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A level Chemistry > Chapter 3 - amounts of substance > Flashcards

Chapter 3 - amounts of substance Flashcards

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1
Q

what is a mole?

A

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

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2
Q

the mass of one mole of an element is?

A

the relative formula mass in grams

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3
Q

The Avagadro constant value?

A

6.02 x 10 (^23)

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4
Q

molar mass gives?

A

the mass in grams in each mole of a substance

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5
Q

units of molar mass are?

A

gmol (^-1)

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6
Q

NUMBER OF MOLES EQUATION?

A

n = mass/ molar mass

m/ M

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7
Q

molecule definition

A

2 or more atoms held together by covalent bonds

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8
Q

Molecular formula definition?

A

the number of atoms of each element in a molecule

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9
Q

empirical formula definition?

A

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

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10
Q

the empirical formula is important for?

A

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

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11
Q

analysis definition?

A

investigating the chemical composition of a substance

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12
Q

what is a hydrated salt?

A

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

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13
Q

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

A

water

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14
Q

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

A

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

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15
Q

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

A

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

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16
Q

1cm (^3) =

A

1 ml

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17
Q

1 dm (^3) =

A

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

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18
Q

concentration definition?

A

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

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19
Q

moles, conc, vol equation

A

n = c x v

V IN DM (^3)

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20
Q

What is a standard solution?

A

a soolution of known conc

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21
Q

Convetring from moldm(^-3)

A

conc x Mr

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22
Q

at the same temp and pressure,

A

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

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23
Q

molar gas volume definition

A

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

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24
Q

RTP is abt?

A

20 degrees and 101 kPa

25
Q

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

A

approx 24dm (^-3)

26
Q

RTP gas equation

A

n = v/24 or 24,000

27
Q

4 assumptions making up the ideal gas equation?

A

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

28
Q

IDEAL GAS equation?

A

pV = nRT

29
Q

ideal gas constant, R has a value of

A

8.314 (given on data sheet)

30
Q

Temp units for ideal gas equation?

A

K (Kelvin)

degrees Celsius + 273 = K

31
Q

pressure units

A

Pa

32
Q

volume units

A

m(^3)!!!!!!

33
Q

cm (^3) to m(^3)

A

x 10 (^-6)

34
Q

dm (^3) to m (^3)

A

x 10 (^-3)

35
Q

prob with assumptions for real gases

A
  • 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
36
Q

stoichiometry def?

A

the ratio of the amount in moles of each substance

37
Q

theoretical yield def

A

the max poss amount of product

38
Q

why is theoretical yield diff to achieve?

A
  • 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
39
Q

% yield equation?

A

actual / theoretical yield x 100%

note: both values are in MOLES not GRAMS

40
Q

limiting reagent def

A
  • the reactant that is not in excess, will be completely used up first, will stop the reaction
41
Q

calculations MUST be based on what?

A

limiting reagent

42
Q

atom economy def

A

is a measure of how well atoms have been utilised

43
Q

atom economy assumes a

A

100% yield

44
Q

atom economy equation

A

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

45
Q

amount of molecules means use

A

avagadro’s constant

46
Q

how many moles

A

look at formula

47
Q

salts made by neutralisation have to be

A

ionic

48
Q

anhydrous salt =

A

the water of crystallisation has been removed

49
Q

hydrated salt =

A

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

50
Q

water of crystallisation =

A

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

51
Q

% error equation

A

+ or - uncertainty/ quantity measured x100

52
Q

to reduce % error we can:

A
  • decrease uncertainty (use balance that reads to 3.d.p 0.001)
    or - increase quantity measured
53
Q

molar mass

A
  • mass of one mole of a substance

- takes same value as Atomic/ Molecular/ Formula mass

54
Q

‘ideal behaviour of gases’ (snap)

A
  • 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 ⬆
55
Q

what is a crystal?

A

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

56
Q

. H(2)O represents…

A

the number of waters of crystalisation

57
Q

note: atom economy

A

USE BIG NUMBERS IN EQUATION

58
Q

2 types of reaction?

A
  • addition - 100% atom economy, no by-products

- substitution and elimination reactions - < 100% atom economy

A level Chemistry (39 decks)

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