Chapter 3: Amount of substances

What does 6.02 X 10²³ mean?

it means in 1 mole there is 6.02 X 10²³ particles

What is Mr?

is the mass per mole of a substance

What’s the difference between Ar and Mr?

Ar = The weighted mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom.

Individual elements = (C=12), (O= 16)

Mr = The sum of the Ar values of all the atoms in a chemical formula

Like molecules like CO₂ [ Ionic Compounds, covalent structures ]

What is molecular formula?

Definition: the exact number and type of atoms of each element present in a molecule

Is the number of atoms of each elements in a molecule.

What is Empirical Formulae?

the simplest whole-number ratio of atoms of each element present in a chemical compound

For Hydrated Salts what’s the common salt they use?

CuSO₄ Copper (II) Sulfate

For Copper (II) Sulfate during the experiement what happens to it?

• When heated; the bonds are broken as H₂O evaporates.

• Leaving the white anhydrous Copper (II) Sulfate.

What’s the Colour Change in Hydrated Salts Experiment?

Blue to white

What are the steps in the Hydrated Salt’s experiment?

1. Weigh an empty Crucible

2. Add the hydrated Salt into the Crucible ( weigh crucible + Hydrated salt)

3. Heat Crucible

4. Leave Crusible to cool —- ( weight Cruscible + anhydrous salt)

What’s the before and after version of the Hydrated salt experiment?

• Before = Hydrated Salt

• After = Anhydrous salt

How do you find the mass of the H₂O?

CuSO₄ . 5H₂O — CuSO₄

What if the experiment isn’t acurate results?

1. If the anhydrous salt and hydrated salt are simmilar colours it can be hard to differenitate the 2 / or if the H₂O is removed!! - Heat to Constant mass —- Crystals are reheated repeatedly untill the mass of the residue no longer changes ——> All Water has been removed!!

2. If it heated longer then needed: This causes the salts to decompose further ——> Copper (II) Sulfate decomposes to Black Copper (II) Oxide. — No further decomposition needed!!

Give me the units for Volume in the equation: N= C X V?

cm³

Calculate the mass of Na₂CO₃ required to prepare 100cm³ of a 0.250 mol dm^-3 ?

N= 0.0250mol

Vm ( Molar Volume) definition and what are the conditions?

Volume per mole of gas molecule at a stated temperature and pressure RTP— room temperature pressure.

• 101Kpa

• 1 mole of gas molecules = 24 dm³ / 24,000 cm³

• The molar gas volume = 24.0 dm³ mol^-1

Calculate the amount (mol) of hydrogen, H₂ (g), in 480cm³ at RTP?

• If the question is in cm³ then the working out should also be cm³

• N= V( cm³ ) / 24,000 = [480/ 24000] = 0.0200 mol

What are the 4 assumptions of the ‘ Ideal gas’ ?

1. Random motion

2. No intermolecular forces

3. Negligible Size

4. Elastic Collisions

What is the units in the Ideal Gas equation?

PV = nRT

P = Pa (pressure)

V = Volume ( m³ )

N = Amount of gas molecules (mol)

R = The Ideal gas constant in data booklet

T = K

Whats the conversion for [ m³ —— cm³ ——- dm³ ] and [^oC —— K] and [ kPa——Pa]?

M³ — cm³ (X10⁶) cm³ —- M³ ( divide 10³)

cm³ —- dm³ ( divide 10³ ) —— dm³ —— cm³ ( X 10³ )

^oC ———> K [ +273]

Kpa———> Pa [ X10³]

How to identify an unknown Group 2 metal X ?

1. Weigh a sample of the metal of the metal and add to the flask.

2. Using a measuring cylinder ; - HCl excess ; quickly replace the bung

3. Measure the maximum volume of gas in the syringe.

Why is the Theoretical Yield is hard to achieve because…….?

• Reaction may not have gone to completion

• Other reaction ( side reactions) may have taken place

• Purification of the products —- can results in loss of some products.

What is percentage Yield and incomparison with the equations?

% Yield = ( Actual Yield / Theoretical Yield ) X 100%

Actual Yield is the mass and Mr given in question and you calculate

Theoretical Yield is calculating it based on the equation they give you.

Theoretical Yield = What you should get—— [if reaction was 100% successfull!!]

Actual Yield = What you did to get ( Reactant)

What does a high atom economy mean?

• Large proportions of desired products / few unwanted waste products

• Important for sustainability —- best use of natural resourses.

• Assumes 100% yield: [ Sum of Mr of desired Products / Sum Mr of all reactants] X 100%

What does improving the atom economy look like in the long run?

• Makes industrial processes more efficient

• Peserves raw materials

• Reduces waste

According to the equations how would you classify the equation according to it?

• In the question might state the desired product […..] is the raw material.

• the one next to the desired product is the unwanted product.

Definition of atom economy in our understanding?

The percentage of atoms from the reactants end up in the usefull products you actually want!!

What does High atom economy want and Low economy?

High economy = Less waste

Low economy = More waste