3 - Stoichiometry

Question 1

How do you find the amount of mass in a compound to represent 1 mole

Answer 1

Add atomic masses together

H2O = 1 + 1 + 6 = 8g = 1 mole

MgO = 24 + 16 = 40 g = 1 mole

C6H12O6 = 6 (12) + 12 (1) + 6 (16) = 72 +12 + 96 = 180 g = 1 mole

Question 2

How do you find the amount of mass needed of an element to have 1 mole ?

Answer 2

Mass number = number of grams needed for 1 mole

e.g. 2
He
4

Question 2

How do you find the amount of mass needed of an element to have 1 mole ?

Answer 2

Mass number = number of grams needed for 1 mole

Question 3

What is a mole

Answer 3

A mole is a UNIT used to MEASURE PARTICLES

1 mole = 6.022 x 10^23

a small burrowing mammal with dark velvety fur HAHA! Just kidding

Question 4

Detail percentage of gases in the air

Answer 4

78% N2
21% O2
1% Others —> 0.04% CO2
— > 0.96% Noble gases —> Ar (most common)
—> He
—> Ne
+ The % of water isn’t counted because it varies

Question 5

What is the formula to find the volume of gas in the air given moles?

Answer 5

Volume of gas (dm³) = Moles of gas x 24

Question 6

What is the formula to find the number of moles in an element?

Answer 6

Number of moles = mass (g)/m_r

Question 7

What is Avogadro’s constant ?
Explain how to calculate the number of moles of a substance
- compound
- element

Answer 7

6.022 x 10²³

Mr (all of the Ar combined)
Ar

Question 8

What is Avogadro’s law for gases ?

Answer 8

Equal volumes of gas contain the same number of particles (at the same temperature and pressure)

Question 9

What is the relationship in gases between Volume and Number of Particles

Answer 9

Volume and number of Particules are directly proportional

Question 10

What is the formula for finding the volume of a gas

Answer 10

n = V/24

n = number of moles
v = volume (dm^3)

Question 11

Which factors affect gas volume -

Answer 11

• Container ?
• Pressure
• Temperature
• size of molecules (negligable)

Question 12

What is the formula to find the number of moles in a substance

Answer 12

n = m/mr

n = number of moles
m = mass
mr = average relative molecular mass

Question 13

Does the kind of gas affect / determine the volume one mole will take ?

Answer 13

NOPE
At room temperature, 1 mole of gas always takes up 24 dm^3

Question 14

What is r.t.p?

Answer 14

Room Temperature and Pressure
(25degrees)
(1atm ) atmosphere

Question 15

Def. A_r

Answer 15

Relative atomic mass is the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of C-12

Question 16

Def. M_r

Answer 16

Relative molecular mass is the sum of Ars.
Relative formula mas, Mr, will be used for ionic and macro molecular compounds

Question 17

What is the formula for Percentage composition?

Answer 17

% of element = Mass of element in 1 mole of compound/Mr x 100

Question 18

What is the formula for concentration in g/dm³?

Answer 18

c = m/v

c = Concentration (g/dm³)
m = Mass (g)
v = Volume (dm³)

Question 19

What is the formula for concentration in mol/dm³?

Answer 19

c = n/v

c = Concentration (mol/dm³)
n = Moles (mol)
v = Volume (dm³)

Question 20

What is the formula for concentration in mol/dm³ when the number of moles of the substance is unknown?

Answer 20

c = m/M_rv

c = Concentration (mol/dm³)
m = Mass (g)
v = Volume (dm³)
M_r = Molecular mass

Question 21

Def. Concentration

Answer 21

A measure of solute in a volume of solvent.

The higher the concentration, the more particles of a solute are in a given volume of solvent