Chemistry: SAT 3 Revision

What is the formula to calculate how many particles are in a substance?

6.02 × 10²³ multiplied by substance mols

What is the formula to calculate molar mass?

The sum of all relative atomic masses per atom within the substance

What is relative atomic mass?

The weighted average of all naturally occurring isotopes an element, usually the mass number of the element on the periodic table.

How to calculate the relative atomic mass?

Mass number of the isotope times its abundance (%)

What is the unit of measurement for molar mass?

g/mol

State the general formula for alkanes and alkenes

Alkane: C_nH_2n + 2
Alkenes: C_nH_2n

State the definition of solubility

A measure of the mass of solute that will dissolve in a solvent at a given temperature

State the definitions for solute and solvent

Solute: the substance dissolved in a solvent to form a solution
Solvent: the substance that dissolves the solute to form a solution

State the definition of solution

A homogeneous mixture formed when a solute dissolves into a solvent

State the definition of miscibility

The ability for two or more substances to dissolve and create a homogenous mixture

What is a kink?

A physical bend or structural distortion in a long molecular chain

At room temperature, what is the physical state of fats and oils?

Fats are solids; oils are liquids.

Why is oil a liquid at room temperature

It is an unsaturated compound, which has loose packing of dispersion forces that require little energy to overcome

What does concentration measure?

The quantity of solute dissolved in a solvent.

What does molar concentration measure?

The quantity of solute dissolved in a solvent but in moles per unit volume (mol/L).

Explain the difference between concentration and molar concentration

Concentration is a general term whereas molar concentration is a specific measurement of concentration using moles per litre.

State the formulas for concentration and density in this respective order

c = m/V

p = m/V

What is the difference between solubility and miscibility?

Solubility describes the ability of solid, gas, and liquid solutes to dissolve in a solvent whereas miscibility describes the ability of a liquid to dissolve into another liquid.

What is the rule for dissolution?

The particles of the solvent must separate and fully surround the particles of the solute.

What are classified as particles?

Atoms, molecules, and ions.

How can solvent particles separate and surround solute particles?

The secondary forces created between solute and solvent molecules must be stronger or equally strong to the secondary forces between solvent molecules and solute molecules.

What secondary forces are present between polar solvent molecules?

Hydrogen bonding and dipole-dipoles

What secondary forces are created between solute and solvent molecules when the solute and solvent are non-polar?

Solvent molecules are attracted together with dispersion forces and induced dipoles to form intermolecular attraction with solute molecules. Dissolution occurs as solute-solvent molecule intermolecular forces are equal in strength to solvent-solvent molecules.

Provide examples of non-polar compounds

Fats (triglycerides), oils, and lipids

Which secondary force is stronger: hydrogen bonding or ion-dipoles

Ion dipoles

Why is oil and water immiscible?

Oil is a non-polar liquid whereas water is a polar solvent. Oil will form induced-dipoles with water using dispersion forces but these interactions are weaker than the hydrogen bonding between water molecules. Thus, dissolution does not occur and the two liquids are immiscible.

Generally, do molecules have only polar or non-polar regions? If not, how can you determine whether the molecule is polar or non-polar?

No. The polarity of molecules can be determined by observing whether the polar or non-polar regions are larger.

Why are short hydrocarbon chain alcohols miscible in water whereas long hydrocarbon chains of alcohol are not?

Short hydrocarbon chain alcohols have smaller non-polar regions, making the molecule overall polar. Polar solutes dissolve in polar solvents. Conversely, long hydrocarbon chain alcohols have larger non-polar regions, making the molecule overall non-polar. Non-polar solutes do not dissolve in polar solvents.

How can you help dissolve non-polar solutes in polar solvents?

By adding an amphiphilic compound

Name the two types of amphiphilic compounds

Emulsifier and surfactant

What is an amphiphilic compound?

Molecules that have both polar and non-polar regions

Explain the difference between an emulsifier and surfactant

Surfactants are substances that lower surface tension between liquids, solids, and gases whereas emulsifiers are a type of surfactant that stabilises a mixture of two immiscible liquids.

List two types of emulsifiers

Soap and detergent

What is a micelle?

A spherical structure that is formed by amphiphilic compounds trapping solutes in solvent with opposite polarity.

What is hard water?

Water containing high concentrations of magnesium and calcium

What is the structure of soap (amphiphilic compound)?

It has a hydrophobic tail and hydrophilic head.

What does hydrophobic and hydrophilic mean?

Hydrophobic: molecular regions in amphiphiles that avoid or repel water molecules due to weak dispersion forces
Hydrophilic: molecular regions in amphiphiles that attract water molecules via secondary interactions

What is scum?

An insoluble product formed by reacting soap molecules with hard water

How are micelles created?

Non-polar tails interact with non-polar solutes via dispersion forces. Polar heads interact with polar solvents via strong secondary interactions (dependent on solvent). Non-polar tails pull non-polar solutes inwards and polar heads push polar solvents outwards, creating a spherical shape.

How are micelles created when soap is used to clean oil out of water?

When soap is added, it lies at the boundary between oil and water with hydrophobic tails in the oil and hydrophilic heads in the water. During agitation, like scrubbing, oil layer is broken into tiny droplets. Soap molecules surround these oil solutes and traps them with their hydrophobic tails via dispersion while hydrophilic heads bind surrounding water molecules via hydrogen bonds.

What are the hydrophilic groups in soap and detergent?

Soap = carboxylate ions (-COO^-)
Detergent = sulfonate (-SO_3^-) or sulphate

What is the reaction of soap in hard water?

Carboxylate ions create insoluble scum with calcium or magnesium ions because of their opposite charges.

What is the reaction of detergent in hard water?

No insoluble precipitate is formed when sulfonate interacts with calcium or magnesium ions

Compare which compound is better for the skin: soap or detergent

Soap

Where do soap molecules come from?

When fats like triglyceride react with NaOH

Define stoichiometry

It describes the relationship between the amount of reactant to the amount of products or amount of other reactants in a chemical reaction, determined by a balanced equation.

How do you use mole ratio?

1. Find the balanced equation between your known and unknown chemical substances.

2. The coefficients of the two chemical substances is their ratio.

3. Convert your known chemical substance to moles 

4. Find the moles of the unknown chemical substance using mole ratio equation

What is internal energy?

The stored chemical energy in reactants and products.

Where does external energy go during reaction?

It is always absorbed by reactants to break chemical bonds

How is internal energy released during reaction?

When dissociated atoms bond to create new substances

What is enthalpy?

The sum of a thermodynamic system's internal energy and the product of its pressure and volume

When pressure and volume are constant, enthalpy is the...

Chemical energy stored

The enthalpy change of a reaction is the change in....

heat energy in a system where a physical or chemical change occurs.

When is pressure constant?

When reactions occur in open atmospheres

If change in enthalpy is negative, the reaction is?

Exothermic

Outputs from change in enthalpy equations must always be written with...

a positive or negative sign and in kj/mol

What is the formula for enthalpy in solution?

Change in enthalpy = lattice energy + hydration energy

What is lattice and hydration energy?

Lattice energy is the energy required to break the ionic bonds in the lattice whereas hydration energy is the energy released when dissociated ions form secondary interactions with water molecules.

What is the enthalpy in solution specifically applicable to?

Dissolving ionic solutes in water

When lattice energy is greater than hydration energy, the reaction and change in enthalpy is...

Endothermic and positive

When hydration energy is greater than lattice energy, the reaction is...

Exothermic and negative

What do thermochemical equations must have?

States of matter at room temperature
Be balanced
The enthalpy of reaction at the side

What do the coefficients in chemical equations represent?

The number of moles in reactants combined to form the number of moles in products

State the two equations for change in enthalpy (general case).

Change in enthalpy = enthalpy products - enthalpy reactants
Change in enthalpy = Q over 1000 x n (if measured enthalpy in kj and Q in J)

What does Q represented?

The energy released or absorbed.

What is the specific heat capacity of water?

4.18 J/g

What is a calorimeter?

The instrument used to measure changes in enthalpy.

What does a calorimeter assume?

All heat is transferred to water when it could be lost to the environment or its contents.
The maximum and minimum temperatures are reached before heat is lost to the environment.
All solutions have the same heat capacity and density as water.

What is the chemical equation for incomplete combustion?

Hydrocarbon + oxygen → carbon monoxide + water + carbon

What is the molar mass of 2Fe and Fe_2?

The first is 55.85g/mol whereas the latter is 111.7g/mol

What is an emulsion?

A mixture of two immiscible liquids

What is the difference between emulsifier and emulsion?

Emulsion is a mixture of two immiscible liquids and emulsifier stabilises an emulsion by allowing oil droplets to remain dispersed in water longer.

What are the characteristics of a dilute solution?

Low number of solute particles in a fixed volume of solvent

This is an image of sodium dodecanoate. What type of compound is this? Provide evidence.

It is a soap molecule because it has a carboxylate ion (-COO^-) attracting a positively charged sodium ion through ion-dipole forces.

Which is better at absorbing energy and why?

A salt with highly positive enthalpy change but low solubility
vs.

A salt with not so positive enthalpy change but high solubility

A salt with high solubility but not so positive enthalpy change because it would yield a greater total absorption of energy for energy is only absorbed when the salt dissolves.

Which applies to an endothermic reaction and what does it mean?
H products < H reactants
vs.
H products > H reactants

H products > H reactants.
More energy is required to break bonds in reactants than form new bonds.