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A Level Chemistry > 3 Amount of Substance > Flashcards

3 Amount of Substance Flashcards

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1
Q

Define a mole in Chemistry.

A

One mole is the amount of a substance that contains 6.02x1023 particles.

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2
Q

What is NA?

A

The Avogadro constant, NA, is 6.02x1023 particles per mole.

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3
Q

How many moles of oxygen atoms are in 1 mole of water?

A

1 mole of H20 has 2 moles of water.

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4
Q

What are the units of molar mass?

A

Molar mass is grams per mole. (g/mol)

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5
Q

What is the formula for finding the mass when

you know moles and molar mass?

A

Mass = n x Mr

Mass = moles x molar mass

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6
Q

How do you convert from mass to moles?

A

n = mass / Mr

Convert the mass to grams and divide by the

molar mass from the periodic table.

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7
Q

Is it possible to find the molar mass if you

know the mass and the moles?

A

Yes. Use Mr = mass / moles

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8
Q

What does the molecular formula tell you?

A

The molecular formula gives the number of atoms

of each element in a molecule.

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9
Q

Define empirical formula.

A

The empirical formula is the simplest whole-number

ratio of atoms of each element in a compound.

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10
Q

What is the empirical formula of P4O6?

A

P2O3

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11
Q

What is the empirical formula of C9H12O3?

A

C3H4O

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12
Q

What is relative molecular mass and how do you find it?

A

Relative molecular mass (Mr) complares the mass of a molecule with the mass of an atom of carbon-12. You calculate Mr by adding the relative atomic masses of the elements in the molecule.

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13
Q

What is the difference between relative molecular mass and relative formula mass?

A

They are both found in the same way by adding the molar masses of the elements. They difference is that molecular mass is for a discreet molecule. Formula mass is for ionic compounds that are giant lattices. Since ionic lattices are not molecular, a ratio of elements is used to give a formula.

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14
Q

CuSO4.5H2O

What is the term and meaning of the “.5H2O” in the above formula?

A

The term is water of crystallisation.

Here is means that there are five water molecules in the crystalline structure for every one molecule of CuSO4.

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15
Q

Complete the equation for when the substance is heated:

CuSO4.5H2O →

A

CuSO4(s) + 5H2O(l)

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16
Q

A sample of 1.173 grams of hydrated, blue CoCl2 is heated.

After heating to a constant mass, 0.641 grams of solid purple crystals remain.

What is the value of the water of crystalisation?

A

6

CoCl2.6H2O

17
Q

When we heat a substance to remove water, how can we be certain that all of the water is really gone?

What is a potential problem when you do this?

A

Heat to a constant mass to be sure all of the water has been removed.

A potential problem with repeated heating could be if the anhydrous salt can decompose further with heat.

18
Q

Convert 1 litre to cm3.

A

1000 cm3

19
Q

Convert 523 ml to dm3.

A

0.523 dm3

20
Q

What is the relationship between moles, volume, and concentration?

A

c = n / V

n = c x V

V = n / c

21
Q

Calculate the amount of NaCl, in mol, in 30.0 cm3 of a 2.00 M solution.

A

20.3 cm3

22
Q

Define molar gas volume.

A

The molar gas volume, Vm, is the volume per mole of gas molecules at a stated temperature and pressure.

23
Q

What does RTP mean?

A

Room temperature (20°C) and pressure (101 kPa/1 atm).

24
Q

At RTP, 1 mole of gas molecules has a volume of approximately:

A

24.0 dm3 or 24 000 cm3

25
Q

Calculate the amount(mol) of hydrogen gas in 480 cm3 at RTP.

A

0.0200 mol of H2

26
Q

In the ideal gas equation, what are the units for pressure?

A

Pascals (Pa)

27
Q

In the ideal gas equation, what are the units for temperature?

A

Kelvin (K)

28
Q

In the ideal gas equation, what are the units for volume?

A

m3

29
Q

Rearrange PV = nRT to find T.

A

T = PV / nR

30
Q

True or False

Standard conditions temperature and RTP temperature are the same.

A

False.

Standard conditions 25°C

Room temperatue 20°C

31
Q

The ideal gas equation relies on what two assumptions?

A

The ideal gas equation assumes:

  • forces between molecules are negligible
  • gas molecules have negliglible size compared to the size of their container.

Note: When these are not true, the real gas equations must be used.

32
Q

What is stoichiometry?

A

The stoichimetry of a reaction is the ratios of each component in a balanced reaction. It is used to convert from the amount of one substance to predict the amount of another substance in the equation.

33
Q

Describe a simple experiment that you could do to identify a small sample of an unknown metal.

A
  • Record the mass of the metal.
  • React it with excess acid and collect the hydrogen gas.
  • Use the volume of gas to determine the moles of gas evolved.
  • Use stoichimetry to convert moles of gas to moles of metal.
  • Use Mr = mass / moles to find Mr and thus identify the metal.
34
Q

Define theoretical yield.

A

The maximum possible amount of product.

35
Q

Why is it very unlikely the actual yield is equal to the theoretical yield?

A

In any reaction, the actual yield is less that the theorectical yield because:

  • the reaction may not have gone to completeion
  • other reactions may also take place (side reactions)
  • purication of the product may result in some loss of product.
36
Q

How do you calculate percentage yield?

A

Percent Yield = (Actual / Theoretical) x 100%

37
Q

What is a limiting reagent?

A

The limiting reagent is the reactant that is not is excess and will be completely used up in the reaction.

38
Q

What is atom economy? How is it calculated?

A

The atom economy of a chemical reaction is a measure of how well atoms have been utilised.

atom economy = (mass of desired products / mass of all products) x 100

39
Q

What does it tell you if the atom economy for a reaction is high?

A

Reactions with high atom economies:

  • produce a large proportion of desired products and few unwanted waste products
  • are important for sustainability as they make the best use of natural resources.

A Level Chemistry (17 decks)

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