3.1 Physical Chemistry: .2 Amount of Substance

Question 1

what is the relative atomic mass?

Answer 1

the average mass of an atom compared with 1/2 of the mass of carbon12 atom

Question 2

why is carbon12 used as the comparison rather than hydrogen for relative atomic mass?

Answer 2

because the mass of carbon12 Is more accurate than the mass for hydrogen

Question 3

what is the relative molecular mass? how do you calculate?

Answer 3

the average mass of a molecule compared with 1/2 of the mass of a carbon12 atom. It is calculated by adding together relative atomic mass of each element

Question 4

what is the relative molecular mass?

Question 5

what is the equation for finding the number of moles?

Answer 5

no. of moles= mass/rmm

Question 6

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Question 7

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Question 8

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Question 9

how do you calculate the number of particles in a substance?

Answer 9

number of particles= (masss/molar mass) x (6.02 x 10^23)

Question 10

what is the Avogadro’s constant

Answer 10

6.02 x 10^23

Question 11

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Question 12

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Question 13

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Question 14

how do you calculate a reacting mass question?

Answer 14

1.) Find the moles of the known chemical 2.) Find the ratio for substance that you’re look for the unkown mass so that you can link the moles to it 3.) Once you have the moles of the substance you don’t have a mass for do another moles=mass/rmm bu rearrange so that mass is the subject

Question 15

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Question 16

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Question 17

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Question 18

what is the formula for finding moles from concentration and volume?

Answer 18

mole= C x V

Question 19

what is the unit for concentration?

Answer 19

dm^-3

if you are finding the volume;

you multiply your concentration by a 1000

Question 20

what is the unit for volume?

Answer 20

cm³

so when you are finding the concentration;

you divide the volume by a 1000

Question 21

how do you work out the volume?

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Question 22

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Question 23

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Question 24

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Question 25

what is the empirical formula?

Answer 25

it is the simplest ratio of the atoms of each element in a compound.

Question 26

what is the molecular formula?

Answer 26

the actual number of atoms of each element in the compound

Question 27

how do you find the empirical formula?

Answer 27

!. state the elements in the chemical 2. find the moles of those elements 3. divide their moles by the smallest amount (of moles you got) 4. you should have a ratio and this will give you the number of each element in the empirical formula (if you have a ratio where you come out with 1.50 times it by 2 and the other number by 2 so you get all round whole numbers)

Question 28

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Question 29

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Question 30

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Question 31

why may you never get 100% yield when making a chemical?

Answer 31

-chemicals can be lost in the process e.g gases might escape, chemicals may not be transferred from one piece of apparatus to the next e.g through filtering and some chemicals may not fully react

Question 32

what is the theoretical yield?

Answer 32

the mass of product that should be formed in a reaction

Question 33

what is the equation for percentage yield?

Answer 33

-percentage yield= actual mass/theoretical mass x 100

Question 34

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Question 35

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Question 36

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Question 37

what is the equation for working out the moles of a volume of gas in cm3 and dm3

Answer 37

-dm3; moles = V/24 -cm3; moles = v/ (24/1000)

Question 38

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Question 39

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Question 40

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Question 41

state the ideal gas equation, state each symbol represents and its required unit

Answer 41

PV=nRT -P= Pressure (Pa) so (kPa —> 1000 x Pa) -V= volume (m3) so (dm3—> m3/ 1000) (cm—> m3/1,000,000) -n= no. of moles -R= Gas constant

Question 42

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Question 43

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Question 44

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