Chapter 2: Amount of substance

Question 1

What is the Avogadro constant?

Answer 1

6.022 × 10^23 mol-1

Question 2

What is a mole? And what is the equation of it?

Answer 2

The amount of substance that contains 6.022x10^23 particles.

Mole(n) = Mass (g) / Mr

Question 3

what is the Concentration formula?

Answer 3

Concentration (mold dm^-3) = Moles (n) / Volume (dm^3)

Question 4

What is the Ideal Gas Equation?

Answer 4

pV = nRT

Where p = Pressure in Pa, standard pressure = 100,000 Pa

V = Volume in meters cubed

n = Number of moles of gas

R = The Ideal Gas Constant at 8.31 J/K/mol

T = Temperature in K, standard temprature = 298K(25°C)

Question 5

What does PV equal?

Answer 5

PV = nRT

Question 6

What is the Empirical formula?

Answer 6

Number of moles = mass of element / mass of 1 mole of element

Question 7

Find the empirical formula of clacium carbonate

10.1 g of a white solid contains:

• 4.01 g of calcium,
• 1.20g of carbon,
• 4.80 g of oxygen

Ar = Ca(40.1) C(12.0) O(16.0)

Answer 7

moles of calcium = 4.01 / 40.1 = 0.1

moles of carbon = 1.2 / 12 = 0.1

moles of oxygen = 4.8 / 16.0 = 0.3

therefore the ratio is calcium : carbon: oxygen:

1 : 1 : 3

= CaCO3

Question 8

What is the molecular Formula?

Answer 8

The molecular formula is the number of atoms of each element in 1 molecule of a compound.

Question 9

The Emprical formula of compound x is

x also has an Mr of 58

C : H : O

3 : 6 : 1

Find the molecular formula.

Answer 9

The Mr of C : H : O = 58

Therefore the molecular formula is also

C3H6O

Question 10

What is the equation for moles

Answer 10

Mole = Mass/Mr

Question 11

What is the equation for atom economy?

Answer 11

% atom economy = Mass of desired product total mass of reactants x100

Question 12

Find the atom econmy of sodium chlorate in:

2NaOH + CL2 → NaCl + H2O + NaOCl

Mr of Na = 23

Mr of Cl = 35.5

Mr of O = 16

Mr of H = 1

Answer 12

Moles = 2 : 1 → 1 : 1 : 1

Therefore the masses must = 80g : 71g → 58.5g : 18g : 74.5g

% atom economy = 74.5/151 x 100

= 49.3%

Question 13

What is the formula for percentage yield?

Answer 13

percentage yield = Number of moles of product max nubmber of moles of the product x100