Acids and Bases What are Acids and Bases??? Acids Acids have a very tart, sour taste to them. Many acids are highly caustic and should not be put to a taste test. Acids are electrolytes (they dissociate in water) They break down into H3O+ ions which have a positive charge and is just passed from water molecule to water molecule. Electricity can be passed through an acidic solution and is able
to light a light bulb. Acids and Metals Acids react with many metals In these reactions, the hydronium reacts with the metal to produce hydrogen gas as one of the products. 2 H3O+(aq) + Zn(s) 2 H2O(l) + H2(g) + Zn2+(aq) Notice that the HCl have been replaced with _____________. HCl will break down into _________ ions and _________ ions. The chlorine ions cancel out and do not appear in the net ionic equation. Why is this??
Strong Vs. Weak Some electrolytes are strong and others are weak, depending on whether they dissociate completely or partially. Acids are electrolytes and therefore can be classified as strong or weak acids. Strong acid will dissociate COMPLETELY in water. HNO3(l) + H2O(l) H3O+(aq) + NO3-(aq) The strong acids are: Weak Acids When a weak acid is dissolved in water, only a small fraction of its molecules are ionized at any given time.
These reactions are usually reversible Example: HOCl(l) + H2O Which acids are weak acids? H3O+(aq) + ClO-(aq) Polyprotic Acids What do you think the term polyprotic means? A single molecule can react to form more than one hydronium ion. This occurs with stronger acids containing more than one
hydrogen atom (hydronium ion). Consider sulfuric acid: H2SO4(l) + H2O(l) H3O+(aq) + HSO4-(aq) Now, it can go one more step (it has one more H): HSO4-(aq) + H2O(l) H3O+(aq) + SO42-(aq) Bases Solutions of bases are slippery to the touch. If you are working with a strong base and your fingers feel slippery like soap, wash them immediately! This slippery feeling comes from the base reacting with the oils in your skin, converting them to soaps.
This property is why bases are often used as cleaning agents (ammonia) Alkali metals react with water VIOLENTLY to produce bases. They are very reactive and will actually react with the water in the air to form hydroxides. These solutions are said to be basic or alkaline. Strong Vs. Weak Bases Acids generate the ___________ ion, bases generate the hydroxide, or OH- ion. A strong base is a base that ionizes completely in a solvent.
This solvent can be water or, if the base is insoluble in water, a ____________ solvent may be used. A weak base is a base that releases few hydroxide ions in aqueous solution. Example: Ammonia Weak Bases Weak bases, like ammonia, also DO NOT completely dissociate: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
A few of the ammonia molecules react with water to reach equilibrium. The vast majority of ammonia molecules, however, remain unionized at any given time. Brnsted-Lowry Classification Brnsted-Lowry acids donate protons Any species that donates a proton can be called an acid by this definition. HCl + H2O H3O+ + Cl This can also be thought of as: HCl H+ + ClFollowed byH+ + H2O H3O+
Brnsted-Lowry Classification Brnsted-Lowry bases accept protons Any species that accepts a proton can be called a base by this definition. Ammonia serves as the proton acceptor and is therefore the Brnsted-Lowry base. NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
Conjugate Acids and Bases When considering Brnsted-Lowry acids and bases, an acid-base reaction is very simple: One molecule or ion passes a proton to another molecule or ion. Whatever loses the proton in the ____________ and whatever gains the proton is the ____________ . NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
The water donates the proton to ammonia so it is an acid. The ammonia then is going to be the ___________ because it _____________ the proton. Conjugate Acids and Bases The conjugate acid is the acid that forms when a base gains a proton. The conjugate base is the base that is formed when an acid loses a proton. Conj Acid Conj Base
NH3(aq) + H2O(l) Base NH4+(aq) + OH-(aq) Acid The ammonia is the base, the water is the acid. The Ammonium ion is the __________________ and the hydroxide ion is the __________________ .
Amphoteric Substances The term amphoteric describes a substance, such as water, that has the properties of an acid and the properties of a base. Usually just depends on who it is with and what role needs to be played. These species can donate AND accept a proton when needed. The hydrogen carbonate ion, HCO3-, is amphoteric in aqueous solution. Amphoteric Substances
HCO3-(aq) + NH3(aq) Acid Base CO32-(aq) + NH4+(aq) Conjugate Base Conjugate Acid
Hydrogen carbonate acts as an acid here with ammonia (a base). Donates a proton to the NH3 Base Acid HCO3-(aq) + H3O+(aq) Conjugate Conjugate H2CO Acid
3(aq) + H2OBase (l) Hydrogen carbonate acts as a base here with hydronium (an acid). Accepts a proton to the H3O+ ion Water Water itself is amphoteric. A water molecule can donate a proton and become a hydroxide ion in the process. It can also accept a proton to become a hydronium ion. This is why water is the product of the N.I.E. of an acid-base
neutralization reactions (DBL displacements with an acid and a base). Continue looking over the notes and tests for the EXAM coming up. Vocab sheet due Monday!!
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