Chemistry 170 Chapter 3
159.8, 159.8
1 Br2 molecule has a mass of _______ amu; thus 1 mol of Br2 molecules has a mass of ________ grams.
mass alum heated = 0.5066 g mass of KAl(SO4)2 = 0.2757 g molar mass H2O = 18.016 g molar mass KAl(SO4)2 = 262.22 g mass of H2O = 0.2309 g 0.2757 g KAl(SO4)2 / 262.22 g KAl(SO4)2 = 0.00105 mol KAl(SO4)2 0.2309 g H2O / 18.016 g H2O = 0.0128 mol H2O 0.0128 mol H2O / 0.00105 mol KAl(SO4)2 = 12 x = 12
Alum [KAl(SO4)2 - xH2O] is used in food preparation, dye fixation, and water purification. To prepare alum, aluminum is reacted with potassium hydroxide and the product with sulfuric acid. Upon cooling, alum crystallizes from the solution. A 0.5066−g sample of alum is heated to drive off the waters of hydration, and the resulting KAl(SO4)2 weighs 0.2757 g. Determine the value of x, the number of water molecules in a formula unit of alum.
2NH3 (g) + 3CuO (s) to 3Cu (s) + N2 (g) + 3H2O (l) Cu2+ plus O2- = copper (II) oxide, the 2's cancel each other out NH3 is ammonia copper metal is Cu nitrogen gas is N2
Ammonia gas with solid copper (II) oxide to copper metal, nitrogen gas, H2O in liquid form
mol to g 1.00 mol x 105.986 g Na2CO3 = 35.3 g which is the mass of sodium carbonate that contains 1.00 mol of O
Calculate the mass of sodium carbonate that contains 1.00 mol of oxygen atoms.
first find mol of glucose then find grams of water then multiply mol of glucose by gram water 78.0 g C6H12O6 / 180.152g C6H12O6 = 0.4329 mol C6H12O6 6 mol H2O x 18.015g H2O = 108.6g H2O 0.4329 mol C6H12O6 x 108.06g H2O = 46.8g water in glucose
Calculate the mass of water produced by the metabolism of 78.0 g of glucose (C6H12O6). C6H12O6 + 6O2 → 6CO2 + 6H2O
What is the mole ratio of CO and CO2? It is the same therefore the amount of moles in CO is the same as the amount of moles in CO2. Answer: 3.77 mol CO2
Consider the combustion of carbon monoxide (CO) in oxygen gas: 2CO(g) + O2(g) → 2CO2(g) Starting with 3.77 moles of CO, calculate the number of moles of CO2 produced if there is enough oxygen gas to react with all the CO.
first it will be g Cu to mol Cu then mol Cu to g Na 82.2 g Cu / 63.55g Cu = 1.29 mol Cu 1.29 mol Cu x 22.99 g Na = 29.7 g Na Answer: 29.7 g Na
Determine the mass of sodium metal that contains the same number of moles as 82.2 g of copper metal.
moles to atoms 22.72 mol CO2 x 6.022e23 atoms = 1.368e25 atoms of C
Determine the number of carbon atoms in 1.00 kg of carbon dioxide.
first mol Ne to g Ne then g Ne to mol He 4.725 mol Ne x 20.18 g Ne = 95.35 g Ne 95.35 g Ne / 4.0026 g He = 23.82 mol He Answer: 23.82 mol He
Determine the number of moles of helium that has the same mass as 4.725 moles of neon.
1.368e25 atoms of C x 2 O atoms = 2.73e25 atoms of O
Determine the number of oxygen atoms in 1.00 kg of carbon dioxide.
first find mol of glucose. then find grams of ethanol with mol of glucose 605.9g glucose / 180.15g glucose = 3.36 mol glucose 6.72 mol glucose x 46.0684g ethanol = 92.1368g ethanol 92.1367g ethanol / 0.789 g/mL = 392.368mL 392.368mL / 1000mL = 0.3924L
Fermentation is a complex chemical process of wine making in which glucose is converted into ethanol and carbon dioxide: C6H12O6 → 2C2H5OH + 2CO2 glucose ethanol Starting with 605.9 g of glucose, what is the maximum amount of ethanol in grams and in liters that can be obtained by this process (density of ethanol = 0.789 g/mL)?
mol to atoms 6.90 mol S x 6.022e23 atoms = 4.16e24 atoms of S
How many atoms are in 6.90 moles of sulfur (S)?
g to mol then mol to molecules 0.231 g C2H6 / 30.156 g C2H6 = 0.00766 mol C2H6 0.00766 mol x 6.022e23 molecules = 4.61e21 molecules
How many molecules of ethane (C2H6) are present in 0.231 g of C2H6?
A) CO = 0.306 mol of O for CO (0.306 x 1 = 0.306) B) CO2 = 0.612 mol of O for CO2 (0.306 x 2 = 0.612)
How many moles of O are needed to combine with 0.306 mole of C to form the following substance?
g to mol 26.8 g of Ca / 40.078 g of Ca = 0.67 mol of Ca
How many moles of calcium (Ca) atoms are in 26.8 g of Ca?
find mol of CaF2 then find mol HF to get percent yield 6150 g CaF2 / 78.074 g CaF2 = 78.77 mol CaF2 2750 g HF / 20.006 g HF = 137.46 mol HF 137.46 mol HF / 2 mol HF = 68.73 68.73 / 78.77 x 100 = 87.3% actual yield / theoretical yield x 100 = percent yield
Hydrogen fluoride is used in the manufacture of Freons (which destroy ozone in the stratosphere) and in the production of aluminum metal. It is prepared by the reaction CaF2 + H2SO4 → CaSO4 + 2HF In one process, 6.15 kg of CaF2 is treated with an excess of H2SO4 and yields 2.75 kg of HF. Calculate the percent yield of HF.
first convert kg to g 4.0 kg x 1000 g = 4000 g then 4000 g limestone / 100.0857 g CaO3 = 39.9657 mol CaO3 39.9657 mol CaO3 x 56.077 g CaO = 2.24e3 g CaO
Limestone (CaCO3) is decomposed by heating to quicklime (CaO) and carbon dioxide. Calculate how many grams of quicklime can be produced from 4.0 kg of limestone.
potassium nitrate = 101.101 g/mol
Molar mass of KNO3
Lithium carbonate = 73.882 g/mol
Molar mass of Li2CO3
magnesium nitride = 100.927 g/mol
Molar mass of Mg3N2
mass = molar mass x number of moles mass = 480,000 x 27 1.3e7 g
Smooth muscle myosin is a motor protein that plays a crucial role in the contraction of smooth muscle. If this protein has a molar mass of 480,000 g/mol, what is the mass, in grams, of 27 moles of smooth muscle myosin?
NaHCO3 to Na2CO3 + H2O + CO2
Sodium hydrogen carbonate reacts to form sodium carbonate, water, and carbon dioxide (unbalanced) sodium hydrogen carbonate is also known as sodium bicarbonate
1.86 carat x 200 mg = 372 mg 372 mg / 1000 mg = 0.372 g 0.372 g / 12.009 g C = 0.030976 mol 0.030976 mol x 6.022e23 atoms = 1.87e22 atoms
The carat is the unit of mass used by jewelers. One carat is exactly 200 mg. How many carbon atoms are present in a 1.86−carat diamond? Enter your answer in scientific notation.
false because subscripts are never changed because it changes the identity of the compound, only coefficients are added to change the balance
True or false: in order to balance the reaction of hydrogen gas (H2) with oxygen gas (O2) to form liquid water (H2O), a student adds a subscript of 2 after the oxygen in H2O. This is an acceptable method of balancing the above reaction.
3O2 2CH3OH + 3O2 ---- 2CO2 + 4H2O
What is the coefficient of O2 when the following equation is properly balanced with the smallest set of whole numbers? ______CH3OH + ______O2 ----- _______ CO2 + ________ H2O
atoms to mol then mol to g 2.80e14 Pb atoms / 6.022e23 atoms = 4.6496e-10 mol Pb 4.6496e-10 mol Pb x 207.2 g Pb = 9.63e-8 g Pb
What is the mass in grams of 2.80e14 lead (Pb) atoms?
atomic mass of Pt is 195.08g 195.08 g / 6.022e23 = 3.24e-22 g
What is the mass in grams of a single atom of Pt?
Ba(ClO4)2 barium perchlorate molecular mass = 336.24 g/mol mass percentage = mass element / molecular mass of compound x 100 oxygen molecules = 8 because 4 x 2 = 8 molar mass of oxygen is 15.999 8 x 15.999 = 127.992 127.992 / 336.24 x 100 = 38 %
What is the mass percent of oxygen in barium perchlorate?
162.23 g/mol
What is the molar mass of nicotine? C10H14N2
21 reactant side product side C = 7 C = 1 (7) = 7 H = 14 H = 2 (7) = 14 O = 2 O = 3 C7H14 + O2 ------- 7CO2 + 7H2O C = 7 C = 7 H = 14 H = 7 x 2 = 14 O = 2 O = 14 + 7 = 21 Add 21 /2 to O2 on reactant side then multiply the whole thing by 2 2 (C7H14 + 21/2 O2 ------ 7CO2 + 7H2O) = 2C7H14 + 21O2 ----- 14CO2 + 14H2O
When a chemical equation is balanced, it will have a set of whole number coefficients that cannot be reduced to smaller whole numbers. What is the coefficient for O2 when the following combustion reaction of a hydrocarbon is balanced? ___ C7H14 + ___ O2 → ___ CO2 + ___ H2O
reactants and products are represented by symbols or molecular formulas, the physical states of the reactants and products should be indicated in a chemical equation
Which of the following statements correctly describe a chemical equation?
combustion
a ______ reaction involves the burning of a substance such as ethane (C2H6) or methanol (CH4O) to produce carbon dioxide and water.
52.2g
a reaction is expected to produce 83.5g of CaCO3. the percent yield is recorded as 62.5%. what is the actual mass of CaCO3 obtained?
NH4NO2 to N2 + H2O
ammonium nitrite reacts to form nitrogen and water (unbalanced)
moles to atoms 1.48e-6 moles He / 6.022e23 atoms = 8.91e17 atoms
calculate the number of atoms in 1.48e-6 moles of helium.
atoms to moles 5.03e21 atoms x 6.022e23 atoms = 0.00835 moles
calculate the number of moles of helium that contains 5.03e21 atoms.
CO2 + KOH to K2CO3 + H2O
carbon dioxide and potassium hydroxide react to form potassium carbonate and water (unbalanced)
when the identity of a substance changes from reactant to product the change is chemical
chemical process
burning in air, burning in the presence of oxygen
combustion
write a balanced equation for the reaction, convert the given mass into moles using molar mass. convert moles of A to moles of B using a conversion factor derived from the balanced equation, convert the moles of the second substance to mass using its molar mass.
correctly order the steps necessary to solve for the mass of a product, or a second reactant required, given the mass of one of the reactants in a chemical process. start with the first step at the top of the list.
when the identity of a substance remains the same from reactant to product, the equation represents a physical process
physical process
KOH + H3PO4 to K3PO4 + H2O
potassium hydroxide + phosphoric acid to form potassium phosphate + water (unbalanced)
a substance formed as the the result of a chemical reaction
product
a starting material in a chemical reaction
reactant
limiting, excess
the ______ reactant in a reaction is one that limits the amount of product formed. this reactant will be completely used up in the reaction. any reagents that are not used up are said be in___________.
moles, atoms
the _______ is the SI unit that expresses the amount of substance. specifically, it is defined as the amount of substance containing the same number of entities as the number of ______ in exactly 12g of carbon 12.
molar, atoms
the _______ mass of a substance is the mass per mole of its entities, where the term "entities" can describe ________, ions, molecules, or formula units.
molecule, formula
the basic unit of a molecular compound is the _______ and the sum of the masses of its atoms is called the molecular mass. the basic unit of an ionic compound is the _________ unit, and the sum of the masses of its atoms is called the formula mass.
sum
the molecular mass of a compound is the _______ of the atomic masses of the elements forming the molecule of a compound.
true
true or false: the limiting reactant is the reactant that produces the smallest amount of product.
CH3 100.0g of the compound contains 79.9g of C and 20.1g of H. Converting to moles gives 6.65 mol of C and 19.9 mol of H. The C:H ratio is 1:3
what is the empircal formula of a hydrocarbon containing 79.9% carbon by mass?
H2O (aq) because (aq) is anything that is dissolved in water and water cannot be dissolved in water because its water
which of the following can never be correct?
cyclopentane C5H10 and methly vinyl ketone C4H6O
which of the following compounds have a molecular mass of 70 amu, rounded to the nearest whole number?
6.022e23 entities / 1 mol
which of the following correctly reflects Avogadro's number?
the symbol (g) indicates a substance in the gas phase and a liquid is indicated by the symbol (l)
which of the following options correctly describe the symbols used to write a a balanced equation?
given mass / molar mass = moles g of substance / g (amu) = moles
which of the following options gives the correct procedure to calculate the number of moles of a substance given the mass?
the formula of a compound and the atomic mass of each element contained in the compound
which of the following pieces of information do you need to calculate the molecular mass of a compound?
number of atoms divided by Avogadro's number (atoms) = moles
which of the following provides the correct mathematical operation to convert the number of atoms of a sample to the number of moles?
the molar mass of a substance is the mass per mole of its entities, the periodic table can be used to calculate the molar mass of any substance, when referring to the mass per mole of an entity the term entities could refer to atoms, molecules, ions, or formula units.
which of the following statements correctly describe molar mass?
the reactant that produces the least amount of possible product is the limiting reactant, calculate the molar masses of any reactants for which a mass has been given, calculate the amount of product that could be formed from each reactant
which of the following statements correctly describe steps used in determining which reactant in a given reaction is limiting?
% yield = actual yield / theoretical yield x 100 the actual yield is almost always less than the theoretical yield
which of the following statements correctly describe the percent yield in a chemical reaction?
the mole contains 6.022e23 entities and the number of entities in a mole is called Avogadro's number
which of the following statements correctly describes the mole?
physical states of reactants and products, relative quantities (moles) of substances involved, identities of reactants and products
which of the following statements describe the information that can be gained from a balanced chemical equation?
an unbalanced equation violates the laws of conservation mass
why is it necessary to balance a chemical equation?
an ionic compound is not composed of individual molecules
why is the term "molecular mass" not appropriate when referring to ionic compounds?
Zn + AgCl to ZnCl2 + Ag
zinc and silver chloride react to form zinc chloride and silver (unbalanced)
