Good mornin’ Lot’s of things to pick up today: Quiz Scantron Quiz version that you took Lab...
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Transcript of Good mornin’ Lot’s of things to pick up today: Quiz Scantron Quiz version that you took Lab...
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Good mornin’Lot’s of things to pick up today:
Quiz ScantronQuiz version that you tookLab SheetFinal Study Guide Dry Erase BoardMarker
10 minutes to look over missed quiz questions & answer the Catalyst
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pHTest Tube [H+] (mol/L) pH
1 0.01 <4
2 0.001 <4
3 0.0001 4
4 0.00001 5
5 0.000001 6
• How does the molarity of H+ change?• How does the pH change?• Why are the pH’s for test tubes 1 and 2 indicated as “<4”?• What is an Arrhenius acid? What is an Arrhenius base?• What is a Bronsted-Loewry acid? What is a Bronsted-Loewry
base?
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Example Brønsted Acids and Bases:
Here, H2O acts as a Brønsted acid by donating a proton to NH3 which acts as a
Brønsted base.
Conjugate base and conjugate acid?
NH3 + HOH NH4+ + OH-
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pHpH is a scale used to reflect the concentration of H+
ions!
Acids and bases are aqueous solutions
Water can act as an acid and a base:
HOH <--> H+ + OH- Why is water neutral?
Acids dissociate and increase the number of protons (H+) in solution
Bases dissociate and increase the number of hydroxide (OH-) in solution either directly (Arrhenius) or indirectly (Bronsted-Loewry)
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Neutralization ReactionRemember that this is just an acid base reaction
What would a product of a neutralization reaction be?
Just like the stoichiometry you’ve been doing, in lab we can use this fact to calculate the molarity of solution whose concentration is unknown
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Titration
Definition
◦ Analytical method in which a standard solution is used to determine the concentration of an unknown solution.
standard solution
unknown solutionCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Buret
stopcock
Erlenmeyer flask
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Titration VocabularyTitrant
◦ The substance added to the analyte in a titration (a standard solution)
Analyte
◦ The substance being analyzed
Equivalence point
◦ The point in a titration at which the quantity of titrant is exactly sufficient for stoichiometric reaction with the analyte.
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Acid-Base Titration
Titrant
Analyte
If the concentration of the titrant is known, then the unknown concentration of the analyte can be determined.
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Buret Reading
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Why do chemists use titrations??
Quantitative analysis — used to determine the amounts or concentrations of substances present in a sample by using a combination of chemical reactions and stoichiometric calculations
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Acidic, basic, or neutral??
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The “perfect pink” for a titration with phenolphthalein
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Indicator - changes color to indicate pH change
Volume base added
Example… phenolphthalein is colorless in acid and pink in basic solution
pH
Endpoint =7
pink
point at which exactly enough reactant has been added for the solution to be neutralized and no more
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Equivalence point (endpoint)
Point at which equal amounts of H3O+ and OH- are present in solution.
Determined by…indicator color changedramatic change in pH
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Titration
moles H3O+ = moles OH-
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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White Board Review!Solubility
Molarity
Dilutions
Solutions Stoichiometry
Acid and Base
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Problem #1What mass of (NH4)2SO4 is required to make 1.25
L of a 0.250 M solution of NH4+?
Answer: 20.6 g (mm=132.14g/mol)
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Problem #2If 25 g of KCl is added to 50 g of water at 40°C, the solution would be:
1)Unsaturated
2)Saturated
3)Supersaturated
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Problem #3Calculate the molarity of a solution prepared by
dissolving 4.1 g of solid KBr in enough water to make 1.10 L of solution
Answer: 0.031 M (mm=119.02 g/mol)
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Problem #4One way to determine the amount of chloride ion in
a a water sample is to titrate the sample of standard AgNO3 solution to produce solid AgCl.
Ag+(aq) + Cl-(aq) AgCl(s)
If a 25.0 mL water sample requires 27.2 mL of 0.104 M AgNO3 in such a titration, what is the concentration of Cl- in the sample?
Answer: 0.113 M
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Problem #5What volume of of a a 5.00M Ca(NO3)2 solution is
needed to prepare 465 mL of a 0.250 M Ca(NO3)2 solution?
Answer: 23.3 mL
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Problem #6Calculate the mass of sodium iodide that must
be added to 425.0 mL of a 0.100 M lead (II) nitrate solution to precipitate all of the lead (II) ions as lead (II) iodide.
Answer: 12.7 g NaI