Presentation on theme: "Mullis Acids, Bases and Salts Acids give up hydrogen ions (H + ) in a water solution. Bases give up hydroxide ions (OH - ) in a water solution."— Presentation transcript:
Mullis Acids, Bases and Salts Acids give up hydrogen ions (H + ) in a water solution. Bases give up hydroxide ions (OH - ) in a water solution.
Mullis Properties of Bases Bitter taste Feel slippery if you touch them pH > 7.0 Strong bases: –Sodium hydroxide (NaOH) –Potassium hydroxide (KOH) Weak bases: –Sodium bicarbonate (NaHCO 3 )
Mullis Properties of Acids Sour taste pH < 7.0 React with metals to form H 2 gas Strong acids: –Sulfuric acid (H 2 SO 4 ) –Hydrochloric acid (HCl) Weak acids: –Acetic acid (vinegar – CH 3 COOH)) –Citric acid (in fruits) –Ascorbic acid (Vitamin C)
Mullis Naming Acids Binary Acid = 2 elements (HCl) –Begin with hydro-. –Use name of 2 nd element and end with –ic. –HCl is hydrochloric acid. Oxyacid = H + O + 3 rd element (H 2 SO 4 ) –Usually incorporates the polyatomic ion name into the acid name. –Written with H first, then the polyatomic ion. –H 2 SO 4 is sulfuric acid.
Mullis Acid Strength Strong acids ionize completely in water. –Many H 3 O + ions –Strong electrolyte Weak acids do not ionize completely in water. –Some H 3 O + ions –Weak electrolyte –The ionized H 3 O + ions are being bonded back to the negative species (reverse reaction) at the same time some acid molecules are being ionized to form H 3 O + ions. Strong and weak bases are similar, except ion involved is OH - instead of H 3 O +.
Mullis Classifying strength of electrolytes from solubility (general rules for compounds) Strong electrolyte –Water soluble AND ionic –Strong acid, water soluble and not ionic –Strong base, water soluble and not ionic Weak electrolyte –Weak acid or base, water soluble and not ionic Nonelectrolyte –None of the above
The Hydronium Ion Until now, we have identified acids by looking for H first, assuming that acids give up an H +. However, H + is a bare proton. It is so highly charged, it bonds to the oxygen of water immediately, forming the hydronium ion. Ionization is the creation of ions from a molecular compound. –If the force of attraction between solvent molecules and parts of the solute are stronger than the covalent bonds of the solute, the solute breaks into ions. –In water, HYDRATION produces heat, which provides energy to break more covalent bonds. In these notes and some textbooks, H 3 O + and H + are used interchangeably in discussion of acids and bases.
Mullis Cl The Hydronium Ion H + attracts other molecules or ions In water, H + becomes a proton bonded to the oxygen of a water molecule. The hydronium ion is H 3 O +. H 3 O + and H + are used interchangeably in discussion of acids. More H 3 O + than OH - = acid Cl O O++ - + H HH H H H
Mullis Acid-Base Systems TypeAcidBaseExamples Arrhenius H + or H 3 O + producer OH - producer HNO 3 + H 2 O H 3 O + + NO 3 - NH 3 + H 2 O NH 4 + + OH - Brønsted -Lowry proton (H + ) donor proton (H + ) acceptor HCl + NH 3 NH 4 + + Cl - Lewis electron pair acceptor electron pair donor BF 3 + F - BF 4 - BF 3 is Lewis acid, F - is Lewis base
Mullis Brønsted-Lowry Acids Brønsted-Lowry acids donate a proton. A monoprotic acid donates one proton per molecule, such as HCl and HClO 4. A polyprotic acid donates more than one proton per molecule, such as H 2 SO 4 and H 3 PO 4. –H 2 SO 4 is a diprotic acid. –H 3 PO 4 is a triprotic acid.
Mullis Conjugate acids and bases The species remaining after a Brønsted-Lowry acid gives up its proton is the conjugate base of that acid: Take off one H from the acid. The species remaining after a Brønsted-Lowry base accepts its proton is the conjugate acid of that base: Take off one H. Add an H to the base. CH 3 COOH(aq) + H 2 O(l) H 3 O + (aq) + CH 3 COO - (aq) acid baseconjugate conjugate (proton donor) acid base
Mullis Examples of conjugate acids and bases HCO 3 - (aq) + H 2 O(l) H 2 CO 3 (aq) + OH - (aq) base acidconjugate conjugate (proton acid base acceptor) HF(aq) + H 2 O(l) H 3 O + (aq) + F - (aq) acid baseconjugate conjugate (proton acid base donor)
Mullis Salts An acid and base combined together react to neutralize each other. Neutralization is a process which produces produces that are not acids or bases. H+ and OH- make water. The remaining reactants combine to make a salt. A salt is an ionic compound made of a metal and a nonmetal. Soluble salts are strong electrolytes. Soap and detergent are organic salts.
Mullis Neutralization HCl + NaOH NaCl + H 2 O HNO 3 + KOHKNO 3 + H 2 O H + + OH - H 2 O ACID + BASE YIELDS SALT + WATER salt acid basewater
Neutralization: Acid + Base To obtain 1 x 10 -7 M hydronium ions, at least one strong acid or base is required. –Either or both components of the acid/base pair must be capable of complete ionization/dissociation –A weak acid and weak base together involve two equilibrium conditions, making true neutralization unlikely Mullis
Neutralization The reaction between an acid and a base which produces a salt and water. Recall: A salt is an ionic compound: metal + nonmetal which is likely to dissociate in water. Ex: You take a dose of the antacid magnesium hydroxide, Mg(OH) 2, to relieve excess stomach acid, HCl. Equations for this neutralization: 2HCl(aq) + Mg(OH) 2 (s) MgCl 2 (aq) + 2H 2 O(l) 2H + (aq) + Mg(OH) 2 (s) Mg 2+ (aq) + 2H 2 O(l)
Mullis Ionic Equations for Acid-Base Reactions Strong acids ionize completely. HCl H + + Cl - Weak acids do not ionize completely. HF H + + F - Water and ammonia are a weak acid and a weak base, respectively. NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq)
Mullis Net Ionic Equations for Acid-Base Reactions strong acid + strong base Chemical equation: HCl + KOH→ H 2 O + KCl Net ionic equation: H + + OH - → H 2 O strong acid + weak base Chemical equation: HCl + NH 4 OH→ H 2 O + NH 4 Cl Net ionic equation: H + + NH 4 OH → H 2 O + NH 4 + weak acid + strong base Chemical equation: HF + NaOH→ H 2 O + NaF Net ionic equation: HF + OH - → H 2 O + F -
Mullis Measuring Strength of Acids and Bases pH is a measurement which indicates acidic or basic strength, measuring the concentration of H+ ions. More H+ ions = lower pH = acid. An indicator changes color depending on pH of a solution. pH paper is treated with indicators to change color when dipped in a solution. 1: acid 7: neutral14: base
Mullis pH and acidity pH is related to the concept of concentration of hydronium ions found in water. Water and all its solutions contain hydronium ions and hydroxide ions. Acidic solutions: More H 3 O + ions. Basic solutions: Fewer H 3 O + ions / more OH - ions. If pH = 2: H 3 O + ion concentration = 0.01 M OH - ion concentration = 0.000000000001 M If pH = 12: H 3 O + ion concentration = 0.000000000001 M OH - ion concentration = 0.01 M
Mullis The pH scale pH stands for “power of hydronium ion.” pH = -log [H 3 O + ] pH value is the exponent on the power of 10 with its sign changed.
Mullis pH examples Example 1: –0.001 M H 3 O + = 1 x 10 -3 M H 3 O + –Concentration is 0.001M H + –pH = -log [H 3 O + ] = -log (1x 10 -3 ) = -(-3.0) = 3.0 –pH is 3.0 - This is an acid. Example 2: –1x 10 -8 M HNO 3 = 1 x 10 -8 mol H 3 O + –Hydrogen ion concentration is 0.000 000 01M H + –pH = -log [H 3 O + ] = -log (1x 10 -8 ) = -(-8.0) = 8.0 –pH is 8.0 - This is a base.
Mullis pOH pOH is the negative of the logarithm of the hydroxide ion (OH - ) concentration. pOH = -log [OH - ] pH + pOH = 14.0 at 25 deg. C
Mullis Example 3: Find the pH for a base. –2.0 x 10 -6 M NaOH= 2.0 x 10 -6 M OH - –pOH = -log [OH - ] = -log (2.0 x 10 -6 ) = 5.70 –pH = 14 – pOH = 14 - 5.70 = 8.3 –pH = 8.3 Example 4: Find the hydronium ion concentration for a solution with pH = 4.8 –Use the inverse function of log, 10 x –4.8 = -log[H + ] so [H + ] = 10 -4.8 = 1.58 x 10 -5 M –This solution has hydronium concentration of 1.58 x 10 -5 M
Relating [H + ] and [OH - ] [H + ][OH - ] = 1 x 10 -14 In any water solution, there are some hydronium ions and some hydroxide ions. In pure water, each ion has concentration of 1 x 10 -7 M. Note that [ ] indicate molarity, but unit required is M Mullis
Concentration Example What is the hydroxide ion concentration of a solution with a hydronium concentration of 3.2 x 10 -4 M? [H + ][OH - ] = 1 x 10 -14 so [OH - ] = 1 x 10 -14 3.2 x 10 -4 [OH - ] = 3.13 x 10 -11 M Mullis
Buffers Why is the pH of some lakes unaffected by acid rain even when they are downwind of big polluters? The lakes are surrounded by soils which neutralize the acidic precipitation. 1.One way to neutralize acid is to add a base. Limestone (CaCO 3 ) is a weak base. 2.Another way to neutralize either an acid or a base is to add a buffer. A buffer is a substance or combination of substances capable of neutralizing limited quantities of either acids or bases.
Mullis Buffers Calcium carbonate around a lake contaminated with acid rain would react this way: CaCO 3 + H 3 O + Ca 2+ + HCO 3 - + H 2 O The polyatomic ion HCO 3 - acts as a buffer: HCO 3 - + H 3 O + 2H 2 O + CO 2 HCO 3 - + OH - H 2 O + CO 3 2- Another buffer is the hydrogen phosphate ion. Possible sources of this ion are Na 2 HPO 4 and NaH 2 PO 4. H 3 O + + H 2 PO 4 2- H 2 PO 4 - + H 2 O