Ch3 top 3 rows
Ch 3 One of these is not conserved in a chemical reaction? atoms, mass, energy or moles
What are moles? N2 + 3H2 --> 2NH3 We see that three moles of reactants can give only 2 moles of product in this case.
Ch 3 Change 36.0 grams of water to moles.
What are 2 moles of water? Cancel units like this: 36.0 g x 1 mol/18.0 g = 2 mol
Ch 3 Simplest formula for hydrazine, N2H4, a rocket propellant is _____. Simplest formula is also called empirical formula. It cannot be divided by an integer to give lower values.
What is NH2? The N2H4 is its molecular formula.
Its molecular weight is 2(14.0) + 4(1.01) = 32.0 g/mol and one molecule weights 32.0 amu's
Ch 3 A soluble salt like KCl is a strong electrolyte because its water solution contains many ____________
What are ions? Positive ions are called cations. Negative ions are called anions. They may be simple like Cl1- or polyatomic like ClO31-. Chloride & chlorate ions.
Ch 3 Sugars like sucrose and alcohols like ethanol produce no ions in water. Such organic molecules are called _____. Ethanol is CH3CH2OH.
What are nonelectrolytes? Ethylene glycol is used in antifreeze/summer coolant in car radiators. It is a nonelectrolyte also. CH2OHCH2OH
Ch 3 Given M = n/V, then the molarity of a KNO3 solution if it contains 2.3 moles of KNO3 in 1.46 liters of solution is _____
What is 1.6 M? So each liter of solution contains enough mass of KNO3 to equal1.6 moles. Please notice that the answer may have just 2 significant figures (SF). Know the definition clearly: # moles/# liters.
Ch 3 One of these is not a strong acid: HF, HCl, HNO3, HBr
What is HF? Weak acids dissociate into ions just a few percent. Strong acids dissociate 100%. Know the 7 strong acids and the 8 strong bases.
Ch 3 Ammonia is a weak electrolyte. It is a base by three different definitions. It is a ______ base.
What is a weak base? NH3 + H20 = NH4+ + OH1-
This proceeds to products only 3-5% in water.
Ch 3 The percentage of S in any sample of pure SO2 is which of these: 32.1%, 21.5% 50.1% or 73.3%
Hint: Consider one mole of SO2 by mass.
What is 50.1%? So 49.9% is oxygen.
SO2 smells like burning sulfur (brimstone).
H2S smells like rotten eggs or sewer gas.
Pure sulfur, S8 rings, has almost no odor.
Ch 3 A solution of NaCl has a volume of 350 mL and a molarity of 0.200 M NaCl. It contains ____ mol NaCl.
What is 0.070 mol NaCl? M x V in liters = n
0.200 mol/L x 0.35 L = 0.070 mol (2 figs. are sig.)
Ch 3 These are omitted in a net ionic equation.
What are spectator ions? Note that these are not part of the precipitate. Memorize solubility rules so you can predict pptn rxns.
Ch 3 The number of particles in a mole of any substance (6.022 x1023) is called ________'s number, N.
What is Avogadro's number? The other way to define a mole is the mass called the molar mass. For H2O, 18 g is the molar mass. It contains many, many molecules.
Ch 3 Given MaVa = MbVb, the new concentration is ___ if the new volume is 1.00 L and the origin molarity and volume were 3.8 M and 0.50 L.
When you see 6.0 M it means 6.0 mol/liter
What is 1.9 M? Note that the solute ID did not matter. The dilution formula is very practical and can use other concentration or volume terms.
Ch 4 The amount of product obtained in a chemical reaction is called the ____ yield.
What is the actual yield?
Ch 4 Given (AY/Th yld) x 100 = % yld The theoretical yield was calculated to be 76.2 g, but students only obtained 65.5 g. The percentage yield was ____.
What is 86.0%? Notice three SFs in the results.
SFs means significant figures/digits.
The last digit in a measured value is doubtful but significant. It could vary up or down by one unit.
Ch 4 MTBE (methyl tertiary-butyl ether) is no longer a popular gasoline ______ in the US and has been phased out due to severe groundwater contamination risks.
What is additive? It was intended to oxygenate like ethanol does to reduce exhaust emissions.
Ch 4 A lab method used to find the exact concentration of an unknown solution using one of known value is called a __________. A chemical reaction is involved.
What is a titration? Examples are Acid-Base or redox type titrations.
How does AI define titration? Claude? Grok? Perplexity? "Let every important fact be confirmed by 2 or 3 witnesses." In court, eye witnesses are far less reliable than DNA to convict or exonerate.
Ch 4 Given N2 + 3H2 --> 2NH3 When 7.0 moles of H2 react with excess N2, the number of moles of NH3 produced is __________.
What are 4.7 mol of NH3? Use factor-label method.
7.0 mol H2 x(2 mol NH3/3 mol H2) = 4.7 mol (2 SF)
Ch 4 Molecules containing only carbon and hydrogen atoms are called _________. There are complex mixtures of these in gasoline, jet fuel and other fuels.
What are hydrocarbons? Only four are gases, CH4, C2H6, C3H8 and C4H10. Methane is the main component in natural gas. Ethane, propane and butane may also be present. Those are all gases. Pentane, C5H12, is the first liquid. C18H38 is the first solid straight chain hydrocarbon. MEPB is a memory device: Juan Orono suggested it.
Ch 4 Given 2H2 + O2 -->2H2O
24.0 g H2 requires ___mol O2 to fully react.
What are 5.94 mol O2?
Notice that this is 190. g (3 SF) since 5.94 mol x 32.0 g/mol = 190. g or 1.90 x 102 g
Ch 4 If 47.5 g of NH3 are wanted, the mass of H2 needed is _____as long as an excess of N2 is available. N2 + 3H2 --> 2NH3 HINT below:
g A --> mol A --> mol B --> g B
What is/are 8.47 g H2?
Why so little? Despite needing 3 moles of H2 to get just 2 mol NH3, the H2 mass is very, very much smaller.
Ch 4 70.2 g KCl in 455 mL of solution has this molarity:___M
HINT: 39.1 + 35.5 = 74.6 g/mol KCl
What is 2.07 M KCl? (3 SF) M = mol/L = n/V
[70.2 g/(74.6g/mol)]/0.455 L = 2.07 mol/L or M
Ch 4 The mass of O2 produced if 97.8 g of KClO3 decomposes completely upon heating is _____g O2 The reaction is: 2KClO3 --> 2KCl + 3O2 FW =122.6 g KClO3/mole
What is/are 38.3 g O2?
Use g A-->mol A-->mol B -->g B and cancel units. 97.8g KClO3 x(1mol/122.6)x(3 mol O2/2 mol KClO3)x (32 g O2/1 mol) = 38.3 g O2 (3 SF retained)
Ch 4 Given: 2 SO2(g) + O2(g) → 2 SO3(g) The number of kilograms of SO3 that can be obtained from 85.6 kg of SO2 is ______.
What is/are 107 kg of SO3? No need to convert to grams since you want the answer in kg units.
85.6 kg SO2(1mol SO2/64.1g)(2mol SO3/2 mol SO2)(80.1 g/1 mol SO3) = 107 kg SO3 (3 SF)
CH 4 The percentage of chlorine in KClO3 is _________.
HINT: Think about the mass of one mole.
Formula Weight = 39.1 +35.5 + 3(16.0) =
What is 32.2% Cl?
(mass of Cl/mass of 1 mol KClO3) x 100 = (35.5 g/122.6 g) x 100 = 29.0% Cl