Chem 121 Exam 1 Practice Questions
FeNO2Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: ammonium phosphide
(NH4)3P; ionic
The compound C4H8O2 has a molar mass of 88.11 g/mol. A sample containing 14.5 g of this compound would have how many moles of hydrogen atoms?
1.32 mol H atoms. 14.5 * (MW C4H8O2) * mol ratio (8 mol H/mol C4H8O2)
How many grams are present in 1.76 moles of fluorine gas (1 pt)
1.76 mol F2 (38.0 g F2/1 mol F2) = 66.9 g F2
Balance this equation, including the states of matter. (1 pt) TiCl4 (s) + H2O (aq) --> TiO2 (s) + HCl (aq)
1; 2; 1; 4
Balance the following chemical equations. (1) Se2F8 + CO2 --> CF4 + SeO2
1; 2; 2; 2
Balance the following chemical equations. (1) Sn(ClO3)4 + NaOH --> Sn(OH)4 + NaClO3
1; 4; 1; 4
Balance, including the states of matter: The reaction of solid aluminum with liquid bromine to form solid aluminum bromide (1 pts)
2 Al (s) + 3 Br2 (l) --> 2 AlBr3 (g)
Balance the following chemical equations. (1) a. The combustion of liquid C4H8O in oxygen gas to form carbon dioxide and water vapor.
2 C4H8O + 11 O2 --> 8 CO2 + 8 H2O
Balance this equation, including the states of matter. (1 pt) The combustion of gaseous C5H10 to form carbon dioxide and water.
2 C5H10 (g) + 15 O2 (g) --> 10 CO2 (g) + 10 H2O (g)
Balance this equation and then answer the questions (4 pts) Li3N (s) --> LI (s) + N2 (g) a. Balance it b. If 87.6 g Li3N is allowed to decompose, how many grams of Nitrogen gas will be formed? c. If only 120.0 g of nitrogen gas is collected, what is the percent yield for the reaction?
2 Li3N (s) --> 6 Li (s) + N2 (g) b. multiply Li3N by MW of Li3N to get 2.51 mol Li3N. Do mol ratio of this by multipling it by 1 mol N2 / 2 mol Li3N to get 1.26 mol N2. Multiply this by MW of N2 to get 35.3 g N2. c. 120.0/35.4 g = 340%. Since it is MORE than the theoretical yield, must be contaminants or error in the final weight.
Significant figures for this: [23.43 (18+9.21) ] / 12.3
2 significant figures. The addition gives 27, with no decimals since the 18 doesn't have any. 2 SD. This dictates the final answer as 52.
Balance, including the states of matter: Al(ClO4)3 (aq) + Ba(OH)2 (aq) --> Ba(ClO4)2 (aq) + Al(OH)3 (g)
3 Al(ClO4)3 (aq) + 3 Ba(OH)2 (aq) --> 3 Ba(ClO4)2 (aq) + 2 AL(OH)3 (s)
Consider the reaction of strontium metal with nitrogen gas to form strontium nitride. Write the equation
3 Sr (s) + N2 (g) --> Sr3N2 (s)
How many significant figures should be in the answer to the following calculation? (2) (4.56)(30.772) - 6.5
3 sf (=134). Multiplication gives 3 (140). Addition keeps no decimals because the 1s place is the last SD for the multiplication
A particular substance has a density of 4.35 g/cm#. What volume will 18.2 g occupy?
4.18 cm#
4 NH3 + 7 O2 --> 4 NO2 + 6 H2O If 5.82 moles of NH3 are reacted with 9.74 moles of oxygen gas, how many moles of NO2 will be formed? Which reactant is limiting? (3 pts)
5.82 mol NH3 ( 4 mol NO2/4 mol NH3) = 5.82; 9.74 mol O2 (4/7) = 5.57 mol NO2 so O2 is limiting and can only make 5.57 moles of NO2
How many significant figures are present in the following calculations (SHOW WORK) (2 pts) (24.3 - 15.44) / 3.242
=8.9/3.242 = 2.7. Two sig figures. The subtraction part gives one decimal place after the decimal, because that was the level of uncertainty in the subtraction. That number thus as 2 sig digits.
A particular compound was found to contain 23.52% cobalt, 50.93% tellurium, and 25.54% oxygen by mass. What is the empirical formula of the compound? (3 pts)
Assuming 100 g of compound, convert to moles of each element => 0.399 mol Co, 0.399 mol Te, and 1.60 mol O. Mole ratios: O/Co = (1.60/0.399) = 4:1 Te/Co = 0.399/0.399 = 1:1 Empirical formula: CoTeO4
Sketch a mental model for the conversion of a solid to a gas for a mixture
Box with a cube of mixed different colored balls to a free floating random assortment of different colored balls.
A combustion analysis of a sample of a compound containing only carbon and hydrogen produces 36.09 g of carbon dioxide and 11.08 g of water. What is the empirical formula of the compound? (3)
C2H3. Calculate moles of each. Use mole ratios of mol X/mol XY to get total moles of each element. Set up mole ratios.
Balance, including the states of matter: The combustion of C5 H10 O in oxygen gas to corm carbon dioxide gas and water vapor
C5H10O + 7O2 --> 5 CO2 (g) + 5 H2O (g)
Give an example of each of the following: (.5 pts each) a. Alkaline earth metal b. noble gas c. transition metal d. metalloid
Ca, Ar, Fe, Si
A compound is found to contain 35.3% Carbon, 8.8% Hydrogen, and 55.8% fluorine. The formula of the compound is: a. CHF b. C4HF6 c. C3H9F3 d. CH3F
D. assume 100 g. Determine moles of each. Set up mol ratios. (NOTE that since the H and F are in a compound, and are not elemental, the H2, F2 gas thing is not relevant)
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: iron (III) nitrate
Fe(NO3)3, ionic
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: iron(I) nitrite
FeNO2; ionic
Consider the following unbalanced reaction: SO2 + O2 --> SO3. A reaction of 13.88 mol of SO2 and 5.28 mol of O2 results in: a. 5.28 mol SO3 b. 6.94 mol SO3 c. 8.60 mol SO3 d. 10.6 mol SO3 e. 13.9 mol SO3
First balance the equation. Then take the mol of SO2 and multiply by the molar ratio (2 SO3/2 SO2) to get 13.88 mol SO3. Do the same for O2, using molar ratio of (2 mol SO3/1 mol O2) to get 10.6 mol SO3. Therefore, O2 is limiting. So the 10.6 is the answer. (D)
How many significant figures would the following calculation's result have? (2 pts) (12.000)(0.9893)+(13.03)(0.0107)
First multiplication gives 4 (11.87). 2nd gives 3 (0.139). added gives 4 (12.01) because it is rounded to uncertainty place of x.xx.
How many moles of silver will be produced from the reaction of 0.420 mol AgNO3 and 0.180 mol solid Al? (How do you solve, given the equation?)
First, determine which is limiting. Then, using mol ratios, determine the answer.
Identify three characteristics that metals have that nonmetals do not. (3)
Metals are silver in color (?), shiny, ductile, malleable, and conduct electricity. They are almost all solids at room temperature.
Balance this equation, including the states of matter. (1 pt) Solid lead(II) sulfide reacts with aqueous hydrogen iodide to form solid lead(II) iodide and dihydrogen sulfide gas.
PbS (s) + 2 HI (aq) --> PbI2 (s) + H2S (g)
A compound contains 10.37% nitrogen, 47.46% sulfur, and the rest is fluorine. What is the empirical formula of the compound? (3)
Percentage of F: 42.17% by subtraction. Assuming 100 g, get 0.740 mol N, 1.48 mol S, 2.22 mol F Mole ratios: S/N = 1.48/0.740 = 2/1 (or 2:1) F/N = 3:1 Formula = NS2F3
Briefly describe precision and accuracy. How do we determine each of them in the laboratory? (3)
Precision is getting a consistent answer or the same answer over and over. In the lab, we find this by looking at the correlation coefficient. Accuracy is getting the correct answer. In the lab we find this by looking at the y-intercept.
Briefly explain the Rutherford model of the atom and how his gold foil experiment helped us uncover more information about atoms. (3)
Rutherford determined that atoms are mostly empty space with a tiny, dense, and positive nucleus. He did this by firing alpha particles at gold foil, and found that most of the particle s went straight through while some were deflected and some collided with the nuclei of the gold atoms.
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: trisulfur hexafluoride (1 pt)
S3F6, molecular
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: diselenium octafluoride
Se2F8; molecular
Which of the following is a property of metal? a. brittle b. gaseous c. conducts electricity d. comes in many different colors
She wants c, conducts electricity
One aspect of Dalton's atomic theory is the Law of Multiple Proportions. Explain what this law means. (2)
The Law of Multiple Proportions states that two elements can combine in different ratios to make different compounds. Thus, we end up with compounds such as CO2 and CO.
Why does the mass of an element in the periodic table not have whole numbers (2 pts)
The mass in the periodic table is a weighted average of all isotopes of bromine. So no atom has a mass of 79.9 amu, but the average of all the isotopes, weighted by their abundance is 79.9 amu.
Which has the smallest formula weight? a. (NH4)3PO4 b. Ba3N2 c. SBr6 d. Al(C2H3O2)3
a. (NH4)3PO4, at 149.10 amu
Consider the following balanced equation: 2 Fe + 6 HC2H3O2 --> 2 Fe(C2H3O2)3 + 3 H2 a. How many grams of iron would be required to react with 0.720 moles of HC2H3O2? b. If 145.3 g of HC2H3O2 is reacted with excess iron, how many grams of H2 will be formed? c. If only 1.42 g H2 are formed, what is the percent yield of the reaction?
a. 13.4 g Fe b. 2.44 g H2 c. 58.2%. Exam 1 SP13 key for math
Write the atomic symbol notation for the following atoms: a. a neutral atom of platinum-197 b. the sulfide ion with 18 neutrons
a. 197/78 Pt b. 34/16 S^2-
For each of the following atomic symbols, identify the number of protons, neutrons, and electrons in the atom. a. 79/34 Se^2- b. 43/21 Sc^+
a. 34 protons; 45 neutrons; 36 electrons b. 21; 22; 20
Determine the number of protons, neutrons, and electrons for each of the following OR the chemical symbol(1 pt each) a. 96/42 Mo^3+ b. 30 protons; 66 neutrons; 30 electrons c. 34 protons; 76 neutrons; 36 electrons d. 88/38 Sr
a. 42 protons; 54 neutrons; 39 electrons b. 96/30 Zn c. 113/34 Se^2- d. 38;50;38
Which quantity is largest? a. 7.8 x 10^-3 km or 78 cm b. 6500 ug or 6.5 x 10^7 ng
a. 7.8 x 10^-3 km b. 6.5 x 10^7 ng
Which one of the following statements is true? a. All atoms of an element will have the same number of protons. b. Two different elements cannot have the same number of neutrons. c. No two compounds can have the same empirical formula. d. In a neutral atom, the number of neutrons and electrons will be the same.
a. All atoms of an element will have the same number of protons.
Which of the following is a postulate of Dalton's atomic theory? a. Atoms combine in whole number ratios to form compounds b. Atoms contain a tiny dense nucleus c. Protons are found in the nucleus of an atom d. The number of neutrons in an atom determines the identity of the element e. Atoms contain electrons.
a. Atoms combine in whole number ratios to form compounds
Which one of the following statements is not a part of Dalton's Atomic Theory? a. Atoms contain a tiny, dense nucleus. b. Atoms cannot be created nor destroyed. c. The same two elements can combine in different ratios to form different compounds. d. Atoms of different elements differ in properties.
a. Atoms contain a tiny, dense nucleus. (Dalton thought of the atom as the smallest, indivisible thing)
A certain compound contains only carbon and hydrogen. Combustion of a sample of the compound produced 57.30 g of carbon dioxide and 35.22 g of water. What is the empirical formula of the compound? a. CH3 b. CH2 c. C3H d. C2H e. C2H3
a. CH3. NOTE from this example that the chemical compound need not be real, as CH3 does not exist. For a solution, see exam 14 key
Tell whether each compound is ionic or molecular and give its formula or name (whichever is missing) a. cadmium(II) sulfite b. S2I6 c. calcium fluoride d. Cr(C2H3O2)3 e. triphosphorus heptaiodide
a. CdSO3, ionic b. disulfur hexaiodide, molecular c. CaF2, ionic d. chromium(III) acetate, ionic e. P3I7, molecular
Tell whether each compound is ionic or molecular and give its formula or name (whichever is missing) a. cesium sulfite b. I2F6 c. tetracarbon octaiodide d. Ni(CN)2
a. Cs2SO3, ionic b. diiodine hexafluoride, molecular c. C4 I8, molecular d. nickel(II) cyanide, ionic
Determine the molar mass for: a. Copper(i) sulfide
a. Cu2S
Balance the following equations: a. The reaction of manganese metal with liquid bromine to form solid manganese(IV) bromide b. the combusion of liquid C6H6
a. Mn(s) + 2 BR2 (l) -> MnBr4 (s) b. 2 C6H6 (l) + 15 O2 (g) -> 12 CO2 (g) + 6 H2O (g)
Tell whether each compound is ionic and give its formula or name (whichever is missing) a. Sulfur dioxide b. NH4Cl c. Chlorine gas d. Phosphorus pentafluoride e. BrF2
a. SO2, molecular b. ammonium chloride, ionic c. Cl2, element, not a compound d. PF5, molecular e. bromium difluoride, molecular
Tell whether each compound is ionic or molecular and give its formula or name (whichever is missing) a. CaSO3 b. molybdenum(IV) nitrite c. Se2O3 d.Mg(Clo)2 e. tetracarbon octahydride
a. calcium sulfite, ionic b. Mo(NO2)4, ionic c. diselenium trioxide, molecular d. magnesium hypochlorite, ionic e. C4H8, molecular
Fill in the blanks with either the appropriate formula or the appropriate name of the compound. a. Mn(OH)2 b. disulfur tribromide c. KC2H3O2 d. nickel(II) chlorite
a. manganese (II) hydroxide b. S2Br3 c. porassium acetate d. Ni(ClO2)2
Which one of the following is the largest mass? a. 2 x 10^-4 kg b. 2 x 10^3 mg c. 2 x 10^5 ng d. 2 x 10^-2 g e. 2 x 10^4 ug
b. 2.5 g (convert all to same unit)
How many moles of carbon would be found in 52.4 g C3H8
b. First calculate how many moles of C3H8 there are (1.19 moles). Then multiply by molar ratio (3 mol C/1 mol propane) = 3.57 mol C
Which one of the following statements is false about protons? a. Protons are found in the nucleus of an atom. b. Protons have about the same mass as electrons. c. Protons are positively charged. d. The number of protons determines the identity of an element. e. In the second period of the periodic table, the elements are listed in order of increasing number of protons.
b. Protons have about the same mass as electrons.
Which of the following statements is true? a. All atoms of chlorine have a mass of exactly 35.45 amu. b. The most common isotope of calcium is most likely calcium-40 c. A neutral atom of fluorine will have 19 electrons d. The most common ion of potassium has 20 electrons.
b. The most common isotope of calcium is most likely calcium-40
_____ typically form ions with a +2 charge a. alkali metals b. alkaline earth metals c. transition metals d. halogens e. noble gases
b. alkaline earth metals
A combination of sand, salt, and water is an example of a __________. a. homogeneous mixture b. heterogeneous mixture c. compound d. pure substance e. solution
b. heterogeneous mixture
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: Ba(MnO4)2
barium permanganate, ionic
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: BrO3
bromine trioxide, molecular
Consider the following aspects of Dalton's atomic theory (I) Each element is composed of extremely small particles called atoms (II) Atoms cannot be divided into smaller particles. (III) Atoms of a given element are identical (IV) Atoms of different elements have different properties. Which of the above postulates is(are) no longer valid? a. (I) and (II) b. (II) only c. (II) and (III) d. (III) only e. (III) and (IV)
c. (II) and (III)
Which one of the following atoms has the greatest number of neutrons? (the number is on the upper left of the element) a. 112 In b. 109 Ag c. 112 Cd d. 106 Pd
c. 112 Cd has 64 neutrons. (a) has 63; (b) has 62; (d) has 60
Which one of the following statements about metals is false? a. Metals conduct electricity. b. Metals are malleable. c. Metals form anions by losing electrons. d. Metals are typically shiny and silvery in color.
c. Metals form anions by losing electrons.
Which one of the following equations is an example of a decomposition reaction? a. Pb + O2 --> PbO2 b. Na + H2O --> NaOH +H2 c. P4O10 --> 2 P2O5 d. C2H2 + O2 --> CO2 + H20
c. P4O10 --> 2 P2O5
The density of an unknown substance is 8.76 g/cm3. How many cm3 would a 98.3 g sample of this substance occupy?
c. multiply 98.3 g by (1 cm3/8.76 g) to make 11.2 g/cm3
How many moles of chlorine atoms are in 54.8 g of C4H3Cl3
convert g to mol. Then multiply by ratio (3 mol Cl / 1 mol crap) = 1.04 mol Cl atoms
Which of the following will have the smallest mass? a. 5.40 mL of ethanol (density of 0.78 g/mL) b. 0.0632 mol CF4 c. 8700 mg of AlCl3 d. 2.75 mL of syrup (density = 1.37 g/mL)
d. 2.75 mL of syrup (density = 1.37 g/mL)
Which one of the following statements is true? a. When the periodic table shows that the mass of a chlorine atom is 35.45 amu, that means that all chlorine atoms have a mass of 35.45 amu. b. The primary difference between atoms of two different elements is their number of neutrons. c. Two isotopes of the same element will differ in the number of protons. d. For two different atoms to have the same number of electrons, one of those atoms has to be an ion.
d. For two different atoms to have the same number of electrons, one of those atoms has to be an ion.
A compound consists of 20.9% Li, 31.0% P, and 48.1% O by mass. The empirical formula of the compound is: a. Li3PO4 b. Li6P2O3 c. Li2P3O4 d. Li3PO3
d. Li3PO3. See key exam 2017
Which one of the following was determined by Millikan's Oil Drop Experiment? a. Atoms contain negatively charged particles. b. Atoms contain a tiny, dense nucleus. c. The nucleus of an atom has a positive charge. d. The charge on an electron is -1.60 x 10-19 coulombs. e. The nucleus of an atom contains neutrons.
d. The charge on an electron is -1.60 x 10-19 coulombs.
Which one of the following statements is false? a. Lithium is an alkali metal and its most common ion has a +1 charge. b. Chlorine is a halogen and its most common ion has a -1 charge. c. Hydrogen and nitrogen both exist as diatomic gases in their natural state. d. The most common ion of silicon will have a -3 charge. e. Neon will most likely not form an ion.
d. The most common ion of silicon will have a -3 charge.
Which statement is TRUE? a. Only halogens exist as diatomic molecules in their elemental form b. Barium is an alkali metal c. Aluminum is a metalloid d. When potassium forms an ion, he charge on the ion will be +1
d. When potassium forms an ion, he charge on the ion will be +1
Which of the following statements is TRUE about these 3 atoms: 43/23 V (this means Vanadium with a 43 on upper left and 23 on lower left); 40/20 Ca^2+; 37/17 Cl^- a. All of the atoms are isotopes of one another b. All of the atoms have the same number of electrons c. All of the atoms have the same number of protons d. All of the atoms have the same number of neutrons e. All of the atoms belong in the fourth period
d. all of the atoms have the same number of neutrons
Gases and liquids are similar in that they both: a. have a definite shape b. completely fill the container which holds them c. have very little motion d. are typically less dense than solids e. cannot be compressed
d. are typically less dense than solids
The element Yttrium, Y, has a mass of 88.91 listed on the periodic table. Which one of the following statements is false? a. The mass of 88.91 amu is the weighted mass of all possible isotopes of yttrium. b. The most common isotope of yttrium is probably yttrium-89. c. All atoms of yttrium will have 39 protons. d. No single atom of yttrium will have a mass of 88.91 amu. e. The mass of the neutrons in all atoms of yttrium is 49.91 amu.
e. The mass of the neutrons in all atoms of yttrium is 49.91 amu.
what is the state of matter of C4H10
gas
Which picture is a liquid compound?
loose, at the bottom, 2 colors joined together
Identify an element that meets the appropriate description (0.5 pt each) a. An element in the 5th period which is a transition metal b. An element that always forms +1 ions c. A halogen d. An alkaline earth metal e. An element that exists as a diatomic molecule in its natural state f. A metalloid g. An element that always forms -1 ions h. An element in the 6th period that is a transition metal i. An alkali metal
many options. In order, for example, a. Zr b. Li c. F d. Mg e. H f. Si g. Cl h. Au i. Na
4 Cr + 3O2 --> 2 Cr2O3 How many moles of oxygen gas are required to react with 8.31 moles of chromium?
multiply moles Cr by molar ratio (3 mol O2/4 mol Cr) to get 6.23 mol O2
How many grams are present in 5.3 x 10^-4 moles of lead
multiply. 0.11 g Pb
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: PI3
phosphorus triiodide; molecular
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: KOH
potassium hydroxide, ionic
Consider the unbalanced chemical equation below (5) a. balance Y + P4 --> Y3P b. If 1520 g of Y is reacted with 775 g of P4, how many grams of Y3P can be produced? c. If the actual yield is 1562 g, what is the percent yield?
so a. 12 Y + P4 --> 4 Y3P b. This is a limiting reactant problem. The Y's 1520 g gives 5.70 mol Y3P (multiply g*MW of Y * mol ratio of 4 mol Y3P to 12 mol Y). The P4 's 775 g correspond to 25.0 mol Y3P. So Y is limiting and we can make 5.70 mol Y3P * 297.70 g/mol = 1700 g Y3P c. 1562 g/1700 g = 91.9% (NOTE: even tho 1700 looks like 2 sig digits, it is actually 3!! so we have 91.9, not 92 )
How many sig digits: (2 pts) (65.42-62.788)/4.900
subtraction gives 2.63 (3 sig digits) so final answer has 3 sig dig.
How many significant digits? [(0.427 g/mL)(45.234 mL) + 0.872 g]
the multiply part gets 3. so 19.3. Adding keeps the tenth place, so answer of 20.2 has 3 sig digits
How many g is 43.5 cg?
there is 1 g per 100 cg, so this would be 0.436 g
Identify the type of the compound, name it, write the correct formula, and say if it is ionic or molecular: V(CN)4
vanadium(IV) cyanide; ionic