DOCSLIB.ORG

Solute Concentration: Molality

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Solute Concentration: Molality 5/25/2012 Colligative Properties of Solutions . Colligative Properties: • Solution properties that depend on concentration of solute particles, not the identity of particles. Previous example: vapor pressure lowering. Consequences: change in b.p. and f.p. of solution. © 2012 by W. W. Norton & Company Solute Concentration: Molality . Changes in boiling point/freezing point of solutions depends on molality: moles of solute m kg of solvent • Preferred concentration unit for properties involving temperature changes because it is independent of temperature. © 2012 by W. W. Norton & Company 1 5/25/2012 Calculating Molality Starting with: a) Mass of solute and solvent. b) Mass of solute/ volume of solvent. c) Volume of solution. © 2012 by W. W. Norton & Company Sample Exercise 11.8 How many grams of Na2SO4 should be added to 275 mL of water to prepare a 0.750 m solution of Na2SO4? Assume the density of water is 1.000 g/mL. © 2012 by W. W. Norton & Company 2 5/25/2012 Boiling-Point Elevation and Freezing-Point Depression . Boiling Point Elevation (ΔTb): • ΔTb = Kb∙m • Kb = boiling point elevation constant of solvent; m = molality. Freezing Point Depression (ΔTf): • ΔTf = Kf∙m • Kf = freezing-point depression constant; m = molality. © 2012 by W. W. Norton & Company Sample Exercise 11.9 What is the boiling point of seawater if the concentration of ions in seawater is 1.15 m? © 2012 by W. W. Norton & Company 3 5/25/2012 Sample Exercise 11.10 What is the freezing point of radiator fluid prepared by mixing 1.00 L of ethylene glycol (HOCH2CH2OH, density 1.114 g/mL) with 1.00 L of water (density 1.000 g/mL)? The freezing-point-depression constant of water, Kf, is 1.86°C/m. © 2012 by W. W. Norton & Company The van’t Hoff Factor . Solutions of Electrolytes: • Need to correct for number of particles formed when ionic substance dissolves. van’t Hoff Factor (i): • number of ions in formula unit. • e.g., NaCl, i = 2 . ΔTb = i∙Kb∙m & ΔTf = i∙Kf∙m . Deviations from theoretical value due to ion pair formation. © 2012 by W. W. Norton & Company 4 5/25/2012 Values of van’t Hoff Factors © 2012 by W. W. Norton & Company Sample Exercise 11.11 The salt lithium perchlorate (LiClO4) is one of the most water-soluble salts known. At what temperature does a 0.130 m solution of LiClO4 freeze? The Kf of water is 1.86°C/m; assume i = 2 for LiClO4 and the freezing point of pure water is 0.00°C. © 2012 by W. W. Norton & Company 5 5/25/2012 Osmosis . Osmosis: • Movement of solvent through semi-permeable membrane from region of low solute concentration to region of higher solute concentration. Osmotic Pressure (π): • Pressure required to halt flow of solvent through membrane due to osmosis. • π = iMRT (M = molarity of solution) © 2012 by W. W. Norton & Company Osmosis at the Molecular Level Direction of solvent flow. Osmotic Pressure (π) © 2012 by W. W. Norton & Company 6 5/25/2012 Osmosis: Medical Application © 2012 by W. W. Norton & Company Reverse Osmosis . Use of high pressure to move solvent across membrane from region of high solute concentration to region of lower solute concentration. Application: desalination/water purification. © 2012 by W. W. Norton & Company 7 5/25/2012 Molar Mass from Colligative Properties Calculations: Sample Exercise 11.13 At the beginning of this section, we mentioned that the concentration of solutes in a red blood cell is about a third of that of seawater—more precisely, about 0.30 M. If red blood cells are bathed in pure water, they swell, as shown in Figure 11.22(c). Calculate the osmotic pressure at 25°C of red blood cells across the cell membrane from pure water. © 2012 by W. W. Norton & Company 8 5/25/2012 Sample Exercise 11.15 What is the reverse osmotic pressure required at 20°C to purify brackish well water containing 0.355 M dissolved particles if the product water is to contain no more than 87 mg of dissolved solids (as NaCl) per liter? © 2012 by W. W. Norton & Company Sample Exercise 11.16 Eicosene is a molecular compound and nonelectrolyte with the empirical formula CH2. The freezing point of a solution prepared by dissolving 100 mg of eicosene in 1.00 g of benzene was 1.75°C lower than the freezing point of pure benzene. What is the molar mass of eicosene? (Kf for benzene is 4.90°C/m.) © 2012 by W. W. Norton & Company 9 5/25/2012 Sample Exercise 11.17 A molecular compound that is a nonelectrolyte was isolated from a South African tree. A 47 mg sample was dissolved in water to make 2.50 mL of solution at 25°C, and the osmotic pressure of the solution was 0.489 atm. Calculate the molar mass of the compound. 10 .
Load more

Recommended publications
  • Reverse Osmosis Bibliography Additional Readings
    8/24/2016 Osmosis ­ AccessScience from McGraw­Hill Education (http://www.accessscience.com/) Osmosis Article by: Johnston, Francis J. Department of Chemistry, University of Georgia, Athens, Georgia. Publication year: 2016 DOI: http://dx.doi.org/10.1036/1097­8542.478400 (http://dx.doi.org/10.1036/1097­8542.478400) Content Osmotic pressure Reverse osmosis Bibliography Additional Readings The transport of solvent through a semipermeable membrane separating two solutions of different solute concentration. The solvent diffuses from the solution that is dilute in solute to the solution that is concentrated. The phenomenon may be observed by immersing in water a tube partially filled with an aqueous sugar solution and closed at the end with parchment. An increase in the level of the liquid in the solution results from a flow of water through the parchment into the solution. The process occurs as a result of a thermodynamic tendency to equalize the sugar concentrations on both sides of the barrier. The parchment permits the passage of water, but hinders that of the sugar, and is said to be semipermeable. Specially treated collodion and cellophane membranes also exhibit this behavior. These membranes are not perfect, and a gradual diffusion of solute molecules into the more dilute solution will occur. Of all artificial membranes, a deposit of cupric ferrocyanide in the pores of a fine­grained porcelain most nearly approaches complete semipermeability. The walls of cells in living organisms permit the passage of water and certain solutes, while preventing the passage of other solutes, usually of relatively high molecular weight. These walls act as selectively permeable membranes, and allow osmosis to occur between the interior of the cell and the surrounding media.
    [Show full text]
  • Solutes and Solution
    Solutes and Solution The first rule of solubility is “likes dissolve likes” Polar or ionic substances are soluble in polar solvents Non-polar substances are soluble in non- polar solvents Solutes and Solution There must be a reason why a substance is soluble in a solvent: either the solution process lowers the overall enthalpy of the system (Hrxn < 0) Or the solution process increases the overall entropy of the system (Srxn > 0) Entropy is a measure of the amount of disorder in a system—entropy must increase for any spontaneous change 1 Solutes and Solution The forces that drive the dissolution of a solute usually involve both enthalpy and entropy terms Hsoln < 0 for most species The creation of a solution takes a more ordered system (solid phase or pure liquid phase) and makes more disordered system (solute molecules are more randomly distributed throughout the solution) Saturation and Equilibrium If we have enough solute available, a solution can become saturated—the point when no more solute may be accepted into the solvent Saturation indicates an equilibrium between the pure solute and solvent and the solution solute + solvent solution KC 2 Saturation and Equilibrium solute + solvent solution KC The magnitude of KC indicates how soluble a solute is in that particular solvent If KC is large, the solute is very soluble If KC is small, the solute is only slightly soluble Saturation and Equilibrium Examples: + - NaCl(s) + H2O(l) Na (aq) + Cl (aq) KC = 37.3 A saturated solution of NaCl has a [Na+] = 6.11 M and [Cl-] =
    [Show full text]
  • Tutorial 2 FORMULAS, PERCENTAGE COMPOSITION
    T-6 Tutorial 2 FORMULAS, PERCENTAGE COMPOSITION, AND THE MOLE FORMULAS: A chemical formula shows the elemental composition of a substance: the chemical symbols show what elements are present and the numerical subscripts show how many atoms of each element there are in a formula unit. Examples: NaCl: one sodium atom, one chlorine atom in a formula unit CaCl2: one calcium atom, two chlorine atoms in a formula unit Mg3N2: three magnesium atoms, two nitrogen atoms in a formula unit The presence of a metal in a chemical formula indicates an ionic compound, which is composed of positive ions (cations) and negative ions (anions). A formula with only nonmetals indicates a + molecular compound (unless it is an ammonium, NH4 , compound). Only ionic compounds are considered in this Tutorial. There are tables of common ions in your lecture text, p 56 (cations) and p 57 (anions). A combined table of these same ions can be found on the inside back cover of the lecture text. A similar list is on the next page; all formulas needed in this and subsequent Tutorial problems can be written with ions from this list. Writing formulas for ionic compounds is very straightforward: TOTAL POSITIVE CHARGES MUST BE THE SAME AS TOTAL NEGATIVE CHARGES. The formula must be neutral. The positive ion is written first in the formula and the name of the compound is the two ion names. EXAMPLE: Write the formula for potassium chloride. The name tells you there are potassium, K+, and chloride, Cl–, ions. Each potassium ion is +1 and each chloride ion is -1: one of each is needed, and the formula for potassium chloride is KCl.
    [Show full text]
  • 2•Stoichiometry: Chemical Arithmetic Formula Conventions (1 Of
    Superscripts used to show the charges on ions Mg2+ the 2 means a 2+ charge (lost 2 electrons) Subscripts 2•Stoichiometry: Chemical Arithmetic used to show numbers of atoms in a formula unit Formula Conventions H2SO4 two H’s, one S, and 4 O’s (1 of 24) Coefficients used to show the number of formula units 2Br– the 2 means two individual bromide ions Hydrates CuSO4 • 5 H2O some compounds have water molecules included stoichiometry study of the quantitative relationships in chemical formulas and equations. atomic mass weighted average mass of an atom, found on the periodic table 2•Stoichiometry: Chemical Arithmetic formula mass sum of the atomic masses of the Stoichiometry Terms atoms in a formula molecular mass sum of the atomic masses of the (2 of 24) atoms in a molecular formula gram molecular mass molecular mass written in grams molar mass same as gram molecular mass empirical formula formula reduced to lowest terms Formula or molecular mass is found by simply summing the atomic masses (on the periodic table) of each atom in a formula. H2SO4 2•Stoichiometry: Chemical Arithmetic 1.01 + 1.01 + 32.06 + 16.0 + 16.0 + 16.0 + 16.0 = 98.08 u Calculating Formula Mass 2(1.01) + 32.06 + 4(16.0) = 98.06 u or 98.06 g/mole (3 of 24) Generally, round off your answers to the hundredths or tenths place. Don’t round off too much (98.06 g/mol or 98.1 g/mol is OK, but don’t round off to 98 g/mol) Units Use u or amu if you are referring to one atom or molecule A mole (abbreviated mol) is a certain number of things.
    [Show full text]
  • The New Formula That Replaces Van't Hoff Osmotic Pressure Equation
    New Osmosis Law and Theory: the New Formula that Replaces van’t Hoff Osmotic Pressure Equation Hung-Chung Huang, Rongqing Xie* Department of Neurosciences, University of Texas Southwestern Medical Center, Dallas, TX *Chemistry Department, Zhengzhou Normal College, University of Zhengzhou City in Henan Province Cheng Beiqu excellence Street, Zip code: 450044 E-mail: [email protected] (for English communication) or [email protected] (for Chinese communication) Preamble van't Hoff, a world-renowned scientist, studied and worked on the osmotic pressure and chemical dynamics research to win the first Nobel Prize in Chemistry. For more than a century, his osmotic pressure formula has been written in the physical chemistry textbooks around the world and has been generally considered to be "impeccable" classical theory. But after years of research authors found that van’t Hoff osmotic pressure formula cannot correctly and perfectly explain the osmosis process. Because of this, the authors abstract a new concept for the osmotic force and osmotic law, and theoretically derived an equation of a curve to describe the osmotic pressure formula. The data curve from this formula is consistent with and matches the empirical figure plotted linearly based on large amounts of experimental values. This new formula (equation for a curved relationship) can overcome the drawback and incompleteness of the traditional osmotic pressure formula that can only describe a straight-line relationship. 1 Abstract This article derived a new abstract concept from the osmotic process and concluded it via "osmotic force" with a new law -- "osmotic law". The "osmotic law" describes that, in an osmotic system, osmolyte moves osmotically from the side with higher "osmotic force" to the side with lower "osmotic force".
    [Show full text]
  • Osmosis and Osmoregulation Robert Alpern, M.D
    Osmosis and Osmoregulation Robert Alpern, M.D. Southwestern Medical School Water Transport Across Semipermeable Membranes • In a dilute solution, ∆ Τ∆ Jv = Lp ( P - R CS ) • Jv - volume or water flux • Lp - hydraulic conductivity or permeability • ∆P - hydrostatic pressure gradient • R - gas constant • T - absolute temperature (Kelvin) • ∆Cs - solute concentration gradient Osmotic Pressure • If Jv = 0, then ∆ ∆ P = RT Cs van’t Hoff equation ∆Π ∆ = RT Cs Osmotic pressure • ∆Π is not a pressure, but is an expression of a difference in water concentration across a membrane. Osmolality ∆Π Σ ∆ • = RT Cs • Osmolarity - solute particles/liter of water • Osmolality - solute particles/kg of water Σ Osmolality = asCs • Colligative property Pathways for Water Movement • Solubility-diffusion across lipid bilayers • Water pores or channels Concept of Effective Osmoles • Effective osmoles pull water. • Ineffective osmoles are membrane permeant, and do not pull water • Reflection coefficient (σ) - an index of the effectiveness of a solute in generating an osmotic driving force. ∆Π Σ σ ∆ = RT s Cs • Tonicity - the concentration of effective solutes; the ability of a solution to pull water across a biologic membrane. • Example: Ethanol can accumulate in body fluids at sufficiently high concentrations to increase osmolality by 1/3, but it does not cause water movement. Components of Extracellular Fluid Osmolality • The composition of the extracellular fluid is assessed by measuring plasma or serum composition. • Plasma osmolality ~ 290 mOsm/l Na salts 2 x 140 mOsm/l Glucose 5 mOsm/l Urea 5 mOsm/l • Therefore, clinically, physicians frequently refer to the plasma (or serum) Na concentration as an index of extracellular fluid osmolality and tonicity.
    [Show full text]
  • 16.4 Calculations Involving Colligative Properties 16.4
    chem_TE_ch16.fm Page 491 Tuesday, April 18, 2006 11:27 AM 16.4 Calculations Involving Colligative Properties 16.4 1 FOCUS Connecting to Your World Cooking instructions for a wide Guide for Reading variety of foods, from dried pasta to packaged beans to frozen fruits to Objectives fresh vegetables, often call for the addition of a small amount of salt to the Key Concepts • What are two ways of 16.4.1 Solve problems related to the cooking water. Most people like the flavor of expressing the concentration food cooked with salt. But adding salt can of a solution? molality and mole fraction of a have another effect on the cooking pro- • How are freezing-point solution cess. Recall that dissolved salt elevates depression and boiling-point elevation related to molality? 16.4.2 Describe how freezing-point the boiling point of water. Suppose you Vocabulary depression and boiling-point added a teaspoon of salt to two liters of molality (m) elevation are related to water. A teaspoon of salt has a mass of mole fraction molality. about 20 g. Would the resulting boiling molal freezing-point depression K point increase be enough to shorten constant ( f) the time required for cooking? In this molal boiling-point elevation Guide to Reading constant (K ) section, you will learn how to calculate the b amount the boiling point of the cooking Reading Strategy Build Vocabulary L2 water would rise. Before you read, make a list of the vocabulary terms above. As you Graphic Organizers Use a chart to read, write the symbols or formu- las that apply to each term and organize the definitions and the math- Molality and Mole Fraction describe the symbols or formulas ematical formulas associated with each using words.
    [Show full text]
  • Mol of Solute Molality ( ) = Kg Solvent M
    Molality • Molality (m) is the number of moles of solute per kilogram of solvent. mol of solute Molality (m ) = kg solvent Copyright © Houghton Mifflin Company. All rights reserved. 11 | 51 Sample Problem Calculate the molality of a solution of 13.5g of KF dissolved in 250. g of water. mol of solute m = kg solvent 1 m ol KF ()13.5g 58.1 = 0.250 kg = 0.929 m Copyright © Houghton Mifflin Company. All rights reserved. 11 | 52 Mole Fraction • Mole fraction (χ) is the ratio of the number of moles of a substance over the total number of moles of substances in solution. number of moles of i χ = i total number of moles ni = nT Copyright © Houghton Mifflin Company. All rights reserved. 11 | 53 Sample Problem -Conversions between units- • ex) What is the molality of a 0.200 M aluminum nitrate solution (d = 1.012g/mL)? – Work with 1 liter of solution. mass = 1012 g – mass Al(NO3)3 = 0.200 mol × 213.01 g/mol = 42.6 g ; – mass water = 1012 g -43 g = 969 g 0.200mol Molality==0.206 mol / kg 0.969kg Copyright © Houghton Mifflin Company. All rights reserved. 11 | 54 Sample Problem Calculate the mole fraction of 10.0g of NaCl dissolved in 100. g of water. mol of NaCl χ=NaCl mol of NaCl + mol H2 O 1 mol NaCl ()10.0g 58.5g NaCl = 1 m ol NaCl 1 m ol H2 O ()10.0g+ () 100.g H2 O 58.5g NaCl 18.0g H2 O = 0.0299 Copyright © Houghton Mifflin Company.
    [Show full text]
  • The Physics of Osmotic Pressure
    bioRxiv preprint doi: https://doi.org/10.1101/116806; this version posted March 14, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. The physics of osmotic pressure M. G. Bowler Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH a) Abstract The proper application of the virial theorem to the origin of osmotic pressure provides a simple, vivid and complete explanation of the physical processes involved; osmosis is driven by differential solvent pressures. This simple and intuitive notion is widely disregarded, but the virial theorem allows an exact formulation and unifies a number of different treatments. It is closely related to a kinetic treatment devised by Ehrenfest over 100 years ago. I. INTRODUCTION Consider two reservoirs, one filled with a solvent such as pure water and the other with a solution, such as salt or sugar in water (Fig.1). If the two are separated only by a semi-permeable membrane that passes water in both PL PR L R Figure 1 shows two compartments separated by a semi-permeable membrane. The left contains pure solvent (water) and the right contains solution (such as salt in water). Water streams from left to right until the right hand pressure exceeds the left hand pressure by the osmotic pressure. Fij directions but does not pass salt at all, then water streamsFin into the solution and the flow is only arrested if the external pressure applied to the solution exceeds w w that applied to the solvent by the osmotic pressure Π.
    [Show full text]
  • A New Approach to Derivation of Van't Hoff Equation for Osmotic Pressure of a Dilute Solution
    American International Journal of Available online at http://www.iasir.net Research in Science, Technology, Engineering & Mathematics ISSN (Print): 2328-3491, ISSN (Online): 2328-3580, ISSN (CD-ROM): 2328-3629 AIJRSTEM is a refereed, indexed, peer-reviewed, multidisciplinary and open access journal published by International Association of Scientific Innovation and Research (IASIR), USA (An Association Unifying the Sciences, Engineering, and Applied Research) A new approach to derivation of Van’t Hoff equation for osmotic pressure of a dilute solution Rita Khare Department of Chemistry, Government Women’s College, Gardanibagh, Patna, Bihar, INDIA. Abstract: Relative lowering of vapour pressure which is a colligative property of dilute solution of non volatile solute in a volatile solvent has been determined theoretically by applying conditions of Raoult’s law. Other colligative properties also have theoretical basis but osmotic pressure which is also a colligative property is expressed by an equation which was deduced empirically by Van’t Hoff. Van’t Hoff’s theory of dilute solutions supports the view that solute particles in a dilute solution behave in a manner similar to that of gas molecules in a gas i.e solute molecules obey Boyle’s law, Charles law and Avogadro’s law. In this paper it is suggested that it is not the solute molecules but volatile solvent molecules present in a dilute solution that behave like gas molecules in a gas. Here an attempt is made to derive Van’t Hoff equation by applying Raoult’s law and by considering the pressure exerted by molecules of the solvent in liquid state on the basis of proposed “theory of solvent pressure”.
    [Show full text]
  • Zumdahl Chapter 5 Gases
    5 Gases Contents 5.1 Pressure • Units of Pressure 5.2 The Gas Laws of Boyle, Charles, and Avogadro • Boyle’s Law • Charles’s Law • Avogadro’s Law 5.3 The Ideal Gas Law 5.4 Gas Stoichiometry • Molar Mass of a Gas 5.5 Dalton’s Law of Partial Pressures • Collecting a Gas over Water 5.6 The Kinetic Molecular Theory of Gases • Pressure and Volume (Boyle’s Law) • Pressure and Temperature • Volume and Temperature (Charles’s Law) • Volume and Number of Moles (Avogadro’s Law) • Mixture of Gases (Dalton’s Law) • Deriving the Ideal Gas Law • The Meaning of Temperature • Root Mean Square Velocity 5.7 Effusion and Diffusion • Effusion • Diffusion 5.8 Real Gases 5.9 Characteristics of Several Real Gases 5.10 Chemistry in the Atmosphere The steaming fumaroles located in Bjarnarflag, Iceland release a variety of gases. 178 Matter exists in three distinct physical states: gas, liquid, and solid. Although rel- atively few substances exist in the gaseous state under typical conditions, gases are very important. For example, we live immersed in a gaseous solution. The earth’s atmosphere is a mixture of gases that consists mainly of elemental nitrogen (N2) and oxygen (O2). The atmosphere both supports life and acts as a waste receptacle for the exhaust gases that accompany many industrial processes. The chemical reactions of these waste gases in the atmosphere lead to various types of pollution, including smog and acid rain. The gases in the atmosphere also shield us from harmful radiation from the sun and keep the earth warm by reflecting heat radiation back toward the earth.
    [Show full text]
  • Chapter 7 Preview
    Section 1 Chemical Names and Chapter 7 Chapter 7 Formulas Lesson Starter Preview • CCl4 MgCl2 • Lesson Starter • Guess the name of each of the above compounds • Objectives based on the formulas written. • Significance of a Chemical Formula • What kind of information can you discern from the • Monatomic Ions formulas? • Binary Ionic Compounds • Guess which of the compounds represented is • Writing the Formula of an Ionic Compound molecular and which is ionic. • Naming Binary Ionic Compounds • Chemical formulas form the basis of the language of • Naming Binary Molecular Compounds chemistry and reveal much information about the • Covalent-Network Compounds substances they represent. • Acids and Salts Section 1 Chemical Names and Section 1 Chemical Names and Chapter 7 Formulas Chapter 7 Formulas Objectives Significance of a Chemical Formula • Explain the significance of a chemical formula. • A chemical formula indicates the relative number of atoms of each kind in a chemical compound. • Determine the formula of an ionic compound formed between two given ions. • For a molecular compound, the chemical formula reveals the number of atoms of each element • Name an ionic compound given its formula. contained in a single molecule of the compound. • Using prefixes, name a binary molecular compound from its formula. • example: octane — C8H18 • Write the formula of a binary molecular compound The subscript after the C The subscript after the H indicates that there are 18 given its name. indicates that there are 8 carbon atoms in the hydrogen atoms in molecule. the molecule. Section 1 Chemical Names and Section 1 Chemical Names and Chapter 7 Formulas Chapter 7 Formulas Significance of a Chemical Formula, continued Reading Chemical Formulas • The chemical formula for an ionic compound Click below to watch the Visual Concept.
    [Show full text]