Chapter 6: Chemical Composition

Question 1

Describe how to count (calculate) the number of jelly beans in a sample by weighing the
sample of jelly beans. What key piece of information about jellybeans do you need to
know before weighing the sample?

Answer 1

To count how many jellybean there are based on the weight. We need to know how much one jellybean weighs

Question 2

Remember that the atomic mass of every element is found in the Periodic Table of the Elements. This value is the average atomic mass of the element and has the unit atomic mass unit (amu).

Answer 2

The amu is found below each element. Usually not a whole number

Question 3

Define these related terms: formula mass and molecular mass. The unit of each term is
amu

Answer 3

Formula mass is the total mass of all the molecules, elements, and compounds in a formula. Molecular mass is the total mass of the elements in a molecule.

Question 4

Remember that the mole unit represents the amount (by count) of a substance.

Answer 4

How many of each element or molecule is in a formula. ALWAYS a whole number

Question 5

Remember that 1 mole of any item contains 6.02 × 10^23of those items. This quantity is called Avogadro’s number

Answer 5

Avogadro’s number: 6.02 x 10^23

Question 6

Remember that 1 mole of an element is equal to its average atomic mass in grams. This
quantity is called molar mass and has the unit g/mol

Answer 6

1 mole is equal to the amu of an element

Question 7

Remember that a chemical formula lists the number of individual atoms present in the
compound or molecule

Answer 7

consisting of the subscripts and coefficients

Question 8

Remember that 1 mole of a compound is equal to the sum of the average atomic masses
in grams of the elements present. This quantity is called molar mass and has the unit
g/mol.

Question 9

Use the Periodic Table of the Elements to find the molar mass of any element.

Answer 9

the amu is under each individual element

Question 10

Calculate the molar mass of any chemical compound given its formula.

Answer 10

use the periodic table of elements and the subscripts and coefficients.

Question 11

Given the amount of moles that are present in a sample, calculate the number of particles in the sample using the unit conversion method (mol to number conversion).

Answer 11

Multiply number of moles by Avogadro’s number (6.02 x 10^23)

Question 12

Given the number of particles in a sample, calculate the amount of moles that are present in the sample using the unit conversion method (number to mol conversion).

Answer 12

number of particles divided by Avogadro’s number

Question 13

Given the mass in grams of a sample, calculate the amount of moles in the sample using the unit conversion method (mass to mol conversion).

Answer 13

Divide the mass of the sample by the mass of the unit (ex: mass of element) to get number of moles

Question 14

Given the amount of moles in a sample, calculate the mass in grams of the sample using
the unit conversion method (mol to mass conversion).

Answer 14

Multiply number of moles by the mass of the unit (ex: mass of element) to get mass

Question 15

Given the mass in grams of a sample, calculate the number of particles in the sample using the unit conversion method (mass to number conversion)

Answer 15

Divide sample mass by unit mass the get moles. Then multiply the number of moles by Avogadro’s number.

Question 16

Given the number of particles in a sample, calculate the mass in grams of the sample using the unit conversion method (number to mass conversion).

Answer 16

divide number of particles by Avogadro’s number to get the moles. Then multiply the moles by the unit of mass

Question 17

Define percent, %. Remember the basic algebraic equation for percent

Answer 17

part/whole x 100

Question 18

Calculate the percent composition of each element in a compound based on mass

Answer 18

mass of element/mass of compound x 100

Question 19

Calculate the percent composition of each element in a compound from the chemical formula.

Answer 19

using the coefficients, subscripts and periodic table of elements