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Chemistry LibreTexts

6: Concentrations

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  • This chapter will describe some of the fundamental chemical principles related to the solubility and provide the quantitative methods for calculating concentrations.

    Unit 6 Objectives

    By the end of this unit, you will be able to:

    • Define solution and differentiate between the solute and the solvent in a solution.  
    • Predict the solubility of two substances based on their polarity.
    • Explain“like dissolves like”. 
    • Define electrolyte and list examples of common electrolytes.  
    • Describe the effects of temperature and pressure on solubility
    • Explain the degrees of solubility possible for liquid-liquid solutions
    • Define emulsifying agent.  
    • Draw a picture of the molecular structure of an emulsifying agent and label the polar and nonpolar ends.
    • Give 3 examples of common emulsifying agents.
    • Calculate solution concentrations in g/L, g/dL, %, mg/dL, mg%, and molarity (M)
    • Perform dosage calculations.
    • Appropriately use the solution dilution formula.
    • Accurately use the % by volume formula for calculations.
    • Perform computations relating a solution’s concentration and its components’ volumes and/or masses. 
    • Calculate concentration in ppm and ppb.  Use the resulting concentrations to evaluate the level of toxins in a sample. 
    • Accurately perform a titration to calculate the unknown concentration of a solution in a neutralization reaction.
    • Perform stoichiometric calculations using typical titration data.

    • 6.1: The Dissolution Process
      A solution forms when two or more substances combine physically to yield a mixture that is homogeneous at the molecular level. The solvent is the most concentrated component and determines the physical state of the solution. The solutes are the other components typically present at concentrations less than that of the solvent. Solutions may form endothermically or exothermically, depending upon the relative magnitudes of solute and solvent intermolecular attractive forces.
    • 6.2: Electrolytes
      Substances that dissolve in water to yield ions are called electrolytes. Electrolytes may be covalent compounds that chemically react with water to produce ions (for example, acids and bases), or they may be ionic compounds that dissociate to yield their constituent cations and anions, when dissolved. Dissolution of an ionic compound is facilitated by ion-dipole attractions between the ions of the compound and the polar water molecules.
    • 6.3: Solubility
      The extent to which one substance will dissolve in another is determined by several factors, including the types and relative strengths of intermolecular attractive forces that may exist between the substances’ atoms, ions, or molecules. This tendency to dissolve is quantified as substance’s solubility, its maximum concentration in a solution at equilibrium under specified conditions. A saturated solution contains solute at a concentration equal to its solubility.
    • 6.4: Colloids and Emulsifying Agents
      An emulsifying agent is a molecule possessing both hydrophobic (nonpolar) and a hydrophilic (polar) parts used to stabilize colloids formed from immiscible liquids.
    • 6.5: Weight by Volume and 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.
    • 6.6: 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.
    • 6.7: Titrations - Lab 8
      These are homework exercises to accompany the Textmap created for "Chemistry" by OpenStax.
    • 6.8: Unit 6 Practice Problems
      Unit 6 practice problems related to solutions, concentrations, and solubility.



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