Nat 5 Chemistry Unit 1 Chemical Changes and Structure

Exothermic

A reaction or process that releases heat energy

Endothermic

A reaction or process that absorbs heat energy

How can the rate of a reaction be increased

-By increasing the temperature

- By increasing the concentration of the reactant

- By increasing surface area/decreasing particle size

- Through the use of a catalyst

Catalysts

Catalysts are substances that speed up chemical reactions and be recovered chemically unchanged at the end

Physical Changes

Physical changes are usually reversible (e.g. change of state)

Chemical changes

Chemical changes are usually permanent and always produce a new substance

When measuring the rate of reaction by measuring the rate of reactant usage, why do we put cotton wool on the opening of the conical flask

It is to allow the gas to escape but stopped bits of chalk from escaping or droplets of acid escaping affecting our mass making the experiment unfair/inaccurate

OR

To seal the flask and prevent any gas or acid spray from leaving the flask affecting our mass and creating an unfair/inaccurate experiment

Ions

Ions are atoms which have lost or gained electrons, to become stable (They have a full outer shell of electrons which is 8 electrons) and their number of protons ≠ electrons (charged particles)

In general what do metals do to form ions

They lose electrons (Lithium 2,1 which becomes 2)

In general, what do non-metals do to for ions

They gain electrons (Oxygen 2,6 which becomes 2,8)

What is the maximum number of electrons the first shell of an atom can hold

2

What is the maximum number of electrons the second shell can hold

8

What is the maximum number of electrons the third shell can hold

8

Why do atoms lose electrons?

To become stable with a full outer shell of 8 electrons

Ok number of protons, mass number and neutrons there are ways we can calculate for this using information that we know

Number of protons = Atomic Number

Number of protons = number of electrons (IN AN ATOM)

Mass number = protons + neutrons

Neutrons = mass - number of protons

What do you do when you have a non metal ion

You change it to make it end in ide oxygen becomes oxide

Elements with a group have?

The same valency (determines their charge)

Similar chemical properties due to having the same number of electrons in their outer shell

They all want to lose __________ electrons to become stable

The 7 diatomic elements are

hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine

Isotopes

Isotopes are defined as atoms with:

- The same atomic number but different mass numbers

- The same number of protons but different number of neutrons

intermolecular forces

The weak forces of attraction between molecules

Electrolysis

Electrolysis is the decomposition of an ionic compound into its elements using electricity

Electrolysis of an ionic compound what happened at the positive and negative electrode

Positive electrode: Effervescence (bubbling)

Negative electrode: Copper (or your metal) stuck to the electrode (Make sure you read the question so you write the correct metal)

Why must a D.C supply be in electrolysis of an ionic compond?

A D.C. Supply must be used if the products of electrolysis are to be identified

Relative Atomic Mass

The relative atomic mass is the average mass of an element's isotopes taking into account their relative abundance

Metallic Bonding

Metallic bonding is the electrostatic force of attraction between positively charged ions and delocalised electrons

Covalent Bonding

A covalent bond is a shared pair of electrons attracted to the nuclei of 2 bonded atoms

Ionic bonding

An ionic bond is the electrostatic force of attraction between positive and negative ions

Standard Solution

A solution of accurately known concentration produced using a calculated mass of solute to make a specific volume

Base

A base is a substance which reacts with acids moving the pH towards 7 forming a salt and water

Alkali

An alkali is a soluble base

Salts

Salts are formed by the metal ion from the base and the non-metal ion from the acid (In a neutralisation reaction)

Acids and their chemical and ionic formula (Hydrochloric Acid, Sulfuric Acid, Nitric Acid and Phosphoric Acid)

Hydrochloric Acid

Chemical Formula: HCl (aq)

Ionic Formula: H⁺ Cl⁻ (aq)

Sulfuric Acid

Chemical Formula: H₂SO₄ (aq)

Ionic Formula: (H⁺)₂ SO₄²⁻ (aq)

Nitric Acid

Chemical Formula: HNO₃ (aq)

Ionic Formula: H⁺ NO₃⁻ (aq)

Phosphoric Acid

Chemical Formula: H₃PO₄ (aq)

Ionic Formula: (H⁺)₃ PO₄³⁻ (aq)

Alkalis and their chemical and ionic formula (Sodium Hydroxide, Calcium Hydroxide, Ammonium Hydroxide

Sodium Hydroxide

Chemical Formula: NaOH

Ionic Formula: Na⁺ OH⁻

Calcium Hydroxide

Chemical Formula: Ca(OH)₂

Ionic Formula: Ca²⁺ + (OH⁻)₂

Ammonium Hydroxide

Chemical Formula: NH₄OH

Ionic Formula: NH₄⁺ OH⁻

Water Dissociation chemical formulae

H₂O(l) ⇌ H⁺(aq) + OH⁻(aq)

Spectator Ions

Spectator ions are ions which are present in the reaction mixture but they do not take part in the reaction i.e. they do not change state in any way

Titration

A titration is an analytical technique used to determine the accurate volumes involved in a chemical reaction such as neutralisation. (An indicator is used to show the end point of a reaction)

Precipitation Reaction

A precipitation reaction is the reaction of two solutions to form an insoluble product called a precipitate

Covalent Molecular/Molecules

- Low melting and boiling points

- Generally insoluble in water but maybe dissolve in other solvents

-Do not conduct electricity (No charged particles (electrons) which are free to move)

- Solid liquid or gas at room temp

Covalent Network

- Very high melting and boiling points

-Insoluble in water

-generally do not conduct electricity (No charged particles that are free to move) carbon as graphite is an exception though

Intermolecular Forces (Description)

The forces between molecules are called intermolecular forces

They are weak forces or attraction compared to the strong covalent bonds within molecules

The stronger the intermolecular forces are, the higher the melting/boiling point of a covalent molecular substance

In general, the higher the melting/boiling point, the stronger the intermolecular forces

Within a covalent network, all the bonds are strong covalent bonds, therefore they have very high melting/boiling points

Ionic bonding (Description)

Ionic bonds are the electrostatic attraction between positive and negative ions

They tend to form between metal and a non-metal elements since metals form positive ions and non-metals form negative ions

Ionic compounds from lattice structures of oppositely charged ions

Ionic compounds have high melting and boiling points as strong ionic bonds must be broken to break up the lattice

They tend to be soluble in water

Will conduct electricity on when in molten or in solution as the lattice structure breaks allowing the ions to be free to move

Metallic Bonding (Description)

Metallic bonding is the electrostatic force of attraction between positively charged ions and delocalised electrons

The delocalised electrons allow metals to conduct electricity

How does a covalent bond form?

A covalent bond forms when 2 positive nuclei are held together by their common attraction for a shared pair of electrons

What is a group ion?

A group is is a charged particle that contains more than 1 type of ion. The charge is on/applies to the whole group not on any particular atom (e.g. OH⁻)

What do you do when putting a number after a group ion

Add brackets because it would be really weird having 32 oxygens Ca(NO₃)₂

Formula mass

The mass of an atom is measured on the relative mass scale. The mass of a unit of a compound is called formula mass

Neutral Solution (Dissociate)

H₂O molecules can split up to make a hydroxide ion OH⁻ and 1 hydrogen ion (Dissociate into ions)

So there is an equal concentration of OH⁻ ions and hydrogen ions

Soluble bases (aren't on solubility table)

carbon dioxide, nitrogen dioxide, sulfur dioxide

Soluble non-metal oxides dissolve in water to

decrease the pH increasing H⁺ ion concentration and forming an acidic solution

Metal oxides (Soluble?)

Increase the pH increasing OH⁻ ion concentration and formula an alkali solution

_______, ______________, ______________ and ______________ all neutralise acids and are called bases

Metal oxides, Metal hydroxides, Metal carbonates and Ammonia (NOT AMMONIUM!!!!!)

Metal hydroxide + Acid

salt + water (neutralisation)

Metal oxide + Acid

salt + water (neutralisation)

Metal carbonate + acid

salt + water + carbon dioxide (neutralisation)

Metal + acid

salt + hydrogen (NOT NEUTRALISATION as water isn't produced)

Concordant Results

Results that are within 0.2 cm³ of each other. (DO NOT USE ROUGH RESULT IN ANY CALCULATIONS)