Calculations, Formulae and Relative Mass (2.3 + Chapter 3) Flashcards by Rebecca Webb

From mass to moles?

n = m / Mr
m = n x Mr
Mr = m / n

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Units of n?

mols

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Units of m?

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Units of Mr?

gmol-1

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From concentration to moles?

n = c x v 
c = n / v
v = n / c

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Units of c?

moldm-3

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Units of v?

dm-3

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How to convert from concentration in gdm-3 to concentration in moldm-3?

c (gdm-3) = c (moldm-3) x Mr (gmol-1)

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From gas volumes to moles?

n = V / 24
V = n x 24
24 = n / V  *at RTP/STP

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What is the ideal gas law equation?

pV = nRT *not at RTP/STP

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What is the value of p, V, n, R and T in the ideal gas law equation?

p = Pa
v = m3
n = mol
R = 8.31
T = K

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What is the equation for atom economy?

(Sum of the Mr of desired products / sum of Mr of all products) x 100

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What is the equation for yield?

(actual yield / expected yield) x 100

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What is important to remember about the atom economy equation?

To include molar ratio numbers in calculation the equations e.g. Mr of 2Na = 2 x 23 = 46

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What is the limiting reagent (i.e the reagent to use in mols ratio)?

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

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How do you convert cm3 to m3?

x 10^-6

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How do you convert dm3 to m3?

x 10^-3

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How do you convert degreesC to K?

+ 273

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How do you convert kPa to Pa?

x 10^3

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What is the Vm constant?

24dm3mol-1 or 24,000cm3mol-1

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How do you convert atm to Pa?

x 101,325

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What is 0.98atm equal to?

100,000 Pa

What assumptions does the ideal gas law make?

1) Random motion
2) Elastic collisions
3) Negligible size
4) No IM forces

What is the empirical formula?

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

What is the molecular formula?

The number and type of atoms of each element in a molecule

What is the Avogadro's constant (NA)?

6. 02 x 10^23 mol-1 | - The number of particles in each mole of carbon-12

How would you find out the number of particles in a substance?

6.02 x 10^23 x number of moles

What is a binary compound?

A compound that contains 2 elements only

What are polyatomic ions?

Ions containing atoms of more than one element bonded together

What does aqueous mean?

Dissolved in water

What is the formula unit?

The formula worked out from the ionic charges

What is the amount of substance (n)?

A quantity used to count the number of particles in a substance, measured in mols

What is one mole?

The amount of substance that contains 6.02x10^23 particles

What is the molar mass?

The mass per mole of a substance

What are the units of molar mass?

g/mol

What is the molar gas volume?

The volume per mole of gas molecules at a stated temperature and pressure

What are the units of molar gas volume?

dm3/mol

What is the relative molecule mass (Mr)?

Compares the mass of a molecule with the mass of an atom of carbon-12

What is the relative formula mass?

Compares the mass of a formula unit with the mass of an atom of carbon-12

What does hydrated mean?

That water molecules are part of the crystalline structure of a crystal

What is the water of crystallisation?

The water molecules that are part of the crystalline structure

What does anhydrous mean?

That the bonds holding together the water within the crystal are broken and the water is driven off

What assumptions are you making when you dehydrate a hydrated crystal?

1) All of the water has been lost | 2) There has been no further decomposition

What is one dm3 equal to?

1 litre

What is RTP

20 degrees and 101kPa (1atm)

What is the molar gas volume at RTP?

24 dm3/mol

What is the stoichiometry of a reaction?

The ratio of the amount, in moles, of each substance in a balanced equation

Why is it difficult to achieve the theoretical yield of a reaction?

1) The reaction may not have gone to completion 2) Side reaction may have taken place 3) Purification of the product may result in some loss of the product

How do you work out which reactant is in excess?

1) Working out the amount in moles of each reactant and comparing with the equation 2) Calculations must be based on the limiting reagent (i.e. use this in moles ratio) - e.g. when hydrogen and oxygen react to form water, 2 mol of hydrogen are required for every 1 mole of oxygen - therefore, if equal amounts of hydrogen and oxygen are allowed to react, hydrogen will be used up first, and half the oxygen will be unreacted - the limiting reagent is therefore hydrogen

What is the atom economy?

A measure of how well atoms have been utilised

What do reactions with high atom economies produce?

A large proportion of desired products and few unwanted waste products

What are reactions with high atom economies important for?

Sustainability as they make the best use of natural resources

What are the benefits for sustainability for developing chemical processes with a high atom economy?

1) Makes industrial processes more efficient 2) Preserves raw materials 3) Reduces waste