Chapter 4 - Types of Chemical Reactions and Solution Stoichiometry Flashcards
What is a solution?
- combination of two or more substances that exist as a homogeneous mixture
What is a solvent?
- the substance present in the greatest quantity in a solution
What is a solute?
- the substance of lesser quantity in a solution
What is solubility?
- a measure of the amount of substance that will dissolve in a given amount of solvent at a given temperature
What is an aqueous solution?
- solution in which water is the solvent
Which is more electronegative? oxygen or hydrogen
- hydrogen
is the O-H bond polar or non-polar?
- polar bond
Explain the hydration process.
- polar solvents such as H2O dissolve ionic solids by forming a shell around the ion
What is the rule of thumb?
- like dissolves like
for aqueous solutions of ionic compounds, what is the amount of dissolved ion related to?
- related to its electrical conductivity (ability to conduct current)
What are the 3 classifications of solutes in solutions?
- strong electrolytes
- weak electrolytes
- non-electrolyte
explain strong electrolytes
conduct electricity efficiently (HCl)
- substances that are (essentially) completely ionized in an aqueous solution
explain weak electrolytes
conduct only a small current (CH3COOH)
- substances that only partially ionize in solution
explain non-electrolyte
no current flow (sugar)
- substances (molecular compounds) that are soluble but do not ionize)
Give 3 examples of strong electrolytes
- soluble salts - ionic compounds that, when dissolved in water, completely dissociate into cations and anions (NaCl, NH4NO3, BaCl2)
- Strong acids - acids (HA) that totally dissociate into H+ and A- in aqueous solutions (HCl, HNO3, H2SO4, HI, HBr, etc.)
- strong bases - soluble compounds containing OH- ions; totally dissociate to give OH- ions in solution (NaOH, KOH, etc.)
give 2 examples of weak electrolytes
- weak acids - partially dissociate to H+ and A- but mostly remain as HA in solution (Acetic acid - CH3COOH -> H+ + CH3COO-)
- weak bases - produces only a small amount of OH- in aqueous solution (ammonia - NH3 + H2O -> NH4+ + HO-)
What are 5 evidences for a (possible) chemical reaction?
- formation of a precipitate (an insoluble solid)
- formation of a gas
- change in colour
- change in temperature
- dissolution of a precipitate
What are the 3 most common reactions classified as?
- precipitation reactions
- acid-base reactions
- redox reactions
explain precipitation reactions
- reactions of 2 soluble ionic compounds that yield an insoluble product (precipitate)
- can predict the nature of the insoluble product
REVIEW
- not all ionic compounds are soluble in H2O, but those that are completely dissociate
- when 2 or more aqueous solutions of ionic compounds are mixed, all the ions are uniformly distributed in the mixture
- some pairs of oppositely charged ions may form new compounds that are insoluble
- ionic solids that precipitate out of solution must be electrically neutral
- ionic compounds form pairs of oppositely charged ions
review - stoichiometry of precipitation reactions
similar to reaction stoichiometry
- identify ions present in solution and predict which reaction(s) will occur
- write a balanced net ionic equation for each reaction
- calculate # of moles of each reactant
- determine which reactant is limiting
- use balanced net ionic equation to predict the theoretical yield of product(s)
- convert grams if needed
Mix 100.0mL 0.150M CaCl2 and 150.0mL 0.120M Pb(NO3)2
What mass of PbCl2(s) is obtained?
What is the concentration of excess PB2+ and Cl-?
Look at solubilities
ME: CaCl2(aq) + Pb(NO3)2(aq) -> PbCl2(s) + Ca(NO3)2(aq)
CIE: Ca2+(aq) +2Cl-(aq) + Pb2+(aq) + 2NO3-(aq) -> PbCl2(s) + Ca2+(aq) + 2NO3-(aq)
NIE: 2Cl-(aq) + Pb2+(aq) -> PbCl2(s)
Limiting reagent
- CaCl2 0.100L *0.150mol/L = 0.0150moles CaCl2
- moles Cl- -> 2*0.0150moles Ca2+(aq) = 0.0300moles Cl-(aq)
- Pb(NO3)2 0.150L * 0.120mol/L = 0.0180moles Pb2+(aq)
Required ratio: Pb2+:Cl -> 1:2
Actual ratio: 0.0180:0.0300
Therefore, Cl- is limiting and will be used completely in the reaction
- 0.0300 moles Cl- reacts with 0.0150moles Pb2+ (0.0150moles PbCl2 precipitate)
PbCl2 = 278.1g/mole
mass of PbCl2(s) = 4.17g PbCl2(s)
Excess Pb2+: (0.0180mol - (0.0300mol/2))/0.250L bc 0.1L+0.15L
= 0.0120mol/L
no excess Cl-!
What is selective precipitation?
- separating ions (and identifying them) by performing a series of reactions and precipitating the ions one at a time
- the precipitate is then separated from the solution and the next reaction is done on the remaining ions in the solution
- process used for qualitative analysis
What is the Arrhenius concept?
- acids produce hydrogen ions in aqueous solutions, and bases produce hydroxide ions
What is the Bronsted/Lowry Definition?
- acid: a proton donor (H+)
- base: a proton acceptor
review the types of acid/base reactions
- Strong base+ strong acid (neutralization reaction):
HCl+NaOH _> NaCl+H2O
=
H+ + OH- -> H2O
ex. products: salt and water - Strong base + weak acid
KOH + CH3OOH
=
HC2H3O2 + K+ + OH- -> K+ + H2O + C2H3O2-
=
OH- + HC2H3O2 -> H2O + C2H3O2-
reacts completely - Strong acid+weak base
HCl + NH3
=
H+ + Cl- + NH3 -> NH4+ + Cl-
=
H+ + NH3 -> NH4+
reacts completely
What is an indicator?
- a compound that is a different colour when it is in an acidic solution compared to when it is in a basic solution
What is an equivalence or stoichiometric point?
- point in the titration at which enough titrant has been added to react completely with the unknown acid
What are acidic hydrogens?
- hydrogen atoms in an acid that can dissociate as protons
ex. acetic acid, CH3COOH, only the H attached to the oxygen is acidic and can be donated as a proton - monoprotic acids
ex. HCl, HNO3, CH3COOH - polyprotic acids have more than one acidic hydrogen
ex. - diprotic acids (H2SO4) and triprotic acids (H3PO4)
What is a redox reaction?
- a reaction in which one or more electrons are transferred between atoms or molecules
- oxidation and reduction always occur together. Electrons lost by one species must be gained by another
What is an oxidation state?
- a system for keeping track of electrons
What is a covalent bond?
- imaginary “formal” charges that would result if electrons were to be assigned to the atom with greater affinity instead of sharing
Review these rules for assigning oxidation states
- the oxidation state of an atom in an element is: zero
ex. Na, Cl2, O2, etc - the oxidation state of a monoatomic ion is the same as its charge:
group 1A: +1 (Na+, K+, …)
group 2A: +2 (Ca2+, Mg2+)
Cl-: -1 - oxygen is assigned an oxidation state -2 in its covalent compounds:
CO, CO2, H2O, SO2, SO3, …
exceptions:
O is -1 in peroxides: H2O2, Na2O2
O is +2 in OF2 (ex. when bonded to fluorine)
O is -0.5 in superoxides (contains O2-) - Hydrogen is assigned an OS of +1 in its covalent compounds except in metal hydrides (H is -1, ex. NaH, CaH2, etc)
- Fluorine is always assigned an OS of -1 in its compounds
- other halogens (Cl, Br, I) are -1 except in combination with oxygen or other halogens
ex. NaCl - Cl = -1
but, NaClO4 - Cl = +7
What is oxidation
- loss of electrons
- increase in OS
What is reduction?
- gain of electrons
- decrease in OS
What is an oxidizing agent?
- gains electron (ex. is reduced) in order to oxidize a compound or ion
What is a reducing agent?
- loses electrons (ex . is oxidized) in order to reduce a compound or ion
Review 2 methods on balancing redox reactions
- Oxidation state method: (useful for non-aqueous reactions)
- assign OS for all atoms
- determine change in OS for each element
- determine coefficients based on: total increase in OS = total decrease
- balance rest of equation by inspection - half-reaction method: (for simple electron transfer reactions in solution where H+ and OH- are available; best for aqueous reactions)
- Zn + Cu2+ -> Zn2+ + Cu
— balance oxidation and reduction reactions separately
- # of e- gained = # of e- lost
- obtain the overall equation by summing both half reactions
