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Understanding Solution Concentration: Definitions, Calculations, and Dilution Techniques

This chapter covers the fundamentals of solution concentration, defining it as the quantity of solute per volume of solution. Various methods to express concentration, including mass (ppm, ppb, %W/V), moles (molar concentration), and volume (% by volume), are detailed. The chapter introduces key formulas for calculating concentration and addresses the dilution process, illustrating how to prepare solutions with desired concentrations. Practical examples and exercises are included to reinforce understanding of the topic.

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Understanding Solution Concentration: Definitions, Calculations, and Dilution Techniques

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  1. Chemistry 20 - Chapter 5Solutions 5.3 Concentration of a Solution

  2. Concentration • is defined as the quantity of solute per volume of solution • quantity of solute can be communicated as a mass, as a quantity in moles, or sometimes as a volume • many ways of communicating concentration

  3. Concentrations using mass • ppm (parts per million or 1 drop in a full bathtub) = mg/L • ppb (parts per billion or 1 drop in a full swimming pool) = mg/kL • %W/V = g/100 mL • mass per litre = g/L

  4. Concentrations using moles • molar concentration = mol/L • this is by far the most common way of expressing concentration of solutions in chemistry courses

  5. Concentrations using volumes • % by volume = mL of solute per 100 mL of solution • eg. 5% acetic acid (by volume) means that there are 5 mL of acetic acid for every 100 mL of solution • can also be measured in L of solute/100L of solution

  6. Calculations • for concentrations using mass use: C=m/v • for molar concentrations use: C=n/v • for concentrations using volume use: C=v(solute)/v(solution)

  7. Dilution • the process of decreasing the concentration of a solution by adding more solvent. • eg. making orange juice from frozen concentrate • during a dilution the volume increases and the concentration decreases

  8. Dilution Problems • four variables: C1, v1, C2, v2 • use the formula: C1v1=C2v2

  9. Example What volume of concentrated hydrochloric acid is required to prepare 1.0 L of 6.0 mol/L HCl(aq)?

  10. Example What volume of concentrated hydrochloric acid is required to prepare 1.0 L of 6.0 mol/L HCl(aq)? C1=11.6 mol/L (from data sheet) v1 = ??? C2 = 6.0 mol/L v2= 1.0 L

  11. Solution

  12. Concentration of Ions • to calculate the concentration of an ion: • first write a dissociation equation • set up a ratio between the coefficient of the reactant and the concentration of the reactant and the coefficient of the cation and the conc. of the anion

  13. Example Calculate the concentration of the cations and anions in a 0.25 mol/L solution of Na3PO4(aq).

  14. Example Na3PO4(aq) ---> 3Na+(aq) + PO4-3(aq) 0.25 mol/L 0.75 mol/L 0.25 mol/L

  15. Communicating H+ ion Conc. • acids turn blue litmus red • acids have low pH’s (below 7) • bases turn red litmus blue • bases have high pH’s (above 7) • a pH of 7 is neutral • pH = -log [H+] • eg. pH 7 = 1.00x10-7 mol/L

  16. Assignment • Read pages 203-214 • Do # 1-3 on pg 205 • Do #4-6 on page 206 • Do #7-12 on page 208 (By end of class) • Do #13-16 on page 210 • Do #17-19 on page 212 • Section Review page 214

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