Chapter 3 - amounts of substance

Question 1

what is a mole?

Answer 1

1 mole is the amount of substance that contains 6.02 x 10 (^23)

Question 2

the mass of one mole of an element is?

Answer 2

the relative formula mass in grams

Question 3

The Avagadro constant value?

Answer 3

6.02 x 10 (^23)

Question 4

molar mass gives?

Answer 4

the mass in grams in each mole of a substance

Question 5

units of molar mass are?

Answer 5

gmol (^-1)

Question 6

NUMBER OF MOLES EQUATION?

Answer 6

n = mass/ molar mass

m/ M

Question 7

molecule definition

Answer 7

2 or more atoms held together by covalent bonds

Question 8

Molecular formula definition?

Answer 8

the number of atoms of each element in a molecule

Question 9

empirical formula definition?

Answer 9

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

Question 10

the empirical formula is important for?

Answer 10

substances that do not exist as molecules - this includes metals, some non metals and ionic compounds. these substances form giant crystalline structures of atoms or ions

Question 11

analysis definition?

Answer 11

investigating the chemical composition of a substance

Question 12

what is a hydrated salt?

Answer 12

water molecules are part of their crystalline structure. This water is known as the water of crystalisation

Question 13

is it very difficult to remove the last traces of what in a hydrated salt?

Answer 13

water

Question 14

what are assumptions in working out a formula for hydrated salts? 1

Answer 14

1 - all of the water has been lost - only surface of crystals can be seen and some water could be left inside
solution: heat to a constant mass - the crystals are reheated repeatedly until the mass of the residue no longer changes, suggesting all water has been removed

Question 15

what are assumptions in working out a formula for hydrated salts? 2

Answer 15

2- no further decomposition - many salts decompose further when heated. this can be very difficult to judge if no colour change

Question 16

1cm (^3) =

Answer 16

1 ml

Question 17

1 dm (^3) =

Answer 17

1000 cm (^3) = 1000 ml = 1 litre

Question 18

concentration definition?

Answer 18

the amount of solute, in moles, dissolved in each 1dm (^3) of solution

Question 19

moles, conc, vol equation

Answer 19

n = c x v

V IN DM (^3)

Question 20

What is a standard solution?

Answer 20

a soolution of known conc

Question 21

Convetring from moldm(^-3)

Answer 21

conc x Mr

Question 22

at the same temp and pressure,

Answer 22

equal volumes of different gases contain the same no. of molecules

Question 23

molar gas volume definition

Answer 23

the volume per mole of gas molecules at a stated temp and pressure

Question 24

RTP is abt?

Answer 24

20 degrees and 101 kPa

Question 25

At RTP, 1 mole gs molecules has a volume of?

Answer 25

approx 24dm (^-3)

Question 26

RTP gas equation

Answer 26

n = v/24 or 24,000

Question 27

4 assumptions making up the ideal gas equation?

Answer 27

1- random motion 2- elastic collisions 3- negligible size compared to size of their container 4 - no inter molecular formula

Question 28

IDEAL GAS equation?

Answer 28

pV = nRT

Question 29

ideal gas constant, R has a value of

Answer 29

8.314 (given on data sheet)

Question 30

Temp units for ideal gas equation?

Answer 30

K (Kelvin) | degrees Celsius + 273 = K

Question 31

pressure units

Answer 31

Pa

Question 32

volume units

Answer 32

m(^3)!!!!!!

Question 33

cm (^3) to m(^3)

Answer 33

x 10 (^-6)

Question 34

dm (^3) to m (^3)

Answer 34

x 10 (^-3)

Question 35

prob with assumptions for real gases

Answer 35

- when gas molecules are close together, the vol of the molecules compared with the vol of the container becomes sig - also if gas molecules move slowly, they have less energy and intermolecular forces may become sig

Question 36

stoichiometry def?

Answer 36

the ratio of the amount in moles of each substance

Question 37

theoretical yield def

Answer 37

the max poss amount of product

Question 38

why is theoretical yield diff to achieve?

Answer 38

- the reaction may not have gone to completion - side reactions may have taken place alongside the main - purification of the product may result in loss of some of the product

Question 39

% yield equation?

Answer 39

actual / theoretical yield x 100% | note: both values are in MOLES not GRAMS

Question 40

limiting reagent def

Answer 40

- the reactant that is not in excess, will be completely used up first, will stop the reaction

Question 41

calculations MUST be based on what?

Answer 41

limiting reagent

Question 42

atom economy def

Answer 42

is a measure of how well atoms have been utilised

Question 43

atom economy assumes a

Answer 43

100% yield

Question 44

atom economy equation

Answer 44

mr of desired products/ mr of all products x 100%

Question 45

amount of molecules means use

Answer 45

avagadro's constant

Question 46

how many moles

Answer 46

look at formula

Question 47

salts made by neutralisation have to be

Answer 47

ionic

Question 48

anhydrous salt =

Answer 48

the water of crystallisation has been removed

Question 49

hydrated salt =

Answer 49

a salt that has water of crystallisation as a part of its structure

Question 50

water of crystallisation =

Answer 50

it's the water that's bonded as part of the crystal structure in hydrated salts

Question 51

% error equation

Answer 51

+ or - uncertainty/ quantity measured x100

Question 52

to reduce % error we can:

Answer 52

- decrease uncertainty (use balance that reads to 3.d.p 0.001) or - increase quantity measured

Question 53

molar mass

Answer 53

- mass of one mole of a substance | - takes same value as Atomic/ Molecular/ Formula mass

Question 54

'ideal behaviour of gases' (snap)

Answer 54

- molecules act as tho they are rigid spheres - molecules are in constant motion - mols exert a constant pressure on walls of container - collisions of mols are completely elastic - as temp ⬆, KE ⬆

Question 55

what is a crystal?

Answer 55

a substance whose atoms are ordered in a regular 3D pattern

Question 56

. H(2)O represents...

Answer 56

the number of waters of crystalisation

Question 57

note: atom economy

Answer 57

USE BIG NUMBERS IN EQUATION

Question 58

2 types of reaction?

Answer 58

- addition - 100% atom economy, no by-products | - substitution and elimination reactions - < 100% atom economy