Chemistry Chapter 19 Practice with acids and bases

Calculate the pH A solution is found to contain 3.65 x mol/liter HCl, a strong acid. –What is the pH of the solution? –What is the hydroxide ion concentration in the solution?

Calculate the pH A solution is found to contain 3.65 x mol/liter HCl, a strong acid. –What is the pH of the solution? »pH = -log[H + ] »- log(3.65 x ) = 2.44 »Because the solution has an ion concentration of greater than 1 x 10 -7, it is an acidic solution. »Also because the pH is less than 7, we know it is acidic.

Calculate the pH A solution is found to contain 3.65 x mol/liter HCl, a strong acid. –What is the hydroxide ion concentration in the solution? »OH - ion concentration can be found by using K w. »K w = [H + ][OH - ] »1 x = (3.65 x )(x) »2.74 x

Working backwards A solution has a pH of 9.3. Using a mathematical approach, show that the solution is acidic or basic.

Solution Acids have an H + concentration of 1 x or greater. We will therefore calculate the concentration using pH = -log[H + ]. 9.3 = -log(x) or antilog -9.3 = x x = 3.17 x The solution is basic because the H + ion concentration is less than 1 x 10 -7

More practice What is the pH of a solution that contains 5.44 x 10 –5 M NaOH?

Solution What is the pH of a solution that contains 5.44 x 10 –5 M NaOH? Two ways to do this: solve for the H +, or calculate pOH and then use pK w to get pH

Solution What is the pH of a solution that contains 5.44 x 10 –5 M NaOH? 1 x = [H + ][OH - ] 1 x /5.44 x = [H + ] = 1.84 x pH = -log(1.84 x ) = basic

Other solution What is the pH of a solution that contains 5.44 x 10 –5 M NaOH? pOH = -log[OH - ] -log(5.44 x ) = 4.26 pK w = pH + pOH or 14 – 4.26 = pH pH = 9.74 (answers are the same)

Polyprotic acids Many acids release more than one proton. Examples: H 2 SO 4, H 3 PO 4, H 2 C 2 O 4 When these dissociate, they change the pH differently. Strong acids will donate all protons from H +, weak will not donate even all the first ions.

Example Calculate the pH of a M H 2 SO 4 solution.

Solution Calculate the pH of a M H 2 SO 4 solution. [H+] = 2(0.002) 0r M H + ions pH = -log(0.004) = 2.40

Problem What is the H + ion concentration if the OH - ion concentration is 1 x M? K w for water is 1.0 x Is this solution an acid or a base?

Problem Show the neutralization reaction of acetic acid, a weak acid, and sodium hydroxide, a strong base.

Problem If I were to put sodium acetate salt into water, would the solution be acidic, basic, or neutral? Why?

Problem What acids and bases will produce ammonium chloride? When placed in water, would the solution be acidic, basic, or neutral? Why?

Problem When placed in water would the solution of sodium bromide be acidic, basic or neutral? What color would it turn a strip of litmus paper?

Questions What consitutes a strong acid? What constitutes a weak acid? What is a conjugate acid? How does it differ from a conjugate base? What is the difference between Bronsted – lowry acids and Arrhenius acids?