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Chemistry > 3) Amount of substance > Flashcards

3) Amount of substance Flashcards

1
Q

Define amount of substance

A

the quantity whose unit of the mole, is used as a means of counting any species such as atoms, ions and molecules

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2
Q

Define Avogadro constant

A

the number of atoms per mole of the carbon-12 isotope (6.02 s 10^23 mol^-1)

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3
Q

What does the mass of 1 mole of atoms of an element equal?

A

the relative atomic mass in grams

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4
Q

Define molar mass, M

A

the mass per mole of a substance, in g mol^-1

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5
Q

State the equation linking n, M and m

A

n = m / M

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6
Q

Define molecular formula

A

the number of atoms of each element in a molecule

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7
Q

Define empirical formula

A

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

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8
Q

What type of substance is the empirical formula especially important for?

A

those forming giant crystalline structures

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9
Q

Define relative molecular mass Mr

A

the weighted mean mass of a molecule of a compound compared with 1/12 of the mass of an atom of carbon-12

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10
Q

Define relative formula mass

A

the weighted mean mass of a formula unit of a compound compared with 1/12 of the mass of an atom of carbon-12

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11
Q

How do you calculate relative molecular mass Mr?

A

add together relative atomic masses of the elements making up a molecule

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12
Q

How do you calculate relative formula mass?

A

add together relative atomic masses of the elements in the empirical formula

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13
Q

Define analysis

A

investigating the chemical composition of a substance

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14
Q

Give the 2 steps for determining empirical formula from mass

A
  1. convert mass to moles using n = m / M

2. divide by the smallest whole number

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15
Q

Give the 2 steps for determining molecular formula

A
  1. work out empirical formula
  2. find the number of units in one molecule by dividing the relative molecular mass of the compound by the relative mass of the empirical formula
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16
Q

Many coloured salts are _ - which means they have water molecules / _ as part of their crystalline structure.

A

hydrated

water of crystallisation

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17
Q

Give 3 measurements and 5 steps for calculating the formula of a hydrated salt

A

measurements: mass of crucible, mass of crucible + hydrated salt, mass of crucible + anhydrous salt
1. heat the crucible + contents gently (1min) strongly (3min)
2. leave to cool
3. calculate the moles of anhydrous salt, mass and moles of water
4. find the smallest whole-number ratio of the moles calculated
5. write the value of x + the formula of the hydrated salt

18
Q

State 2 assumptions taken when calculating the formula of a hydrated salt and how one can be corrected

A

all water has been lost -> heat to a constant mass

no further decomposition when heated

19
Q

1cm^3 = _ml?

A

1

20
Q

1dm^3 = _cm^3?

A

1000

21
Q

_ ml = 1 litre?

A

1000

22
Q

Give the equation linking moles, concentration and volume

A

n = concentration (mol dm^-3) x volume (dm^3)

23
Q

Define standard solution

A

a solution of known concentration

24
Q

Define molar gas volume Vm

A

the volume per mole of gas molecules at a stated temperature and pressure (24.0 dm^3 mol^-1 at RTP)

25
Q

Give the equation linking moles, volume and molar gas volume

A

n = volume / molar gas volume

26
Q

Give the ideal gas equation with units

A

pV = nRT

pressure (Pa) x volume (m^3) = amount of gas molecules (mol) x ideal gas constant (8.31Jmol^-1 k^-1) x temperature (K)

27
Q

cm^3 -> m^3?

A

x 10^-6

28
Q

dm^3 -> m^3?

A

x 10^-3

29
Q

°C-> K?

A

+ 273

30
Q

kPa -> Pa?

A

x 10^3

31
Q

Define stoichiometry

A

the ratio of the amount, in moles, of each substance in a chemical equation

32
Q

Give 1 key piece of apparatus and 3 steps for identifying an unknown group 2 metal

A

gas syringe
1. calculate moles of H2 collected
2. calculate amount of metal X using the equation:
X(s) + 2HCl(aq) -> XCl2(aq) + H2(g)
1 : 1
3) calculate the relative atomic mass and compare to the periodic table

33
Q

Define theoretical yield

A

the yield resulting from complete conversion of reactants into products

34
Q

Give 3 reasons why the theoretical yield is difficult to achieve

A

reaction not going to completion
other side reactions
purification resulting in the loss of some product

35
Q

Define actual yield

A

the amount of product obtained from a reaction

36
Q

Give the equation for percentage yield

A

percentage yield = (actual yield / theoretical yield) x 100%

37
Q

Define limiting reagent

A

the reactant that is not in excess, which will be used up first and stop the reaction

38
Q

How can you identify the limiting reagent?

A

calculate moles of each reactant and compare with the equation

39
Q

Give the equation for atom economy

A

atom economy = (sum of molar masses of desired products / sum of molar masses of all products) x 100%

40
Q

Reactions with high atom economies will produce _ and few _ - making _ use of natural resources. However, sustainability / efficiency will also depend on _.

A

large proportion of desired products
unwanted waste products
best
percentage yield

Chemistry (31 decks)

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