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CHEM 121 > Chapter 4 - Types of Chemical Reactions and Solution Stoichiometry > Flashcards

Chapter 4 - Types of Chemical Reactions and Solution Stoichiometry Flashcards

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1
Q

What is a solution?

A
  • combination of two or more substances that exist as a homogeneous mixture
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2
Q

What is a solvent?

A
  • the substance present in the greatest quantity in a solution
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3
Q

What is a solute?

A
  • the substance of lesser quantity in a solution
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4
Q

What is solubility?

A
  • a measure of the amount of substance that will dissolve in a given amount of solvent at a given temperature
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5
Q

What is an aqueous solution?

A
  • solution in which water is the solvent
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6
Q

Which is more electronegative? oxygen or hydrogen

A
  • hydrogen
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7
Q

is the O-H bond polar or non-polar?

A
  • polar bond
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8
Q

Explain the hydration process.

A
  • polar solvents such as H2O dissolve ionic solids by forming a shell around the ion
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9
Q

What is the rule of thumb?

A
  • like dissolves like
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10
Q

for aqueous solutions of ionic compounds, what is the amount of dissolved ion related to?

A
  • related to its electrical conductivity (ability to conduct current)
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11
Q

What are the 3 classifications of solutes in solutions?

A
  • strong electrolytes
  • weak electrolytes
  • non-electrolyte
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12
Q

explain strong electrolytes

A

conduct electricity efficiently (HCl)

  • substances that are (essentially) completely ionized in an aqueous solution
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13
Q

explain weak electrolytes

A

conduct only a small current (CH3COOH)

  • substances that only partially ionize in solution
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14
Q

explain non-electrolyte

A

no current flow (sugar)

  • substances (molecular compounds) that are soluble but do not ionize)
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15
Q

Give 3 examples of strong electrolytes

A
  1. soluble salts - ionic compounds that, when dissolved in water, completely dissociate into cations and anions (NaCl, NH4NO3, BaCl2)
  2. Strong acids - acids (HA) that totally dissociate into H+ and A- in aqueous solutions (HCl, HNO3, H2SO4, HI, HBr, etc.)
  3. strong bases - soluble compounds containing OH- ions; totally dissociate to give OH- ions in solution (NaOH, KOH, etc.)
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16
Q

give 2 examples of weak electrolytes

A
  1. weak acids - partially dissociate to H+ and A- but mostly remain as HA in solution (Acetic acid - CH3COOH -> H+ + CH3COO-)
  2. weak bases - produces only a small amount of OH- in aqueous solution (ammonia - NH3 + H2O -> NH4+ + HO-)
17
Q

What are 5 evidences for a (possible) chemical reaction?

A
  • formation of a precipitate (an insoluble solid)
  • formation of a gas
  • change in colour
  • change in temperature
  • dissolution of a precipitate
18
Q

What are the 3 most common reactions classified as?

A
  • precipitation reactions
  • acid-base reactions
  • redox reactions
19
Q

explain precipitation reactions

A
  • 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
20
Q

review - stoichiometry of precipitation reactions

A

similar to reaction stoichiometry

  1. identify ions present in solution and predict which reaction(s) will occur
  2. write a balanced net ionic equation for each reaction
  3. calculate # of moles of each reactant
  4. determine which reactant is limiting
  5. use balanced net ionic equation to predict the theoretical yield of product(s)
  6. convert grams if needed
21
Q

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-?

A

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-!

22
Q

What is selective precipitation?

A
  • 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
23
Q

What is the Arrhenius concept?

A
  • acids produce hydrogen ions in aqueous solutions, and bases produce hydroxide ions
24
Q

What is the Bronsted/Lowry Definition?

A
  • acid: a proton donor (H+)
  • base: a proton acceptor
25
Q

review the types of acid/base reactions

A
  1. Strong base+ strong acid (neutralization reaction):
    HCl+NaOH _> NaCl+H2O
    =
    H+ + OH- -> H2O
    ex. products: salt and water
  2. Strong base + weak acid
    KOH + CH3OOH
    =
    HC2H3O2 + K+ + OH- -> K+ + H2O + C2H3O2-
    =
    OH- + HC2H3O2 -> H2O + C2H3O2-
    reacts completely
  3. Strong acid+weak base
    HCl + NH3
    =
    H+ + Cl- + NH3 -> NH4+ + Cl-
    =
    H+ + NH3 -> NH4+
    reacts completely
26
Q

What is an indicator?

A
  • a compound that is a different colour when it is in an acidic solution compared to when it is in a basic solution
27
Q

What is an equivalence or stoichiometric point?

A
  • point in the titration at which enough titrant has been added to react completely with the unknown acid
28
Q

What are acidic hydrogens?

A
  • 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)
29
Q

What is a redox reaction?

A
  • 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
30
Q

What is an oxidation state?

A
  • a system for keeping track of electrons
31
Q

What is a covalent bond?

A
  • imaginary “formal” charges that would result if electrons were to be assigned to the atom with greater affinity instead of sharing
32
Q

Review these rules for assigning oxidation states

A
  1. the oxidation state of an atom in an element is: zero
    ex. Na, Cl2, O2, etc
  2. 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
  3. 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-)
  4. Hydrogen is assigned an OS of +1 in its covalent compounds except in metal hydrides (H is -1, ex. NaH, CaH2, etc)
  5. 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
33
Q

What is oxidation

A
  • loss of electrons
  • increase in OS
34
Q

What is reduction?

A
  • gain of electrons
  • decrease in OS
35
Q

What is an oxidizing agent?

A
  • gains electron (ex. is reduced) in order to oxidize a compound or ion
36
Q

What is a reducing agent?

A
  • loses electrons (ex . is oxidized) in order to reduce a compound or ion
37
Q

Review 2 methods on balancing redox reactions

A
  1. 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
  2. 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

CHEM 121 (5 decks)

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