1. What is the formula for the binary ionic compound of magnesium and fluorine?
Mg is in group 2, thus has 2 valence electrons, therefore has greater tendency to give these 2
electrons to become more stable. While F is in group 7, meaning has 7 valence electrons and
therefore has greater tendency to attract only one electron to achieve the most stable form.
(Remember the octet rule). Therefore Mg forms ionic bond to Fluorine in ratio of 1:2, this means
that one magnesium forms ionic bond with 2 fluorine. Why 2 fluorine, because Mg donates 2
electrons, however F needs only one, therefor one Mg can donate electrons to 2 Fluorine.
So the answer is MgF2
A. MgF
B. Mg2F
C. MgF2
D. Mg2F3
E. Mg3F2
2. The atomic number of the element radium is 88. How many neutrons does
radium-226 have?
Answer: Atomic number of protons. In this case the number of protons are 88, while the mass
number of radium is 226. The mass number is the sum of the number protons and neutrons.
Thus the number of neutrons= 226-88=138
D is the answer
A. 88
B. 98
C. 116
D. 138
E. 226
3. What is the empirical formula for the ionic compound containing cobalt(III)
and dichromate ions?
Dichromate ions, Cr2O7, charge of -2, you agree, right? While Cobalt has +3, which is
given by (III). Now why is +3? Because Co would like to give electrons to become
stable. And why give electrons? Because it is 5 electrons away to become stable by
gaining electron, while 3 electrons away to become stable by giving electrons,
therefore the easiest way is to give.
You have Co3+ and (Cr2O7)2-, to balance them, you need 2 Co and 3 of (Cr2O7)2-, to get a
+6 and -6 respectively, which gives you a charge of zero.
The answer is A. Co2(Cr2O7)3
A. Co2(Cr2O7)3
B. CoCr2O7
C. Co2(CrO4)3
D. CoCrO4
E. Co(CrO4)3
4. What is the empirical formula for the compound C 14H8O2?
Empirical formula is the arrangement of the elements in a compound as a whole number in
the smallest ratio possible. To get the smallest ratio you divide by 2 here. You get
The answer is E. C7H4O
A. C14H8O2
B. CHO
C. C7H4O2
D. C8H4O
E. C7H4O
5. Which solution of the equation x = (74.9786 - 12.867) × (0.044904 ÷ 3.5634)
shows the appropriate number of significant figures?
(74.9786 - 12.867)= 62.1116
(0.044904 ÷ 3.5634)=0.01260144806
X=0.01260144806 x 62.1116= 0.78256961013, but we need to quote it, having the same number significant
figure as the least precise value, 62.1116, 6 significant figures. The answer is B.
B. x = 0.78270
By the way zero after 7 is as a result of rounding of 9 after 6 in the original answer.
A. x = 0.7826961
B. x = 0.78270
C. x = 0.783
D. x = 0.78
E. x = 0.8
6. Water is an example of which of the following:
The answer is C. Water itself is a compound.
A. heterogeneous mixture
B. homogeneous mixture
C. element
D. compound
E. ion
Don’t know this Number
7. 53.96 g of solid aluminum reacts completely with 479.42 g of liquid diatomic
bromine to form only solid aluminum bromide. What is the balanced chemical
equation for this reaction?
But, the answer would be B
A. Al (s) + Br2 (g) → 2AlBr3 (s)
B. 2 Al (s) + 3 Br2 (l) → 2AlBr3 (s)
C. 53.96 Al (s) + 761.4 Br2 (l) → Al2Br6 (s)
D. 6 Al (s) + 2 Br (l) → 2AlBr3 (s)
E. 2 Al (s) + 3 Br (l) → 2AlBr3 (s)
8. 53.96 g of solid aluminum reacts completely with 479.42 g of liquid diatomic
bromine to form only solid aluminum bromide. What is the mass of solid
aluminum bromide formed in the reaction?
I can not solve this because I don’t know the first number brother. If you know the number, here
is what to do. Find the number of moles of solid Aluminium and mono atomic Broimine, not
diatomic. Then use the Balanced equation to find the limiting reagent. Then calculate the number
of moles of solid aluminum bromide.
OR you can just calculate molar mass of solid aluminum bromide and multiply with 3. This is
from the balanced equation above.
A. 54.0 g
B. 425.5 g
C. 479.4 g
D. 533.4 g
E. 587.4 g
9. Which of the following is not one of the postulates of Dalton’s atomic theory?
C is the answer, not all atoms contain equal numbers of Protons and Neutrons. I think you know
this one.
A. Atoms are small, indivisible particles.
B. Atoms cannot be created nor destroyed.
C. All atoms contain equal numbers of protons and neutrons.
D. All the atoms of an element are identical in mass and in other properties.
E. Atoms combine in whole number ratios.
10. Which of the following differs between the isotopes of an element?
An isotopes of an element has different number of neutrons, but same protons. Therefore they
have different mass Number. The answer is D.
A. Atomic number
B. Number of electrons
C. Number of protons
D. Mass number
E. The mass of the proton