2015 Midterm Answer Key

1) B. The mass of a proton and of a neutron is 1 amu. The mass of an electron is 1/1836 amu.

2) B. The atomic mass is a weighted average that accounts for all naturally occurring isotopes percent abundances

and atomic mass.

3) A. The atomic number or number of protons is 11 which identifies the elements as sodium.

4) B. The wave-mechanical model (electron cloud model) has protons and neutrons in the nucleus with electrons

outside of the nucleus in orbitals that make up the electron cloud because electrons are constantly moving.

5) A. Electrons are negatively charged and attract to the positive protons in the nucleus. Electrons are most stable

in lower energy levels because they are closer to the nucleus.

6) B. 2-0-1: The second energy level is empty and an electron has moved to the higher energy level (3rd

level).

Electrons in the ground state will always fill the lower energy levels first.

7) D. Electrons that are excited release energy as light when they return their lower energy levels and the ground

state.

8) A. Malleability and conducting electricity are properties of metals.

9) D. Being brittle and a poor conductor is a nonmetallic property. Sulfur is the only solid nonmetal at STP in this

question. Neon is a noble gas, not a solid.

10) A. Equal volumes of any gas will always have an equal number of particles (atoms OR molecules) because

22.4 L = 6.02 x 1023

particles.

1.0 L x (6.02 x 1023

particles) = 2.69 x 1022

particles

22.4 L

Therefore 1.0 L of He and 1.0 L of Ne each have 2.69 x 1022

atoms

11) D. Metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.

12) B. “Br I N Cl H O F” Nitrogen is the element in group 15 with diatomic molecules.

13) A. A magnesium atom contains 12 e- (2-8-2). When it forms a Mg+2

ion it loses 2 electrons and the e-

configuration becomes 2-8, like neon.

14) B. F- is a fluoride ion. It contains 9 protons inside its nucleus which makes it fluorine.

15) A. He is a smaller noble gas with only 1 PEL.

16) B. When phosphorus forms P-3

is gains 3 electrons. This causes the radius to increase.

17) B. Down any group the atomic radius increases because the # of PEL’s increases. This causes more nuclear

shielding (blocking of the nucleus) which causes electronegativity and ionization energy to decrease down a

group.

18) C. The greatest tendency to gain electrons means electronegativity. Chlorine has the greatest electronegativity

out of the choices.

19) A. As you move across period 3 and the atomic number increases this causes the nuclear charge to increase

which strengthens the attraction for electrons and increases the electronegativity.

20) D. Nonmetals are located on the right side of the table and as you move across a period the ionization energy

and electronegativity go up because nuclear charge increases. High ionization energy and high electronegativity

are nonmetallic properties.

21) D. Fluorine is the most electronegative nonmetal, this means it gains it’s valence electrons the most easily. This

makes it the most reactive nonmetal.

22) A. All compounds must undergo a chemical change that will break the bonds between the different atoms it is

composed of. Compounds can be covalent or ionic and can consist of 2 atoms (HF)

23) D. The molecules contain two different types of atoms bonded together and the composition is uniform. Only

one compound is represented.

24) B. Iron is a transition metal with a +2 or +3 oxidation state. The other metals only have one oxidation state.

25) D. Sr+2

and PO4-3

need to combine to make a neutral compound. You need 3 Sr+2

and 2 PO4-2

ions in the

compound making the formula Sr3(PO4)2.

26) B. Energy will always flow from higher temperature (average kinetic energy) to lower temperature (average

kinetic energy). All things in nature flow high to low. The water is 45°C while the ice is 0°C. Heat flows from

the water into the ice, causing the ice to melt.

27) C. Solubility and density are intensive properties and do not depend on the size or quantity of a substance.

28) D. Ideal gas on a beach, “PLIGHT- pressure low ideal gas high temperature”. Gases behave ideally when under

low pressure and high temperature. This favors the particles being far apart and not attracting together because

they are moving rapidly.

29) B. Density=mass/volume. Samples A and C have the same density. This means they are the same substance.

30) A. Use the combined gas law. P1V1=P2V2 (0.90 atm)(50.0 ml)= (1.0 atm)V2 V2= 41 mL

@STP P=1.0atm, T=273K (Table A) T1 T2 298 K 273 K

31) D. Pressure and volume have an indirect relationship. When you have high volume (large space between

particles) you have very few collisions which causes pressure to be low. When you have a small volume (small

space between particles) you have a very high pressure due to more collisions.

32) C. P1V1=P2V2 (40.0 mL) = (80.0 mL) Cross multiply- (40.0 mL)T2 = (80.0mL)(293K)

T1 T2 293 K T2

(40.0 mL)T2 = (80.0mL)(293K)

(40.0 mL) (40.0mL)

T2 = 293 K x 80.0mL

40.0mL

33) B. q=mcΔT 168J= m (4.18J/g°C)(30.0°C-10.0°C) 168= m83.6 m= 2.00 g

34) C. Read Table H.

35) C. NaCl(aq) is sodium chloride dissolved in water as a solution. All solutions are homogeneous mixtures. The

other choices are pure substances in a regular phase as solid, liquid or gas.

36) B. C-14 is spontaneously releasing a beta particle to decay. Natural transmutation only has ONE nuclide as a

reactant releasing a particle and mutating into a different nuclide.

37) B. According to Table N, N-16 emits a beta particle and has a half-life of 7.13 s. (7.2 s was the old value before

the reference tables were updated, this question is from the 2002 chemistry reference tables.)

38) C. Fusion is the combining of small nuclei to form one larger nucleus and release massive quantities of energy.

The nuclei will be hydrogen for fusion. Anything much bigger will not fuse because the positive charges of the

nuclei repel.

39) A. According to Table O, an alpha particle is There is a conservation of mass number and charge in all

nuclear reactions.

40) D. K= °C + 273 so 200+273= 473K.

Scanned by CamScanner

Scanned by CamScanner