1 AP WORKSHEET 01a: Elements, Mixtures & Compounds 1. Classify each of the following as either, an element, a compound or a mixture. If you classify something as a mixture then also state whether it is a homogeneous or a heterogeneous mixture. (10) (a) Helium (b) Nitrogen (c) Pure water (d) Pure table salt (sodium chloride) (e) Flat (un-carbonated) Coca-Cola (f) Air (g) Fruit cake 2. If three, different samples of a particular compound are found to have exactly the same elemental % by mass, what does that tell us about; (a) the three samples in relation to one another? (2) (b) the purity of the three samples? (2) 3. Visit the following URL: http://www.darvill.clara.net/multichoice/emc.htm and answer the question found there. (11)
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AP WORKSHEET 01a: Elements, Mixtures & Compounds
1. Classify each of the following as either, an element, a compound or a mixture. If you classify
something as a mixture then also state whether it is a homogeneous or a heterogeneous mixture.
(10)
(a) Helium
(b) Nitrogen
(c) Pure water
(d) Pure table salt (sodium chloride)
(e) Flat (un-carbonated) Coca-Cola
(f) Air
(g) Fruit cake
2. If three, different samples of a particular compound are found to have exactly the same elemental %
by mass, what does that tell us about;
(a) the three samples in relation to one another? (2)
(b) the purity of the three samples? (2)
3. Visit the following URL: http://www.darvill.clara.net/multichoice/emc.htm and answer the question
4. Match the following particulate diagrams to the correct description. In each case a black circle and a
red circle represent the atoms of different elements. (4)
1 2 3 4 5A. A single, pure, monatomic element.
B. A mixture of two elements.
C. A single, pure compound.
D. A mixture of two compounds.
E. A mixture of an element and a compound.
1
AP WORKSHEET 01b: Empirical Formula
1. A common oxide of nitrogen contains 25.93% N. Deduce the empirical formula of the oxide.(2)
2. A compound that is usually used as a fertilizer can also be used as a powerful explosive. Thecompound has the composition 35.00% nitrogen, 59.96% oxygen and the remainder beinghydrogen. What is its empirical formula? Given it is ionic, suggest a name for the compound.(3)
3. What are the empirical formulae for these compounds, that both contain five carbon atoms?(2)
(a) C5H10
(b) C5H12
4. A substance has an empirical formula of CH2Br and a molar mass of 188 g mol-1
. What is themolecular formula of the compound? (1)
2
5. The common pain medicine, Advil, contains the active ingredient Ibuprofen that has a molarmass of 206 g mol
-1. Ibuprofen contains 75.73% C, 8.74% H, the remainder being oxygen.
What are the empirical and molecular formulae for Ibuprofen? (4)
6. The molar mass of the common antibiotic oxytetracycline is found to be 460 g mol-1
and a2.000 g sample contains 1.1478 g of carbon, 0.10435 g of H, 0.62609 g of oxygen and theremainder being nitrogen. What is the molecular formula of the oxytetracycline? (4)
1
AP WORKSHEET 01c: Isotopes and Mass Spectrometry
1. Many elements have a number of isotopes.
(a) Define the term isotope. (2)
(b) Complete the following table. (22)
Row Isotope symbol Atomic # # Protons # Neutrons Mass #
1 13
C6
2 17 18
3 26 56
4 17 37
5 2 3
6 52 128
7 50 70
(c) Consider the 2nd
and 4th
row in the table. What three things do they have in common?
(3)
(d) Consider the 2nd
and 4th
row in the table. Give two differences? (2)
(e) Naturally occurring Ni is found to have the following approximate isotopic abundance;
58Ni 68%,
60Ni 26%,
62Ni 4.0% and
61Ni 2.0%
Calculate the average relative atomic mass of Ni to two decimal places. (2)
2
2. The results taken from a mass spectrum of chlorine gas show peaks at m/z 35.00 and m/z
37.00 (The m/z peaks on a mass spectrum identify the different isotopes of an element that
are present in the sample).
(a) Given that the relative abundances of Cl 35.00 and Cl 37.00 are 77.50% and 22.50%
respectively, calculate the average relative atomic mass of chlorine atoms to four
significant figures. (2)
(b) Suggest all the possible masses of CI2 molecules that are made when two chlorine
atoms bond together. (3)
(c) Which of the molecules you have suggested in (b) will be the most abundant? Explain
your answer. (2)
3
3. Naturally occurring bromine molecules, Br2 have masses of 158, 160 and 162. They occur in
the relative abundances 25.69%, 49.99% and 24.31% respectively. What is the average
atomic mass of bromine atoms? What is the relative abundance of 79
Br and 81
Br isotopes? (4)
4. An unknown element ‘Z’ is analyzed in a mass spectrometer and is found to have the
following isotopes with the corresponding relative abundances.
Isotope Z50
Z52
Z53
Z54
Relative
abundance 4.34 83.79 9.50 2.37
(a) Using the axis below, sketch the expected mass spectrum that these data would
provide. Label the axes and pay attention to the size of any lines that you draw. (4)
(b) Calculate the average atomic mass of Z and identify the element. (3)
4
5. Consider the following mass spectrum that was generated from the analysis of an element.
Rela
tive
Ab
un
da
nce
m/z
24 25 26 27 2928
100
(a) What does the existence of only a single peak in the spectrum suggest about the
element?
(b) Identify the element.
6. Copper has an atomic mass of 63.5456 amu and has two stable isotopes. Copper-63 has a
mass of 62.9296 amu, and copper-65 has a mass of 64.9278 amu.
(a) Calculate the percent abundance of each isotope of copper.
(b) Sketch the expected mass spectrum of the copper.
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AP WORKSHEET 01d: Quantitative aspects of electrons
1. This question is about breaking covalent bonds.
(a) The bond energies of the single bonds between two chlorine atoms within a chlorine molecule
and two fluorine atoms within a fluorine molecule are calculated to be 4.02 x 10-19
J and 2.64 x
10-19
J respectively. For each bond, calculate the following;
(i) The frequency of a photon that could be used to break the bond. (2)
(ii) The wavelength of each photon in (i). (2)
(b) When an excited electron falls back to its ground state, what can be said of the energy change
that occurs when compared to the energy change of the original, promotion process? Explain.
(2)
2. Lithium ions give a distinctive red flame test. In one such experiment the energy of this red light is
found to have an energy of 3.06 x 10-19
J. Calculate the wavelength of the light from the lithium ions in
nm. (2)
3. Which of the following process will release the greatest amount of energy? Explain your answer. (2)
Promoting an electron from n = 1 to n = 6
Promoting an electron from n = 1 to n = 4
An electron falling from n = 6 to n = 2
An electron falling from n = 6 to n = 5
4. When an electron falls from n = 5 to its lowest possible state in the Lyman series, the energy that is
released is greater than the energy that is released when an electron falls from n = 5 to its lowest
possible state in the Balmer series. Explain. (2)
5. Electron transitions are expected to absorb or emit greater magnitudes of energy in the He+ ion
than in the hydrogen atom. Why? (2)
Page 1 of 2
AP WORKSHEET 01e: Orbital filling rules
The rules that you have been applying in order to determine the electronic configuration of an atom are summarized below.
A. Lowest energy orbitals are filled first. THE AUFBAU PRINCIPLE.
B. Orbitals can only contain a maximum of two electrons and when two electrons enter the same orbital they must have opposite spins (+ ½
or – ½) so that each electron has a unique set of quantum numbers. (In the electrons in boxes diagram they must be drawn NOT
OR ). THE PAULI EXCLUSION PRINCIPLE.
C. When orbitals of identical energy (degenerate) are available electrons enter these orbitals singly before any spin pairing takes place. HUNDS RULE.
Consider each of the elements listed and the INCORRECT electronic configuration associated with each one. In each case identify which of the above rules or principles (A, B or C) is violated and insert the correct electronic configuration (in a similar format to that of the incorrect configuration). Then add a possible set of quantum numbers for the outer most electron. An example is completed for you. (34)
Page 2 of 2
ELEMENT INCORRECT
CONFIGURATION VIOLATION
CORRECT CONFIGURATION
N 1s2 2s2 2px2 2py1 C 1s2 2s2 2px1 2py1 2pz1
Al 1s2 2s
2 2p
6 3p
3
B 1s2 2s
3
P 1s2 2s
2 2p
6 3p
5
Mg [Ne]
C 1s2 2s
1 2px
1 2py
1 2pz
1
C 1s2 2s
2 2px
2
Mn [Ar] 4s1 3d
6
Ni [Ar] 4s2 3dxy
2 3dxz
2 3dyz
2 3dz2
2 3dx2-y2
0
Cl [Ne]
Sc [Ar] 3d3
B 1s2 2s
1 2px
1 2py
1
Na 1s1 2s
2 2p
6 3s
2
S [Ne] 3s2 3px
2 3py
2
V [Ar] 3d5
P [Ne] 3s2 3px
2 3py
1
Kr [Ar] 4s2 3d
16
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AP WORKSHEET 01f: Electronic Configuration Summary
1. Give full and abbreviated (noble gas core method) electronic configurations for the following.
(8)
(a) Br FULL ______________________________
NOBLE GAS CORE ______________________________
(b) Cr FULL ______________________________
NOBLE GAS CORE ______________________________
(c) Fe FULL ______________________________
NOBLE GAS CORE ______________________________
(d) S2-
FULL ______________________________
NOBLE GAS CORE ______________________________
2. For each of the following sets of orbitals, indicate which orbital is higher in energy. (4)
(a) 1s, 2s _________
(b) 2p, 3p _________
(c) 4s, 3dyz _________
(d) 3px, 3py, 3pz _________
3. Indicate the block (s, p or d) in which each of the following elements found. (5)
BLOCK
(a) Sc ______
(b) P ______
2
(c) Fr ______
(d) Ni ______
(e) As ______
4. An atom has two electrons with principal quantum number (n) = 1, eight electrons with
principal quantum number (n) = 2 and seven electrons with principal quantum number (n) = 3.
From these data, supply the following values (if insufficient information is given, say so).
(a) The mass number. (2) _________
(b) The atomic number. (1) _________
(c) The electron configuration. (2) ___________________________
5. Identify the element from the electron configurations of atoms shown below. (3)
(a) [Ne] 3s2 3p
2_________
(b) [Ar] 4s2 3d
7_________
(c) [Xe] 6s2
_________
6. Give the symbol of the atom or ion represented by the following sets of atomic numbers and
electronic configurations. (4)
Atomic # Electronic Configuration Symbol of Atom or Ion
(a) 8 1s2 2s
2 2p
4________
(b) 11 1s2 2s
2 2p
6________
(c) 14 1s2 2s
2 2p
6 3s
2 3p
2________
(d) 22 1s2 2s
2 2p
6 3s
2 3p
6 3d
2________
3
7. Give the electron configurations for the following transition metal ions. (3)
(a) Sc3+
__________________________________
(b) Cr2+
__________________________________
(c) Ni3+
__________________________________
8. Consider the element Scandium, atomic # 21.
(a) If the electronic configuration of the element were constructed "from scratch", into which
orbital (and into which shell) would the final electron be placed? (1) _________
(b) When scandium forms an ion with a charge of +1, from which orbital (and from which
shell) would the electron be removed? (1) _________