Module 2 - Intro to Quantitative Chemistry

Question 1

State the features of an Empirical Formula.

Which type of compounds always feature an empirical formula? Explain.

Answer 1

The simplest ratio of atoms or ions in a compound/equation.

Ionic compounds are always represented in an empirical formula since they generally form repeating, lattice patterns, making it easier to represent as a ratio.

Question 2

Explain what stoichiometry is.
State its relation to a chemical equation.
(Hint: Law of C of M)

Answer 2

The quantitative relationship between mass, energy and no. of atoms.

The mass and no. of atoms of products and reactants must be equal.

Question 3

State the Law of Conservation of Mass, in regards to reactants and products.

Explain its use with reactants and products.

Answer 3

States:
Total mass of reactants = Total mass of products

Useful to determine mass of reactants required to produce a given amount of a product.

Question 4

State the density formula.

Explain it’s relationship:
Temperature ↑, density =?

Answer 4

Density = mass/Volume (d=m/v)

As temperature ↑, Density ↓.
High temperature expands the solution’s area due to particles vibrating more.

Question 5

State Avogadro’s constant (N).

What does it measure?

Answer 5

6.022 x 10^23 particles.

Used to measure MOLES (n).

Question 6

State the formula relating mole (n), molar mass (MM) and given mass of a substance (m).

Answer 6

n = m/MM

n (no. of mole) = m (mass in grams) / Molar Mass (g.mol-1)

Question 7

Explain what Limiting Reagents are and excess reagents.

Answer 7

Limiting Reagent: Reactant that is fully used up in a chemical reaction.

Excess reagent: Product that is left over (not fully consumed by reaction).

Question 8

What is Percentage Composition by mass?

State its formula.

Answer 8

The mass (%) of an element in 1mol of a compound.

Formula: (mass of element / total mass of compound) x 100

Question 9

List the 5 steps of calculating Limiting Reagents in a chemical reaction when given the mass of each reactant.

Answer 9

1) Balance the equation.
2) Calculate no. of moles for each LHS reactant.
3) Determine the limiting reagent from the mole ratios. (E.g.: 2:1, multiply the no. of moles by each ratio)
4) Compare final vs initial mole ratios:
(Calculated mole > Given mole = Limiting Reagent)
5) Calculate the final mass.

Question 10

Explain the process of Dilution. What is it used for?

State the formula.

Answer 10

Adding water to an aqueous solution to reduce the concentration of the solvent. Used to determine the concentration of an unidentified solution/substance
Formula: C(1) x V(1) = C(2) x V(2)

Question 11

What is the measurement accuracy for:

1) Measuring cylinders
2) Pipettes & Burettes
3) Volumetric Flasks

Answer 11

1) Measuring Cylinders: ±5%
2) Pipettes & Burettes: ±0.2% to ±0.5%
3) Volumetric Flasks: ±0.2% to ±0.5%

Question 12

State Charles Law and the formula linked with it.
(T | V)
Is the relationship directly or inversely proportional?

Answer 12

VOLUME of gas at a fixed volume is directly proportional to TEMPERATURE.
V1 / T1 = V2 / T2

Question 13

State Boyles Law and the formula linked with it.
(P | V)
Directly or Inversely proportional?

Answer 13

VOLUME of a fixed amt. of gas is inversely proportional to PRESSURE.
P1 V1 = P2 V2

Question 14

State Gay-Lussac’s Law and the formula linked with it.
(P | T)
Directly or Inversely proportional?

Answer 14

PRESSURE at a fixed volume is directly proportional to TEMPERATURE.
P1 / T1 = P2 / T2

Question 15

State Avogadro’s Law and the formula linked with it.
V, n, k(constant)
V, n

Answer 15

EQUAL VOLUMES of gas, at the same temperature and pressure, contain an EQUAL no. of MOLES.
V/n = k OR V1 / n1 = V2 / n2

Question 16

State the formula for Ideal Gas Law and also state each letter within the equation.

Answer 16

PV = nRT
P=Pressure
V=Volume
N= No. of gas moles
R= Universal gas Constant (8.314K/mol.K)
T=Temperature (K)

Question 17

State the formula for Universal Gas Law.

Answer 17

P1V1 / T1 = P2V2 / T2

or PV/T = a (constant)

Question 18

Explain what Molar Volume is and the formula associated with it.

Answer 18

The volume occupied by one mole of the gas at a given temperature and pressure. (Vm)
Vm = V / n

Question 19

List the mnemonics for remembering Gas Law Equations.

C | T | G | P | B | V

Answer 19

Can These Guys Possibly Be Victorious
C=Charles Law, T=Temperature, G=Gay Lusaac’s Law,
P=Pressure, B=Boyles Law, V=Volume

Question 20

For limiting reagents and excess reagents, state how to determine each one.
(Hint: n and N)

State the formula (in words to find this).

Answer 20

Lowest quantity per coefficient ratio, after comparing mole ratios.
(Works for no. of mols (n) & molecules (N) )

Reactant’s no. of mol ÷ Given quantity (mass, molar mass, etc.)

Question 21

Explain what Titration is and the process involved.

State what must be prepared before conducting a titration experiment.
Also, state 1 common example.

Answer 21

The slow addition of a solution with known concentration to determine the concentration of an unidentified solute/solution.

A primary standard solution of known concentration and volume must be prepared. E.g.: Sodium Carbonate

Question 22

State the 3 features of a Primary Standard which are commonly used in Titrations and Dilutions.

List 2 common examples.

Answer 22

1) High Molar Mass
2) Does not react with moisture or atmosphere
3) High purity levels
E.g.: Sodium Carbonate,
Potassium Dichromate.