Chapter 7 Chemistry w/ Practice Problems

How to name molecular compounds?

- the element with the smaller group number typically goes first - the first element is only given a prefix if it contributes more than one atom to the compound - the second element is named by adding the prefix indicating the number of atoms it contributes to the compound (including mono), dropping the end of the element's name, and adding -ide

Determine the number of moles in 4.50g H2O

0.250 mol

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: KNO3

1 mole of K 1 mole of N 3 moles of O

Rules for assigning oxidation numbers

1) pure elements (regular atoms)have oxidation # = 0 2) in binary compounds the oxidation # = ionic charge (1+, 2-, etc.) 3) Fluoride = -1 4) oxygen = -2 (except in peroxides H2O2 and Na2O2 when ox # = -1) 5) hydrogen = +1 (except when combined with metals when ox# = -1) 6) sum of oxidation # in a neutral compound= 0 7) sum of oxidation # in polyatomic ion = charge on the ion 8) oxidation # of ions = charge of ions

Determine the molar mass of KNO3

101.11 g/mol KNO3

Determine the molar mass of (NH4)2SO2

116.17 g/mol (NH4)2SO2

Find the formula mass of KCIO3

122.55 u

Determine the molar mass of Na2SO4

142.05 g/mol Na2SO4

Molar Mass of H2O

18.02 g/mol

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: (NH4)2SO3

2 moles of N 8 moles of H 1 mole of S 3 moles of O

What is the molar mass of barium nitrate Ba(No3)2?

261.35 g/mol

Determine the molar mass of Al2(CrO4)2

285.95 g/mol Al2(CrO4)2

Find percent composition of Na and Cl in NaCl

39.35% Na in NaCl 60.65% Cl in NaCl

Determine the molar mass of Ca(OH)2

74.10 g/mol Ca(OH)2

Find the percentage composition of copper (1) sulfide, Cu2S.

79.85% Cu and 20.15% S

What is the mass in grams of 2.50 mol of oxygen gas?

80.0gO2

What is the empirical formula for a compound that contains 63.50% silver, 8.25% nitrogen, and 28.25% oxygen?

AgNO3

The percent composition of a compound was found to be 63.5% silver, 8.2% nitrogen, and 28.3% oxygen. Determine the compound's empirical formula.

AgNo3

Write the formula and indicate the charge of a aluminum ion.

Al+3

write the formula for aluminum sulfate

Al2(SO4)3

name Al3+

Aluminum ion

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: Ba

Ba+2

Determine the empirical formula for a compound with 66.0% Ba and 34.0% Cl.

BaCl2

Write a formula for barium and fluorine

BaFl2

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: Br

Br-

Determine the empirical formula for a compound with 52.11% C, 13.14% H, and 34.75%O.

C2H6O

What is the molecular formula for a molecule that has a formula mass of 42.08 u and contains 85.64% C and 14.36% H?

C3H6

What is the molecular formula of the molecule that has an empirical formula of CH2O and a molar mass of 120.12 g/mol?

C4H8O4

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: Ca

Ca+2

Write a formula for calcium and sulfur

CaS

Write out the name of Cs2O

Cesium oxide

name Cl-

Chloride

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: Cl

Cl-

Write the formula and indicate the charge of a chloride ion

Cl-

An oxide of chromium is found to have the following % composition: 68.4% Cr and 31.6% O. Determine the compound's empirical formula.

Cr2O3

Write the chemical formula for cesium phosphide

Cs3P

A compound containing 5.9265% H and 94.0735% O has a molar mass of 34.01468 g/mol. Determine the empirical and molecular formula of this compound.

Empirical = HO Molecular = H2O2

Write the formula and indicate the charge of an iron (II) ion.

Fe+2

Write the formula and indicate the charge of an iron (III) ion.

Fe+3

Assign oxidation numbers to each atom in the following compound: H2SO4

H = +1 S = +6 O = -2

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: K

K+

Write out the name for potassium chloride

KCl

Write a formula for lithium and oxygen

Li2O

Write the chemical formula for lithium oxide

Li2O

name Mg2+

Magnesium ion

write out the name for HgI2

Mercury Iodine

Determine the percentage composition of each in Mg(OH)2

Mg = 41.68% O = 54.86% H = 3.46%

write the formula for magnesium nitrate

Mg(NO3)2

Write the formula and indicate the charge of nitride ion.

N-3

Write the formula and indicate the charge of a sodium ion.

Na+

A 170.00 g sample of an unidentified compound contains 29.84 g sodium, 67.49 g chromium, and 72.67 g oxygen. What is the compound's empirical formula?

Na2Cr2O2

Quantitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. Find the empirical formula of this compound.

Na2SO4

Write a formula for sodium and iodine

NaI

Analysis of a 10.150 g sample of a compound known to contain only phosphorus and oxygen indicates a phosphorus content of 4.433 g. What is the empirical formula of this compound? What is the molecular formula is the molar mass is 283.89 g/mol?

P2O5; P4O10

A 60.00 g sample of tetraethyl lead, a gasoline additive, is found to contain 38.43 g lead, 17.83 g carbon, and 3.74 g hydrogen. Find its empirical formula.

PbC8H20

Using only the periodic table, write the symbol of the ion most typically formed by each of the following element: S

S-2

write the chemical formula for Tin(IV) oxide

SnO2

Assign oxidation numbers to each atom in the following compound: UF6

U = +6 F = -1

Write a formula for zinc and chlorine

ZnCl

empirical formula

a chemical formula that shows the composition of a compound in terms of the relative numbers and kinds of atoms in the simplest ratio

binary compound

a compound composed of two different elements

oxyanion

a polyatomic ion that contains oxygen

Ibuprofen, C13H18O2 , is the active ingredient in many nonprescription pain relievers. Its molar mass is 206.31 g/mol. a. If the tablets in a bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle? b. How many molecules of ibuprofen are in the bottle? c. What is the total mass in grams of carbon in 33 g of ibuprofen?

a. 0.16 mol C13H18O2 b. 9.6 x 1022 molecules C13H18O2 c. 25 g C

monatomic ion

an ion formed from a single atom

name Ca2+

calcium

Name Ca(OH)2

calcium hydroxide

How to name binary compounds?

cation first - just element's name anion second - take away ending add ide (no prefixes for ions)

How are binary compounds written?

cation then anion

How are monatomic ions named?

cations: just the name anions: element's name - ending + ide

Name of N20

dinitrogen monoxide

Name of N2O5

dinitrogen pentoxide

nomenclature

naming system

What does a subscript tell you?

number of atoms of a n element in the formula

Name O2-

oxide

Name K+

potassium

Name NaC2H3O2

sodium acetate

oxidation number

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

percent composition

the percent by mass of each element in a compound

What does the roman numeral indicate in the stock system of nomenclature?

the positive charge of the element

formula mass

the sum of the average atomic masses of all the atoms represented in the formula of any molecule, formula unit, or ion