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OCR A A-Level Inorganic Chemistry > Chapter 3 > Flashcards

Chapter 3 Flashcards

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1
Q

How do chemists count the number of particles in a substance? Give 2 details.

A
  • They use a quantity called the amount of substance
  • Its symbol is ‘n’
  • Its unit is moles (mol)
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2
Q

What is a mole?

A
  • The amount of a substance that contains 6.02x10^23 of those particles
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3
Q

What is Avogadro’s constant? Give 2 details.

A
  • The number of particles in each mole of carbon-12; 6.02x10^23
  • Its symbol is N subscript A
  • Its unit is mol^-1
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4
Q

What is the mass of 1 mole of any substance?

A
  • The relative atomic mass of its atom (/atoms added together) in grams
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5
Q

What is molar mass? Give 2 details.

A
  • The mass per mole of a substance
  • Its symbol is M
  • Its unit is g mol^-1
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6
Q

What is the equation for finding out the number of moles in a substance?

A
  • Amount of substance, n (moles, mol)= mass, m (grams, g)/ molar mass, M (g mol^-1)
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7
Q

What is a molecular formula?

A
  • The number of atoms of each element in a molecule
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8
Q

What is an empirical formula? Required.

A
  • The simplest whole-number ratio of atoms of each element in a compound
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9
Q

What is the water of crystallisation?

A
  • Water molecules that are bonded into the crystalline structure of a compound
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10
Q

What happens when hydrated copper (II) sulfate is heated?

A
  • Bonds holding the water within the crystal are broken, and the water is driven off
  • Anhydrous copper (II) sulfate is left behind
  • It changes from blue crystals to white powder
  • CuSO4∙5H2O -> CUSO4 + 5H2O
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11
Q

How do you determine the water of crystallisation in hydrated crystals?

A
  • Weigh an empty crucible
  • Add the salt to the crucible, and weigh them together
  • Using a pipe clay triangle, tripod, Bunsen burner and heatproof mat, heat the crucible
  • Leave the crucible to cool, and weigh it with the anhydrous salt inside
  • Heat it again, leave it to cool and weigh it
  • Repeat the process until the final mass reading no longer changes
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12
Q

What 2 assumptions are made when calculating the water of crystallisation?

A
  • All of the water has been driven off
  • There has been no further decomposition of the reactant
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13
Q

How can you ensure that all of the water has been driven off? What happens if you don’t?

A
  • You “heat to a constant mass”
  • If you don’t do this, your calculated value for the water of crystallisation will be too small, as your calculated mass of water would have been too small
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14
Q

What happens if you heat your salt to the point where it decomposes further? What is the problem with further decomposition happening?

A
  • Your calculated value for the water of crystallisation will be too big, as you’ve lost more mass than just the water’s mass
  • There may be a colour change, but sometimes there isn’t, so it can be hard to tell
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15
Q

What is molar gas volume, and its unit?

A
  • The volume per mole of gas
  • dm^3 mol^-1
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16
Q

What is the molar gas volume at RTP?

A
  • 24 dm^3 mol^-1 (1 mole of gas molecules take up 24dm^3 at RTP)
17
Q

When is the ideal gas equation used?

A
  • When gases are at different temperatures and pressures to RTP
  • For more accurate calculations
18
Q

What is the ideal gas equation?

A
  • pV= nRT
  • p= pressure (Pascals, Pa)
  • V= volume (m^3)
  • n= amount of substance (moles, mol)
  • R= ideal gas constant: 8.314 (J mol^-1 K^-1)
  • T= temperature (Kelvin, K)
19
Q

What are 3 reasons why it’s difficult to get the theoretical yield of a reaction?

A
  • The reaction may not have gone to completion
  • Other (side) reactions may have also taken place
  • Purifying the product may cause some of it to be lost
20
Q

Why can it be difficult to get the theoretical yield of a gas?

A
  • Gases need to be cooled to room temperature before measuring their volume if using the formula for gases at RTP
21
Q

What is the equation for percentage yield?

A
  • (Actual yield/ theoretical yield) x100
22
Q

What is atom economy? How is it calculated?

A
  • A measure of how well atoms have been utilised
  • (sum of molar masses of desired products/ sum of molar masses of all products) x100
23
Q

What are 2 reasons why it’s important for a reaction to have a high atom economy?

A
  • Preserves raw materials
  • Reduces waste
24
Q

How do you calculate percentage uncertainty?

A
  • [(Uncertainty × multiplied by how many readings you take) ÷ (amount recorded)] × 100

OCR A A-Level Inorganic Chemistry (14 decks)

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