Download UNIT 2 EXTRA PROBLEMS FOR THE WEBSITE

UNIT 2 EXTRA PROBLEMS FOR THE WEBSITE (Honors & Regents):
Atomic Structure, Nuclear Chemistry , Nomenclature, and the Mole.
[Note that the Regents and Honors courses are slightly different in unit 2. The questions
which pertain to Regents are indicated (R)]
1. What is the approximate number of molecules in a drop of water which weighs 0.09 g?
(R)
[3.01 x 1021]
2. How many moles are present in 100. g quantities of each of the following? (a) calcium
carbonate (b) H2O (c) hydrochloric acid (d) aluminum sulfate (R)
[1; 5.55; 2.74; 0.292]
3. An unknown compound consists of 82.98% potassium and 17.02% oxygen. What is
the empirical formula of the compound? (R)
[K2O]
4. A compound subjected to analysis was found to have the following composition by
mass: 69.96% carbon, 7.83% hydrogen, and 22.21% oxygen. If the molecular mass of the
compound is 360 g/mol, what is its molecular formula? (R)
[C21H28O5]
5. Calculate the percentage composition of aluminum sulfate.(R)
[15.8% Al; 28.1% S; 56.1% O]
6. Calculate the percent by mass of each element in magnesium chloride.(R)
[25.5% Mg; & 4.5% Cl]
7. When a piece of magnesium ribbon weighing 0.32 g is burned in oxygen, the resultant
oxide weighs 0.53 g. What is the percentage composition of the oxide?
[60.% Mg; 40.% O]
8. Natural chlorine is a mixture of isotopes. Determine its average atomic mass if 75.53%
of the naturally occurring element is chlorine-35, which has a mass of 34.968, and 24.4%
is chlorine-37, which has a mass of 36.956.
[35.45 amu]
9. How many protons, neutrons, and electrons are in an atom of the following elements?
a) boron, mass number 11 , b) krypton, mass number 84 , c) scandium, mass number 45 ,
d) potassium, mass number 39
[5,6,5; 36, 48, 36; 21, 24, 21; 19, 20, 19]
10. The mass number of an isotope of oxygen is 17. Write the name and symbol for this
isotope.
[oxygen-17; 178O]
11. What is an atomic mass unit?
[1/12 the mass of the carbon-12 isotope]
12. An atom has 22 neutrons and 18 protons in its nucleus. What is the atomic number,
mass number, and symbol of this element?
[18, 40, Ar]
13. Name each of the following substances:
(a) CaO (b) Ba3(PO4)2 (c) I2 (d) FeSO4 (e) Mg(OH)2 (f) NO2 (g) CuC2H3O2 (h) HClO4 (i)
Cl2O (j) HgF2 (k) (NH4)2C2O4 (l) NO2[calcium oxide; barium phosphate; iodine; iron(II) sulfate; magnesium hydroxide;
nitrogen dioxide; copper(I) acetate; perchloric acid; dichlorine monoxide; mercury(II)
fluoride; ammonium oxalate; nitrite ion]
14. Write formulas for these compounds:
(a) silver chloride , (b) aluminum carbide , (c) lithium hydride , (d) nitric acid , (e) ferric
carbonate , (f) hypochlorous acid , (g) tin(IV) cyanide , (h) hydrocyanic acid, (i)
potassium iodide , (j) calcium hydrogen carbonate , (k) carbon tetrachloride , (l) trisilicon
tetranitride
[AgCl; AlC3; LiH; HNO3; Fe2(CO3)3; HClO; SnCN4; HCN; KI; Ca(HCO3)2; CCl4; Si3N4]
The following problems are for Honors only:
15. Determine the relative abundance of each isotope in naturally occurring gallium from
the following data: average atomic mass of gallium is 69.72. Mass of 69Ga = 68.926 and
mass of 71Ga = 70.925.
[60% 69Ga; 40% 71Ga]
16. A chemist is given an unknown element X. She finds that it has an atomic mass of
210.197 amu, and consists of only two isotopes, 210X and 212X. If the masses of these
isotopes are, respectively, 209.64 and 211.66 amu, what is the relative abundance of the
two isotopes?
[210X = 72.42%; 212X = 27.58%]
17. Complete the following nuclear equations: (a) 7N14 + 2He4 ---> 8O17 + (b) 1H3 --->
3
9
4
12
30
30
2He + (c) 4Be + 2He ---> 6C + (d) 15P ---> 14Si +
[1H1, -1e0, 0n1, +1e0 ]
18. 2.000 picogram (pg) of 33P decays by beta minus emission to 0.250 pg in 75.9 days.
Find the half-life of 33P. [25.3 days]
The following is an example of an Honors test:
Multiple Choice:
1. Dalton's Atomic Theory included which idea?
a) all atoms of all elements are the same size (b) atoms of different elements combine in
one-to-one ratios only (c) atoms of the same element are always identical (d) individual
atoms can be seen with a microscope (e) in a chemical reaction, atoms change into atoms
of other elements
2. Select the correct statement about subatomic particles
a) electrons are the heaviest subatomic particles and are negatively charged (b) protons
are the lightest subatomic particles and are positively charged (c) neutrons have no
charge and are the lightest subatomic particle (d) electrons, protons, and neutrons all have
the same mass (e) the mass of a neutron nearly equals the mass of a proton
3. Isotopes of the same element have different
a) mass numbers b) atomic numbers c) symbols d) numbers of electrons e) numbers of
protons
4. Which two characteristics do radioisotopes have that makes them useful for medical
diagnosis?
a) long half-lives and quick elimination from the body b) long half-lives and slow
elimination from the body c) short half-lives and quick elimination from the body (e)
short half-lives and slow elimination from the body
5. Which pair of nuclei can undergo a fusion reaction?
a) potassium -40 and cadmium -113 (b) zinc -64 and calcium -44 (c) uranium -238 and
lead -208 (d) hydogen -2 and hydrogen -3
6. Which is the formula for magnesium sulfide?
a) MgSO4 b) MgS2 c) MgS d) MnS
7. If element X is an alkali metal, what is the formula of its oxide?
a) XO b) XO2 c) X2O d) X2O2
8. Which element forms more than one binary compound with chlorine?
a) calcium b) potassium c) iron d) zinc
9. A radioactive element will lose the greatest amount of mass when it emits
a) a neutron b) a proton c) a beta particle d) an alpha particle
10. In the equation: 2411Na ----> 2412Mg + X, X represents
a) a neutron b) a proton c) a beta particle d) an alpha particle
11.The number of neutrons in the nucleus of an atom can be calculated by
a) adding together the number of electrons and protons b) subtracting the number of
electrons from the number of protons c) subtracting the number of protons from the mass
number d) adding the mass number to the number of electrons
12. If an isotope undergoes beta emission:
a) the mass number changes b) protons are given off c) the atomic number changes d) the
number of neutrons remains the same
13. The most penetrating form of radiation is:
a) alpha b) beta c) gamma d) visible
14. Nuclear fusion:
a) takes place in the sun b) occurs when large nuclei fuse together c) produces hydrogen
nuclei d) all of the above are true
15. Which of the following particles is needed to complete this reaction?
a) 5525Mn + 21H ---> _______ + 210n
a) 5627Co (b) 2725Mn (c) 5526Fe (d) 5824Cr
16. Which of these naturally occurring radioisotopes would be most useful in dating
objects thought to be millions of years old?
a) 14C: t1/2 = 5730 years (b) 40K: t1/2 = 1.28 x 109 years (c) 234Th: t1/2 = 25 days (d) 222Ra:
t1/2 = 3.8 days
17. Which of these statements is not true?
a) atoms of the same element can have different masses b) atoms of isotopes of an
element have different numbers of protons c) the nucleus of a neutrl atom has a positve
charge d) atoms are mostly empty space
18. Dalton theorized that atoms are indivisible and that all atoms of the same lement are
identical. We now know that:
a) Dalton's theories are correct b) atoms of a given element can have different numbers of
neutrons c) atoms contain no smaller subatomic particles d) all atoms of a given element
are not identical but they must all have the same mass
19. After 252 days, a 12.0 g sample of 42Sc contains only 1.5 g of the isotope. What is the
half-life of 42Sc?
a) 252 days b) 84 days c) 3 days d) 1.5 days
20. Which atom when combined with chlorine would most likely form a molecular
compound?
a) lithium b) calcium c) nickel d) phosphorus
21. An empirical formula:
a) gives information about molecular structures b) shows the number and kinds of atoms
in a molecule of a substance c) shows the simplest whole number ratio in which elements
combine d) uses superscipts to show the number of each kind of atom in a molecule
22. What is the ionic charge on the manganese ion in the ionic compound manganese
oxide written as MnO2?
a) +2 (b) -2 (c) +4 (d) -4
23. The metals in Groups 1, 2, and 13:
a) gain electrons when they form ions (b) all form ions with a -1 charge (c) lose electrons
when they form ions (d) form only negative ions
24. A 10.3 g sample of NiO was formed from 8.1 g of nickel and 2.2 g of oxygen. What
is the percent compositon of this oxide?
a) 81% Ni and 22% O (b) 79% Ni and 21% O (c) 73% Ni and 27% O (d) none of these
choices is correct
25. What percent of an original 20.0 g sample of 131I remains after 32 days?
a) 50% b) 6.25% c) 12.5% d) 1.25%
Problems:
26. a) One method for producing plutonium -238 is by bombarding uranium -238 with
deuterons. This process produces neptunium -238 and another type of particle. The
unstable neptunium then decays to form plutonium -238. Write balanced nuclear
equations for this two step process.
(b) With what particle would you bombard sulfur -32 to produce hydrogen -1 and
phosphorus -32? Write the appropriate nuclear equation.
(c) Complete the following nuclear equations:
87
37Sr
---> 8738Sr + _________
230
92U
---> 42He + _________
27. The two principal isotopes of copper are 63Cu and 65Cu. The atomic mass of Cu-63 is
62.9298 amu, and the atomic mass of Cu-65 is 64.9278 amu. determine the percent
abundance of each isotope if the average atomic mass of copper is 63.546 amu.
28. Refer to the graph below (get diagram from Ms. Fed) which represents the radioactive
decay of strontium -90.
a) Based on the graph, what is the half-life of strontium -90?
b) How much of the original sample would remain after about 140 years?
c) If an original sample of strontium -90 contains 300.0 g, how much of the original
sample has decayed after 84 years?
29. Complete the table below by supplying the missing information - either formula or
name:
.................NAME ....................................................FORMULA
potassium bromate ..............................................________________
______________ ...............................................H2SO3(aq)
dinitrogen pentoxide ............................................________________
periodic acid .......................................................________________
hydrosulfuric acid ................................................________________
_____________ ................................................NaHCO3
tin (II) fluoride .................................................... ________________
potassium permanganate .................................... ________________
_____________ ............................................... HNO3(aq)
_____________ ............................................... CuO
30. Each term in column A refers to a nuclear reactor. Match each term in column A with
the appropriate description or substance in column B.
........Column A .............................................................Column B
a. moderator ___________ ...........................................1. water
b. control rods __________ ...........................................2. lead or concrete
c. breeder reactor ________ ..........................................3. slows down neutrons
d. shielding _____________ ...........................................4. cadmium
e. coolant ______________ ........................................... 5. uranium 235
f. fuel rods _____________ ............................................ 6. produces plutonium -239
Answers:
1 c, 2 e, 3 a, 4 c, 5 d, 6 c, 7 c, 8 c, 9 d, 10 c, 11 c, 12 c, 13 c, 14 a, 15 c, 16 b,
17 b, 18 b, 19 b, 20 d, 21 c, 22 c, 23 c, 24 b, 25 b.
26. 238U92 + 21H ---> 23893Np +210n ;23893Np ---> 23894Pu + 0-1e
27. 69% Cu -63; 31% Cu -65
28. (a) 30 years (b) 0.31 g (c) 262.5 g has decayed
29. NAMES : sulfurous acid ; sodium hydrogen carbonate ; nitric acid ;
copper(II) oxide. FORMULAS : KBrO3 ; N2O5 ; HIO4 ; H2S ; SnF2 ;
KMnO4.
30. a) 3 b) 4 c) 6 d) 2 e) 1 f) 5