Pre-AP Chemistry SE Mock Exam--version 1

Compared to the charge and mass of an electron, a proton has

• the same charge and smaller mass

• the same charge and the same mass

• an opposite charge and a greater mass

• an opposite charge and the same mass

Answer explanation

The mass of a proton = 1 AMU. The mass of a neutron also equals 1 AMU. The proton and neutron are each 10,000 times larger than the mass of an electron.

p = positive 1 charge

n = no charge (neutral)

e = negative 1 charge

Consider the Bohr Model of Phosphorous below. Which statement is false?

• The electrostatic potential energy of ALL electrons is negative.

• The electrons with the least potential energy are closest to the nucleus.

• Energy is released when the electron is ejected from the atom.

• When an electron is very far away from the atom, the electrostatic potential energy is 0.

Answer explanation

In order for an electron to be ejected (or emitted) from the atom, it has to ABSORB energy.

Which best represents the isotope shown above?

• 28 protons, 26 electrons, and 34 neutrons

• 26 protons, 26 electrons, and 36 neutrons

• 28 protons, 26 electrons, and 26 neutrons

• 26 protons, 24 electrons, and 36 neutrons

Answer explanation

62 = the mass number = #p + #n.

26 = atomic number = #p

2+ = charge = gain or loss of electrons.

62 - 26 = 36 neutrons.

Charge of 2+ = loss of 2 electrons. = 26 - 2 = 24 electrons.

Chemists can identify the composition of some unknown salts by conducting a flame test. When potassium salts are heated in a flame, a purple color is observed. This is due to the movement of electrons between energy levels. What is the electron configuration of a potassium atom at ground state?

• 1s²2s²2p⁶3s²3p⁶4d¹

• 1s²2s²2p⁶3s²3p⁶3d¹

• 1s²2s²2d⁶3s²3d⁶4s¹

• 1s²2s²2p⁶3s²3p⁶4s¹

Answer explanation

Electron configuration always starts at hydrogen. 1s2 2s2...until you get to your element. Remember, the sum of the superscripts tells us the number of protons for a neutral atom.

In a 3.7-gram sample, there are _________________ atoms of gold (Au).

• 1.1 x 10²² atoms of gold

• 3.2 x 10²⁵ atoms of gold

• 4.4 x 10²⁶ atoms of gold

• 3.1 x 10^-26 atoms of gold

Answer explanation

We need to go from grams to atoms of gold. So, we first divide by the atomic mass of gold, and then we multiply by Avogadro's Number to get atoms.

$3.7\ grams\ Au\times\frac{1\ mol\ Au}{196.967\ g\ Au}\times\frac{6.626\ x\ 10^{23}\ Au\ atoms}{1\ mol\ Au}$ = 1.1 x 10^22 Au atoms

Which total mass is the largest?

• The mass of 2 electrons

• The mass of 2 neutrons

• The mass of 1 electron plus the mass of 1 proton

• The mass of 1 neutron plus the mass of 1 electron

Answer explanation

The mass of a proton = 1 AMU. The mass of a neutron also equals 1 AMU. The proton and neutron are each 10,000 times larger than the mass of an electron.

Which of the following has the smallest ionic radius?

• P^3-

• K¹⁺

• Sc³⁺

• Ar

Answer explanation

The smallest ionic radius will have the greatest positive charge. Cations (positive ions) are smaller than anions (negative ions).

According to the mass spectrum above, the average mass of tin in this is sample is

• 219.76 amu

• 118.79 amu

• 118.00 amu

• 61.67 amu

Answer explanation

1) calculate the relative abundance for each isotope.

isotope abundance = abundance/total abundance

total abundance = sum of abundances = 27 + 58 + 100 = 185

isotope 1 = 27/185 = 0.1459

isotope 2 = 58/185 = 0.3135

isotope 3 = 100/185 = 0.5405

2) Multiply each mass by its relative abundance:

116 = isotope 1 = 0.1459*116 = 16.924

118 = isotope 2 = 0.3135*118 = 36.993

120 = isotope 3 = 0.5405*120 = 64.865

3) Add the masses together to get the WAAM (weighted average atomic mass) of the element:

WAAM = 16.924 + 36.993 + 64.865 = 118.79 amu

What information do the experimental results above reveal about the nucleus of the gold atom?

• The nucleus contains less than half the mass of the atom.

• The nucleus is small and is the densest part of the atom.

• The nucleus contains small positive and negative particles.

• The nucleus is large and occupies most of the atom’s space.

Answer explanation

Observation 1 = the atom is mostly empty space.

Observation 2 = The nucleus is positively charged like the alpha particles.

Observation 3 = The nucleus is very dense and tiny and contains most of the atom's mass.

Which of the following does not match the others?

• 
• 
• 1s²2s²2p⁵

• 

Answer explanation

A. PES Graph. e- configuration reads from left to right (count each horizontal line as 1 electron): 1s²2s²2p⁵; 9 total electrons. 7 valence.

B. Bohr Model; 9 total electrons, 7 valence and 2 core.

C. e- configuration: 1s²2s²2p⁵; 9 total electrons. 7 valence.

D. Lewis Dot Diagram (LDD). 5 valence electrons. This does not match the others.