Chem 1000A Midterm
Oct 18th, 2002: 8:00 to 8:50 am
Your name _______________
Instructor: Dr. M. Gerken
Student ID _______________
Time: 50 min
No. of pages: 4
Report all your anwers using significant figures.
Question 1 (4 Marks)
Give the formula for each of the following ionic compounds:
(a) nickel(II) sulfate
___NiSO4_________________________________
(b) calcium chlorite
___Ca(ClO2)_______________________________
(c) calcium chloride
___CaCl2__________________________________
(d) ammonium perchlorate
____NH4ClO4______________________________
Question 2 (6 Marks)
Complete the following table.
187
16
Os
O2-
Number of electrons
__76_______
___10______
Number of neutrons
__111______
___8_______
Number of protons
__76_______
___8_______
Question 3 (4 Marks)
Diamonds consist of pure carbon. The largest diamond ever found is the Cullinan, which
had 3106 carat (1 carat is exactly(!) 0.2 g). How many moles of C were in the Cullinan?
3106 carat × 0.2 g/1 carat = 621.2 g
621.2 g/ (12.0107 g mol-1) = 51.72 mol
51.72 mol of carbon was in the Cullinan.
1
Question 4 (10 Marks)
(a) Give the electron configuration of Cr in the spectroscopic notation and orbital box
notation (include all electrons).
Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
↑↓
↑↓
↑↓ ↑↓ ↑↓
↑↓
1s
2s
2p
3s
↑↓ ↑↓ ↑↓
3p
↑
4s
↑ ↑ ↑ ↑ ↑
3d
(b) How many unpaired electrons are present in the Cr atom?
Six unpaired electrons.
(c) Is Cr paramagnetic and diamagnetic? Explain your answer.
Cr is paramagnetic since it has unpaired electrons.
(d) Give the electron configuration for Cr3+ in the orbital box notation (include all
electrons).
Cr3+:
↑↓
↑↓
1s
2s
↑↓ ↑↓ ↑↓
2p
↑↓
3s
↑↓ ↑↓ ↑↓
3p
2
4s
↑ ↑ ↑
3d
Name _________________________
Student ID _________________
Question 5 (8 Marks)
A gas with a molar mass of 146.0564 g mol-1 that is used as an electrical insulator for
high-voltage installations is composed of 22.0 % S and 78.0 % F.
(a) What is its empirical formula?
100 g of the gas contains: 22.0 g S, 78.0 g F
moles S: n(S) = 22.0 g S / (32.065 g S/ mol S) = 0.686 mol S
moles F: n(F) = 78.0 g F / (18.984032 g F/ mol F) = 4.11 mol F
n(S) : n(F)= 0.686 : 4.11= 1 : 5.99
≈1:6
empirical formula: SF6
The empirical formula of the sulfur fluoride gas is SF6.
(b) What is its molecular formula?
molar mass of SF6: M(SF6) = 146.0564 g mol-1
experimental molar mass of nicotine: M(gas) = 146.0564 g mol-1
molecular formula: SF6
The molecular formula of the sulfur fluoride gas is SF6.
(c) Draw the Lewis structure of this sulfur fluoride.
Structure is given on page 396 in your textbook.
Question 6 (2 Marks)
Which equation is deBroglie’s equation?
(a) E = hν
(b) HΨ = EΨ
(c) λ = h / (mv)
(c) is deBroglie’s equation
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Question 7 (6 Marks)
A sample of an unidentified element was determined to be composed of only two
isotopes, one of which had an exact atomic mass of 150.919847 amu and was found to be
47.8% abundant, the other 152.921225 amu and 52.2% abundant.
(a) Determine the average atomic mass of the unknown element.
150.919847 amu × 0.478 + 152.921225 amu × 0.522 = 72.1 amu + 79.8 amu
= 151.9 amu
The element has an average atomic mass of 151.9 amu.
(b) Do you think the unknown element is a known element? If yes, identify the element
that you think it is.
The element is Eu (europium) since europium has an atomic mass of 151.964 amu.
h = 6.626 × 10-34 Js
c = 2.997 × 108 ms-1
Rydberg’s constant = 1.097 × 107 m-1
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NA = 6.022 × 1023 mol-1