Chem 2 (Quiz 2): Chapter 15 (Acids and Bases)
What are the structures of acids?
*Binary acids*: have hydrogens attached to a nonmetal atom (i.e. HCl) *Oxyacids*: have hydrogens attached to an oxygen atom (the hydrogens that oxyacids will donate will be attached to oxygen. i.e. so in H2SO4, it's not the sulfur that has the hydrogen - its the oxygen attached to the hydrogen) Carboxylic acids: have COOH group
What are the 2 most common indicators? *NEED TO KNOW*
1) *Litmus* (made from spanish moss): red when solution is acidic, blue when solution is basic 2) *Phenolphthalein*: red when basic, colorless when acidic - won't tell exact pH, but will tell there has been a pH change
What are the general trends in acidity?
1) Higher oxidation number = stronger oxyacid (REVIEW OXIDATION RULES) 2) With ions & polyatomic ions, the greater the positive charge it has = stronger acid - the better it is as an acid (more acidic) - because when gives up proton, it gives away that positive charge. (and also, when something has a large negative charge, the better it is as a base)
How can you tell if you have a neutral, acidic, or basic solution?
All aqueous solutions contain both H3O+ and OH- ions. The acidity or basicity of the solution depends on the relative amounts you have of H3O+ and OH-: - If have equal molar concentrations of H3O+ and OH-, then have a neutral solution. - If have a larger molar concentration of H3O+ than the molar concentration of OH-, then have an acidic solution. - If have a larger molar concentration of OH- than H3O+, then have a basic solution.
What is *pOH*? How can you use the pOH value to find the pH value of a solution (and vice versa)?
Another way of expressing the acidity/basicity of a solution (just as with the concenrtation of H3O+ and OH- mirror each other in the opposite way, there's also a counterpart to pH: the pOH scale.) if pH is the -log [H3O+], then pOH= -log [OH] just as concentration of concentration of OH- multiplied by the concentration of H+ equals the same number, pH + pOH always equals the same number: *pH + pOH = 14.0* (i.e., a solution that has a pH of 5 must have a corresponding pOH of 9 to total it to 14) because pOH scale follows the OH ions instead of the H+ ions, then: - anything with pH < 7 is basic (opposite of pH scale) - anything with pH >7 is acidic (opposite of pH scale) - anything with pH = 7 is neutral (i.e. water)
What are *indicators*?
Chemicals that change color depending on the solution's acidity or basicity (testing in changes in pH) - many vegetable dyes are indicators (i.e. red cabbage)
What are the 3 definitions of acids and bases? *NEED TO KNOW*
Definition had to be continually redefined over time 1) *Arrhenius* definition - an acid produces H+ions when dissolved in (aq) solution - a base produce OH ions when dissolved in (aq) solution 2) *Bronsted-Lowry* definition - based on reactions in which H+ is transferred - acid = H+ donors - Base = H+ acceptors (redefined so that base does not have OH molecule directly attached to act as a base. i.e, ammonia - NH3 - has no hydroxides) 3) *Lewis* definition - based on reactions in which electron pairs are transferred - acid = electron pair acceptors - base = electron pair donors - *anything with lone pair electrons on it can be a Lewis base* (i.e NH3, ammonia, has a lone pair on the nitrogen - makes a very good Lewis base)
What is a *hydronium ion*?
H+ ions only have protons (hydrogen doesn't have neutrons and only have that 1 electron that will be taken away, so only donating the protons that are highly reactive). the protons don't really exist in water by itself. so will immediately bind to a water molecule, forming an H3O+, a hydronium ion. Arrhenius acids produce hydronium ions, H3O+, in (aq) solution - some will refer to the concentration of the H3O+ ions or will refer to the concentration of H+ ions or protons. ALL MEAN THE SAME THING H3O+ is the same thing as H+. Can be used interchangeably.
What is the *ion product of water, Kw* / *dissociation constant of water*? What is the value of [H3O+] x [OH-] and what is their relationship to each other?
In any sample of water, their molar concentrations of H3O+ and OH- are always the same, so then their product will also always be the same (called the *ion product of water, Kw*. also called the *dissociation constant of water*) - in any sample of water, the molar concentration of H3O+ multipled by the molar concentration of OH- will always be 1.00x10^-14. [H3O+] x [OH-] = Kw = 1.00 x 10^-14 - but if add base or acid to water, this value will still hold true. - PRODUCT IS CONSTANT, SO INVERSE RELATIONSHIP BETWEEN [H3O+] AND [OH-]. So, if increase molar concentration of H3O+, then the molar concentration of OH- must be decreased (and vice versa) to always get the product to equal 1.00 x 10^-14
What is the Bronsted-Lowry Acid-Base Theory?
It defines acids and bases based on what happens in a reaction - the acid is an H+ (proton) donor - the base is an H+ (proton) acceptor (don't necessarily don't need a OH to be be a proton acceptor, so ammonia fits this definition) often written like this: H-A + B (with lone pair) <-> A- + H-B+ - acid has attached hydrogen (H-A) - proton gets transferred to the base (Positive charge gets transferred from acid to base) - acid is left with a negative charge - still have conservation of charge ACID TRANSFERS PROTON (H+) TO BASE, BASE ACCEPTS PROTON AND IT'S POSITIVE CHARGE. ACID GETS NEGATIVE CHARGE AND ACCEPTS THE LONE PAIR.
What are the 6 strong bases?
LiOH NaOH KOH Ca(OH)2 Sr(OH)2 Ba(OH)2
What are the general properties of acids?
Sour taste Ability to dissolve many metals Ability to neutralize bases Change blue litmus paper to red
Are strong acids and strong bases weak or strong electrolytes?
Strong acids and strong bases are *strong electrolytes* (*will completely ionize in (aq) solution*, so solution can conduct electricity) - i.e. NaCl can conduct electricity vs. sugar (non-electrolyte)
What are *amphoteric substances* (in Bronsted-Lowry definition)?
Substances that *can act as either an acid or base* depending on the conditions. (because they *have both a transferable proton, H+, and an atom with lone pair electrons) - i.e., WATER (acts as a base when react with HCl), but acts as acid when reacts with ammonia (ammonia has that lone pair so acts a a base. water will donate its proton to ammonia)
What are the properties of bases?
Taste bitter (alkaloid compounds in poisonous berries) Feel slippery Ability to turn red litmus paper blue Ability to neutralize acids
How did Arrhenius define acid-base reactions?
The H+ from the acid combines with the OH- from the base to make a H20 molecule. *The cation from the base combines with the anion from the acid to make a salt (which may or may not be soluble).* acid + base --> salt + water
What is *pH*? What is its value? How does the pH scale work? How can the molar concentration be found given the pH value? What is the magnitude of difference between solutions that have a pH difference of 1, of 2, etc?
The acidity or basicity of a solution. It is equal to the -log of the molar concentration of the hydronium ion/proton (can be written both ways): pH = -log [H3O+] or also, pH = -log [H+] pH scale: - anything with pH = 7 is neutral (i.e. water) - anything with pH < 7 is acidic - anything with pH >7 is basic If given the pH value, then can calculate the molar concentration of the hydronium ions: [H3O+] = 10 ^-pH or also, [H+] = 10 ^-pH (i.e. something with pH of 4.7 will have its molar concentration of H3O+ equal to 10^-4.7). as exponent becomes less negative, the value becomes bigger (i.e. 10^-4 is bigger than 10^-6) - so even though value of pH scale is getting smaller, the concentration of the hydronium ion is getting bigger. pH is a logarithmic scale, so differences of 1 between 2 values of pH is a 10-fold difference (i.e. pH=5 is 10x greater than pH=4. if difference of 2 between the pH, then it is a 100-fold increase. if difference of 3, then it is a 1000-fold increase, etc.)
What is *autonionization* of water? What are the 2 ways in can occur?
Water is amphoteric; it can act either as an acid or a base - therefore, there must only be a few ions present in a sample of water. However, about 2 out of every 1 billion *water molecules form ions through a process called autoionization* 2 ways that autoionization can occur: 1) single water molecule can break apart directly into a proton and a OH ion. the proton ion (H+) will then go off in search of a water molecule to form hydronium ion, H3O+ 2) two water molecules can directly interact and a proton can be transferred directly from 1 molecule to the other *All aqueous solutions contain both H3O+ and OH- - when have pure neutral water, the concentration of H3O+ and OH- are equal to each other (will be equal to 10^-7 Molar)*
Are weak acids and weak bases weak or strong electrolytes?
Weak acids and weak bases are weak electrolytes - only a small percentage of the molecules ionize (will conduct a moderate amount of electricity) - can be as little as 1% that will ionize
What are problems with Arrhenius Theory?
ammonia, sodium carbonate, etc. - during chemical testing, found they acted as bases but if look at chemical formula don't have OH (so Arrhenius definition is incomplete)
Calculate: What is *pKa*? How is it calculated? What is the relationship between acid/base strength and pKa/pKb (and how does it compare to the relationship between acid/base strength and Ka)?
another way of expressing the strength of an acid or base on a logarithmic scale: for acid: pKa = -log(Ka), Ka = 10^-pKa for base: pKb = -log (Kb), Kb = 10^-pKb ON QUIZ: if give Ka, calculate pKa. And do reverse: calculate Ka given pKa The relationship between acid or base strength and pKa/pKb is INVERSE. - the opposite of the relationship between acid strength and the Ka, which is DIRECT. SMALL pKa = STRONG ACID BIG pKa = WEAK ACID SMALL pKb = STRONG BASE LARGE pKb = WEAK BASE ON QUIZ: given list of pKa values, asked which is strongest? SMALLEST VALUE
What can potentially be a Bronsted-Lowry acid?
anything that has a hydrogen can potentially be a Bronsted-Lowry acid
What are *conjugate acid-base* pairs?
as soon as something acts as a base or acid, it becomes its own conjugate. the identity of its conjugate is the opposite of what it originally acted as - bases form conjugate acids - acids form conjugate bases And, strength is also inverse of what it originally was: - a strong acid will form weak conjugate base, vice versa
How did Arrhenius define bases?
bases produce OH- ions when dissolved in (aq) solutions (i.e. NaOH (aq) --> Na+ (aq) + OH (aq)
What are the 6 strong acids?
binary acids: Hydrochloric acid (HCl) Hydrobromic acid (HBr) Hydroiodic acid (HI) Oxyacids: Nitric acid (HNO3) Perchloric acid (HClO4) Sulfuric acid (H2SO4) EVERYTHING ELSE IS A WEAK ACID
What is the *acid ionization constant, Ka*?
can apply same concept of equilibrium constant (product/reactants) to acids, and get the acid ionization constant, Ka. When take acid and dissolve it into (aq) solution, the unionized acid and the liquid water are the reactants and the hydronium ion and ionized acid are the products. So, can put these in equilibrium constant formula and get hydronium ion and ionized acid divided by unionized acid: Ka = [H3O+] [A-] / [HA] = [H+] [A-]/[HA] * water left out because its a pure liquid - Ka has a DIRECT relationship with the strength of the acid. the stronger the acid, the more it should favor products over reactants. *THE LARGER THE Ka, THE STRONGER THE ACID (AND VICE VERSA) ON QUIZ: Compare acids based on their Ka (i.e. chart, p. 7: acid that is the strongest is the one with the biggest Ka value and acid that is the weakest is the one with the smallest Ka value.)
How can the strength of acids and bases be thought in terms of?
can be thought of in terms of the equilibrium constant. a very strong acid should completely ionize into its own conjugate base and a hydronium ion. So strong acid has a large equilibrium constant, Keq, because when it reaches equilibrium, the products (ionized acid and hydronium) should far outnumber the reactants, the un-ioniozed acid. will have high equilibrium constant. same thing with strong bases - should almost completely ionize - so will have more products and when products outnumber the reactants, the constant will be greater than 1 and also large. THE STRONGER THE LARGER THE BASE OR ACID, THE LARGER THE Keq (EQUILIBRIUM CONSTANT) IS GOING TO BE. ON QUIZ: given equilibrium constant for several different acids - which one is the strongest? THE ONE WITH THE BIGGEST EQUILIBRIUM CONSTANT. the weakest? THE ONE WITH THE SMALLEST EQUILIBRIUM CONSTANT
What is a *polyprotic acid*?
many protons (i.e. sulfuric acid) fairly easy to remove one of the protons, but becomes successively harder to remove subsequent others
Do strong acids have a weak or strong bond (attraction between proton and the rest of the molecule)? Do weak acids have a weak or strong bond?
strong acids are good at giving up their proton. the bond between the proton and the rest of the molecule will be a weak bond. strength of acid is defined by its ability to give up its proton (by their reactivity). so a strong acid will have a weak attachment to it because it gives up its proton easily. IN *STRONG ACIDS*, THE BOND BETWEEN THE PROTON AND THE REST OF THE MOLECULE IS *WEAK*. FOR *WEAK ACIDS*, THE THE BOND BETWEEN THE PROTON AND THE REST OF THE MOLECULE IS *STRONG*.
What is one of the advantages of Bronsted-Lowry theory? REVIEW THIS ONE
they are *reversible* - once the acid donates its proton to the base, the base can donate the proton right back to the acid i.e. Slide 24: - in forward reaction, acts as base, accepts proton - when in reverse reaction, donated back the proton, so acted as acid
When comparing a cation to the 6 listed strong bases, which will be the stronger acid - the cation or the listed strong base? When comparing an anion to the 6 listed strong acids, which will be the stronger base - the anion or the listed strong acid?
when acids or bases act as acids or bases, they form their conjugate and the strength is the inverse of their parent. and there are certain strong acids and strong bases. LiOH, NaOH, KOH - when act as bases (get rid of H+ ion) then left with Li ion, Na ion, K ion. So know that because LiOH, NaOH, KOH are the conjugate acids of strong bases, so should be weak acids. HOwever, if had MgOH which is weak base. therefore, the Mg ion being the conjugate acid of a weak base, should be a stronger acid that the LiOH, NaOH, KOH. So, any metal (cation) with a positive charge could theoretically be the conjugate acid of a weak base (i.e. there could be titanium hydroxide, magnesium hydroxide, etc). *The metal cations will be stronger acids than the 6 listed strong bases (because they will have cojugate weak acids).* Anions and cations can differ in their strength as acids or bases. Certain salt solutions made up of ionic compounds can be aciidc or basic based on which ions are used to make them. Metal cations = conjugate acids of bases. Metal cations can act as strong or weak acids. *On quiz: given pairs of anions or cations - which is the stronger base and which one is the weaker base? For anions, if comparing any of the 6 listed strong acids/bases to each other, then should be equally weak. but if comparing any of the 6 listed with a non-listed one, then the non-listed one will be the stronger base. which one is the stronger acid and which one is the weaker acid? For cations, all 6 listed will be the weak acid. If comparing one of the 6 listed with a non-listed one, then the non-listed one will be stronger acid.*
How are neutralization reactions like redox reactions?
when have any neutralization reaction, one must act as the acid and one must be the base (like redox reactions, one is getting oxidized so the other is getting reduced) - i.e., when HCl dissolves in water, the HCl acts as the acid because HCl transfers an H+ (proton) to the water. So HCl is donating its proton (is the acid) and the water is acting as a base because it is accepting the proton
