L4 - Chemical Equations, The Mole & Molarity

Question 1

What is the Mole?

Answer 1

The SI unit for amount of substance.

Question 2

Define Avogadro’s Number (NA).

Answer 2

The number of atoms found in 12g of Carbon-12.

Question 3

What is 1 Mole?

Answer 3

6.0221367 * 10^23

Question 4

What is the mass of 1 mole of any substance?

Answer 4

Mass of 1 Mole of any substance is its relative atomic mass (elements) or relative molecular mass (compound) expressed in grams.

Question 5

Define Molar Mass.

Answer 5

Mass of one mole of a substance.

Question 6

How do you calculate the Number of Moles using mass?

Answer 6

Number of Moles (mol) = Mass (g) / Molar Mass (g mol-1)

n = m / mm

Question 7

For any molecule: Molecular Mass (amu) = _____ ____ _______.

Answer 7

Molar Mass (grams)

Question 8

State the Ideal Gas Law.

Answer 8

“1 mole of any gas occupies the same volume at standard temperature and pressure.”

Question 9

At STP, Molar Gas Volume is always V = ___________.

Answer 9

22.4 L / 22.4 dm^3 mol^-1

Question 10

How do you calculate the Number of Moles using volume?

Answer 10

Amount of Substance (mol) = Volume (dm^3) / Molar Volume (dm^3 mol^-1)

n = V / MV

Question 11

State the Ideal Gas Law mathematically.

Answer 11

pressure (Pa) * volume (m^3) = number of moles (mol) * gas constant (J mol^-1 K^-1) * temperature (K)

PV = nRT

Question 12

What is the gas constant?

Answer 12

R = 8.314 J mol^-1 K^-1

Question 13

What is the IUPAC defined Standard Temperature?

Answer 13

273 K

Question 14

What is the IUPAC defined Standard Pressure?

Answer 14

100 kPa

Question 15

What is the IUPAC defined Standard Room Temperature?

Answer 15

298 K

Question 16

Define Molarity.

Answer 16

Solution concentration expressed as moles of solute dissolved in one litre of solution.

Question 17

How do you calculate Molarity?

Answer 17

Molarity (mol L^-1) = Moles (mol) / Volume (L)

M = n / V

Question 18

What is the calculation for unknown concentration and volume of solutions?

Answer 18

concentration 1 * volume 1 = concentration 2 * volume 2

c1 v1 = c2 v2

Question 19

How many litres is 1 ml?

Answer 19

1 ml = 1 / 1000 L

Question 20

How many grams is 1 mg?

Answer 20

1 mg = 1 / 1000 g

Question 21

What do chemical reactions involve?

Answer 21

• Changes in identity of compounds
• Energy changes
• Breaking and making chemical bonds
• Rearrangement of valence electrons

Question 22

How can chemical reactions be described by chemical equations?

Answer 22

• Symbols represent elements
• Formulae describe composition of compounds
• Equations show changes in compounds

Question 23

What does a coefficient represent?

Answer 23

Coefficient represents number of molecules of compound / atom needed in reaction.

Question 24

What can coefficients be changed to achieve?

Answer 24

Coefficients can be changed to achieve mass balance but subscripts are never changed to balance an equation.

Subscripts indicate the number of bonded atoms in a molecule.

Changing the subscripts changes the compound.

Question 25

Define Yield.

Answer 25

Amount of product produced.

Question 26

How is percentage yield calculated?

Answer 26

Percentage Yield = Actual Yield / Theoretical Yield * 100%

Question 27

Matter cannot be _______ or ____ in a closed system.

Answer 27

Matter cannot be created or lost in a closed system.