H 2 o a polar molecule because of the asymmetric

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General, Organic, & Biological Chemistry
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Chapter 15 / Exercise 15-83
General, Organic, & Biological Chemistry
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H 2 O a polar molecule Because of the asymmetric charge distribution in the water molecule, adjacent water molecules are held together by attractive electrostatic (δ+…δ−) interactions between the partially negatively charged oxygen atom of one molecule and the partially positively charged hydrogen atoms of adjacent molecules. 46 d + d - H 2 O
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General, Organic, & Biological Chemistry
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Chapter 15 / Exercise 15-83
General, Organic, & Biological Chemistry
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A Brønsted acid is a proton donor A Brønsted base is a proton acceptor No OH - is present in either reactant acid base acid base A Brønsted acid must contain at least one ionizable proton! 47
Brønsted Lowry acid base theory In chemistry, the Brønsted Lowry theory is an acid base reaction theory, proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. The fundamental concept of this theory is that an acid (or Brønsted acid) is defined as being able to lose, or " donate " a proton (the hydrogen cation, or H + ) while a base (or Brønsted base) is defined as a species with the ability to gain, or " accept ," a proton . 48
Brønsted Acid-Base Theory Brønsted argued that all acid-base reactions involve the transfer of an H + ion, or proton. Water reacts with itself, for example, by transferring an H + ion from one molecule to another to form an H 3 O + ion and an OH - ion. 49
Brønsted Acid-Base Theory According to this theory, an acid is a "proton donor" and a base is a "proton acceptor." Acids are often divided into categories such as "strong" and "weak." One measure of the strength of an acid is the acid-dissociation equilibrium constant, K a , for that acid. 50
Lewis acid definition of acid or base A Lewis acid is therefore any substance, such as the H + ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor . A Lewis base is any substance, such as the OH - ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor . 51
Lewis acids and bases The modern-day definition of Lewis acid, as given by IUPAC is a molecular entity (and the corresponding chemical species) that is an electron-pair acceptor and therefore able to react with a Lewis base to form a Lewis adduct, by sharing the electron pair furnished by the Lewis base an electron-pair donor . This definition is both more general and more specific the electron pair need not be a lone pair (it could be the pair of electrons in a π bond, for example), but the reaction should give an adduct (and not just be a displacement reaction). 52
Key to acid base calculations! Ability to identify if the acid or base is mono-,di-, or tri- protic or hydroxic!! You must also be able to write a balanced equation with the correct acid or base. 53
Summary of definitions Arrhenius acid is a substance that produces H + ( H 3 O + ) in water, a base is a substance that produces OH - in water. Examples of Arrhenius acids: H Cl, H NO 3 , H 2 SO 4 Examples of Arrhenius bases: Na OH , Ba( OH ) 2 , Al( OH ) 3 54
Summary of definitions Brønsted Acid-Base Theory: According to this theory, an acid is a "proton donor" and a base is a "proton acceptor." Acid example: HNO 3 (aq) + H 2 O NO 3 - (aq) + H 3 O + (aq) Base example: NH 3 (aq) + H 2 O NH 4 + (aq) + OH - (aq) 55

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