[H + ] =10 ph poh = -Log [OH - ] [OH - ]=10 poh

Transcription

1 Self Ionization of Water H 2 O H + + OH - Acids & Bases ph poh [H + ] [OH - ] Pure Water [H + ] = [OH - ], remember: [ ] means concentration 1 x 10 7 = 1 x 10 7 [H + ] > [OH - ], there is an acidic solution [OH - ] > [H + ], there is a basic (alkaline) solution ph Values acidic basic H 2 O Neutral ph + poh = 14 To find ph or poh substitute [H + ] or [OH - ] into [H + ] [OH - ] = 1 x = K w To find [H + ] or [OH - ] substitute ph or poh into ph = -Log [H + ] [H + ] =10 ph poh = -Log [OH - ] [OH - ]=10 poh

2 Given: [OH - ] = 1 x 10 4 find ph, poh, [H + ] Given: poh = 2.3 find ph, [H + ], [OH - ]

3 1. Determine the ph of each solution. a. [H + ] = 1.0 x 10-6 M b. [OH - ] = 1.0 x What is the hydroxide ion concentration For a solution with the ph values of 12? 3. Calculate the ph for the solutions. a. [OH - ] = 1.0 x 10-2 M b. [H + ] = 1.0 x 10-6 M 4. Calculate the ph for each solution. a. [OH - ] = 2.4 x 10-6 M b. [H + ] = 9.1 x 10-9 M

4 5. For each of the following reactions, identify each substance as a Brønsted- Lowry acid or Brønsted-Lowry base (on the reactant side of the equation), and as a conjugate acid or conjugate base (product side). a. NH 4 + (aq) + CN - (aq) HCN(aq) NH 3 (aq) b. (CH 3 ) 3 N(aq) + H 2 O(l) (CH 3 ) 3 NH + (aq) + OH - (aq) 6. For each of the following bases, write the formula for its conjugate acid; for each acid write the formula of the conjugate base. Base Conjugate Acid Acid Conjugate Base a. I - HClO 4 2- b. SO 3 H 2 S 3- c. PO 4 - HCO 3 - d. C 2 H 3 O 2

5 Ionization & Dissociation You should recall from our unit on solutions that electrolytic solutions are those that conduct electricity because the substance dissolves in water to produce ions. Solutions that conduct electricity well are strong electrolytes they are good conductors because they break down well and produce many ions in solution. Weak electrolytes do not conduct electricity as well because fewer ions are produced in solution. This concept of strong and weak will have an important role in our discussions of acids and bases, so it is important to understand the difference now. Ionic compounds and some molecular compounds can produce electrolytic solutions, but a different name is usually given to the processes... Dissociation When ionic compounds dissolve to produce ions the process is typically called dissociation. Dissociation of ionic compounds occurs when water molecules pull apart the ionic crystal. This occurs due to strong attractions between the polar ends of the water molecule and the positive and negative ions within the crystal. Water molecules then surround the positive cations and negative anions; this is called hydration.

6 Examples of dissociation equations: Write Products Below NaOH (s) Na + (aq) + OH (aq) KOH (s) K + (aq) + OH (aq) Mg(OH) 2 (s) Mg 2+ (aq) + 2 OH (aq) NaCl (s) Na 2 SO 4 (s) (NH 4 ) 3 PO 4 (s) There are two important things to notice about writing dissociation equations: 1. Generally DO NOT include H 2 O as a reactant. We know something has been dissolved in water when we see the (aq) notation. We will make some exceptions later to this rule, however. 2. Ion charges MUST BE included! An ion, such as the sodium ion Na + is not the same as a sodium atom, Na. Be sure to get in the habit of writing charges for all ions; refer to your Table of Common Ions when needed, but by now you should be memorizing the charges of ions we commonly use, including polyatomic ions.

7 Ionization When molecular compounds dissolve in water to produce ions the process is typically called ionization. Recall that molecular compounds are held together by covalent bonding; ionic compounds are held together by ionic bonding Most molecular compounds do not undergo ionization. Acids are an exception. All acids produce hydrogen ions in solution. Some examples: HCl (g) H + (aq) + Cl - (aq) H 2 SO 4 (g) 2 H + (aq) + SO 4 2- (aq) HC 2 H 3 O 2 (l) H + (aq) + C 2 H 3 O 2 - (aq) (The reason a double arrow is used for acetic acid will be discussed later) The reactions as written above are actually simplified versions of what really occurs. Evidence suggests that the hydrogen ion, H +, actually bonds to a water molecule (H2O) to form the hydronium ion, H3O + : HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) H 2 SO 4 (g) + H 2 O (l) 2 H 3 O + (aq) + SO 4 2- (aq) Your Turn: HC2H3O2 (l) + H2O(l) 5.Write balanced equations for the: a. Dissociation of calcium hydroxide, Ca(OH) 2 b. Ionization of nitric acid, HNO 3