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Chemistry > Quantitative Chemistry C3 > Flashcards

Quantitative Chemistry C3 Flashcards

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1
Q

What is relative formula mass?

A

Relative formula mass (M_r) is the sum of the relative atomic masses of all the atoms in a molecular formula.

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2
Q

How do you find the relative formula mass of MgCl2?

A

1) Look up the relative atomic masses: A of Mg = 24, A of Cl = 35.5.
2) Calculate: M_r = 24 + (2 x 35.5) = 95.

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3
Q

How do you calculate the percentage mass of an element in a compound?

A

Percentage mass = (A x number of atoms of that element / M_r of the compound) x 100.

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4
Q

What is the percentage mass of sodium in sodium carbonate (Na2CO3)?

A

M_r of Na2CO3 = (2 x 23) + 12 + (3 x 16) = 106.
Percentage mass of sodium = (23 x 2 / 106) x 100.

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5
Q

How do you find the mass of iron in a mixture containing 20% iron ions?

A

In a 50 g mixture, the mass of iron = 50 x 0.20 = 10 g.

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6
Q

How do you calculate the percentage mass of iron in iron chloride (FeCl3)?

A

M_r of FeCl3 = 56 + (3 x 35.5) = 142.5.
Percentage mass of iron = (56 / 142.5) x 100 = 39.44%.

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7
Q

What is the relative atomic mass (A) of an element?

A

The relative atomic mass is the same as its mass number and can be found on the periodic table.

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8
Q

How much iron chloride is needed to provide 10 g of iron in a mixture?

A

To provide 10 g of iron, you need to calculate the mass of iron chloride based on its percentage mass of iron.

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9
Q

What is the percentage composition by mass of potassium in potassium hydroxide (KOH)?

A

Calculate using the formula: (A of K / M_r of KOH) x 100.

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10
Q

What is a mole?

A

A mole is simply the name given to an amount of a substance, similar to how ‘a million’ represents 1,000,000.

The Avogadro constant is 6.02 x 10^23.

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11
Q

How many particles are in one mole?

A

One mole of any substance contains Avogadro’s number of particles, which is 6.02 x 10^23. The particles could be atoms, molecules, ions, or electrons.

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12
Q

What is the relationship between moles and mass?

A

The mass of one mole of atoms or molecules of any substance is equal to the relative atomic mass (A_r) or relative formula mass (M_r) of that substance in grams.

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13
Q

What is the mass of one mole of carbon?

A

One mole of carbon has a relative atomic mass (A_r) of 12 g.

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14
Q

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

A

One mole of nitrogen gas (N2) has a relative formula mass (M_r) of 28 g (2 x 14).

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15
Q

What is the mass of one mole of carbon dioxide (CO2)?

A

One mole of carbon dioxide (CO2) has a relative formula mass (M_r) of 44 g (12 + [2 x 16]).

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16
Q

How do you calculate the number of moles from mass?

A

Number of moles = mass in grams (of an element or compound) / M_r (of the element or compound).

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17
Q

How many moles are in 66 g of carbon dioxide (CO2)?

A

To find the number of moles in 66 g of CO2, use the formula: 66 g / 44 g/mol = 1.5 mol.

18
Q

What is the mass of 4 moles of carbon?

A

The mass of 4 moles of carbon is 4 x 12 g = 48 g.

19
Q

What is the formula triangle for calculating moles?

A

The formula triangle is: M = mass / number of moles. Cover the variable you want to find.

20
Q

What is a common misconception about moles?

A

Calculations involving moles can be confusing, but they don’t need to be. Understanding the basics can help alleviate the confusion.

21
Q

What is the Conservation of Mass?

A

You can’t create or destroy matter; mass is always conserved in chemical reactions.

22
Q

What happens to atoms during a chemical reaction?

A

No atoms are destroyed and no atoms are created.

23
Q

What can be said about the number and types of atoms in a reaction equation?

A

The same number and types of atoms are present on each side of a reaction equation.

24
Q

What does it mean when mass is conserved?

A

No mass is lost or gained during a chemical reaction.

25
Q

How can you show that mass is conserved in a reaction?

A

By adding up the relative formula masses of the substances on each side of a balanced equation.

26
Q

Example of mass conservation in a reaction: 2Li + F2 → 2LiF.

A

Total mass of reactants equals total mass of products: 52 = 52.

27
Q

What happens if the mass seems to change during a reaction?

A

Usually, a gas is involved.

28
Q

What does it indicate if the mass increases during a reaction?

A

It likely means one of the reactants is a gas from the air.

29
Q

What happens when a gas reacts and is contained in a reaction vessel?

A

The total mass inside the vessel increases as the gas is now accounted for.

30
Q

What does it indicate if the mass decreases during a reaction?

A

It likely means one of the products is a gas that escapes the reaction vessel.

31
Q

What happens when a metal carbonate decomposes?

A

The mass of the reaction vessel decreases if it’s not sealed, but the total mass of products equals the mass of the reactants.

32
Q

What is a key takeaway about mass in reactions?

A

The total mass of reactants is always equal to the total mass of products.

33
Q

What is concentration in chemistry?

A

Concentration is the amount of a substance (e.g. mass or number of moles) in a certain volume of a solution.

34
Q

How does the amount of solute affect concentration?

A

The more solute there is in a given volume, the more concentrated the solution.

35
Q

What are the units for measuring concentration?

A

Concentration can be measured in g/dm³.

36
Q

How do you calculate concentration in g/dm³?

A

Concentration = mass of solute / volume of solvent in dm³.

37
Q

What is the concentration of a solution with 30 g of sodium chloride in 0.2 dm³ of water?

A

The concentration is 150 g/dm³.

38
Q

How do you convert cm³ to dm³?

A

1 dm³ = 1000 cm³.

39
Q

What is the concentration of a solution with 15 g of salt in 500 cm³?

A

First, convert 500 cm³ to dm³: 500 cm³ = 0.5 dm³. Then, concentration = 15 g / 0.5 dm³ = 30 g/dm³.

40
Q

How can you find the mass of solute if you know its concentration?

A

Use the formula: mass = concentration x volume.

41
Q

What mass of salt is needed to create a solution with a concentration of 24 g/dm³ in 0.40 dm³ of water?

A

mass = 24 g/dm³ x 0.40 dm³ = 9.6 g.

42
Q

What should you remember about measurements?

A

All measurements have some uncertainty.

Chemistry (10 decks)

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