Chapter 3, Study Guide Questions

The mole __

-Contains AN of entities -Contains 6.022(10*23) entities

Rounding for atomic masses

-Have 4 significant figures

What is the empirical formula of a compound that consists of .039 moles of iron atoms combined with .052 moles of oxygen atoms

Fe3O4

A nitrogen oxide contains 30.45% N mass, if the molar mass of the compound is 90. +/-5g/mol what is its molecular formula

N2O4

Calculate empirical formula of compound if the masses of each element of the compound are provided

The molar mass of each element

Information gained from a balanced chemical equation

-The physical states of reactants and products, often - The relative quantities (moles) of substances involved - The identities of substances involved.

Steps to balance a chemical equation.

1. Write skeleton equation. 2. Balance the atoms. 3. Adjust the coefficients such that they are the smallest whole number coefficients 4. Do a final check to make sure its balanced.

What is the mass of Cs present in 15 g of cesium acetate,

10.4g

One molecule of Br2 has a mass of __ amu

159.8

Balance _SO2 + _O2 = _SO3

2,1,2

Correct numbers of moles and correct number of atoms in 3.54 g sample of Cu

3.35(10*22) atoms 5.57(10*-2) mol

A chemical equation is a statement using chemical __ that express both the identities and the relative __ of the reactants and products involved in a chemical or physical change

formulas, quantity

In order to calculate the mass of an element in a given sample of a compound, the mass of the compound is multiplied by the mass __ of the element in the compound

fraction

The __ formula of a compound is an integer multiple of the __ formula

molecular, empirical

The mass % of Ca in CaSO4 is 29.45%. To calculate the mass of Ca present in a 25.6 g sample of this compound, the correct procedure is given by __

(29.45/100) * 25.6

Avogadros Number

(6.022(10*23) entities/1 mol)

Options identifieing the correct coefficients for molecules of CO to CO2

- CO2 is a product and has the coefficient 2 - The reactant CO must have the coefficient 2

Which of the following statements describe combustion analysis correctly?

- Every 1 mole of carbon in the compound will produce 1 mole of CO2 -The mass of hydrogen in the compound is determined from the amount of H2O produced - Combustion analysis involves burning a compound in O2

To calculate the mass % of an element in a given compound you need to know ___.

- Formula of compound - Molar mass of compound - Number of moles of the element in one mole of the compound.

Menthol is a compound of carbon, hydrogen, and oxygen. When .1595 g of menthol underwent a combustion alalysis, .449 g of CO2 and .184 g of H2O were produced.

- The mass of C present is .123g - There are 2.04(10*-2) moles of H in the sample.

Statements which correctly describe molar mass

- The molar mass of a substance is the mass per mole of its entities - The periodic table can be used to calculate the molar mass of any substance - When referring to the mass per mole of an entity, the term "entities" could refer to atoms, ions, molecules, or formula units.

Statements for empirical formula

-Gives the smallest whole number ratio of atoms in a compound. -Different compounds can have the same empirical formula.

Steps required to determine empirical formula of a compound from the mass %.

-If it contains 52% C then it can be assumed that 52g are present in a 100g compound. -The ratio of atoms of each element must be a ratio of integer numbers. -mass % can be converted to moles by (mass/molar mass)

Symbols used to balance an equation

-Liquid indicated by (l) -(g) indicates a substance in the gas phase.

Actions permitted for balancing equations

-Multiply all coefficients by common factor. -Inserting coefficients in front of the reactants and the products.

Statements for molecular formula for compound

-Possible that the molecular formula is the same as the empirical formula. -Molecular formula gives the actual number of each type of atom in a compound. -A molecular formula may give little or no information about the structure of a compound.

Statements which correctly reflect Avagadros Number

-The number of entities in a mole is AN -Mole contains 6.022*10*23 entities

__Al2S3 + __H2O = __Al(OH3)3 + __H2S

1, 6, 2, 3

Steps to calculate the empirical formula of a compound, assuming the masses of each element have been given

1. Calculate the number of moles of each element of the sample using (mass/ molar mass) 2. Write chemical formula containing fractional subscripts 3. Divide each subscript by the smallest subscript 4. If integers are not obtained, multiply each subscript by the smallest integer that gives all integer subscripts 5. Verify that the integer subscripts cannot be divided by a common factor

1.52(10*24) atoms of Au correspond to __ mol of Au

1.52(10*24) atoms Au *(1mol of Au/ 6.022(10*23) atoms Au) = 2.52 moles

Correct mathematical operation to calculate the number of molecules in 2 moles of CH4

2mol * Avagadros Number

When hyrdrogen gas is passed over powdered iron(III) oxide, iron metal and water vapor are formed. Which of the following is the correct balanced equation for this process

3H2 + Fe2O3 = 2Fe + 3H2O

A sample of NO2 contains 15g of nitrogen. What is the mass of the NO2 the mass % of N in this compound is 30.45%

49.3g

1 formula unit of KOH= __amu which = __g

56.11, 56.11

The mole relates the atomic mass of an element expressed in amu with the mass of 1 mole of that element expressed in __. The mass of 1 mole of oxygen atoms is therefore equal to __

grams, 16.00

Isomers

have same molar mass have same empirical formula have same molecular formula

The __ mass of a substance is the mass per mole of its entities, where the term "entities" can describe __, ions, molecules, or formula units.

molar, compounds/atoms

The molecular mass of a compound expressed in amu is numerically the same as the mass of one __ of the compound expressed in grams

mole

Calculate mass of substance given the moles

multiply the moles by the molar mass

A chemical equation must be balanced. This means that the same __ and __ of atoms must appear on both sides of the equation

number, type.

Empirical formula of hydrocarbon containing 79.9% carbon by mass

CH3