types of chemical reactions and solution stoichiometry – part 2 chapter 4 part 3
TRANSCRIPT
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Types of Chemical Reactions and Solution Stoichiometry – Part 2
Chapter 4Part 3
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Calculations
All calculations must use factor label method or dimensional analysis
Ratio is NOT acceptable
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Using Molarities inStoichiometric Calculations
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Using Molarity to Calculate Grams of Solute
SAMPLE EXERCISE 4.13. How many grams of Na2SO4 are required to make 0.350 L of 0.500 M Na2SO4?
Plan: Use the definition of molarity to determine the number of moles of solute, and then convert moles to grams using the molar mass of the solute.
Solve: Determine moles of solute
Using Molar Mass to determine grams
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Calculating Molar Concentrations of Ions
SAMPLE EXERCISE 4.12. What are the molar concentrations of each of the ions present in a 0.025 M aqueous solution of calcium nitrate?
Plan: Use the subscripts in the chemical formula of the compound to determine the relative concentrations of the ions.
Solve: The chemical formula for calcium nitrate is Ca(NO3)2. Because there are two NO3
– ions for each Ca2+ ion in the compound, each mole of Ca(NO3)2 that dissolves dissociates into 1 mol of Ca2+ and 2 mol of NO3
–. Thus, a solution that is 0.025 M in Ca(NO3)2 is 0.025 M in Ca2+ and 2 0.025 M = 0.050 M in NO3
–.
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Acid – Base Titration
The analytical technique in which one can calculate the concentration of a solute in a solution.
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Titration
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Titration
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Volumetric analysis
Titration –deliver a measured volume of a known concentration of titrant into a solution containing the analyte.
Titrant – solution of known concentration that is added
Analyte- solution of unknown concentration that can be analyzed
Measure the volume of titrant added to neutralize the analyte using a color indicator.
Titration - Use known volumes of each solution and known concentration of titrant to calculate the concentration of the analyte.
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Acid Base Titrations
Equivalence point – stoichiometric equivalent quantities of acid and base
Indicator – chemical that changes color at the end point
Acid-base indicators change color at end point.
Indicator is chosen so end point corresponds to equivalence point of titration.
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Using Mass Relations in a Neutralization Reaction
SAMPLE EXERCISE 4.15. How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3?
Solution
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Determining the Quantity of Solute by Titration
SAMPLE EXERCISE 4.16. The quantity of Cl– in a municipal water supply is determined by titrating the sample with Ag+. The reaction taking place during the titration is below. The end point in this type of titration is marked by a change in color of a special type of indicator. (a) How many grams of chloride ion are in a sample of the water if 20.2 mL of 0.100 M Ag+ is needed to react with all the chloride in the sample? (b) If the sample has a mass of 10.0 g, what percent Cl– does it contain?
Solution. (a) Plan: We begin by using the volume and molarity of Ag+ to calculate the number of moles of Ag+ used in the titration. We can then use the balanced equation to determine the moles of Cl– in the sample and from that the grams of Cl–.
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Solution
Comment: Chloride ion is one of the most common ions in water and sewage. Ocean water contains 1.92% Cl–. Whether water containing Cl– tastes salty depends on the other ions present. If the only accompanying ions are Na+, a salty taste may be detected with as little as 0.03% Cl–.
(b) Solve:
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Conclusion
Use Molarity to calculate molarity and then use stoichiometry to determine moles or grams in a chemical reaction.
Use titration to neutralize solution of unknown concentration with color indicator. The titrant has known concentration and measured volume. Using stoichiometry, the unknown concentration can be determined.