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Question 1: Name the acid HBr Question 2:Name the acid H 3 PO 4 Academic Chemistry March 21,2012
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Section 20.3 – Other definitions of Acids and Bases Arrhenius Acids and Bases: Acid: Hydrogen containing compound that ionize to yield a hydrogen ion in solution. Base: Compounds that ionize to yield a hydroxide ion in solution.
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Brønsted – Lowry Acids and Bases They felt the Arrhenius definition was too limiting. Acids: Hydrogen ion donor Bases: Hydrogen ion acceptor
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Brønsted – Lowry Acids and Bases Examples: NH 3 + H 2 O ↔ NH 4 + + OH - H 2 O donated the H + - Acid NH3 accepted the H + - Base HCl + H 2 O ↔ H 3 O + + Cl - HCl donated the H + - Acid H 2 O accepted the H + - Base
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Conjugate Acids: Particle formed when a base gains a hydrogen ion. Ex: NH 3 + H 2 O ↔ NH 4 + + OH - B A CA CB Conjugate Base: Particle that remains when an acid has donated a hydrogen ion. Ex: HCl + H 2 O ↔ H 3 O + + Cl - A B CA CB Amphoteric: Substance that can act as both an acid or a base.
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Strong Acids and Bases Strong Acids/Bases: Those that ionize completely in solution. Ex: HCl, NaOH Weak Acids/Bases: Those that only slightly ionize in solution. Ex: NH 3, Acetic Acid (vinegar) Tooth decay is caused by the weak acid – lactic acid: C 3 H 6 O 3
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Section 21.1 Neutralization Reactions occur when… Acid + Base ↔ Water + “Salt” Salt: Anion from acid and the cation from the base join together to form a salt. Where do we see this process? Antacids Farmers controlling the pH of soil Formation of caves
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Section 21.1 A strong acid + a strong base = neutral solution Examples: HCl + NaOH ↔ H 2 O + NaCl HCl + KOH ↔ H 2 O + KCl How many moles of HCl are needed to neutralize 6 mols of KOH? 1 st ask, what is the mol ratio and then set it up as a proportion.
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Neutralization Reactions So far, everything we’ve talked about is a 1mol ratio – 1 mol acid : 1 mol base Sometimes, this reaction is not 1:1 H 2 SO 4 + 2NaOH ↔ Na 2 SO 4 + 2H 2 O One mol of sulfuric acid is needed to neutralize 2 mols of NaOH. How many mols of NaOH are needed to neutralize 4 mols of H 2 SO 4 ?
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Question 1: If the pH is 2.3 what is the pOH? Question 2: what is the pH for a neutral substance Academic Chemistry March 23,2012
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Titrations Titration: The process of adding a known amount of solution of known concentration to determine the concentration of the other solution. If you don’t know the concentration of one solution, you can figure it out by performing a neutralization reaction, or titration, with a standard solution. A standard solution is one of known concentration.
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Performing Titrations Steps in a neutralization reaction: 1. A measured volume of an acid solution of unknown concentration is added to a flask. 2. Several drops of indicator are added to the solution. 3. Measured volumes of a base with a known concentration are mixed into the acid until it barely changes color.
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Performing Titrations, cont. End Point: The point at which the indicator changes color. Once you have reached the end point, you can perform calculations to find the unknown solution. Let’s show a video!
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Performing Titrations, cont. Example: A 25 mL solution of H 2 SO 4 is completely neutralized by 18 mL of 1.0 M NaOH. What is the concentration of H 2 SO 4 solution? Step 1: Balanced equation ____H 2 SO 4 + ____NaOH ↔ ____Na 2 SO 4 + ____H 2 O Step 2: Use formula to solve for unknown. M a V a = M b V b A B A = Number of moles of your Acid B = Number of moles of your Base M = Molarity V = Volume (in Liters)
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