Compounds

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AP Chemistry › Compounds

Questions 1 - 10
1

Which of the following is the correct name of ?

Dinitrogen tetraoxide

Dinitrogen monoxide

Nitrogen monoxide

Nitrogen dioxide

Dinitrogen pentoxide

Explanation

In order to answer the question, it is important to first determine what kind of bonding is occurring in order to properly name the molecule. When nitrogen and oxygen form an molecule, electrons are shared between the atoms, so a covalent bond is formed.

Because a covalent bond is formed, we can determine that name of the molecule will be based on number of each atom in the molecule. There are two nitrogen atoms in the resulting molecule, so the prefix in front of the "nitrogen" part of the name will be "di-," meaning two. There are four oxygen atoms in the resulting molecule, so the prefix in front of the "oxygen" part of the name will be "tetra," meaning four.

The molecules names will be arranged alphabetically, and the second atom will have "-ide" as the suffix. Therefore, the correct answer is "dinitrogen tetroxide."

2

What is the oxidation state of manganese () in the polyatomic permanganate anion ()?

Explanation

When assigning oxidation states to elements of a given compound, non-transition metal elements are assigned specific oxidation states corresponding to their group number and valence relative to a complete octet.

Group 1 elements have 1 valence electron and an oxidation state of +1.

Group 2 elements have 2 valence electrons and an oxidation state of +2.

Group 8 elements (the noble gases) have a complete octet, thus their assigned oxidation state is 0.

Group 7 elements (halogens) have 7 valence electrons and an oxidation state of -1.

Group 6 elements such as oxygen have 6 valence electrons and an oxidation state of -2.

Permanganate has 4 oxygen atoms and an overall charge of -1. The oxidation state of the atom may be found by first calculating the combined oxidation state of the oxygen atoms:

and finding the difference between their combined oxidation state and the overall charge of the ion (-1):

3

What is the oxidation state of manganese () in the polyatomic permanganate anion ()?

Explanation

When assigning oxidation states to elements of a given compound, non-transition metal elements are assigned specific oxidation states corresponding to their group number and valence relative to a complete octet.

Group 1 elements have 1 valence electron and an oxidation state of +1.

Group 2 elements have 2 valence electrons and an oxidation state of +2.

Group 8 elements (the noble gases) have a complete octet, thus their assigned oxidation state is 0.

Group 7 elements (halogens) have 7 valence electrons and an oxidation state of -1.

Group 6 elements such as oxygen have 6 valence electrons and an oxidation state of -2.

Permanganate has 4 oxygen atoms and an overall charge of -1. The oxidation state of the atom may be found by first calculating the combined oxidation state of the oxygen atoms:

and finding the difference between their combined oxidation state and the overall charge of the ion (-1):

4

What is the formula for the compound formed from calcium and sulfate ions?

Explanation

In order to answer this question correctly, it is important to have knowledge of the formation of ionic bonds, polyatomic ions, and the periodic table. First, it is important to notice that calcium ions and sulfate ions will form an ionic bond. Knowing this, it can be understood that valance electrons will be exchanged between the ions and therefore, oppositely charged ions that are attracted to each other will be formed.

Calcium is in the second column of the periodic table, so it will provide two ions to the sulfate polyatomic ion. This will form a calcium cation () and a sulfate polyatomic anion ().

One calcium ion provides two electrons, which are both accepted by a sulfate polyatomic ion, so the ratio of calcium ions used to sulfate polyatomic ions used is 1:1. This means that only one of each ion is needed to form the compound, making the formula .

Initially it may be tempting to write the formula as ; however, since both ions have a "2" subscript in this form, it is redundant to the formula in this way. Only one of each ion is needed to form the compound.

5

All of the following are properties of zinc. Which of the following are chemical properties of zinc?

A. Zinc produces hydrogen gas when placed in acid.

B. Zinc melts at .

C. The density of zinc is .

D. Zinc is a grey metal.

E. Zinc corrodes in moist air.

A and E

C

B

A, C, and E

B and C

Explanation

Physical properties are aspects of matter that can be observed and measured without changing it. Chemical properties measure the potential for undergoing a chemical change. How zinc reacts to acid and in moist air are both chemical properties because the zinc is undergoing chemical change in each environment. The color, density, and melting point of the zinc can all be observed without changing the nature of the matter, so these are physical properties of zinc.

6

Which of the following are strong electrolytes?

Three

One

Two

Four

All five

Explanation

Strong electrolytes are substances that exists in solutions as only ions. These substances dissociate 100% in solutions. Strong acids, strong bases, and salts are all examples of strong electrolytes. is a strong acid. is a salt. is a salt. is a weak acid. is a weak base. Therefore the answer is three.

7

Calculate the percent by mass of each element in .

Explanation

The total molar mass of lead (II) sulfate is . Lead contributes , sulfur contributes , and oxygen contributes .

The percent by mass of each element in the compound is found by dividing the mass contribution of that element by the total molar mass of the compound.

8

Calculate the percent by mass of each element in .

Explanation

The total molar mass of lead (II) sulfate is . Lead contributes , sulfur contributes , and oxygen contributes .

The percent by mass of each element in the compound is found by dividing the mass contribution of that element by the total molar mass of the compound.

9

What is the percent by mass of bismuth in the compound ?

Explanation

The mass percentage of bismuth in the compound will be equal to the mass of bismuth in one mole of compound divided by the total molar mass of the compound.

Bismuth has a molar mass of . One mole of the compound would result in two moles of bismuth, a total of 417.96g.

Tellurium has a molar mass of . One mole of the compound would result in three moles of tellurium, a total of 382.8g.

Add the mass of bismuth and the mass of tellurium per mole to find the total molar mass.

Divide the mass of bismuth by the total molecular mass to find the percent by mass of bismuth in the compound.

10

Calculate the percent by mass of each element in .

Explanation

The total mass of one mole of aluminum (II) chromate is calculated by:

Aluminum, chromate, and oxygen contribute and respectively. Therefore, we can divide each contribution by the total molecular mass to determine percentages by mass.

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