Chapter 3 - Amount of Substance Flashcards

Amount of substance and the mole, Determination of formulae, Moles and volumes and Reacting quantities

1
Q

What is Avogadro’s Constant?

A

The number of atoms per mole of the carbon-12 isotope.

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2
Q

What is a mole?

A

The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.

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3
Q

What is the equation for the number of moles of a substance?

A

n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)

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4
Q

What is relative formula mass?

A

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

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5
Q

What is the molecular formula?

A

The number of atoms of each element in a molecule.

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6
Q

What is the empirical formula?

A

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

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7
Q

How is the empirical formula found?

A
E   Element
M  Mass or %
---  ----------------
M  Molar mass
A   Answer (moles)
     ------------------------
     Smallest answer
R   Ratio
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8
Q

How is the molecular formula found?

A

Find empirical formula.
Divide molar mass of a molecule by molar mass of empirical formula.
Multiply empirical formula by the result.

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9
Q

What is relative molecular mass?

A

The mass of a molecule compared with the mass of an atom of carbon-12.

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10
Q

In hydrated salts, what is the name given to water molecules?

A

Waters of crystallisation

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11
Q

What is the concentration of a solute?

A

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

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12
Q

What is the equation for finding a solution’s concentration?

A

c=n/v
c - concentration (mol/dm^3)
n - number of moles (mol)
v - volume (dm^3)

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13
Q

What is molar volume?

A

The volume per mole of a gas.

Measured in dm^3/mol

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14
Q

What is the value of molar volume at room temperature and pressure?

A

24 dm^3/mol

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15
Q

What is the equation for molar volume?

A

mgv=V/n
mgv - molar gas volume (dm^3/mol)
n - number of moles (mol)
V - volume (dm^3)

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16
Q

What are the assumptions made about an ideal gas?

A

Random motion
Elastic collisions
Negligible size
No intermolecular forces

17
Q

What is the equation for the ideal gas law?

A
pV=nRT
p - pressure (Pa)
V - volume (m^3)
n - number of moles (mol)
R - ideal gas constant (J/mol/K)
T - temperature (K)
18
Q

What are the standard conditions?

A

298K or 25C

101kPa or 1 atm of pressure

19
Q

What is stoichiometry?

A

The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation.

20
Q

What are the balanced equations used to find?

A

The quantities of reactants required to prepare a required quantity of a product.
The quantities of products that should be formed from certain quantities of reactants.

21
Q

What is the percentage yield?

A

The actual yield divided by the theoretical yield expressed as a percentage.

22
Q

Why is the theoretical yield so hard to achieve?

A

The reaction is incomplete.
Competing side reactions giving different products.
Loss of product in handling and purification.
Reversible reaction.

23
Q

What is the limiting reagent?

A

The reactant that is not in excess.

24
Q

What is atom economy?

A

The molar mass of desired products divided by the sum of the molar masses of all products expressed as a percentage.

25
Q

What are the benefits of a high atom economy?

A

Produce a larger proportion of desired products and few waste products.
Important for sustainability, the best use of natural resources.