(3)The pH of a solution of Ba(OH) 2 10.66 at 25✬. (2) Find the hydronium ion concentration in a solution with pH = 4.83Īnswer: = 10 -pH = 10 -4.83 =1.5 x 10 -5 M Common examples of strong bases are the hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH) 2.Ī weak acid will have a strong conjugate base and a strong acid will have a weak conjugate base. Compounds with a pKa of more than about 13 are called strong bases. This is because the –log K W = -log(1 x 10 -14) = 14.Ī strong base is able to deprotonate very weak acids in an acid-base reaction. The sum of the pH and pOH must always equal 14. The pH of a neutral solution is therefore 7. The pOH of a solution is defined as the negative log 10 (NOTE: H + and H 3O + are interchangeable ways to describe the presence of protons in solution) The pH of a solution is defined as the negative log 10 If the base concentration is greater than the acid concentration, the solution is basic and the pH will be greater than 7. If the acid concentration is greater than the base concentration, the solution is acidic and the pH will be less than 7. If there is an equal amount of acid and base present in any solution, the solution is called "neutral" and the pH of the solution is 7. As you can see from the very small value of K W, water is not very dissociated at room temperature and our assumption that the concentration of water being constant is a good one.įor pure water, the values of and are equal and thus their values are both 1.0 x 10 -7. The value of this constant at 25 oC is 1.0 x 10 -14. The resulting equation is given a special designation K W called the ionization constant of water: If we now write this reaction into an equilibrium expression:īut remember one of our rules regarding the writing of equilibrium expressions states that we do not include solvents (liquids) as their concentration stays pretty constant during a reaction so the water portion of the equation is essentially equal to 1 and thus "disappears". This reaction does fit the Brønsted-Lowry definition since one water molecule is acting as an acid "donating" a proton and the other is acting as a base "accepting" the proton: Let's start by looking at the Ionization of Water: And we will now tie the concept of acids and bases into equilibrium: According to this theory, an acid is a "proton donor" and a base is a "proton acceptor."įor now we will stick with the Brønsted-Lowry definition. Water reacts with itself, for example, by transferring an H + ion from one molecule to another to form an H 3O + ion and an OH - ion. The Brønsted-Lowry definition: Brønsted argued that all acid-base reactions involve the transfer of an H + ion, or proton. The Lewis definition: A Lewis acid is one that can accept a pair of electrons and form a coordinate covalent bond. The Arrhenius definition: By the 1884 definition of Svante Arrhenius (Sweden), an acid is a material that can release a proton or hydrogen ion (H +). There are several definitions of what constitutes an acid:
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