Download Practice Exam-1A Fall 2016

CHEM 1411 Practice Exam-1 (Chapters 1- 4)
Multiple Choice: Select one best answer.
1. Convert 0.3980 m to mm.
(First see how many significant figures are there in meters and convert to mm and see there are
same significant figures)
A)
B)
C)
D)
E)
2. A scientist obtains the number 0.0470056800 on a calculator. If this number actually has three
(3) significant figures, how should it be written?
A)
B)
C)
D)
E)
0.0470
0.047
0.4700
0.047006
0.47006
3. Perform the indicated operations and express the answer with the proper number of significant
digits. 28.1 cm + 0.53 cm + 75.321 cm =
(When adding or subtracting the least decimal place is used in the product)
A) 104
B) 1.04 x 102
C) 103.95
D) 103.951
E) 104.0
4. How many significant figures are appropriate to show in the result after carrying out the
operation below? (When multiplying or dividing the least significant numbers are used in the
product)
(223.7 + 0.27) ÷ 4.21 =?
A) 1
B) 2
C) 3
D) 4
E) 5
5. What is the equivalent temperature for 98.6 Fahrenheit in Kelvin?
First convert oF to oC and then oC to K
F = 9/5(C) + 32
C = 5/9(F − 32)
K = C + 273.15
(a) 37
(b) 310
(c) 471.6
(d) 594.8
(e) -273.1
6. An unknown sample has a mass of 13.9 g and a volume of 17.4 mL. What is its density
(g/mL)? Use equation d = m/v
(a) 0.799
(b) 1.04
(c) 3.16
(d) 4.62
(e) 5.07
7. Which of the following is a heterogeneous mixture?
(a) milk
(b) salt, water, and sugar
(c) oil and water
(d) 14-K gold ring
(e) air
8. Which of the following is a physical change?
A) Color of carpet faded (by sun light)
B) Zinc strip dissolves in vinegar (to produce hydrogen gas)
C) Burn a wood block
D) Water freezes
E) Iron rusts
9. How many protons, electrons, and neutrons are there in 79Br- (bromide anion)?
Isotopes with number on front top represent mass number. Mass # = # Protons + Neutrons
Look for atomic number of bromine from periodic table (top one). In a neutral molecule, # of
protons = # of electrons.
(a) 35p, 35e, 79n
(b) 34p, 35e, 45n
(c) 35p, 36e, 79n
(d) 36p, 34e, 79n
(e) 35p, 36e, 44n
10. Which of the following pairs would have similar chemical and physical properties?
(a) Ni, Mg
(b) H, Na
(c) C, Si
(d) Cu, Ca
(e) Cr, Cl
Hint: The elements from the same group (i.e. the vertical column) will have
similar physical and chemical properties.
11. Which of the following is a molecular compound?
(a) KCl
(b) CsF
(c) HCN
(d) AlBr3
(e) NaOH
Hint: Molecular compound is composed by nonmetal reacting with nonmetal atoms.
12. Which of the following is not a correct match?
(a) AlCl3, aluminum chloride
(b) H2O dihydrogen monoxide
(c) CrF3, chromium (III) fluoride
(d) HNO3, nitrous acid
(e) CuSO4.5H2O, copper (II) sulfate pentahydrate
Hint: Follow the rules of naming the compounds.
13. Which of the following pairs is a correct match?
(a) Ba3(PO4)2, barium (II) phosphate
(b) (NH4)2SO3, diammonium sulfate
(c) Na2O2, sodium oxide
(d) Ca(NO3)2, calcium nitrate
(e) CH3COOH, carbonic acid
Hint: Follow the rules of naming the compounds. Be able to differentiate the rules
between ionic and molecular compounds.
14. The atomic masses of 10B and 11B are 10.0129 amu (natural abundance 19.78% = 0.1978)
and 11.0093 amu (natural abundance 80.22% = 0.8022), respectively. What is the average atomic
mass of B?
(a) 9.467
(b) 9.966
(c) 10.042
(c) 10.504
(e) 10.810
Hint: You must convert the % into decimals first and then apply the formula and
memorize it: M = M1X1 + M2X2 = 10.0129x0.1978 + 11.0093x0.8022 =
15. What is the molar mass for calcium nitrate, Ca(NO3)2?
(a) 44
(b) 56
(c) 87
(d) 93
(e) 164
Hint: Formula, Ca(NO3)2, indicates that there are 1 Ca, 1x2 = 2 N and 3x2 = 6 O Go to
the periodic table and locate the atomic mass for each atom. Thus the formula mass of
Ca(NO3)2 = 1x40 + 2x14 + 6x16 =
16. How many hydrogen atoms are there in 48.0 g of CH4?
(a) 1.81x1023 (b) 7.22x1024 (c) 6.02x1023 (d) 1.20x1025 (e) 4.70x1025
Hint: According to the chemical formula, one mole of CH4 contains 1 mole of C atoms
and 4 moles of hydrogen atoms. Thus, the mole of H = 4 x {mass of CH4/molar mass of
CH4}. When converting moles into atoms, it needs to multiply the Avogadro’s number,
that is, 6.02x1023. Thus the number of H atoms = moles of H atoms x Avogadro’s number
= (6.02x1023)x{4x(48.0/16.0)} =
17. What is the mass percent (%) for O in SO2?
(a) 38.09
(b) 45.41
(c) 50.00
(d) 53.86
(e) 56.43
Hint: % O = (mass of 2 O ÷ mass of SO2) x 100% = 2x16 ÷ (1x32+2x16) x 100% =
18. Which of the following is the empirical formula?
(a) C8H18
(b) CH3COOH
(c) C4H10O2
(d) NH4NO3
(e) B2H6
Hint: Empirical formula is the simplest integral ratio among each atom.
19. Chemical analysis shows the composition of a compound containing carbon, hydrogen,
chlorine, and oxygen, to be 37.84% C, 2.12% H, 55.84% Cl, and 4.20% O. What is its empirical
formula?
(a) CHClO
(b) C2HClO4
moles of C = 37.84/12
moles of H = 2.12/1
moles of Cl = 55.84/35.45
moles of O = 4.20/16
(c) C12H8Cl6O
Moles
= 3.15
= 2.12
= 1.58
= 0.26
(d) C12H8Cl6O4
Ratio of elements
3.15/0.26
12
2.12/0.26
8
1.58/0.26
6
0.26 /0.26
1
20. Chemical analysis shows the composition of a compound containing carbon and hydrogen, to
be 80.00% carbon and 20% hydrogen and the molar mass is 30 g. What is its molecular formula?
(a) CH
(b) C2H4
(c) C2H6
(d) C6H12
(e) C10H22
Hint: The molecular formula is an integral multiple of empirical formula. That is, the
molar mass /empirical molar = integer. First find empirical formula
Moles
= 6.67
= 20
moles of C = 80/12
moles of H = 20/1
Ratio of elements
6.67/6.67
1
20/6.67
3
So the empirical formula is CH3 and the empirical molar mass of CH3 = 12x1+1x3 =15.
So the integer = 30/15 = 2. Thus MF = 2 x CH3 = C2H6
21. What are the coefficients respectively when the equation
__PH3 + __O2
→
__P2O5 + __H2O is balanced?
(a) 2, 2, 1, 3
(b) 2, 1, 3, 4
(c) 2, 3, 1, 2
(d) 2, 4, 1, 3
(e) 1, 1, 3, 3
22. In the reaction of Al(OH)3 with H2SO4, how many moles of water can be produced If the
reaction is begun with 5.500 mole of Al(OH)3?
2Al(OH)3 + 3H2SO4
(a) 2.50
(b) 4.75
→
Al2(SO4)3 + 6H2O
(c) 6.32
(d) 7.58
(e) 16.50
23. How many grams of H2O could be formed by the reaction of 16.0 g of CH4 with 48.0 g of
O2? First find if any limiting reagent.
CH4 + 2O2 →
CO2 + 2H2O
(a) 27.0
(b) 37.3
48.0g O2 x 1mole O2
32.0g O2
(c) 46.8
x
2H2O
2 O2
(d) 54.1
x
18.0g H2O
1mole H2O
= 27
24. What is the excess reagent in the above reaction (Q.23) of CH4 and O2? How many grams of
the excess reagent were consumed?
(a) CH4, 12 grams
(b) O2, 12 grams
(c) CH4, 4 grams
(d) O2, 4 grams
(e) CH4, 8 grams
1 mole CH4
2 moles O2
x
1.5 moles O2 x
16.0g CH4 = 12g
1 mole CH4
25. A 15.6 grams of benzene (C6H6) is mixed with excess HNO3 to prepare nitrobenzene
(C6H5NO2). After the reaction there are 15.6 grams of nitrobenzene produced. What is the
percent yield of nitrobenzene?
C6H6 + HNO3 → C6H5NO2 + H2O
(a) 34.3%
(b) 47.6%
(c) 58.9%
(d) 63.4%
(e) 71.2%
Hint: The amount of product calculated according to the road map is the theoretical yield
and the one obtained by weighing is the actual yield.
% yield = (actual yield/ theoretical yield) x 100%
Now from the road map, we calculate the theoretical yield (note that since the actual
yield given is in unit of grams, so we need to complete the entire road map).
15.6 g C6H6-------0.2mole C6H6 ----- 0.2mole C6H5NO2 x 123g/mol = 24.6g C6H5NO2
78 g/mol
x
1C6H5NO2 /1C6H6
Theoretical yield 24.6g
% Yield = Actual yield ÷Theoretical yield x 100 = 15.6 g ÷ 24.6 g x 100 = 63.4%
26. Which of the following is a weak electrolyte?
A) Sodium hydroxide solution
B) He gas
C) Sugar
D) Water
E) Potassium chloride
Others examples of weak electrolytes: Aceti acid, HF, HNO2 , NH3, etc.
27. Which of the following is paired incorrectly?
A)
B)
C)
D)
E)
HF – strong acid
H2SO4 – strong acid
Ba(OH)2 – strong base
HCl – strong acid
NH3 – weak base
Examples of weak acids: Aceti acid, HF, HNO2, phosphoric acid, etc.
Examples of weak bases: Ammonia, many alkyl amines, , pyridine, etc..
28. Which pair of ions would not be expected to form a precipitate when dilute
solutions of each are mixed?
A)
B)
C)
D)
E)
Al3+, S2–
Pb2+, OH–
Ba2+, PO43–
Mg2+, SO42–
Pb2+, Cl–
All Group IA salts and all metal nitrates will not form a precipitate
All Group IIA salts with some exceptions are soluble (see formula sheet).
29. In the reaction 2Cs(s) + Cl2(g)  2CsCl(s), Cs is
A)
B)
C)
D)
E)
the reducing agent
the oxidizing agent
Oxidized
the electron donor
All of the above except B
30. Which of the following redox reactions will occur according to activity series?
A) Cu(s) + 2HCl(aq)  CuCl2(aq) + H2(g)
B) Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)
C) Fe(s) + ZnSO4(aq) FeSO4(aq) + Zn(s)
D) 2Al(s) + 3Ca(NO3)2(aq)  2Al((NO3)3(aq) + 3Ca(s)
Other example Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
31. How many grams of KOH are present in 35.0 mL of a 5.50 M solution?
A) 5.5
B) 10.8
C) 15.7
D) 17.8
E) 21.3
First convert 35 mL to L = 0.035L, the calculate moles of KOH in 0.035L
5.50 M x 0.035L = 0.1925 mol x 56.1g KOH = 10.8 g
1L
1 mol KOH
32. What is the final concentration (in M) of a solution when water is added to 25.0
mL of a 0.866 M KNO3 solution until the volume of the solution is exactly 500.0 mL?
A) 0.0252
B) 0.0368
C) 0.0117
D) 0.0534
E) 0.0433
Hint: Mi x Vi = Mf x Vf,
Mf = Mi x Vi/Vf = 25.0mL x 0.866M/500 mL =
33. What volume (in mL) of a 0.500 M HCl solution is needed to neutralize 10.0 mL of a 0.2000
M Ba(OH)2 solution?
A) 8.00
B) 4.00
C) 2.00
D) 1.00
E) 0.50
2HCl + Ba(OH)2 → 2H2O + BaCl2
M1 x V1 = M2 x V2
V1 = M2 x V2 / M1 = 0.2000 M x 10 mL/0.500 M = 4 mL x 2 mol HCl
= 8.00 mL
1 mol Ba(OH)2
Key to Practice Exam-1:
1-A, 2-A, 3-E, 4-C, 5-B, 6-A, 7-C, 8-D, 9-E, 10-C, 11-C,
12-D, 13-D, 14-E, 15-E, 16-B, 17-C, 18-D, 19-C, 20-C, 21-D, 22-E,
23-A, 24-A, 25-D, 26-D, 27-A, 28-D, 29-E, 30-B, 31-B, 32-E, 33-A