s20 2011 week 1 day 3

s20 2011 week 1 day 3 - Chemistry S-20ab Week 1 Chemistry...

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Brønsted-Lowry Acids and Bases One of the most useful theories of acidity and basicity is the Brønsted-Lowry Theory . In this theory, acids and bases are defined as follows: A Brønsted Acid is a species that can donate a proton (H + ). A Brønsted Base is a species that can accept a proton. Every Brønsted acid, therefore, must have a conjugate base . What are some examples of Brønsted acids? For each one, identify its conjugate base. Brønsted Acid Conjugate Base When a Brønsted acid reacts with a Brønsted base, a proton is transferred from the acid to the base. These reactions are called proton-transfer reactions . Give some examples of proton-transfer reactions using the above list of acids and bases. Reading : Section 3.4 Chemistry S-20ab Week 1 39
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Strengths of Acids and Bases: K a and p All proton-transfer reactions are reversible (at least in principle). In general, though, one direction of the reaction will predominate over the other (that is, the proton transfer will tend to be unequal). For instance, consider the reaction between the ammonium ion and the hydroxide ion. Do you have a sense of whether this reaction proceeds mainly to the right or mainly to the left? Because so much chemistry takes place in water, we typically use water as a “standard reference” for the strengths of acids and bases. For any Brønsted acid HA, the reaction with water will reach some equilibrium: The equilibrium constant of this reaction is K a = * Just as “pH” means “the negative log of the H + concentration,” we use the term “pKa” to refer to “the negative log of the K a How can we express that fact mathematically? Fill in the blanks: “A strong acid will have a ______________________ pKa” “A strong base will have a conjugate acid with a _____________________ pKa” Reading : Section 3.4 Chemistry S-20ab Week 1 40
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pKa Values for Common Acids Here are some important pKa values. You should memorize these values
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This note was uploaded on 07/28/2011 for the course CHEM S20 taught by Professor Evan during the Spring '11 term at Belhaven.

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s20 2011 week 1 day 3 - Chemistry S-20ab Week 1 Chemistry...

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