(physical) 3.1.2 Amounts of a substance

Question 1

What is relative atomic mass (Ar) ?

Answer 1

Average mass of an atom of an element compared to 1/12 of a carbon 12 atom

Question 2

What is relative molecular mass (Mr) ?

Answer 2

Average mass of a molecule compared to 1/12 of a carbon 12 atom

Question 3

What is Avogadro’s constant (NA)?

Answer 3

6.02 times 10^23
- number of carbon atoms in 12 grams of carbon
- number of particles in a mole

Question 4

What does mole mean ?

Answer 4

The number of particles/atoms/molecules in one mole (6.02 times 10^23)

Question 5

How do you calculate the number of particles/a/m using moles ?

Answer 5

(6.02 times 10^23 ) times (amount of moles) = p/a/m

note - (particles/atoms/molecules )

Question 6

What is the unit for moles ?

Answer 6

mol^-1

Question 7

what is the formula for moles ?

Answer 7

mass = Mr times moles

Question 8

What is the formula for concentration ?

Answer 8

mass = concentration times volume

Question 9

What is concentration measured in ?

Answer 9

mol dm ^ -3

Question 10

What is molar mass (Mr ) measured in ?

Answer 10

g mol^-1

Question 11

What is mass measured in ?

Answer 11

g

Question 12

What is volume measured in ?

Answer 12

dm ^-3

Question 13

What is the ideal gas equation ?

Answer 13

PV = nRT

Question 14

What does P stand for and what are its units ?

Answer 14

Pressure ( Nm^-2 or Pa)

Question 15

What does V stand for and what are its units ?

Answer 15

volume ( m^3)

Question 16

What does n stand for and state the unit ?

Answer 16

number of moles (mol^-1)

Question 17

What does R stand for and what are its units ?

Answer 17

The ideal gas constant ( 8.31 J K ^-1 mol^-1)

Question 18

What does T stand for and what are its units ?

Answer 18

Temperature (K)
K = kelvin

Question 19

(volume) how do you convert m3 to dm3 to cm3 ?

Answer 19

m3 - times 1000 = dm3 - times 1000 = cm3

cm3 - divide 1000 = dm3 - divide 1000 =m3

Question 20

(pressure) How do you convert KPa to Pa?

Answer 20

times 1000 (KPa to Pa)
divide 1000 (Pa to KPa)

Question 21

(temp ) How do you convert degrees C to Kelvin ?

Answer 21

+ 273 to get kelvin

Question 22

What is the number for atmospheric pressure ?

Answer 22

100,000

Question 23

What are the kinetic theory assumptions about ideal gases?

Answer 23

• There are no (or entirely negligible ) intermolecular forces between the gas molecules
• The volume occupied by the molecules themselves is entirely negligible relative to the volume of the container

Question 24

What is the meaning of negligible ?

Answer 24

very small that it is not worth considering

Question 25

What is the meaning of empirical formula ?

Answer 25

simplest whole number ratio of atoms of each element present in a compound

Question 26

What is the meaning of molecular formula ?

Answer 26

actual number of atoms of an element in a compound

Question 27

How do you find the empirical formula ?

Answer 27

• write element
• mass for each element
• Ar
• find moles
• divide by smallest mole
• you get ratio (empirical)

Question 28

How do you find molecular formula ?

Answer 28

• you will be given molecular mass
• find empirical
• calculate the Mr of empirical
• molecular mass divided by empirical

Question 29

How do you find percentage composition ?

Answer 29

Ar /Mr times 100