook - PDF- Georges Férard, René Dybkaer, Xavier Fuentes-Arderiu(Authors)
- 2016(Publication Date)
- Royal Society of Chemistry(Publisher)
Composition is usually stated in terms of intensive compositional kinds-of-quantity (Table 7.1). Conversion between different compositional kinds-of-quantity is pos-sible by means of material kinds-of-quantity (Table 7.2). Molality , n B / m A ( y 9.91.2), falls outside this scheme, but is also widely used in clinical chemistry, having advantages over substance Concentration in its independence of temperature and pressure. 7.1.5 The amount-of-substance of a portion of a pure chemical component, n B* , i.e. a defined portion of chemical substance, is proportional to its mass. The coefficient of proportionality is the molar mass of that substance, which may be calculated if the molecular formula and the molar mass ( y 9.92.1) of each constituent element are known. Values are regularly revised and published by the Committee on Data for Science and Technology. 2 Even if the molecular formula of a substance is unknown, its molar mass may be estimated empirically. Choice and Use of Kinds-of-property for Different Examination Purposes 63 7.1.6 Ionic strength of solution 1 is usually defined as half of the sum of the products of the charge number squared of each solute component, z B 2 , and a compositional Table 7.1 Terms and symbols of compositional kinds-of-quantity, derived from two extensive kinds-of-quantity Q and Q 0 : number, volume, mass, amount-of-substance, catalytic activity and radioactivity, q B ¼ Q B / Q 0 1 .
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