Chapter 4 - Types of Chemical Reactions and Solution Stoichiometry Flashcards

(37 cards)

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
review the types of acid/base reactions
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
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
27
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
28
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)
29
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
30
What is an oxidation state?
- a system for keeping track of electrons
31
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
32
Review these rules for assigning oxidation states
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
What is oxidation
- loss of electrons - increase in OS
34
What is reduction?
- gain of electrons - decrease in OS
35
What is an oxidizing agent?
- gains electron (ex. is reduced) in order to oxidize a compound or ion
36
What is a reducing agent?
- loses electrons (ex . is oxidized) in order to reduce a compound or ion
37
Review 2 methods on balancing redox reactions
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