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Chemistry > Quantitative Chemistry > Flashcards

Quantitative Chemistry Flashcards

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1
Q

State the law of conservation of mass

A

No atoms are lost or made during a chemical reaction so total mass of products = total mass of reactants

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2
Q

In experiment, how can you easily compare mass of products with reactants?

A

Add up the mass of all the containers and the reactants and do the same with the products and their containers

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3
Q

When might the total mass of products appear to be more than the reactants?

A

If a gas reacts and its particles enter the container

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4
Q

When might the total mass of products appear to be less than the reactants?

A

If a gas is formed and the particles leave the container

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5
Q

What is the symbol for relative formula mass?

A

Mr

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6
Q

How is relative formula mass calculated?

A

It is the sum of the relative atomic masses of all atoms in the formula

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7
Q

How does relative formula mass relate to conservation of mass in a balanced symbol equation?

A

Sum of relative formula masses of reactants = sum of the relative formula masses of the products

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8
Q

In experiments, how can you calculate uncertainty?

A

Uncertainty = Range/2

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9
Q

To how many decimal places should uncertainty be quoted?

A

The same number as the data used to calculate it

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10
Q

What is the unit for mole?

A

mol

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11
Q

Define a mole

A

The mass of one mole of a substance in grams is numerically equal to its relative formula mass

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12
Q

The mole is a constant numerical value called the Avogrado constant, what is this number?

A

6.02 x 10(23)

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13
Q

What is the equation that links moles to amount of substance and Avogrado’s constant?

A

Moles = amount of substance / 6.02x 10(23)

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14
Q

What is the equation that links moles to mass and relative formula mass?

A

Moles = mass / Mr

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15
Q

What are the three steps involved in calculating an unknown mass in a balanced symbol equation?

A
  1. Use n = M x Mr to calculate moles
  2. Use the molar ratio to find moles of unknown
  3. Use M = n / Mr to calculate unknown mass
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16
Q

What is the common error made when completing a reacting mass calculation?

A

Balancing numbers are used when calculating Mr

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17
Q

How are kg’s converted into grams?

A

Divide by 1,000

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18
Q

How are tons converted into grams?

A

Divide by 1,000,000

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19
Q

How do balancing numbers relate to moles?

A

They give us the molar ratio of all substances in the reaction

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20
Q

If given masses, how can you calculate molar ratios?

A
  1. Use moles = M/Mr
  2. Use the molar ratio to find moles of unknown
  3. Convert to whole numbers by multiplying through
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21
Q

What does excess reactant mean?

A

More of the reactant is used than is required

22
Q

Why add a reactant to excess?

A

To ensure all the limiting reactant is used up

23
Q

What does limiting reactant mean?

A

A reactant that is completely used up limiting the amount of product

24
Q

When performing chemical calculations, should limiting or excess reactant be used?

A

Limiting reactant

25
Q

How can you determine which reactant is in excess?

A

Calculate the moles of both reactants then compare to the molar ratio

26
Q

At room temperature, what is the value of the molar gas volume?

A

24 dm(3)

27
Q

What is the equation linking volume of gas and moles?

A

moles = volume / 24

28
Q

What unit should volue have in the molar gas equation?

A

dm(3)

29
Q

What is the most common unit of volume?

A

cm(3)

30
Q

How can you convert cm(3) into dm(3)?

A

/ 1000

31
Q

Describe the strategy for finding an unknown volume of gas in a reaction

A
  1. calculate moles using n = v/24
  2. use molar ratio to find moles of unknown
  3. calculate volume of unknown using v = n x 24
32
Q

What are the units of concentration?

A

mol/dm(3) or g/dm(3)

33
Q

What is the equation for calculating concentration from moles?

A

concentration = moles / volume

34
Q

What is the most common unit for volume?

A

cm(3)

35
Q

What unit of volume is required for calculating concentration?

A

dm(3)

36
Q

How can you convert cm(3) into dm(3)?

A

/ 1000

37
Q

What is the equation for calculating concentration from mass?

A

concentration = mass/ volume

38
Q

How can you convert mol/dm(3) into g/dm(3)?

A

x Mr

39
Q

How can you calculate the mass of solute when given concentration and volume?

A

mass= concentration x volume x Mr

40
Q

How is the mean titration volume calculated?

A

By adding up the concordant results and dividing by the number of concordant results

41
Q

Describe the strategy for finding an unknown concentration in titration

A
  1. calculate moles using n = C x v
  2. use molar ratio to find moles of unknown
  3. calculate concentration of unknown using C= n/V
42
Q

Why is it not possible to obtain 100% yield?

A

Reaction might be reversible. Products are lost during separation. Reactants react in unexpected ways

43
Q

What is yield?

A

The amount of product obtained

44
Q

How can you calculate % yield?

A

% yield = (actual mass/ theoretical mass) x 100

45
Q

What is atom economy?

A

A measure of the amount of starting materials that end up as useful products

46
Q

Why is high atom economy important?

A

Sustainable development and for economic reasons

47
Q

How can you calculate atom economy?

A

Atom economy = (Mr desired product / Mr of all reactants) x 100

48
Q

What is unusual about calculating atom economy?

A

The balancing numbers are used when calculating all the Mr’s

49
Q

How can atom economy be improved?

A

By finding a use for the waste products

50
Q

What is the atom economy for a reaction where only one product is made?

A

100%

Chemistry (12 decks)

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