Chapter 7 Review Questions

How do you find the molecular formula from the empirical formula of a compound?

1. Calculate the mass of the empirical formula. 2. Divide the molar mass of the compound by the empirical formula mass. 3. Round the value to the nearest whole number and multiply the value by the empirical formula.

What is the mass in grams of 3.25 mol Fe₂(SO₄)₃?

1.30 x 10^3 g

How many moles of atoms of each element are there in one mole of (NH₄)₂CO₃?

2 mol N, 8 mol H, 1 mol C, and 3 mol O

Calculate the percentage composition of (NH₄)₂CO₃.

29.15% N, 8.407% H, 12.50% C, 49.94% O

How many molecule of aspirin, C₉H₈O₄, are there in a 100.0 mg tablet of aspirin?

3.342 x 10^20 molecules

What is the significance of a chemical formula?

A chemical formula can be used to identify information regarding a compound such as the relative number of atoms of each kind.

How does the chemical formula for the nitrite ion differ from the chemical formula for the the nitrate ion?

A nitrite ion has one less oxygen atom, (nitrite= NO−₂ and nitrate= NO-₃)

What is a salt?

An ionic compound composed of a cations and the anion from an acid.

Determine both formula mass and molar mass of ammonium carbonate (NH₄)₂CO₃.

Formula mass: 96.09 g/mol Molar mass: 96.09 g/mol

What are monatomic ions?

Ions formed from a single atom

What useful functions do oxidation numbers serve?

Oxidation numbers are useful in naming compounds, in writing formulas and in balancing equations.

Give two examples of salts.

Sodium chloride (NaCl) and Sodium bicarbonate (NaHCO₃)

What is meant by the Percentage composition of Compounds?

The % by mass of each element in a compound = (number of atoms x atomic mass / Molecular Mass of compound) x 100

How are molar mass and molecular mass different?

The difference between molecular weight and molar mass is molecular weight is in atomic mass units (amu) because it's the mass of one molecule and molar mass is grams per mole (g/mol) because it's the mass of a mole of molecules.

In what unit is formula mass expressed?

g/mol

What equation represents the relationship between empirical formula mass and molecular formula mass?

x(empirical formula mass)= molecular formula mass

What three types of information are used to find empirical formula from percentage composition data?

1. Percentage composition (percentage of each element within the compound) 2. Mass composition (mass of each element in 100 g) 3. Composition by moles

What are the steps to finding the empirical formula of a compound when you are given the sample mass and the mass of one of two elements within the compound?

1. Subtract the mass of the element given from the sample mass-- this will give you the mass of both elements within the sample mass of the compound. 2. Multiply the mass elements mass within the compound by (1 mol of the substance/ the molar mass of the element). 3. Calculate the moles of each element and divide each value by the smallest number within the values.

What are oxidation numbers?

The number of electrons that must be added to or removed from an atom in a combined state to convert the atom into the elemental form

Name each of the following ions according to the Stock system: a. Fe2+ b. Fe3+ c. Pb2+ d. Pb2+ e. Pb4+ f. Sn2+ g. Sn4+

a. Fe(II) b. Fe(III) c. Pb(II) d. Pb(II) e. Pb(IV) f. Sn(II) g. Sn(IV)

Name each of the following acids: a. HF b. HBr c. HNO₃ d. H₂SO₄ e. H₃PO₄

a. Hydrofluoric acid b. Hydrobromic acid c. Nitric acid d. Sulfuric acid e. Phosphoric acid

Using only the periodic table, write the symbol of the ion most typically formed by each of the following elements: a. K b. Ca c. S d. Cl e. Ba f. Br

a. K+ b. Ca2+ c. S2- d. Cl- e. Ba2+ f. Br-

What is the molecular formula of a compound of phosphorus and oxygen whose empirical formula is P₂O₅ with a molar mass of 283.89 g/mol?

empirical formula mass = 141.94 amu molecular molar mass = 283.89 g/mol molecular formula mass = 283.89 amu x= (283.89 amu/141.94 amu) = 2.0001 --> 2 2 x (P₂O₅)= P₄O₁₀

What equation represents the relationship between the empirical formula and the molecular formula of a compound?

x(empirical formula)= molecular formula x= the factor by which the subscripts in the empirical formula must be multiplied to obtain the molecular formula

What is the significance of molar mass?

Molar mass is used as a conversion factor between amount in moles and mass in grams of a given compound or element.

Determine the oxidation numbers for iron oxide, Fe₃O₄, (recall that oxidation numbers are integers).

Oxygen is -2, one of the iron atoms is +2 and the remaining two iron atoms are +3

What are the steps to finding the empirical formula of a compound when you are given percent composition?

Steps: 1. Convert each percentage comp. into samples of 100 grams (just ignore % sign) 2. Multiply the elements in (g) by (1 mol of the substance/ the molar mass of the element) 3. Calculate the moles of each element and divide each value by the smallest number within the values.

Draw the Lewis structure, give the name, and predict the VSEPR geometry of SCl₂

Sulfur dichloride, bent or angular, and see picture for Lewis diagram and VSEPR geometry

What is the difference between molar mass and formula mass?

The difference between formula mass and molar mass is that, the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula while molar mass is the mass in grams of 1 mol of substance.

Assign oxidation numbers to each atom in the following compounds or ions: a. HF b. CI₄ c. H₂O d. PI₃ e. CS₂ f. Na₂O₂ g. H₂CO₃ h. NO-₂ i. SO2-₄

a. +1, -1 b. +4, -1 c. +1, -2 d. +3, -1 e. +4, -2 f. +1, -1 g. +1, +4, -2 h. +3, -2 i. +6, -2

Write the correct formula and give the names of the compounds formed by the following ions: a. Cr2+ and F1- b. Ni2+ and O2- c. Fe3+ and O2-

a. Chromium fluoride b. Nickel oxide c. Iron (III) oxide

Give three examples of monatomic ions?

Oxide (O2-) and Lithium (Li+)

Give the molecular formulas for each of the following acids: a. Sulfurous acid b. Chloric acid c. Hydrochloric acid d. Hypochlorous acid e. Perchloric acid f. Carbonic acid g. Acetic acid

a. H₂SO₃ b. HClO₃ c. HCl d. HClO e. HClO₄ f. H₂CO₃ g. CH₃COOH

What are the rules of assigning oxidation numbers?

1. The atoms in pure elements have an oxidation number of zero. i.e. Na, O₂, P₄ and S₈ 2. The more electronegative element in a binary molecule compound is assigned the number go the positive charge it would have as a cation. 3. Fluorine has an oxidation number of −1 in all of its compounds because it is the most electronegative element. 4. Oxygen has an oxidation number of −2 in almost all compounds. Exceptions include when it is in peroxides, such as H₂O₂, in which its oxidation number is −1, and when it is in compounds with halogens, such as OF₂, in which its oxidation number is +2. 5. Hydrogen has an oxidation number of +1 in all compounds containing elements that are more-electronegative than it; it has an oxidation number of −1 in compounds with metals. 6. The algebraic sum of the oxidation numbers of all atoms in a neutral compound is equal to zero. 7. The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion. 8. Although rules 1 through 7 apply to covalently bonded atoms, oxidation numbers can also be assigned to atoms in ionic compounds.

Find the empirical formula of a compound with a sample mass of 10.150 g, which is known to contain only phosphorus and oxygen and has a phosphorus content of 4.433 g.

10.150 g - 4.433 g = 5.717 g phosphorus = 4.433 g oxygen = 5.717 g 4.433 g x (1 mol P/ 30.97 g) = 0.1431 mol P 5.717 g x (1 mol O/ 16 g) = 0.3573 mol O 0.1431 mol P / 0.1431 = 1 mol P 0.3573 mol O/ 0.1431 = 2.497 mol O P₂O₅

A sample of hydrated copper (II) sulfate (CuSO₄ x ___H₂O) is heated to 150 degree C and produces 103.74g anhydrous copper (II) sulfate and 58.55g water. How many moles of water molecules are present in 1.0 mol of hydrated copper(II) sulfate?

Molar Mass of H2O = 18g 1. Divide the amount of anhydrous copper sulfate by its molar mass: 103.74/159.61 = 0.649 2. Divide the amount of water by its molar mass: 58.55/18 = 3.25 3. Divide the number of moles of water present (3.25) by the number of moles of copper sulfate present (0.649): 3.25/.649 = 5

How does a empirical formula differ from a molecular formula?

The empirical formula of a compound represents the simplest ratio of elements to one another while a molecular formula represents the actual formula of a compound.

Name the following binary molecular compounds by using the Stock system: a. Carbon tetrabromide b. Sulfur dioxide c. Phosphorus pentabromide d. Iodine trichloride e. Nitrogen triiodide f. Dinitrogen trioxide

a. Carbon (IV) bromide b. Sulfur (II) oxide c. Phosphorus (V) bromide d. Iodine (III) chloride e. Nitrogen (III) iodide f. Nitrogen (III) oxide

Determine the number of moles of each type of monatomic or polyatomic ion in one mole of the following compounds. For each polyatomic ion, determine the number of moles of each atom present in one mole of the ion. a. KNO₃ b. Na₂SO₄ c. Ca(OH)₂ d. (NH₄)₂SO₄

a. K= 1, NO₃= 1, N=1, O=3 b. Na+= 2, SO₄= 1, S= 1, O=4 c. Ca2+= 1, OH-= 2, O= 2, H= 2 d. NH₄+= 2, N= 2, H= 8, SO₃2-= 1, S= 1, O= 3

Write the formula for and indicate the charge on each of the following ions: a. Sodium ion b. Aluminium ion c. Chloride ion d. Nitride ion e. Iron (II) ion f. Iron (III) ion

a. Na+, +1 b. Al3+, 3+ c. Cl-, -1 d. N-3, -3 e. Fe2+, 2+ f. Fe3+, 3+

Write formulas for the binary ionic compounds formed between the following elements. a. sodium and iodine b. calcium and sulfur c. zinc and chlorine d. barium and fluorine e. lithium and oxygen

a. NaI b. CaS c. ZnCl2 d. BaF2 e. Li2O

Give the name of each of the following binary ionic compound: a. KCI b. CaBr₂ c. Li₂O d. MgCl₂

a. Potassium chloride b. Calcium bromide c. Lithium oxide d. Magnesium chloride

Name each of the following monatomic ions: a. K+ b. Mg2+ c. Al3+ d. Cl- e. O2- f. Ca2+

a. Potassium ion b. Magnesium ion c. Aluminium ion d. Chloride e. Oxide f. Calcium ion

Write formulas for each of the following compounds: a. Phosphorus (III) iodide b. Sulfur (II) chloride c. Carbon (IV) sulfide d. Nitrogen (V) oxide

a. P₃I b. S₂Cl c. C₄S d. N₅O

Name the following binary molecular compound according to the stock system: a. CI₄ b. SO₃ c. As₂S₃ d. NCl₃

a. carbon(IV) iodide b. sulfur(VI) iodide c. arsenic(III) sulfide d. nitrogen(III) chloride

Name the following compounds by using the Stock system: a. NaI b. MgS c. CaO d. K₂S e. CuBr f. FeCl₂

a. sodium(I) iodide b. magnesium(II) sulfide c. calcium(II) oxide d. potassium(I) sulfide e. copper(I) bromide f. iron(II) chloride

How do molecular chemical formulas differ from ionic chemical formulas?

Molecular chemical formulas indicate the number of atoms of each element contained in a single molecule of the compound. Ionic chemical formulas represent one formula unit of the ionic compound, indicating the simplest ration of the compounds cations and negative ions.

What determines the order in which the component elements of binary molecular compounds are written?

The element that has the smaller group number is usually given first. If both elements are in the same group, the element whose period number is greater is given first.

A compound contains 36.48% Na, 25.41% S and 38.11% O. What is this compound's empirical formula?

36.48g Na x 23 g/mol = 1.6 moles 38.11g O x 16 g/mol = 2.4 mol 25.41g S x 32 g/mole = 0.8 mol --> (smallest value so must divide all other values by this to get empirical formula) 1.6 mol Na / 0.8 = 2 mol Na 0.8 mol S / 0.8 = 1 mole S 2.4 mol O / 0.8 = 3 mol O Na₂SO₃

Determine the formula mass of each of the following compounds or ions: a. Glucose, C₆H₁₂O₆ b. Calcium acetate, Ca(CH₃COO)₂ c. Ammonium ion, NH+₄ d. Chlorate ion, ClO-₃

a. 180.1559 g/mol b. 158.17 g/mol c. 18.039 g/mol d. 83.4512 g/mol

Write a formula for the following compound: a. Sodium hydroxide b. Lead(II) nitrate c. Iron(II) sulfate d. Diphosphorus trioxide e. Carbon diselenide

a. NaOH b. Pb(NO₃)₂ c. FeSO₄ d. P₂O₃ e. CSe₂

Distinguish between binary acids and oxyacids, and give two examples of each.

Binary acids are binary compounds with hydrogen and second nonmetal element bonded such as hydrochloric acid (HCl) or hydrofluoric acid (HF). Oxyacids are acids that contain hydrogen, oxygen and a third elements (typically a nonmetal) such as nitric acid (HNO₃) or chlorous acid (HClO₂).

Write formulas for the compounds formed between the following: a. Aluminium and Bromine b. Sodium and Oxygen c. Magnesium and Iodine d. Pb2+ and O2- e. Sn2+ and I- f. Fe3+ and S2- g. Cu2+ and NO-₃ h. NH+₄ and SO2₄-

a. AlBr₃ b. Na₂O c. MgI₂ d. PbO e. SnI₂ f. Fe₂S₃ g. Cu(NO₃)₂ h. (NH₄)₂SO₄

Write formulas for each of the following binary molecular compounds? a. Carbon tetrabromide b. Sulfur dioxide c. Phosphorus pentabromide d. Iodine trichloride e. Nitrogen triiodide f. Dinitrogen trioxide

a. CBr₄ b. SO₂ c. PBr₅ d. ICl₃ e. NI₃ f. N₂O₃