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03 Chemistry > Module 2 (Quantitative Chemistry) > Flashcards

Module 2 (Quantitative Chemistry) Flashcards

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1
Q

Law of Conservation of Mass

A

Matter is neither created nor destroyed, only rearranged.

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2
Q

Solving Stoichiometric Ratio Questions

Four steps

A
  1. Write a balanced chemical reaction equation.
  2. Convert given units into moles.
  3. Use the mole ratio to find the moles of the unknown substance.
  4. Convert into desired form.
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3
Q

Avogadro’s Number

A

6.022 x 10²³

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4
Q

Mole Formulas

A

n = p/Na = m/MM

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5
Q

Finding Percentage Composition

Three steps

A
  1. Write the chemical formula of the total compound.
  2. Use the chemical formula to find the molar mass of 1 mole of the compound.
  3. Find the percentage composition using the following formula: [MM(element)/MM(compound)] x 100
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6
Q

Finding Empirical Formula

Five steps

A
  1. Find the mass of each element.
  2. Calculate the number of moles of each element present (n = m/MM).
  3. Divide all the values by the smallest value to make the smallest value into 1.
  4. Multiply all the values until they closely resemble whole numbers.
  5. Write the empirical formula in the form of a chemical formula.

If only given percentages, assume the total sample is 100g (e.g. 76.3% carbon = 76.3g)

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7
Q

Finding Molecular Formula

A

The actual number of atoms of each element present in a molecule rather than the simplest whole number ratio (can be same or different from empirical).

No. of empirical formula units in the molecule = MM (compound) / MM ( one empirical formula unit)

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8
Q

Solving Limiting Reagent Questions

Four steps

A
  1. If necessary, convert all values into moles (n = m/MM).
  2. Write the balanced chemical reaction.
  3. Choose one product of the reaction and using molar ratios in the chemical reaction, determine which reactant produces the least product. This is your limiting reagent.
  4. Use the stoichiometric coefficient of the limiting reagent as a ratio with the unknown element and calculate the desired quantity.
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9
Q

Water of Crystallisation

A

Water that is chemically bonded into a crystal structure.

When a crystal substance has been dehydrated, it is anhydrous.

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10
Q

Aim

Water of Crystallisation Practical

A

To determine the water of crystallisation of copper (II) sulphate. (CuSO₄.5H₂O)

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11
Q

Method

Water of Crystallisation Practical (seven steps)

A
  1. Set up the apparatus as shown below:
    Figure 1: Apparatus used to heat copper (II) sulphate
  2. Heat the crucible and lid for two minutes, then place it on the heat-proof mat using the crucible tongs. Allow it to cool for 5 minutes.
  3. Weigh the crucible and lid and record the mass in a table.
  4. Using a spatula, transfer 2 grams of copper (II) sulphate into the crucible onto the electronic balance.
  5. Place the crucible with lid onto the clay triangle and heat the crucible for 10 minutes until all the copper (II) sulphate is white.
  6. Cool the crucible for 5 minutes then reweigh. Record the mass of the crucible and lid with the anhydrous copper (II) sulphate.
  7. Calculate the mass of water lost and determine the water of crystallisation.
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12
Q

Discussion

Water of Crystallisation Practical (5)

A
  • Repetition was carried out but proved unreliable (varied answers)
  • Weighing errors (small quantities), evaporation of water error (no way to evaporate all the water)
  • Crucible could have been dried in an oven and weighed until constant mass
  • Result expected to be less that true value
  • Inaccurate (averaging improves accuracy for groups with lower results)
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13
Q

Molarity

Measures of Concentration

A

Moles per 1L of solution (molL-1)

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14
Q

% by Weight

Measures of Concentration

A

Grams per 100 grams (% (w/w))

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15
Q

% by Volume

Measures of Concentration

A

Millilitres per 100 millilitres (%(v/v))

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16
Q

Mass per Volume

Measures of Concentration

A

Grams per 1 millilitre (gmL-1)

17
Q

Molarity Formula

A

c = n/V

c = concentration (molL⁻¹)
n = moles of solute
V = volume of solution (L)

18
Q

Dilution Formula

A

C₁V₁ = C₂V₂

c1 = concentration of original solution (mol/L)
V1 = volume of original solution (L)
c2 = concentration of new solution (mol/L)
V2 = volume of new solution (L)

19
Q

Aim

Dilution of Copper (II) Sulphate Pentahydrate Practical

A

To determine the concentration of a primary standard, carry out its preparation and then complete two dilutions to determine the concentration of the final solution.

20
Q

Preparing a Primary Standard

Seven steps

A
  1. Dry the solid in a desiccator for 2 days.
  2. Take a clean and dry 50 ml beaker and place it on an electronic balance (at least 2 decimal places), then zero the balance. Weigh out the required amount of solid.
  3. Add about 25 ml of distilled water to the beaker and stir it with a stirring rod to dissolve the solid.
  4. Place a filter funnel into the desired size volumetric flask, ensuring it does not form a seal. Pour the solution down the stirring rod into the filter funnel.
  5. Rinse the beaker, filter funnel, stirring rod and inside the neck of the volumetric flask thoroughly with distilled water from a wash bottle.
  6. Add distilled water to the flask until it is 1 cm below the engraved mark, then add distilled water drop wise from a dropper until the meniscus is sitting on top of the engraved mark.
  7. Place a stopper on the flask and mix it by inverting the flask five times.
21
Q

What does the volume of gas depend on?

Three things

A

Unlike solids or liquids, the volume of a gas depends on:

  • Number of particles present
  • Pressure
  • Temperature
22
Q

Ideal Gas

A

A gas where the assumptions that the volume of gas particles is negligible because of their lack of intermolecular forces are true.

Ideal gases will always obey the gas laws, simplifying our understanding of gases.

23
Q

Ideal Gas Law

A

PV = nRT

P = Pressure (kPa)
V = Volume (L)
n = Moles
R = Gas constant (8.314)
T = Temperature (Kelvin)

24
Q

Standard Laboratory Conditions (SLC)

Standard Conditions

A

Temperature: 25°C/298 K
Pressure: 100 kPa
Molar volume of ideal gas: 24.79 L mol⁻¹

At SLC, the following formula can be used: n = V/MV. Non-standard conditions require the ideal gas law.

25
Q

Standard Temperature and Pressure (STP)

Standard Conditions

A

Temperature: 0°C/273 K
Pressure: 100 kPa
Molar volume of ideal gas: 22.71 L mol-1

26
Q

Gay-Lussac’s Law

Gas Laws

A

P₁/T₁ = P₂/T₂
(proportional, with volume kept constant)

Increased temperature increases the kinetic energy of the gas particles. The increased collisions with the sides of the container increases the pressure.

27
Q

Boyle’s Law

Gas Laws

A

P₁V₁ = P₂V₂
(inversely proportional, with temperature kept constant)

Increased volume of the container of gas decreases the number of collisions with the sides of the container, therefore decreasing the pressure.

28
Q

Charles’ Law

Gas Laws

A

V₁/T₁ = V₂/T₂
(proportional, with pressure kept constant)

Given that the pressure remains constant, increased temperature increases the kinetic energy of gas particles, increasing the volume of gas.

29
Q

Avogadro’s Law

A

V₁/n₁ = V₂/n₂
(proportional, with pressure and temperature kept constant)

More gas, more volume.

03 Chemistry (6 decks)

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