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Flashcards in chemical_formulae Deck (30):
1

Define empirical formula.

The empirical formula is the chemical formula which represents the simplest whole number ratio of atoms in the compound.

2

Define molecular formula.

The molecular formula is the chemical formula which represents the actual formula of a compound.

3

The molecular formula of hydrogen peroxide is H2O2. What is the empirical formula?

HO is the empirical formula for hydrogen peroxide (H2O2).

4

HO is the empirical formula for hydrogen peroxide. What additional information would you need to determine the molecular formula?

Given the empirical formula (HO), one needs the molar mass to determine the molecular formula. In this case the molar mass for hydrogen peroxide is about 34 g/mol. Given the empirical formula mass is 17 g/mol and 34/17 = 2, the molecular formula is 2 x HO = H2O2.

5

The molecular formula of glucose is C6H12O6. What is the empircal formula?

CH2O is the empirical formula for glucose (C6H12O6).

6

CH2O is the empirical formula for glucose. What additional information would you need to determine the molecular formula?

Given the empirical formula (CH2O), one needs the molar mass to determine the molecular formula. In this case the molar mass for glucose is about 180 g/mol. Given the empirical formula mass is 30 g/mol and 180/30 = 6, the molecular formula is 6 x CH2O = C6H12O6.

7

The molecular formula of aspirin (acetyl salicylic acid) is C9H8O4. What is the empirical formula?

C9H8O4 is already the simplest whole number ratio and therefore this is the empirical formula.

8

What is the empirical formula for magnesium chloride?

The empirical formula for magnesium chloride is MgCl2.

In this question we are not providing data to determine the empirical formula but rather we are asking you to predict the formula based on your knowleged of the charges of magnesium (Mg2+) and chloride (Cl-). Usually we would simply ask you to provide the "formula" for magnesium chloride.

9

Explain how to distinguish between an ionic and a molecular compound.

An ionic compound usually consist of a metal cation and a non metal anion. A molecular compound consists of nonmetal atoms. An exception to this rule of thumb is when the cation is the ammonium ion (NH4+). The compound ammonium chloride (NH4Cl) is ionic even though there is no metal cation.

10

Is the compound barium sulfate BaSO4 ionic or molecular?

Barium sulfate is considered to be an ionic compound because it consists of the barium cation (Ba2+) and the polyatomic nonmetal anion sulfate (SO42-).

11

Is the compound ammonium phosphate (NH4)3PO4 ionic or molecular?

Ammonium phosphate is considered to be an ionic cmpound because it consists of the ammonium cation (NH4+) and the polyatomic nonmetal anion phosphate (PO43-). It is important to recognize the ammonium cation as one of the few cations which are not derived from metals.

12

When is it necessary to use a roman numeral in naming a compound?

A roman numeral is used for an ionic compound when the metal cation can have multiple charges (Fe2+ and Fe3+ for example). The roman numberal indicates the charge.

Essentially all transition elements can have multiple charges - with the exception of Zn2+, Cd2+ and Ag+ (actually strictly speaking Zn and Cd are not considered to be transition elements - but this is not an important detail for this course). Other elements that can have multiple charges, which you need to know, are lead (Pb2+ and Pb4+) and tin (Sn2+ and Sn4+).

13

When is it necessary to use a greek prefix in naming a compond?

A greek prefix is usually used in naming a binary molecular compound. This is because the nonmetals in such compounds can be combined in multiple ratios which are not predictable as with ionic compounds. The greek prefixes are required to indicate how many of each atom in a compound.

As an example the following two compounds (NO and N2O) are called nitrogen monoxide and dinitrogen monoxide. Note that if there is only one atom of the first element, the prefix "mono" is not used. Greek prefixes are also used in the naming of some polyatomic ions. For example H2PO4- is called dihydrogen phosphate.

14

What is a hydrate?

Most ionic compounds exist naturally as hydrates. That is the ionic crystals absorb water from the atmosphere in definite molar proportions.

For example sodium thiosulfate in its natural state has 5 moles of H2O molecules per 1 formula unit of Na2S2O3. The formula is normally written as Na2S2O3 • 5H2O and is called sodium thihosulfate pentahydrate. The water molecules are loosely bound and can be temrporarily removed by heating (with a bunsen burner for example). If the compound is no longer heated and if the compound is in contact with the atmosphere, it will once again adsorb back the water in the appropriate proportions.

15

Give the name for the following compound and indicate if it is ionic or molecular: Ag2SO3

Silver sulfite (ionic)

16

Give the name for the following compound and indicate if it is ionic or molecular: K3PO4

Potassium phosphate (ionic)

17

Give the name for the following compound and indicate if it is ionic or molecular: CoBr2

Cobalt (II) bromide (ionic)

18

Give the name for the following compound and indicate if it is ionic or molecular: NBr3

Nitrogen tribromide (molecular)

19

Give the name for the following compound and indicate if it is ionic or molecular: NaCN

Sodium cyanide (ionic)

20

Give the name for the following compound and indicate if it is ionic or molecular: FeSO4

Iron (II) sulfate

21

Give the name for the following compound and indicate if it is ionic or molecular: ICl3

Iodine trichloride (molecular)

22

Give the name for the following compound and indicate if it is ionic or molecular: KMnO4

Potassium permanganate (ionic and note that the polyatomic anion has a metal + oxygen)

23

Give the name for the following compound and indicate if it is ionic or molecular: Na2Cr2O7

Sodium dichromate (ionic and note that the polyatomic anion has a metal + oxygen)

24

Give the name for the following compound and indicate if it is ionic or molecular: Hg2S

Mercury (I) sulfide (ionic)

25

Give the name for the following compound and indicate if it is ionic or molecular: Zn(NO3)2

Zinc nitrate (ionic)

26

Give the name for the following compound and indicate if it is ionic or molecular: Ba(NO2)2

Barium nitrite (ionic)

27

Give the name for the following compound and indicate if it is ionic or molecular: P2O5

Diphosphorus pentaoxide (molecular)

28

Give the name for the following compound and indicate if it is ionic or molecular: MgI2

Magnesium iodide (ionic)

29

Give the name for the following compound and indicate if it is ionic or molecular: FeCl3 • 6H20

Iron (III) chloride hexahydrate (ionic)

30

Give the name for the following compound and indicate if it is ionic or molecular: NH3

nitrogen trihydride - commonly known as ammonia (molecular)