U5 CHEM: acids and bases

neutralization reactions with strong acids and strong bases

the reaction of an acid and a base to produce a more neutral solution:

acid + base → ionic salt + water

strong acid + strong base = neutralization of a PH of 7

what are strong bases and strong acids?

a strong acid and strong base are substances that completely dissociate into their ions in solution.

• because they can completely disscoiate their ions, acids can completely donate their H+ protons and strong bases can donate their OH- ions completely. when they react, the H and OH are removed from the solution, forming water and resulting in a neutral pH.

• after the reaction no excess H or OH remains and the solution is neutral

• this onlt occurs if both the strong acids and bases are mixed in equal stoich amounts (if one is in excess, it wont be neutral)

explain the process of titration

define:

• titrant

• analyte

• burette

• equivalence point

• endpoint

adding drop by drop of titrant to analyte until the solution is completely neutralized.

• we know when its completely neutralized becuase of a colour changing PH indicator!

titrant: known concentration solution → also known as a standard

analyte: unknown concentration solution

burette: is the glass tube used to hold titrant to be added dropwise

equivalence point: when neutralization is complete! moles of acid = moles of base

end point: the oint where a sudden, observable colour change occurs

• end point and equivalence point are not always equal! we want to pick an indicator with an endpoint close to the equivalence point.

explain pH curves (aka titration curves)

these show how the pH changes during a titration, as one solution is slowly added to another: volume of titrant added vs the pH of the solution

monoprotic strong acid + strong base:

• starts at a low pH or very high pH (either very acidic or basic)

  • where it starts tells you what your analyte is! (ex. if the solution pH is acidic when little to no titrant is added, then the analyte is an acid)

• gradually increases then rises sharply at equivalence point (pH = 7)

• levels off at a high pH or low PH (opposite pH at start)

intial pH

buffer zone → area of slow change in pH

equivalence point → neutralization complete (moles acid = moles base)

steep slope → after neutralization, adding titrant will rapidly skew the pH to basic or acidic

explain back titrations

a back titration is a 2 step titration used when:

• the substance you’re analyzing doesnt dissolve well

• the reaction is too slow/difficult to observe directly

instead of titrating the substance directly:

1. react it with an excess amount of another reactant

2. titrate the leftover amount with a known solution (titrant) to figure out how much reacted

• so this means 2 reactions are occuring!!

Explain the arrhenius thoery of acids and bases

acids: a substance that increases the quantity of H+ ions of more accurately H3O+when dissolved in water

bases: a substance that produces OH- ions when it dissociates in water

what is a conjugate base

what is a conjugate acid

its a molecule that can accept a proton

an acid can become a conjugate base by donating a proton (it can accept it back again)

ex. HCl dissolves in H2O to produce H+ ions which are donated to the H2O —> forms H3O+ (conjugate acid) leaving behind Cl- ion which is the conjugate base (gas)

a conjugate acid is what you get after a base accepts a proton (H+) so its a molecule that can donate a proton after it accepted it

why do acids donate H+ (protons)

because of the lowry bronsted definitions of of acids as H+ donors, when an acid disscoiates, it donates its H+ instead of another species (fully charged ion).

Why is it more accurate to think of acids as forming H3O+ ions than H+?

• H+ is very small and reactive in a solution

• so when this proton is dissociated, it immediately bonds with the H2O molecule to form H3O+

• so H2O is a base! not only does it accept H+, but it also has OH- ions

• so in a solution, its actually the H3O+ ion that makes it acidic, reduces PH and engages in acid base reactions

• HCl → H+ + Cl-

• HCl + H2O → Cl- + H3O+ (is the more correct version)

limitations to Arrhenius

Bronsted lowry acid base theory

so arrhenius is too specific with the definition of bases, because there are some compounds that react in water to produce basic solutions (think about your special case double decomposition)

• NH3, HCO3-, CO3 2-

the bronsted lowry acid base theory is a more broad version of arrhenius:

• acids: H+ (proton) donors

• bases: H+ (proton) acceptors

• after donating or accepting H+, the specie that remains is the conjugate (base and acid respectively)

what happens when you lose an H+ ion

what does it mean to be polyprotic, monoprotic

what does it mean to be considered alkali?

• take away a hydrogen

• subtract a charge (gets more negative)

• polyprotic: substance has multiple H+ protons to donate

• monoprotic: can only donate one H+ proton (this acids only have one point of equivalance)

• if something is soluble it is considered alkali

amphiprotic substances

amphoeteric substances

• what features make a substance amphoteric?

Amphoteric: a substance that can act as both an acid and a base FOR ANY ACID BASE THEORY (not just bronsted lowry)

Amphiprotic: a substance that can donate and accept a proton H+ → ONLY FOR BRONSTED LEWIS

• so amphoteric is less specific than amphiprotic (its a general definition)

features of an aphoteric substance:

1. to be a BL acid → dissociate to produce H+ ions

2. to be a BL base → they need to be able to accept and bond to H+ ions, so they need to have a coordinate bond

• this is because H+ has no electrons! its lost its 1 ve to become positively charged. it has no other electrons besides this one so its just a positvely charged nucleus → so a proton!

• so H+ has empty orbitals, in order for it to bond, the other atom must provide both electrons → so a coordinate bond

• if there is no lone pair = no way to share electrons with H+ (no bonding!) = cant accept H+!!

Autoionization of water:

• why does it occur?

• so explain the effect of water autoionization

• how much water autoionizes is governed by the equilibrium expression Kw

why does it occur:

• so water is amphiprotic (dissociates into H-OH and has 2 LP of electrons) which means it can act as a BL acid and base in the same reaction!

  • so if it can accept and donate H+ in the same reaction, it can produce this:

    • H2O (base) + H2O (acid) → H3O+ (conj. acid) + OH- (conj. base)

Kw = 10^-14 → this is a constant for the ions of water (at 298K, or SATP)

because its a constant for the ions that compose water, it can also be written as the ion product of H2O:

Kw = [H3O+]*[OH-] = 10^-14 → this is why PH +POH = 14

How do you choose an indicator

• indicators can be chosen based on the pH range in which their colour change occurs

• during an acid base titration, the PH will change at the equivalence point where moles of acid = moles of base

• we want to know where the ph change is, so we should pick an indicator that has a range where colour changes near the ph of the equivalence point

equations for PH and POH (3)

• + 1 ph = what change in H+?

• sigfig rules

PH = -log(H+)

POH = -log(OH-)

PH + POH = 14

reversed:

[H+] = 10^-PH
(OH-] = 10^-POH

+1 PH = x10 decrease in H+ concentration

number of sig figs in the concentration = number of decimal places in the PH and POH values

acid reaction review:

acid =

base =

acid + m.OH →

acid + m.O →

acid + m.CO32- → (special case)

acid + m.HCO3 → (special case)

acid + NH3 (aq) →

Ammonium salt + hydroxide →

acid + metal →

acid = nm.O + H2O (not DD, just add up/synthesis)

base = m.O + H2O (DD)
acid + m.OH (hydroxide) → H2O + ionic comp

acid + m.O → H2O + ionic compound

H2CO3 special cases:

acid + m.CO32- → H2O + CO2 + ionic compound

acid + m.HCO3 → H2O + CO2 + ionic compound

acid + NH3 (aq) → ammonium salt (NO H2O)

Ammonium salt + hydroxide → NH3 + ionic comp + H2O

acid + metal → ionic compound + H2 (g)

⚡ Tiny Table of Key Neutralizations:

Type	Example	Products
Acid + Alkali	HCl + NaOH → NaCl + H₂O	Salt + Water
Acid + Metal Oxide	H₂SO₄ + CuO → CuSO₄ + H₂O	Salt + Water
Acid + Carbonate	H₂SO₄ + CaCO₃ → CaSO₄ + H₂O + CO₂	Salt + Water + CO₂
Acid + Bicarbonate	HCl + NaHCO₃ → NaCl + H₂O + CO₂	Salt + Water + CO₂
Acid + Ammonia	HCl + NH₃ → NH₄Cl	Ammonium salt

review:

• binary acids

• oxyacids

binary acids: formed from hydrogen + non metal → uses the the “hydro” prefix and “ic”

oxyacids: hydrogen + nonmental + oxygen → no hydro prefix, ending is based on the oxyanion used → ate- ic / ite- ous

strong acids

weak acids

strong acid:

defintion: an acid that completely dissociates

• if it competely dissociates, this means all its H+ ions are free floating in solution, so they will react with H2O and form H3O+ ions

• it will produce a weak conjugate base, so this base will not be very receptive of hydrogen ions, meaning not likely to revert back

• strong acids include all binary acids (except for HF) and some oxyacids

weak acid:

• partially dissociates, so there will be some leftover, unionized acid

• strong conjugate base (very readily accepts H+) → means the equation can be in equilibrium, reverts back

definition: an acid that partially dissociates

what are the 7 strong acids you need to know?

mnemomic: the show: CSI on NBC

HCl

H2SO4

HI
HNO3

HBr

HClO4

HClO3

strong bases

weak bases

strong bases: completely disscoiate into their ions in water

• this are your group 1 and 2 hydroxides

• produces weak conjugate acid

weak bases: partially ionize in water, some unionized base remains

• produces a strong conjugate acid

• the ionization extent can be represented by an equilibrium constant

what are the strong bases you need to know

group 1 and 2 hydroxides

distinguish between strong and weak acids

• H+ content/concentration

• pH

• electrical conductivity

• rate of reaction with Mg

• rate of reaction with CaCO3

(and for bases, same thing)

• greater [H+ ] content means more dissciation which means stronger acid

• more dissociation means lower pH

• more dissociation means more free floating ions, higher conductivity

• using gas production to determine the rate of reaction (when gas is produced is when the reaction is occuring) → strong acids have faster rates of gas production

Lewis acid base theory

• this is the broadest category of acids and bases

• acids: electron pair acceptors (electrophiles)

• bases: electron pair donors (nucleophiles)

  • these form coordinate bonds, so this would be your complex ions

• they accept electrons in pairs because there is an empty orbital

how to identify acids and bases

bronsted lowry:

• acids: must have at least 1 hydrogen atom that can be released as a proton

• bases: proton acceptors: this is only possible if there is at least one lone pair of electrons available to form a bond (coordinate)

How are oxides formed?

if an oxide dissolved in water an has a pH of 9, the oxide is a ____ oxide

• oxides are formed by burning an element in the presence of oxygen

• bases are formed when metal oxides dissolve in water

ocean acidification:

• how does this happen

• what are the causes

• consequences

• ocean acidification happens when CO2 + H2O form H2CO3. normally this would be ok, because the carbonate (HCO3+) from marine calicifiers would neutralize this.

• this is happening due to combustion of fossil fuels which increases the CO2 in the atmosphere

• consequences: marine organisms are dying because they have difficulty adapting to minor pH changes in their environment. its also disrupting marine food chains and causing coral bleaching

acid rain:

• how does this happen

• what are the causes

• consequences

• acid rain happens due to sulfur and nitrogen oxides (ex. SO2, sulfur dioxide) which form the acids H2SO4 (sulphuric acid) and HNO3 (nitric acid) when they react with water —> so basically there is gonna be acid in the precipitation (rain, snow, fog etc.)

• even through sulfur and nitrogen oxides can be produced naturally, these quanitites are small compared to those produced by industrial acitivty

  • burning impurities in fossil fuels releases SO2 which can form SO3 with O2 in the air

  • nitrogen oxides are produced when N2 in the air reacts with O2 during a combustion reaction of fossil fuels

• consequences: damaging crop yields, infrastructure, trees growth and animal respiratory systems

how does the pH change when you dilute:

• acids

• bases

why?

how much will it change?

diluting acids: will increase the pH because your reducing the concentration of H+ making it more basic

diluting bases: will decrease the pH because your reducing the concentration of OH-, mkaing it less basic

change is based off dilution factor: for every 10x change in concentration of solution, the pH is + (for acids) or - (for bases) 1 pH.

2 different properties that could be used to distinguish between the same concentration of weak and strong acid

strength of acid differs in ionization: strong acids ionize 100% and weak acids only partially ionize. this means strong acids have much higher H concetration than weak acids, which affects ph, lower for strong and higher for weak (ex. 3-6 is weak)

tests you can conduct to determine whether its a strong or weak acid:

• conductivity: strong acids will be more conductive than weak acids because they have more dissociation of their ions to conduct charge

• rate of reaction with metals and carbonates: strong acids will be faster because they release more H+ to react fully with the metal/carbonate (reaction with Mg will produce a more violent gas production)

• temperature rise (when a base is added, neutralization): its higher for strong acids and lower for weak acids → neutralization is an exothermic reaction

distinguishing between a strong base and acid

1. add a base and an acid to a metal ex. Mg and they will differ in gas production. The acid will react in an acid+metal neutralization reaction to produce H2 gas, and the base wont

2. add the base and the acid to a base: acid + base neutralization is exothermic and will release heat, but adding a base to another base wont produce a neutralization reaction so no heat produced.

how do you know if a species is an acid or a base:

(+) charge → want to lose H+ proton to become neutral → losing = acid

(-) charge → want to gain H+ proton to become neutral → gain = base

neutral → lone pairs → base (can accept H+)

binary acids and oxyacids → acids

dissociation and IMFs

when compounds are separated into individual ions

via water is hydration

water can cause an ionic compound to dissociate because the dipoles of water can overcome the electrostatic forces of attraction between the ions of an ionic compound. these are your ion dipole IMFs.

2 substances of similar strength IMF will be miscible because they can mutally overcome IMFs. this means they will mix and form a homogenous solution.

if they are imicisible they will form a heterogenous solution, do not mix

solubility and saturation

solubility = g solute/ 100g solvent

saturation: is how much solute has been dissolved in the solvent

• saturated: max solute at constant temperature (on the solubility curve)

• super saturated: more than max solute on solubility curve

• unsaturated: less than max solute at constant temperature

factors affecting solubility

gas solubility

1. molecule size for solutes: smaller molecules will dissolve better and faster than large ones:

   • this is because the solvent wraps around them more easily. they can fit between water molecules more easily and less energy is needed to overcome their IMFs and interact with the solvent

2. temperature: affects gases and solids differently

   • solid: increased temperature = increased solubility because particles move faster and have more energy to break the lattice

   • gas: increased temperature = solubility decreases because gases escape into air due to more kinetic energy

3. pressure (does affect liquids or solids):

   • higher pressure = increased gas solubility

   • pressure keeps gases compressed into the liquid making it harder for them to escape

factors affecting rate of dissolution

anything that increases the collisions between solute and solvent will increase dissolution:

dissolution = how fast a solute goes into a solvent to form a solution

1. mixing: speeds up dissolution becuase it increases collisions between solute and solvent particles

2. temperature: in solids, higher temperature = faster dissolution because particles have more kinetic energy → they collide more often allowing solvent molecules to break apart solute particles faster

   • for gases, higher temperature = slower dissolution because the solute (gas) wont go into the solvent, it will escape

3. SA of solute: more surface area = faster dissolving because more surface is exposed to solvent, greater area for reaction (SA: V)

solubility of ionic compounds (2)

1. charge density → affects ionic lattice: higher charge desnity ions (small ions with high charges like Al) hold onto each other more strongly → creates stronger ionic bonds → harder to dissolve. lower charge density ions like Na and Cl attract less strongly so its easier for water to pull them apart making them more soluable

2. atomic radius: size of the atom or ion affects how closely the ions are packed together

   • small atomic radius = smaller ions that are packed closer together which results in stronger ionic bonds and lower solubility

   • big radius = bigger ions that are further apart giving them weaker attrations to one another and being more easily separated by water, so higher solubility

why is water the universal solvent

• water has strong polar hydrogen bonds that can overcome the electrostatic forces of ionic compounds and dissolve polar substances

• its has special properties:

  • high surface tension

  • high specific heat capacity

  • high melting and boiling points

  • lower solid desnity

glassware used in:

• beers law and making stock solutions

• titrations

• beers law

beakers, graduated cylinders, volumetric flasks, pipettes

• in labs, beakers are the least precise. they are less precises that pipettes, graduated cylinders and volumetric flasks

• volumetric glassware is the most precise and accurate and most desireable for making solutions

• the uncertainty is normally written on the glassware

beers law: the linear relationship between concentration and absorbance. you can find the concentration of an unknown (coloured solution) by finding the equation of the line of best fit through known concetrations and plugging in the abosrabnce and solving for x (unknown concentration)

can be found using a spectrometer or a colorimeter to accurately find the absorption and hence the concentration.