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A-Level Chemistry > Amount of substance > Flashcards

Amount of substance Flashcards

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1
Q

What is a mole?

A

The amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon 12.

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2
Q

What is relative atomic mass?

A

The average mass of one atom compared to one twelfth of the mass of one atom of carbon 12

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3
Q

What is relative molecular mass?

A

The average mass of a molecule compared to one twelfth of the mass of one atom of carbon 12

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4
Q

How can you use the Avogadro’s constant to calculate the number of particles?

A

Number of particles = Number of moles * Avogadro’s constant

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5
Q

What is the Avogadro constant?

A

One mole contains 6.022*10^23 particles

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6
Q

How do you calculate the number of moles?

A

Moles = mass/relative molecular mass

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7
Q

What is the Ideal Gas equation?

A

pV = nRT

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8
Q

How do you convert temperature to Kelvin?

A

Kelvin = degrees centigrade + 273

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9
Q

How do you convert from cm^3 to dm^3?

A

cm^3 = dm^3 /1000

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10
Q

How do you convert from cm^3 to m^3?

A

m^3 = cm^3 /1000000

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11
Q

How do you convert from dm^3 to m^3?

A

m^3 = dm^3 /1000

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12
Q

What is the concentration of a solution?

A

The number of moles dissolved per 1dm^3.

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13
Q

How do you calculate the number of mole using the concentration and volume of the solution?

A

Number of moles = concentration * volume/1000

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14
Q

What are the units for the concentration of a solution?

A

mol dm^3

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15
Q

What is the empirical formula?

A

The simplest ratio of atoms of each element in a compound

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16
Q

What is the molecular formula?

A

The actual number of atom of each element in a compound

Made up of a whole number of empirical units

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17
Q

What is the theoretical yield?

A

The mass of product that should be formed in a chemical reaction

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18
Q

What is the actual yield?

A

The mass of product formed after the reaction and is always less than the theoretical yield

19
Q

Why is the actual yield always less than the theoretical yield?

A

Not all the starting chemicals react fully

Some chemicals are lost

20
Q

How do you calculate the percentage yield?

A

Percentage yield = Actual yield/theoretical yield * 100

21
Q

What does the percentage yield tell us?

A

Percentage yield tells us how wasteful a process is as it is based on how much product is lost during the process

22
Q

What is the atom economy?

A

Atom economy is a measure of the efficiency of a reaction

23
Q

How do you calculate the atom economy?

A

%Atom economy = molecular mass of desired product/sum of molecular masses of all reactants * 100

24
Q

Why do companies in the chemical industry try to use high atom economies?

A

High atom economy processes are better for the environment as there is less waste

25
Q

Why are high atom economy processes more sustainable?

A

They make more efficient use of raw materials

26
Q

Why are high atom economy processes less expensive?

A

Companies will spend less money on separating the desired product from the waste products

27
Q

What do titrations allow you to do?

A

Titrations allow you to work out the concentration of an acid or alkali

28
Q

Describe how you would find the concentration of an alkali or acid from a titration.

A

-Accurately pipette 25cm^3 of alkali into conical flask
-Touch the surface of the alkali with pipette
-Add a few drops of the appropriate indicator
-Fill a burette with a standard solution of acid using a funnel at eye level
-add the acid into the alkali whilst swirling the mixture
add the acid dropwise at the endpoint
-Repeat the experiment to get 2-3 concordant results

29
Q

What is a standard solution?

A

A solution that has a known concentration

30
Q

What are the two main indicators for acid/alkali?

A

Methyl orange

Phenolphthalein

31
Q

What colour does methyl orange become in acid/alkali?

A

Red in acid

Yellow in alkali

32
Q

What colour does phenolphthalein become in acid/alkali?

A

Colourless in acid

Pink in alkali

33
Q

How do you calculate the apparatus uncertainty?

A

Apparatus uncertainty = (error /measurement) * 100

34
Q

Describe how you would find the relative molecular mass of a substance in a titration.

A
  • Calculate the moles of the acid in the solution
  • Find the ratio of acid/alkali to substance
  • Use the ratio to calculate the number of moles of the substance
  • Calculate the relative molecular mass(mass = Mr * moles)
35
Q

What happens when you increase the amount of equipment being used?

A

The total apparatus uncertainty increases

36
Q

How would you calculate the total apparatus uncertainty?

A

Add all the uncertainties of the equipment together

37
Q

How could you do to decrease the apparatus uncertainty?

A
  • taking a large reading using the equipment

- using more sensitive equipment

38
Q

What factors affect volume?

A

temperature
pressure
number of moles

39
Q

Describe a method for making a solution

A
  • Weigh a beaker using a top pan balance
  • Add the solid into the beaker and weigh them
  • Record the difference in mass
  • Add distilled water into the beaker
  • Stir with a glass rod until all has dissolved
  • Transfer the solution into a volumetric flask with washings using a funnel
  • Add water up to 250cm^3
  • Place a lid on top
  • Shake the flask for the solution to mix
40
Q

Suggest a reason why repeating a titration makes the value for the average titre more reliable

A
  • Anomalies can be eliminated
  • Concordant results can be collected
  • An average can be calculated
41
Q

What effect would an air bubble have on the value of the first titre?

A

The value would be higher than the true value

42
Q

What effect would an air bubble have on the average titre?

A
  • No effect

- The titre value can be discarded

43
Q

Suggest ideas on how the overall technique can be improved when making a solution

A
  • weigh by difference
  • wash the stirring rod/beaker after use
  • shake the final solution
  • make the sure the bottom of the meniscus touches the mark
44
Q

What are the potential errors in using a gas syringe?

A

gas escapes before bung is inserted
syringe sticks
some gases like carbon dioxide and sodium dioxide are soluble in water

A-Level Chemistry (30 decks)

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