Topic 3 - Equations, Calculations & Electrolysis Flashcards

1
Q

relative atomic mass (Ar)

A

average mass of all isotopes of that element

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2
Q

relative formula mass (Mr)

A

sum of relative atomic masses in a compound

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3
Q

how to find percentage mass of an element within a compound

A

Ar of element / Mr of compound

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4
Q

Moles equation

A

Moles = mass / Mr

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5
Q

Avogadro Number

A

6.02x10^23

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6
Q

conservation of mass

A

in a chemical reaction, no atoms are created or destroyed, the bonds are just changed

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7
Q

why might the mass of products be less than the reactants?

A
  • reactants could have spilled
  • products (if gas) could have floated off
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8
Q

why might the mass of products be greater than the reactants?

A
  • gas from air reacting with reactants
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9
Q

Calculating mass in reactions

A
  1. write out balanced equation
  2. find moles of known substance (moles = mass/mr)
  3. find moles of unknown substance (using molar ratio)
  4. find mass of unknown substance (mass = moles x mr)
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10
Q

Volume of gas at RTP equations

A

Volume = moles x 24 dm^3

Volume = moles x 24,000 cm^3

cm -> dm = /1000

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11
Q

Concentration equation

A

concentration = mass / volume

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12
Q

molecular formula

A

actual number of atoms of each element in a compound or molecule

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13
Q

empirical formula

A

smallest whole number ratio of each element in a compound or molecule

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14
Q

Finding empirical formula

A

Create a table with all elements separated

  • identify mass
  • find moles (mass/mr)
  • divide by smallest number of moles
  • find ratio!
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15
Q

Finding molecular formula

A
  • Divide unknown compound’s Mr by Mr of empirical formula
  • multiply all numbers in formula by the result of division
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16
Q

Water of crystallisation

A

when salt crystals contain water molecules

hydrated -> contain water

anhydrous -> do not contain water

E.g. anhydrous copper sulfate turns blue when water is added

17
Q

How is water of crystallisation shown?

A

Using a dot followed by the number of water molecules there are.

18
Q

Percentage yield equation

A

yield obtained / theoretical yield

x100

19
Q

why might the percentage yield be less than 100%

A
  • reactants may not all react
  • products may be lost to surroundings
20
Q

electrolysis

A

when an electric current passes through a substance and causes it to break down

21
Q

positive electrode

A

anode

where negative ions go

22
Q

negative electrode

A

cathode

where positive ions go

23
Q

Oxidation

A

gain of oxygen, loss of electrons

OILRIG

24
Q

Reduction

A

loss of oxygen, gain of electrons

OILRIG

25
Q

electrolyte

A

liquid in which electrolysis takes place

26
Q

How to extract metals from their ore when they are LOWER in reactivity than carbon.

A

displacement reaction with carbon

27
Q

How to extract metals from their ore when they are HIGHER in reactivity than carbon

A

electrolysis

28
Q

What happens to OH- in electrolysis

A

**oxidised ** at the anode

29
Q

What happens to H+ in electrolysis

A

reduced at the cathode