ACIDS and BASES. Not the stuff you already know!!! Ways to define acids- Arrhenius • Arrhenius is one way to characterize acids and bases- it has to do with what they do in water. – Arrhenius Acid (AA)- is one that produces H+ in water. – Arrhenius Base (AB) is one that produces OH- in water – Limiting because only water solutions and only one type of base, an OH Some examples • HCl + H2O H3O + + Cl • HNO3 + H2O H3O + + NO3- Bronsted Lowery acids • A more general way to describe acids and bases • An acid is anything that can donate a H+ ( a proton donor) • A base is anything that accepts a H+ ( a proton acceptor) • That means acid and bases always occur in pairs, you always have one acid and one base as reactants, and one acid/one base on products • A H+ is also called a hydronium ion. When added to water write H3O+ Conjugate acids and bases • A conjugate is anything on the product side that remains after a proton has moved. • HCl + H20 H3O + + ClAcid base conjugate acid conjugate base Keep in mind both bases can compete for the proton, will need to determine which is stronger to establish equilibrium How to write them • HCl + H2O • HNO3 + H2O • H2SO 4 • Try pg 625 + H2O There is an equilibrium expression for this! • • • • Ka = products over reactants, Called an acid dissociation constant Tells you how well the acid comes apart. Ka< 1, mostly reactant ( doesn’t dissociate well) WEAK ACID • Ka >1 comes apart well, mostly product STRONG ACID • Ka = 1, even mix of the 2 in solution Strong and weak, concentrated and dilute • Strong and weak have to do with how reactive they are • Chart gives some idea • Bases, OH is strong • Nice to know (not have to look up) • HCl, NH3,H2SO4, H3PO4, OH • Concentrated and dilute have to do with how much substance per how much water. • This is molarity/ molality. • High molarity is concentrated Other types of acids • many acids are diprotic or triprotic- have 2 or 3 H. The first H to come off is usually strong, but the rest are usually weak • Oxyacids are H attached to a polyatomic ion • Organic acids are carbon chains, usually weak acids • For very strong acids, Ka is not accurate because the equilib. Is so far to right, and therefore not very useful How to get rid of more than one Hydrogen • If an acid has only one H+ to give away, it is called monoprotic acid – ( a Hydrogen without it’s electron is just a proton) • Examples include HCl, HF, HNO3 • If an acid has 2 Hydrogens to give away, Diprotic, or 3, triprotic – Examples include H2S, H2SO4 H3PO4 Base dissociation • • • • Ca(OH)2 becomes Ca + 2OHNa(OH) becomes Na + OHNH3 +H2O NH4+ + OHCH3COO- + H2O becomes CH3COOH + OH- • Strong bases have OH, weak have to compete w/ water to get it, so weak Ka and Kb • Keeping in mind that Ka = products over reactants, and large ka= strong acids, • Kb is the strength of the base, is also products over the reactants, and high Kb= strong bases. • A strong acid will have a weak conj. Base, and • a weak acid will have a strong conjugate base • So the stronger the acid, the weaker its base, and if you are a really strong acid ( HCl, H2SO4) don’t’ even have Ka’s for it. Water as acid and base • Water is amphoteric, it can act as acid or base. It also tends to come apart on it’s own. • Autoionization is the term for water separating into acid and base • The Kw for water describes the number for this. • H2O H+ + OH• at 25 ° the [H+ ] = 1. x10 -7 and • [ OH-] = 1 x 10 -7, • so the Kw= [H+ ][ OH-] • So Kw = 1 x 10 -14 pH • This auto ionization is the whole idea behind pH • Kw is always 1 x 10-14 at 25°, but the ratio of H and OH change with acids and base. • Literally pH stands for the power of the Hydrogen, and pOH stands for the power of the OH. • If H > OH, acid, if H<OH base, if H=OH neutral. pH continued • • • • • Ok, so pH = -log [H+] If [H+] = 1 x 10-3, pH =3 acid If [H+] = 1 x 10-5, pH =5 acid If [H+] = 1 x 10-9, pH =9 base If [H+] = 1 x 10-14, pH =14 base • See a pattern? pH continued • Ok, so pH = -log [H+] • What if it isn’t quite that easy? Since pH is the power of the H, even if it isn’t a “1” the pH will be close to the exponant, but you will need to know how to use your caluclator!!! • If [H+] = 2 x 10-3, pH =2.66 acid • If [H+] = 3.55 x 10-5, pH =4.45 acid • If [H+] = 9.8 x 10-9, pH =8.009 base • If [H+] = 6.99 x 10-14, pH =13.15 base • You try them? H and OH, pH and pOH • H and OH are 2 parts of a whole, the whole being 1.0 x10-14, • Remember that Kw = [H+ ] [OH-] • and Kw = 1 x 10-14 • So… • so if [H+ ]= 1 x 10-5, [OH-] = 1 x 10 -9 • so if [H+ ]= 1 x 10-3, [OH-] = 1 x 10 -11 • so if [H+ ]= 1 x 10-10, [OH-] = 1 x 10 -4 • so if [H+ ]= 1 x 10-2, [OH-] = 1 x 10 -12 • so if [H+ ]= 2.1 x 10-3, [OH-] = 4.76 x 10 -12 • You try them too! Neutralization • Strong Acids and strong bases make water and salt • Not always NaCl salt. Just an ionic compound. • 2HF + Mg(OH)2 2H2O +MgF2 • 2H+ + 2F- + Mg+2 + 2OH- 2H2O +MgF2 Types of salts • A strong acid and weak base = slightly acidic salt • Strong base and weak acid= basic salt • Weak acid and base, varies • When compounds have high oxidizing metals, always slightly acidic ( Al+3, Fe+3) How concentration affects strength • So far worked pH from {H3O}concent. • What if given from chemical? • .001 M HF? – – – – HF H+ + F- , so HF & H+ are same, .001 But what if .001 H2SO4? H2SO4 2H+ + SO4-2 , so H+ is double, .002 Oxides, some acids, some bases • Metal oxides tend to make bases • CaO, + H2O Ca(OH)2, K2O + H2O KOH • NONmetal oxides tend to make acids • SO3 + H20 H2SO3 CO2 +H20 H2CO Lewis acids/bases • Even more broad in definition • Electron pair donor, acceptor • If has a unshared pair of electrons, is the Lewis base • Accepting the electrons, Lewis acid • ( opposite of BL in theory) • NH3, H2O, tend to have the e- pair, are bases • H+, Ni+2, Al +3, acceptors, acid Properties of acid and bases • Acids • Bases • • • • • • • • • • • • • • Taste sour Turn pH paper red pH of 0-6 Acids feel like water Can be caustic Foods like fruits, vinegar, soda, yogurt • Conduct electricity • React with metals Tastes bitter Turn pH paper blue pH of 8-14 Feel slippery Can be caustic Ammonia, soap, pickles Conduct electricity Do not react with metals •Acids + bases = water +salt Common names for acid and base • Acids • Muratic acid- stomach acids and cleaner • Oranges, limes, lemon all have citric acid • Soda, sour candyphosphoric acid • Walnuts- tannic acid • Apples – malaic acids • Vinegar- acetic acid • Vitamin C- ascorbic acid • • • • • Bases Ca(OH)2 - tums NH3 Ammonia Lime CaCO3 Lye NaOH Industrial acids • Muratic acid- HCl, cleaner of pools and concrete, also of steel, food processing, recovering Mg from sea water, and other food creation processes. Stomach acid • Sulfuric acid- most common industrial acid, fertilizer production, car batteries, refining process for many plastics, metals, paint, paper, dyes etc. Great for dehydration process ( sugar refining) More industrial acids • Nitric acid- Not stable, so less commonly used, used in production of rubber and plasitcs, pharmacuitcals and explosives. • Phosphoric acid- beverages and candy, to clean food equipment. also in fertilizers ( DNA is P based) detergents and ceramics • Acetic acid- glacial is very concentrated, vinegar. Synthesizing chemicals used in plastic production, many foods, production of essential amino acids. Also a fungicide. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 12 M HCl is __________ (choose) strong/ weak and it is concentrated/dilute .2 M H2SO4 is (choose) strong/ weak and it is concentrated/dilute 1 M NaOH is ____________ (choose) strong/ weak and it is concentrated/dilute 12 M NH3 is _____________ (choose) strong/ weak and it is concentrated/dilute .5 M H3PO4 is ___________________ (choose) strong/ weak and it is concentrated/dilute 15 M H3P is (choose) strong/ weak and it is concentrated/dilute