Acids and bases

Acids, bases and indicators Concept Map
http://popplet.com/app/index.php#/437753

Acids and bases

Acids:
1. Tastes sour
2. Turns blue litmus paper red
3. PH<7
4. Hydrogen ions must be present- H+
Examples:
Hydrochloric acid-> HCl
Sulfuric acid-> H2SO4
Nitric acid-> HNO3
Ethanoic acid-> CH3COOH
Carbonic acid-> H2CO3
Strong acids: Hydrochloric acid, sulfuric acid, Nitric acid (pH value-1?)
Weak acids: Ethanoic acid, Carbonic acid (pH value- 4?)
HCl(g)- covalent bonding
-H20-> H+(aq)+ Cl-(aq)


1. Remeber all the relevant polyatomic ions- SO4 2-, CO3 2-, NO3 2-, NH4 +.

http://goo.gl/fzROA
- Compare HCl and vinegar.
hydrochloric acid-> stomach acid-> HCl -> H+ Cl-
nitric acid-> acid rain-> HNO3 -> H+ NO3 -
sulfuric acid-> acid rain-> H2SO4 -> H+ H+ SO4 2-
phosphoric acid-> cola-> H3PO4-> H+ H+ H+ PO4 3-
acetic acid-> vinegar-> CH3COOH-> H+ CH3COO-

Particle views:
Weak acid-> mostly molecules, few ions

Strong acids-> all ions (not all dissociated)
- completely dissociate in water (Hydrochloric acid: strong)

Reactions of acids:
1. Acid+ metal-> salt+ hydrogen gas
2. acid+ carbonates-> salt+ water carbon dioxide gas
3. acid+ base-> salt and water
(Salts are mainly ionic compounds- metal and non-metal)

1. Hydrochloric acid+ Magnesium-> magnesium chloride +hydrogen gas

(minus H-> Cl)

Cl-    Chloride

I-     Iodide

Br-    Bromide

N3-    Nitride

O2-    Oxide

S2-    Sulfide

SO4 2-    sulfate

SO3 2-    sulfite

NO3 -     nitrate

PO4 3-    phospate

1. calcium (Ca) +sulfuric acid(H2 S04) -> calcium sulfate+ hydrogen gas
2. sodium carbonate (Na2 CO3)+ hychrochloric acid(HCl)-> Sodium chloride+ carbon dioxide+ water
3. nitric acid(HNO3)+ sodium hydroxide (NaOH)-> sodium nitrate(Na NO3)+ water (H2O)

Common bases:

sodium hydroxide-> drain cleaner-> NaOH-> Na+ (OH)-

magnesium hydroxide-> antacid tablets-> Mg (OH)2 -> Mg2+ (OH)- (OH)-

ammonia-> window cleaner-> NH3-> NH4+ (OH)-

HCl(g)----H2O-----> H+(aq)+ Cl-(aq)

NaOH(s)-------H2O------> Na+(aq)+ OH-(aq)

Alkalis-> soluble in water to form a solution

KOH(s)-----H2O-----> K+(aq) + OH-(aq)

Base: pH>7
Acid: pH<7
Neutral: pH=7
Weak base:pH=8-11 (partial dissociation)

1) Acid+Base- Neutralization reactions
2) Base+ammonium salt

1. nitric acid(HNO3) + ammonia (NH4+  OH-) -> ammonium nitrate+water(H + OH-)
2. ammonium nitrate+ magnesium hydroxide-> magnesium nitrate+water+ammonia gas

ACIDS

-Definition

-Dissociation equation

-Chemical formula

-Reaction of acids

-Propertoes

BASES

-Definition

-Dissociation equation

-Chemical formula

-Reaction of bases

-Properties

Ba

Atomic structure

Atomic structure

-An atom is the smallest particle of an element
Atoms are made up of three different particles- protons, neutrons and electrons.(sub-atomic particles)
Simplified version of an atom:

The blue dot in the center of the represents the nucleus of the atom.
- The nucleus consists of...
protons-> each proton carries 1 positive charge(+1) and has a relative mass of 1.
neutrons-> neutrons carry no charge and has a relative mass of 1.

The green dot circling in the shell around the nucleus is an electron.
Each electron carries 1 negative charge(-1) and has a relative mass of 1/1840.

• The mass and substance of an atom is always concentrated in the nucleus.
• All chemical reactions happen because of changes in the electron arrangements or changes in number of electrons.

Properties 

All atoms are electrically neutral (no charge). Therefore, an atom contains an equal number of positively charged protons and negatively charged electrons so the positive and negative electric charges cancel out exactly.

-> atomic number (no. of protons)= no. of electrons

Proton/ Neutron number

The number of protons in an atom is called the proton number or the atomic number. Since atoms are neutral, the proton number can also tell the number of electrons in the atom. For example, the proton number of nitrogen is 7. This implies that the nitrogen atom has seven protons and seven electrons. Atoms of different elements have different numbers of protons. Each element has a unique proton number. This means that no other element has atoms with this proton number. e.g. Carbon has a proton number of 6, all atoms with 6 protons are therefore carbon atoms. 

• All elements are identified by their atomic number (no. of protons). Particles with the same no. of protons belong to the same element.

Nucleon/ mass number/ atomic mass

Atomic mass= no. of protons+ no. of neutrons. The mass of an atom depends on the number of protons and neutrons in the atom's nucleus. The mass of electrons in the atom is said to be negligible.

e.g. on periodic table:

Isotopes

Particles with the same number of protons (atomic no.) but different number of neutrons (atomic mass) are called isotopes of the same element.

e.g. Hydrogen isotopes:

 They are similar except that hydrogen-1 has no neutrons, hydrogen-2 has one neutron and hydrogen-3 has two neutrons. These hydrogen atoms are known as isotopes.
Isotopes are atoms of the same number of protons but different number of neutrons. Thus, isotopes of the same element have the same proton number but different nucleon numbers. Isotopes have the same chemical properties but slightly different physical properties. The chemical properties of isotopes are similar because chemical reactions involve only electrons and not the protons and neutrons. The relative masses of the isotopes differ.

Arrangement of electrons:
The electrons in an atom move around the nucleus in regions known as electron shells. Each shell can only hold a certain number of electrons.
First shell: closest to the nucleus, can hold a maximum of 2 electrons, always filled first.
2nd, 3rd and subsequent shells: can hold up to 8 electrons each, filled in order, 2nd shell to be fully-filled before the third shell and do on.

Electronic structure:

This atom has 2 electrons in the first shell and 7 electrons on the outer shell. Thus, its electronic structure or electronic configuration can also be represented as (2, 7)

The shell that is furthest from the nucleus is called the outer shell or the valence shell. The electrons in this shell are called valence electrons. The chemical properties of an element depend on the number of valence electrons. Elements of the same number of valence electrons are in the same group. This means that elements in the same group have similar chemical properties.


Ions

• Ions are formed when atoms gain or lose electrons. (chemical reaction)
• Atom loses 2 electrons-> particle now has 2 less electrons (negative charges) compared with protons (positive charges)-> Ion with 2+ charge is formed.-> CATION
• Atom gains one electron-> particle now have 1 electron more than number of protons-> ion with 1- charge is formed-> ANION.

Chemical bonding

Just a few points...
1. nucleon no.-> no. of protons& neutrons
-> relative atomic mass
2. atomic no.- no. of protons
- no. of electrons
3. ions- formed when electrons are lost or gained

In chemical bonding...
- the formation of ions 
- the formation of ionic bonds and covalent bonds
- properties of ionic and covalent compounds
- structures of simple, molecular and giant molecular structures

Structure of noble gases(e.g. He, Ne, Ar, Kr, Xe):
- each atom of a noble gas has 8 valence electrons (except He->2)
- noble gases exist as single atoms 
- do not form compounds-> described as unreactive
- *believed to be stable due to their fully filled outer shells
-> no tendency for a noble gas atom to combine with another atom to form molecules or compounds.

THE OCTET RULE: due to *, all atoms without a fully filled outer shell is said to be unstable.
An atom that is unstable would try to gain stability by surrounding itself with an 'octet'(8) of electrons. This tendency is known as the octet rule.

(*O*) Helium:
- only 2 outer electrons
- still considered a stable atom as the outer shell is fully filled.
- first shell can only hold 2 electrons. (The duplet rule)

Valency:
- number of electrons needed/ required to fill up the outer shell.
e.g. Fluorine has 7 outer/ valence electrons-> needs 1 more to achieve stable octet structure.
-> valency of Fluorine is 1.
- also refers to number of electrons stopping it from having a filled outer shell.

Formation of Ions
- an ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons.
- metals form positively charged ions-> cations
-> positively charged ions are formed by the loss of electrons.
e.g. lithium ion is formed when a lithium atom loses 1 electron

By losing 1 electron, the lithium ion now has the same electronic 

configuration as a helium atom, achieving a duplet structure.

 e.g. Magnesium atom

Metals tend to form positive ions because most metal atoms have less than 4 electrons in the outer shell. Hence it is more likely to lose the few electrons than to gain many more to achieve octet structure.

- non-metals form negatively-charged ions-> anions
(negatively charged ions are formed by the gain of electrons)

Non-metals tend to form negative ions because most non-metals have more than 4 electrons in the outer shell. Hence, it is more likely for the atoms to gain a few more electrons to complete the octet than to transfer their outer electrons to other atoms.

Some metals form more than one type of ion. e.g. iron-> Fe2+, Fe3+

- charge of ion is often shown in the chemical name. e.g. iron(II) sulphate contains Fe2+ ions

Some positive and negative ions can be formed by a group of atoms-> polyatomic ions.

Ionic bonds

- formed between metals and non-metals.

- involves the formation of both positively-charged ions(cations) and negatively- charged ions(anions).

- involves the transfer of electrons from one atom to another.

E.g. formation of calcium oxide:

calcium loses 2 electrons to Ca2+ (same configuration as Argon)

Then, Oxygen gains 2 electrons to form O2- (same configuration as Ar)

- different symbols used to show that the electrons are from different atoms.

The total positive charges balances the total negative charges.

-We can see that an ionic bond is formed when metal atoms transfer their outer electrons to non-metal atoms.

- oppositely charged ions are then formed

- the strong electrostatic force of attraction that holds oppositely charged ions is called ionic bonding.

Metal atoms-> electron donors

Non-metal atoms-> electron receivers

Electron transfer during the formation:

Ionic compounds

- made up of oppositely charged ions, not molecules

- no overall charge in an ionic compound as all the positive charges are balanced by all the negative charges.

Rules when writing the chemical formula of ionic compounds: 

- subscripts are in the simplest terms. e.g. MgO not Mg2O2

- subscript '1' is not written

Polyatomic ions-> to be written in brackets if a subscript is added. e.g. Ca(OH)2

The chemical symbols of metals(cations) are to be written first, followed by non-metals (anions).

<-Ionic bond->

(electrostatic force of attraction)

Group 1-> to lose 1 electron

Group 2-> to lose 2 electrons

Group7-> to gain 1 electron

Covalent bonding

• non-metals tend to have 4,5,6 or 7 valence electrons. Therefore, they are unable to form oppositely-charged ions.
• When a covalent bond is formed, each of the bonding atoms contributes a valence electron to form a pair of electrons (one covalent bond).

Each covalent bond adds one more valence electron to the outermost shell of the atom.
Examples:

Chemical Bonding

Kinetic Particle theory

Kinetic Particle theory

Matter
- all matter is made up of tiny particles
- the particles of matter move or vibrate about randomly in all directions
- the three states of matter, solid, liquid and gas, result from the different arrangements and motion of these particles

Matter
-> No fixed volume (can be compressed)
Gases have...

• no fixed volume
• no fixed shape
• a low density

Arrangement of particles: The particles are very far apart and are are not held together.
Motion: The particles are free to move in any direction within a container and at very high speeds.

-> Fixed volume
No fixed shape- Liquids have...

• a fixed volume
• no fixed shape
• a medium density

Arrangement of particles: The particles are closely packed. They are held together but not rigidly.
Motion: The particles are able to slip and roll over one another.

Fixed shape- Solids have...

• a fixed volume
• a fixed shape
• a high density

Arrangement of particles: The particles are packed very closely together. They are held tightly in a rigid structure.
Motion: The particles can only vibrate about a fixed position.

Start->                                                            Process                                             -> End

Solid:

-Packed 

-Vibrate in fixed positions
-Forces of attraction-> very strong

Process:
- gain heat
- KE increases
- Forces of attraction weakens

Liquid:
-vibrates more vigorously

Relative density

Solid-> high

Liquid-> moderate

Gas-> Low

test- e.g. place in water

solid+ sublimation= gas

solid+ melting= liquid

Liquid+freezing= solid

liquid+boiling=gas

gas+deposition= solid

gas+ condensation= liquid

e.g. Melting of ice- physical change

photosynthesis in plant leaves- chemical change

dissolving sugar in water- physical change

burning a piece of wood- chemical change

Water in 3 states: 

Solid- e.g. iceberg

Liquid- e.g. sea

Gas- e.g. water vapor in surrounding air

Melting

- water spreads out and fills the container

- gases spread out even more, filling any space available

Arrangement of particles

Particles of a solid are in a fixed framework, held close together and vibrate.

Particles of a liquid are still in contact but free to move around

Particles in a gas are far apart. They move quickly and randomly in any direction.

- random movement of smoke particles caused by collisions with invisible air particles.

Diffusion in gases: e.g.

At first

In the process

In the end

It takes time because the air and bromine molecules are colliding with themselves and each other.

Rate of which different gases diffuse into the air

Lighter molecules-> diffuse more quickly

experiments:

 Diffusion in liquids:

Diffusion rate higher in higher temperatures.

                                          

Melting

solid-> liquid

increase in temp.

1. Heat energy is absorbed by particles in the solid. The heat energy is converted into kinetic energy. The particles start to vibrate faster about their fixed positions.
2. When the temp. is high enough, the vibrations of the particles become sufficient to overcome the attractive forces between them. The particles begin to break away from their fixed positions.
3. The particles are  no longer in their fixed positions. The particles slide over one another. The substance is now a liquid.

The temp. at which a solid becomes a liquid is called its melting point.

Freezing

liquid-> solid

decrease in temp.

1. Energy is given out by the particles of the liquid. The particles lose kinetic energy and begin to move more slowly.
2. When the temp. is low enough, the particles no longer have enough energy to move about freely. Some particles start to settle into fixed positions.
3. All the particles settle into fixed positions. Particles can only vibrate about their fixed positions. The substance is now a solid.

The temp. of which a liquid becomes a solid is called its freezing point. Heat energy is given out during the cooling process.

Boiling

liquid-> gas at the boiling temp. (boiling)

1. Energy is absorbed by particles in the liquid. The particles gain kinetic energy and start to move faster as the temp. rises.
2. Eventually the particles throughout the liquid have enough energy to overcome the forces holding them together. The particles can now spread far apart and move rapidly in all directions.
3. The substance is now gas.

The temp. at which a liquid boils to become a gas is called its boiling point. Different substances have different boiling points.

When a liquid boils, bubbles of gas are seen. These bubbles are formed when the liquid changes to vapor. The bubbles also consist of other gases dissolved in the liquid. The bubbles rise to the surface and escape into the air.

Evaporation

Sometimes a liquid can turn into a gas at temperatures lower than the boiling point. This process is called evaporation. Evaporation occurs because some particles have enough energy to escape as a gas from the surface of the liquid.

Liquids that evaporate quickly at room temp. are called volatile liquids. They usually have boiling points just above room temperature. e.g. petrol and perfume.

Both boiling and evaporation involve a liquid changing into a gas, but boiling is different from evaporation in these ways....

Condensation

gas is cooled sufficiently-> liquid

When water vapor touches a cold surface, condensation occurs and liquid water is obtained.

Heat energy is given out during condensation. As the temp. drops, the gas particles lose energy and move more slowly. Eventually, the movement of the particles becomes slow enough for the gas to change into a liquid.

Sublimation

e.g. when dry ice (solid carbon dioxide) is exposed to temperatures higher than -78 degree celsius, it turns directly into carbon dioxide gas without melting. like dry ice, some solids change into gas without going through the liquid state. This is called sublimation.

It occurs because particles at the surface of the solid have enough energy to break away from the solid and escape as a gas. e.g. Iodine and ammonium chloride. Substances that sublime may also change directly from a gas into a solid without going through the liquid state. This process is called condensation.

Dry ice :D

Diffusion in Gases

The process by which move freely to fill up any available space is called diffusion.

Gas particles of different masses diffuse at different rates. Besides being smaller,e.g. hydrogen particles are lighter than other air particles. Gases of different masses diffuse at different rates.

The mass of a gas particles is called its molecular mass. The smaller the molecular mass of the gas, the lighter it is. Hydrogen is the lightest of all gases and is about 20 times higher than air.

Experiment for rate of diffusion:

 
The fumes are formed when the two react. This end that the compound is formed nearer to means that the particles from  the other end moves faster than the particles from this end. Gases with lower molecular masses diffuse faster than those with higher molecular masses.

Diffusion in Liquids

Diffusion also takes place in liquids. 

e.g. a small crystal of potassium manganate(VII) is introduced into a beaker of distilled water. It dissolves to form a deep purple solution, which settles at the bottom of the beaker. Diffusion slowly takes place until the solution becomes uniformly purple.

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. This applies to gases as well.

Effect of temperature on the rate of diffusion:

The rate of diffusion increases as the temperature of the solution increases. (The higher the temperature, the faster the rate of diffusion)

Particles gain more energy as the temperature increases. They can move faster and this increases the rate of diffusion.