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Chemistry Paper 1 > Calculations Involving Masses > Flashcards

Calculations Involving Masses Flashcards

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1
Q

What is a limitation of dot and cross diagrams?

A

They don’t express the relative attraction of shared electrons due to electronegativity.

This limitation becomes more apparent at A-level chemistry.

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2
Q

What types of solids do dot and cross diagrams apply best to?

A

Solids composed of Group 1 and 2 elements with highly electronegative elements such as the halogens.

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3
Q

What do 2D diagrams fail to show?

A

The 3D arrangement of atoms.

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4
Q

What do 3D diagrams not represent?

A

The share or transfer of electrons.

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5
Q

Describe the general characteristics of most metals.

A

Shiny solids, high melting points, high density, good conductors of electricity.

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6
Q

Describe the general characteristics of most non-metals.

A

Low boiling points, poor conductors of electricity.

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7
Q

How do you calculate the relative formula mass (Mr) of a compound?

A

Sum of the relative atomic masses of the atoms in the numbers shown in the formula.

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8
Q

In a balanced chemical equation, what is equal?

A

Sum of Mr of reactants in quantities shown = sum of Mr of products in quantities shown.

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9
Q

Fill in the blank: The relative formula mass (Mr) of a compound is the _______.

A

[sum of the relative atomic masses of the atoms in the numbers shown in the formula]

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10
Q

True or False: Most non-metals are good conductors of electricity.

A

False.

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11
Q

What are the characteristics of most metals?

A

Shiny solids, high melting points, high density, good conductors of electricity

Metals typically exhibit these properties, making them useful in various applications.

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12
Q

How do most non-metals compare to metals in terms of boiling points and conductivity?

A

Most non-metals have low boiling points and are poor conductors of electricity

This distinction is important in understanding the differences between metal and non-metal elements.

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13
Q

What is the formula to calculate the relative formula mass (Mr) of a compound?

A

Sum of the relative atomic masses of the atoms in the formula

Remember to account for multiple atoms of an element in a compound.

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14
Q

In a balanced chemical equation, what does the sum of the Mr of reactants equal?

A

Sum of the Mr of products in the quantities shown

This principle reflects the conservation of mass in chemical reactions.

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15
Q

Fill in the blank: The relative formula mass (Mr) is calculated by summing the relative atomic masses of the atoms in the _______.

A

[chemical formula]

The chemical formula indicates the number and type of atoms present in a compound.

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16
Q

True or False: Most metals are poor conductors of electricity.

A

False

Metals are known for being good conductors of electricity.

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17
Q

List four properties of most metals.

A
  • Shiny solids
  • High melting points
  • High density
  • Good conductors of electricity

These properties make metals suitable for various industrial applications.

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18
Q

List two properties of most non-metals.

A
  • Low boiling points
  • Poor conductors of electricity

Non-metals are generally less versatile than metals in terms of conductivity and thermal properties.

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19
Q

What is the process to calculate the formulae of simple compounds from reacting masses?

A
  1. Work out moles of each using moles = mass / molar mass
  2. Work out the ratio of moles
  3. Simplify the ratio to get the smallest whole numbers
  4. Find the formula by multiplying each element by their number in the ratio
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20
Q

What is the empirical formula derived from the given moles of Fe and O?

A

Fe₂O₃

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21
Q

How do you calculate moles from mass?

A

Moles = Mass / Molar Mass

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22
Q

If the mass of iron (Fe) is 7.83 g, what is the number of moles of Fe?

A

0.140197

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23
Q

If the mass of oxygen (O) is 3.37 g, what is the number of moles of O?

A

0.210625

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24
Q

What is the ratio of moles of Fe to O based on their calculated moles?

A

1 : 1.5

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25
Q

Fill in the blank: To simplify the ratio, you need to get the smallest _______.

A

whole numbers

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26
Q

True or False: The empirical formula represents the actual number of atoms in a molecule.

A

False

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27
Q

What should you remember to use when writing the empirical formula?

A

Use little numbers, not a big number at the front

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28
Q

What is an empirical formula?

A

It shows the simplest ratio of the number of atoms of different types of elements in a compound.

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29
Q

What is the first step in determining the empirical formula of magnesium oxide?

A

Weigh some pure magnesium

This is the initial step to start the experiment.

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30
Q

What process is used to react magnesium with oxygen?

A

Heat magnesium to burning in a crucible

This reaction occurs as magnesium reacts with the oxygen in the air.

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31
Q

What do you need to weigh after forming magnesium oxide?

A

The mass of the magnesium oxide

This measurement is essential for further calculations.

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32
Q

What are the known quantities in this experiment?

A
  • Mass of magnesium used
  • Mass of magnesium oxide produced

These values are crucial for calculating the mass of oxygen.

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33
Q

How do you calculate the mass of oxygen in the experiment?

A

Mass oxygen = mass magnesium oxide - mass magnesium

This calculation determines the amount of oxygen that reacted.

34
Q

How do you calculate the moles of magnesium?

A

Moles magnesium = mass magnesium ÷ molar mass magnesium

This uses the mass of magnesium and its molar mass.

35
Q

How do you calculate the moles of oxygen?

A

Moles oxygen = mass oxygen ÷ molar mass oxygen

Similar to magnesium, this uses the mass of oxygen and its molar mass.

36
Q

What do you calculate after finding the moles of magnesium and oxygen?

A

The ratio of moles of magnesium to moles of oxygen

This ratio is needed to determine the empirical formula.

37
Q

What is the final step in determining the empirical formula?

A

Use the ratio to form the empirical formula

This follows the same method as described in a previous section.

38
Q

What is the law of conservation of mass?

A

No atoms are lost or made during a chemical reaction; the mass of the products equals the mass of the reactants.

39
Q

How can chemical reactions be represented?

A

By symbol equations that are balanced in terms of the numbers of atoms of each element involved on both sides.

40
Q

What occurs in a precipitation reaction in a closed system?

A

A precipitate forms that is insoluble and solid; total mass remains unchanged as all reactants and products are contained.

41
Q

Does the law of conservation of mass hold in an open system?

A

No, mass changes during a reaction in an open flask that takes in or gives out a gas.

42
Q

What is the formula to calculate moles of a substance?

A

Moles = mass / molar mass.

43
Q

How do you find the moles of a desired reactant or product from a balanced equation?

A

Use the balancing numbers to find the moles based on the moles of a known substance.

44
Q

What is the formula to calculate mass from moles?

A

Mass = moles x molar mass (of the reactant/product).

45
Q

Fill in the blank: In a closed system, the total mass is ______ after a precipitation reaction.

A

unchanged.

46
Q

True or False: The law of conservation of mass applies to all chemical reactions regardless of the system.

A

False.

47
Q

What happens to mass when gas is given off in a reaction?

A

Some mass is lost, changing the total mass from what it was at the start.

48
Q

How is the concentration of a solution measured?

A

In mass per given volume of solution, e.g., grams per dm³

49
Q

What is the equation to calculate the concentration of a solution?

A

concentration (g dm³) = mass of solute (g) / volume (dm³)

50
Q

How do you calculate the mass of solute in a given volume of a known concentration?

A

mass = concentration x volume, i.e., g = g/dm³ x dm³

51
Q

What defines one mole of particles of a substance?

A

The Avogadro constant number of particles (6.02 x 10²³) and a mass of ‘relative particle mass’ in grams

52
Q

What is the Avogadro constant?

A

6.02 x 10²³ per mole

53
Q

What is the mass of one mole of particles equivalent to?

A

‘Relative particle mass’ in grams

54
Q

Fill in the blank: The concentration of a solution can be measured in _______.

A

[mass per volume]

55
Q

True or False: One mole of a substance contains 6.02 x 10²³ particles.

A

True

56
Q

What unit is used to measure chemical amounts?

A

Moles

The symbol for the unit mole is mol.

57
Q

What is the relationship between the mass of one mole of a substance and its relative formula mass?

A

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

58
Q

What is the mass of one mole of iron (Fe)?

A

56g

The Ar of Iron is 56.

59
Q

What is the mass of one mole of nitrogen gas (N2)?

A

28g

The Mr of nitrogen gas (N2) is 28 (2 x 14).

60
Q

How many particles are in one mole of any substance?

A

6.02 x 10^23

This number is known as Avogadro’s constant.

61
Q

How do you convert between moles and grams?

A

Use the equation: moles = mass (g) ÷ relative atomic mass.

62
Q

Calculate the number of moles in 42g of carbon.

A

3.5 moles

Calculation: Moles = 42g / 12g/mol.

63
Q

What is the formula to find the number of particles in a given number of moles?

A

Number of particles = moles x Avogadro’s constant.

64
Q

Fill in the blank: One mole of a substance contains the same number of ______ as one mole of any other substance.

A

particles

65
Q

True or False: The number of particles in a given number of moles of a substance is independent of the substance.

A

True

66
Q

What is the Avogadro constant?

A

6.02 x 10^23 per mole.

67
Q

What is the mass of one mole of a substance if its relative formula mass is 40?

A

40g

68
Q

What is the term for the reactant that is used up in a chemical reaction?

A

Limiting reactant

The limiting reactant is the substance that limits the amount of product formed in a reaction.

69
Q

Why is one reactant often used in excess during a chemical reaction?

A

To ensure that all of the other reactant is used

Using one reactant in excess helps to maximize the yield of the desired product.

70
Q

What controls the mass of product formed in a reaction?

A

The mass of the reactant which is not in excess

The limiting reactant determines the maximum amount of product that can be formed.

71
Q

In a reaction with multiple reactants, what happens to the amount of reactant in excess?

A

It is limited to the exact amount that reacts with the limiting reagent

Only the portion of the excess reactant that reacts with the limiting reactant contributes to product formation.

72
Q

Fill in the blank: The amount of product formed is determined by the _______.

A

Limiting reactant

The limiting reactant dictates the maximum yield of products in a reaction.

73
Q

What should you use for calculations involving product formation in a reaction?

A

Moles/mass of the limiting reagent

Calculations for product yield depend on the amount of the limiting reactant.

74
Q

What is stoichiometry?

A

Stoichiometry refers to the balancing numbers in front of compounds/elements in reaction equations.

It is essential for determining the proportions of reactants and products in a chemical reaction.

75
Q

How can balancing numbers in a symbol equation be calculated?

A

Balancing numbers can be calculated from the masses of reactants and products by:
* converting the masses in grams to amounts in moles (moles = mass/Mr)
* converting the numbers of moles to simple whole number ratios.

This process allows chemists to balance chemical equations accurately.

76
Q

What is the formula to convert mass to moles?

A

moles = mass / Mr

‘Mr’ refers to the molar mass of the substance.

77
Q

Given 127 g of Cu, what is the number of moles of Cu?

A

2 moles

Calculation: moles = 127 g / 63.5 g/mol.

78
Q

Given 32 g of O2, what is the number of moles of O2?

A

1 mole

Calculation: moles = 32 g / (16 g/mol × 2).

79
Q

Given 159 g of CuO, what is the number of moles of CuO?

A

2 moles

Calculation: moles = 159 g / (16 g/mol + 63.5 g/mol).

80
Q

What is the mole ratio of Cu:O2:CuO in the reaction?

A

2:1:2

This ratio is derived from the number of moles calculated for each substance.

81
Q

What is the balanced equation for the reaction involving Cu and O2 to form CuO?

A

2Cu + O2 -> 2CuO

This equation is balanced based on the calculated mole ratios.

82
Q

True or False: The stoichiometry of a reaction can be deduced from the masses of the reactants and products.

A

True

The mass of reactants and products provides the necessary information to determine stoichiometric coefficients.

Chemistry Paper 1 (7 decks)

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