Chem Study

Topics: Atom, Energy, Chemistry Pages: 5 (1237 words) Published: December 9, 2012
An example of potential energy is
A) a coiled spring.
B) running water.
C) tree branches blowing in the breeze.
D) a moving elevator.
E) electrical energy.
Points Earned:1.0/1.0

The correct answer is A.
The definition of potential energy is an inactive type of energy that is stored for future use. All of these answers describe active energy, for example, running water is very active but can generate other types of energy. Which one of the following substances will float in gasoline, which has a density of 0.66 g/mL? A) table salt (density = 2.16 g/mL.

B) aluminum (density = 2.70 g/mL.
C) mercury (density = 13.6 g/mL.
D) balsa wood (density = 0.16 g/mL.
E) sugar (density = 1.59 g/mL.

The correct answer is D. According to page 43, objects float that are less dense than the liquid it’s in. All of the answers have density greater than .66g/ml except balsa wood which equals to .16 g/ml. A radioactive sample was measured as having a mass of 160 mg. Six hours later, the sample’s mass was measured at 40 mg. What is the half-life of the sample? A) six hours

B) one and one-half hours
C) twelve hours
D) nine hours
E) three hours
Points Earned:1.0/1.0
The correct answer is E, three hours. The definition of Half-life according to page book is the length of time it takes for one-half of a radioactive sample to decay. 160mg divided by 2 equals 80, (which is the half- life of the sample.) If you divide the six hours it took the sample to reach 40mg by two. The answer will be three hours. a)Is incorrect because it equal 2 half-lives.

The smallest particle of an element that retains the characteristics of the element is a(n) A) atom.
B) electron.
C) nucleus.
D) neutron.
E) proton.
The correct answer is A), atom. According to page 105 an atom retains the characteristic of that element. b)Describes the negative charge of a particle. Even though it has no mass it is not considered the characteristic of that element c)Describes the center of an atom.

d)Describes the neutral charge of a particle.
e)Describes the positive charge of a particle.
To form an ion, a sodium atom
A) loses two electrons
B) gains one electron
C) gains two electrons
D) loses seven electrons
E) loses one electron

The correct answer is E, because an atom becomes an ion when it gains or loses electrons. Because of the Octet rule elements are trying to gain the properties of full electron shells. Sodium has 11 protons and electrons. The odd number left in the last energy level, leaves it subject to lose that electron. Answers A) through D) are wrong because of the Octet rule.

A 5.00-L tank contains helium gas at 1.2 atm. What is the pressure of the gas in mm Hg? A) 760 mm Hg
B) 912 mm Hg
C) 507 mm Hg
D) 1.50 mm Hg
E) 7.5 mm Hg
Correct Answer(s):B

By multiplying 760*1.2 you will get the correct answer is B) because 1atm = 760mmHg. This is stated in the answer for A) but was not fully plugged into an equation. Answers C), D), and E) are too low to be considered correct. A student calculates the mass of a product of a chemical reaction to be 15.75 grams but has been told that this reaction has a 95% yield. What mass of product should the student expect to have at the end of the actual reaction? A) 15.75 g

B) 16 g
C) 14.96 g
D) 17 g
E) 15 g
The correct answer is E). The percent yield is calculated by dividing the actual yield by the theoretical yield, then multiplying by 100%. Question C) is the wrong answer. The initial answer will be 14.96 but the teacher will want you to convert this answer to significant figures. Since the lowest number in this equation has only 2 figures you must round your answer up to 15g. Answer A) denotes the theoretical yield. 42.

What is the concentration, in m/v%, of a solution prepared from 50. g NaCl and 2.5 L of water? A) 0.020%
B) 5.0%
C) 2.0%
D) 0.050%
E) 20.%

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