Chapter 4 - Types of Chemical Reactions and Solution Stoichiometry Flashcards
(37 cards)
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