Revision Notes For
- Elements, Compounds and Mixtures
- Kinetic Particle Theory
- Chemical Bonding
Chem EYA Revision
Notes done by Catherine, Rachel and Tian Min
Topics:
1. Elements, Compounds and Mixtures
2. Separation Techniques
3. Kinetic Particle Theory
4. Atomic Structure
5. Chemical Bonding
6. Acids and Bases
Topic 1: Elements, Compounds and Mixtures
Elements
Elements are pure substances that cannot be split into simpler substances.
Chemical symbols are used to represent elements.
Elements can be classified as metals, non-metals and metalloids.
Metals Non-metals Metalloids
Shiny (LUSTROUS)
when solid
Dull (NON-LUSTROUS)
when solid
Elements that have BOTH
the properties of metals
and non-metals.
SOLIDS at r.t.p Can be in ANY FORM OF
MATTER at r.t.p
–
– MALLEABLE (if solid)
– Sonorous
– Ductile (can be drawn
into wires without
breaking)
BRITTLE (if solid) –
HIGH boiling and melting LOW melting and boiling –
points points
GOOD conductors of heat
and electricity
POOR conductors of heat
and electricity
–
Elements are made up of atoms, which are the smallest particles of elements that have
the chemical properties of that element. However, only noble gases can exist as individual
atoms.
Molecules are two or more atoms chemically combined. Two atoms form a diatomic
molecule, three form a triatomic molecule and four or more form a polyatomic molecule.
Compounds
Compounds are pure substances made of two or more elements that are chemically
combined.
A compound that contains two elements has a name ending with an “-ide”. A compound
with hydroxide ions (OH-) has a hydroxide at the back of it’s name (e.g. Potassium
hydroxide). A compound comprising a polyatomic anion (non-metals) that contains oxygen
normally has a name that ends with “-ate” (e.g. sodium nitrate – 1 nitrate anion contains
3 oxygen atoms).
Compounds have a fixed composition and ratio. The smallest particle of a compound
that is able to exist independently is the molecule.
The chemical formula of a compound, which is unique to the compound, states the type
of atoms and their ratio in the compound. In a chemical formula, the number of atoms is
written to the right of the atom’s symbol as a subscript. However the subscript “1” does
not need to be written. The oxygen atom is normally written at the end of the formula.
For ionic compounds, the symbol of the metallic element is written first.
Heat is used to form and break down compounds. The process of breaking down the
compounds with heat is called thermal decomposition. Electricity can also be used to
achieve the same effect.
Decomposition of Compounds
Compounds are decomposed through means of heat. As the heat is used to break down
compounds into elements or simpler compounds, it is known as thermal decomposition.
Other methods include the use of electricity.
Mixtures
Unlike compounds, mixtures are formed when any two substances are added together
without chemical bonds being formed.
Alloys, a combination of metals, are an example of a mixture. They tend to be stronger
than pure metals. They have similar chemical properties to those of the elements they
contain but their physical properties differ.
Topic 2: Separation Techniques
The common techniques made for separation of compounds are as follows:
- Crystallization
- Recrystallization
- Chromatography
- Filtration
- Distillation
- Fractional Distillation
Crystallization
Purpose
The purpose of crystallization is to purify a substance.
Attributes
The main attributes is that in order to achieve purified solutions, the solution should be saturated. Crystallization involves a changing of state from aqueous (aq) to solid state.
Process
In crystallization, water is first removed by heating the solution. Heating is stopped when the saturated solution is formed. This may be tested by placing a glass rod into the container solution. Because the solution has been evaporated to a much smaller volume, tiny crystals forming on the glass rod would suggest that the solution is saturated. After the solution is confirmed as saturated, if it is allowed to cool at room temperature, the dissolved solution will form crystals. Crystallization may be repeated so that the crystals are more pure, and this is known as recrystallization.
Recrystallization
Purpose
To achieve a mostly, if not completely, pure substance.
Attributes
As the amount of solute that can be dissolved by the solvent increases with temperature, the crystals formed through recrystallization will therefore be purer.
Process
In recrystallization, a solution is created by dissolving an impure solute in a solvent at/ near its boiling point. At this high temperature, the solute has an increased solubility in its solvent, so a smaller quantity of hot solvent is needed, than when the solvent is at room temperature. When the solution has cooled, and after filtering out the insoluble impurities, the amount of solute that remains dissolved would be decreased. At the cooler temperature, the solution is saturated at a much lower concentration of solute. The solute that would not be able to be held in solution form purified crystals of solute and can be later collected.
Chromatography
Purpose
To separate a mixture and to find out the number of components it contained.
Attributes
Chromatography depends on the solubility of the compounds or substances in a solvent. For example, if it is oil-based it would not dissolve in water, and water as a solute would not be feasible for the process to be carried out.
Process
In chromatography, a spot of food coloring is placed on the chromatography paper. When the paper is dipped into its solvent, the solvent is effectively soaked up. The solvent would be able to dissolve the dyes and travel up the paper carrying the dyes. The relatively insoluble dye will not be able to be carried by the solvent as far as the more soluble ones, that will be carried further along the chromatography paper.
Filtration
Purpose
Filtration is used in order to differentiate different sized substances and separate insoluble substance from solvent.
Attributes
It has to be noted that there should be a solution that is insoluble with the other to be able to be filtrated.
Process
A filter paper is placed on filter funnels and a solvent mixed with an insoluble substance is poured through the funnel. The solvent will therefore filter through the funnel and leave the substance on the funnel. The filtered solvent is called filtrate the insoluble substance left on the chromatography is called the residue.
Distillation
Purpose
To purify substances and completely separate different substances.
Attributes
It is often a substance that is dissolved in either water or a solute that has a known boiling point to heat to.
Process
Distillation, a mixture is heated until one of its solvent boils and evaporates. After it evaporates, it meets with the cooler temperature in the condenser that is often water based, and the gas would therefore condense and side down into a container.
Fractional Distillation
Purpose
To separate a mixture into a number of different parts and solutions.
Attributes
The tall fractionating column is fitted at the top and condensers come off at different heights of where the evaporated solutions could rise up to.
Process
A solution that can contain more than one substance is heated and the evaporated gas rises up in the container to the column. As it is seen under attributes, the condensers of the fractionating column comes off that different heights. The column is therefore hot at the bottom and cool on top. Substances with high boiling point condenses at the bottom and the ones with low boiling points, meaning that they will evaporate sooner than the other substances, will condense at the top. Some solvents would evaporate, condense, and slide down again and this is repeated as the substance becomes more pure.
Table Of Comparison Between Simple and Fractional Distillation
Simple Distillation vs. Fractional Distillation
1. Makes use of the boiling point of only one solvent as it can only contain 2.
2. Allows substance to condense, but the condensed substance may still be impure.
1. Makes use of 2 or more boiling point of the different substances in the solution, and the solution is heated accordingly.
2. Makes use of fractionating column to repeatedly condense the substances so that they are around 97%-99% pure. It produces 2 or more liquids with their boiling point variation of around 20˚C, they are distilled and separated.
Topic 3: Kinetic Particle Theory
Definitions:
1. The melting point is the temperature at which a solid changes into a liquid.
2. The boiling point is the temperature at which a liquid turns rapidly into a gas.
3. The freezing point is the temperature at which a liquid becomes a solid.
4. Condensation is the process by which a gas or vapour changes into a liquid or solid.
5. Sublimation is the process by which a solid changes directly into a gas without going through the liquid state.
6. Evaporation is the process by which a liquid changes into vapour at any temperature below its boiling point.
7. Diffusion is the mixing process in gases or solutions due to the random motion of particles.
States of matter and their properties:
SOLIDS:
- has a fixed shape
- has a fixed volume
- cannot be compressed
Theories:
1. Particles are very closely and orderly packed.
2. The attractive forces between particles are very strong.
3. The particles are held together.
4. The particles can vibrate and rotate about their fixed positions, but cannot move
about freely.
LIQUIDS:
- has no fixed shape
- has a fixed volume
- cannot be compressed
Theories:
- The particles are closely but disorderly packed. There are empty spaces between the particles.
- The attractive forces between particles are strong but the particles are not tightlyheld together.
- The particles can vibrate and rotate and move about freely.
GASES:
- has no fixed shape
- has no fixed volume
- can be compressed
Theories:
1. Particles are very far from each other.
2. The attractive forces between particles are weak.
3. The particles can move about rapidly and freely in all directions.
The kinetic particle theory states that all matter is made up of tiny particles that are in constant random motion and constantly collide with each other.
Changes of State and the Kinetic Particle Theory
Changes of state of matter (With reference to physical changes. Chemical changes are, on the other hand, mostly irreversible but sometimes reversible) are reversible by changing the surrounding air temperature and pressure. Heat taken in or given out by matter causes the kinetic energy of the particles to change, which changes the state of the matter.
Gases have the highest energy content while solids have the lowest. (The lower the pressure, the slower the particles of a gas move. Thus, it is false that at any one time, the particles of a gas move faster than that of a liquid because the statement does not rule out the possibility that they may be under different conditions.)
For example, during melting, heat energy is absorbed by the particles in the solid and is converted into kinetic energy, which causes the particles to vibrate faster in their fixed positions. At the melting point of the solid, the vibrations of the particles are enough to overcome the forces of attraction between them, and they begin to break away from their fixed positions. The particles are no longer in their fixed positions and the substance is now a liquid.
During this melting process, the temperature of the substance rises to its melting point and stays constant at that temperature until the substance has fully melted. During that period, there is a mix of the solid and liquid of the substance. The temperature continues to increase after the substance has become a liquid as the heating continues. The graph that shows melting or boiling processes is called the heating curve of the substance.
Similarly, the cooling curve is the graph showing freezing and condensation.
Freezing: is the opposite of that of melting. During the freezing process, heat energy is given out by the particles. They start to lose kinetic energy and begin to move slower. At the freezing point of the substance, the particles no longer have enough energy to move freely. Slowly they settle into fixed positions; hence, a solid is formed.
Boiling: is when the particles of a liquid gain heat energy, which is converted to kinetic energy. At the boiling point of the substance, they have enough energy to overcome the forces holding them together and are able to spread far apart and move in rapid directions.
Note: Bubbles are observed during boiling as they are formed when the liquid changes to vapour. The bubbles also contain gases dissolved in the liquid. As the liquid at the bottom of the container is closest to the heat source, it boils first and thus turns to vapour first. Hence, it travels to the surface to escape in the form of bubbles.
Liquids evaporate when some particles at the surface gain enough heat energy so that they will have enough kinetic energy to escape as a gas from the surface of the liquid.
Volatile liquids are liquids that evaporate quickly at room temperature and usually have boiling points just above room temperature. E.g. Petrol, perfume. Sublimation occurs when particles at the surface have enough heat energy to convert to kinetic energy to enable them to break off from the solid into a gas.
Osmosis
Osmosis is the net movement of water molecules from a region of higher water potential (concentration of water) to a region of lower water potential across a partially permeable membrane.
The difference between osmosis and diffusion is the presence of the partially permeable membrane in osmosis. Osmosis is a subset (part of a larger group of related things) of diffusion.
Diffusion
Diffusion is the process by which particles move freely to fill up any available space. It is the movement of particles from a region of higher concentration to a region of lower concentration. This supports the kinetic particle theory as it shows that particles of gases are constantly moving.
Diffusion as a…
Passive process – energy NOT required (this is because it occurs naturally): From region of higher concentration to lower concentration
Active process – energy IS required (this is because it does not occur naturally): From a region of lower concentration to higher concentration.
Diffusion occurs in both gases and liquids. However, diffusion in gas is faster than that of liquids.
Factors of diffusion:
1. Gases with particles of different sizes diffuse at different rates.
2. Gases with different molecular masses (the mass of the air particles) diffuse at different rates as well. For example, a balloon filled with hydrogen shrinks faster than that of air. This is because the smaller and lighter hydrogen particles diffuse more quickly through the millions of tiny holes in the balloon rubber than the larger and heavier air particles.
Therefore, we conclude that, the lower the molecular mass of a gas, the faster it diffuses.
This can be proved by placing cotton wool soaked in concentrated ammonia solution at one end of a sealed tube and cotton wool soaked in concentrated hydrochloric acid at the other end. After a while, white fumes of ammonium chloride form closer to the end of the tube with cotton wool soaked in concentrated hydrochloric acid, which shows the ammonia gas particles move faster than that of hydrochloric acid.
3. The temperature also affects the rate of diffusion. The rate of diffusion increases as the temperature of the solution increases. For example, why does an inflated balloon shrink faster on a warm day than on a cold day? This is because particles gain more energy as the temperature increases. They can move faster and this increases the rate of diffusion.
4. Another factor is the concentration gradient. The higher the concentration gradient (high concentration), the higher the rate of diffusion of the substance. This is because particles move from a region of higher concentration to a region of lower concentration.
Why does diffusion take place faster in a vacuum?
The process by which particles move freely to fill up any available space is diffusion. In a vacuum, there is no pressure and no other gases’ particles to bump into, thus there is more available space in a vacuum than that of when there are other gases present. Hence, the speed of diffusion is faster in a vacuum.
A simpler, more concise 1 mark kind of model answer for this question: There is no pressure in a vacuum as well as there are no other gas particles present to bump into the particles of the gas that is being diffused and slow down the speed of the diffusion of the gas.
Topic 4: Atomic Structure
Neutrons, Protons and Electrons
These are the components of an atom:
Neutron
It carries no charge and is therefore neutral
Proton
Carries a positive charge of +1
It exists with the neutron in the nucleus
Electron
Protons, neutrons and electrons.
relative mass relative charge
proton 1 +1
neutron 1 0
electron 1/1836 -1
The Nucleus
The nucleus is at the centre of the atom and contains the protons and neutrons. Protons and
neutrons are collectively known as nucleons.
Virtually all the mass of the atom is concentrated in the nucleus, because the electrons weigh so
little.
Working out the numbers of protons and neutrons No of protons = ATOMIC NUMBER of the
atom
The atomic number is also given the more descriptive name of proton number.
No of protons + no of neutrons = MASS NUMBER of the atom
The mass number is also called the nucleon number.
This information can be given simply in the form
How many protons and neutrons has this atom got?
The atomic number counts the number of protons (9); the mass number counts protons +
neutrons (19). If there are 9 protons, there must be 10 neutrons for the total to add up to 19.
The atomic number is tied to the position of the element in the Periodic Table and therefore the
number of protons defines what sort of element you are talking about. So if an atom has 8 protons
(atomic number = 8), it must be oxygen. If an atom has 12 protons (atomic number = 12), it
must be magnesium.
Similarly, every chlorine atom (atomic number = 17) has 17 protons; every uranium atom (atomic
number = 92) has 92 protons.
ISOTOPES
Isotopes are atoms of the same element with different numbers of neutrons and therefore different masses (different nucleon/mass numbers). This gives each isotope of a particular element a different mass or nucleon number, but, being the same element they have the same atomic or proton number and are identical chemically. , Hydrogen-1 is the most common, there is a trace of hydrogen-2(sometimes called deuterium) naturally but hydrogen-3 (sometime called tritium) is very unstable and is used in atomic bombs – nuclear fusion weapons.
The relative atomic mass of an element is the average mass of all the isotopes present compared to 1/12th of the mass of carbon-12 atom
Q. Calculation: 75% of chlorine exist as 35Cl and 25% of chlorine exist as 37Cl. What is the atomic mass of chlorine?
Let’s say there are 100 chlorine atoms (for any question just assume this value, then just sub in the numbers given. Always work). 75 of them will be 35amu (atomic mass unit) and 25 of them will be 37amu.
Total mass= 75 x 35 + 25 x 37 = 3550amu
average mass (aka atomic mass) = 3550100= 35.5amu (UNIT IS VERY IMPORTANT)
The Electrons
Working out the number of electrons
Atoms are electrically neutral, and the positiveness of the protons is balanced by the negativeness of the electrons. It follows that in a neutral atom: no of electrons = no of protons. So, if an oxygen atom (atomic number = 8) has 8 protons, it must also have 8 electrons; if a chlorine atom (atomic number = 17) has 17 protons, it must also have 17 electrons.
The arrangement of the electrons
The electrons are found at considerable distances from the nucleus in a series of levels called energy levels. Each energy level can only hold a certain number of electrons. The first level (nearest the nucleus) will only hold 2 electrons, the second holds 8, and the third also seems to be full when it has 8 electrons. These levels can be thought of as getting progressively further from the nucleus. Electrons will always go into the lowest possible energy level (nearest the nucleus) – provided there is space.
To work out the electronic arrangement of an atom
Look up the atomic number in the Periodic Table – making sure that you choose the right number if two numbers are given. The atomic number will always be the smaller one. This tells you the number of protons, and hence the number of electrons. Arrange the electrons in levels, always filling up an inner level before you go to an outer one.
e.g. to find the electronic arrangement in chlorine
The Periodic Table gives you the atomic number of 17. Therefore there are 17 protons and 17 electrons. The arrangement of the electrons will be 2, 8, 7 (i.e. 2 in the first level, 8 in the second, and 7 in the third).
The electronic arrangements of the first 20 elements
After this the pattern alters as you enter the transition series in the Periodic Table.
Two important generalisations
If you look at the patterns in this table:
The number of electrons in the outer level is the same as the group number. (Except with helium which has only 2 electrons. The noble gases are also usually ca lled group 0 – not group
This pattern extends throughout the Periodic Table for the main groups (i.e. not including the transition elements).
So if you know that barium is in group 2, it has 2 electrons in its outer level; iodine (group 7) has 7 electrons in its outer level; lead (group 4) has 4 electrons in its outer level. Noble gases have full outer levels.
Topic 5: Chemical Bonding
Ionic Bonding
Formation of ions
-An ion is a charged particle formed from an atom or group of atoms by the loss or gain of electrons
-Metals form positively charged ions (cations)
-Non-metals form negatively charged ions (anions)
Formation of Positive ions:
Positively charged ions are formed by the LOSS of electrons. 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 the octet structure!
Formation of Negative Ions:
Negatively charged ions are formed by the GAIN of electrons.
- formed between metals and non-metals
- formation of an ionic bond involves the formation of both positively charged ions
- (cations) and negatively charged ions ( anions)
- ionic bonding involves the transfer of electrons from one atom to another
- 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.
NOTE: all metal atoms are known as electron donors and all non-metal atoms are known
as electron receivers.
Ionic Compounds are made up of oppositely charged ions, NOT molecules. There is no overall charge : all positive charged are balanced by all the negative charges.
Structures and properties of ionic compounds
1. In an ionic compound, oppositely charged ions are arranged together in a giant ionic structure.
2. it is also known as lattice structure or crystal lattice.
3. A giant structure is a three-dimensional network of atoms or ions which are packed together in a regular pattern.
Giant Ionic structure
-> held together very tightly because the oppositely charged ions attract one another strongly.
Physical properties of Ionic Compounds
1. Can be deduced from its giant lattice structure
2. This is because the giant lattice structure (how the ions are arranged) is responsible for the physical properties of ionic compounds.
Melting and Boiling Points
- Ionic compounds have high melting and boiling points.
- ionic solid -> very large amount of heat energy is needed -> break up the strong ionic bonds -> melt
- Hence, all ionic compounds are solids at room temp.
- Substances with low melting and boiling points : volatile
- Ionic compounds are non-volatile
Solubility:
Most ionic compounds can dissolve in water. This is because water molecules can separate the positive ions from the negative ions. Ionic compounds do not dissolve in organic solvents e.g. petrol, alcohol and turpentine
Electrical conductivity:
Solid Liquid Solution
Charge carriers – Moving ions
Ionic compounds are able to conduct electricity in the molten (liquid) state and as an aqueous solution.
Moving ions act as charge carriers to conduct electricity
Covalent Bonding
1. Generally between non-metals
2. electrons are shared
3. Molecules are formed
Metallic Bonding
Metal atoms are held strongly to each other by metallic bonding. In the metal lattice, the atoms lose their valence electrons and become positively charged.
The valence electrons no longer belong to any metal atom and are said to be delocalised.
Hence, this lattice structure is described as a lattice of positive ions surrounded by ‘a sea of mobile electrons’. A metallic bond can hence be defined as the force of attraction between positive metal ions and ‘the sea of delocalised electrons’.
Physical properties of metals: Good conductors of electricity because of the mobility of the valence electrons within the metal lattice.
When a metal is used in an electrical circuit, electrons entering one end of the metal causes a similar number of electrons to be displaced from the other end. The valence electrons move from the negative terminal to the positive terminal of the electrical circuit.
Hence, the metal is able to conduct an electric current.
As the valence electrons do not belong to any atom in particular, if sufficient forcevis applied to the metal, one layer of atoms can slide over another without disrupting the metallic bonding. Hence, metallic bonds are strong and flexible, so metals can be hammered into different shapes (malleable) or drawn into wires (ductile) without breaking.
Topic 6: Acids and Bases
Acids:
The definition of an acid is a substance that produces hydrogen ions when it is
dissolved in water . Acids only show the properties of acids when they are dissolved
in water (in non-scientific terms, water activates the acid’s acidic properties). This is
because acids dissociate in water to produce hydrogen ions, which are responsible for the
acidic properties.
In organic solvents, however, they do not behave as acids. For example, hydrogen
chloride exists as molecules in organic solvents whereas it dissociates (dissolving in water
to give a solution that forms ions) into positive hydrogen ions and negative chloride ions in
water.
List of acids
Name of acid Formula Ions produced in aqueous solution
Ethanoic acid (a.k.a. acetic acid, found in vinegar) C2H4O2 H+(aq) C2H3O2
Hydrochloric acid (hydrogen chloride) HCl H+(aq) Cl-(aq)
Nitric acid (Hydrogen nitrate) HNO3 H+(aq) NO3-(aq)
Sulfuric acid (Dihydrogen sulfate) H2SO4 2H+(aq) SO4
2-(aq)
· Organic acids -> Naturally occurring acids (e.g. citric acid in oranges).
· Mineral acids -> Man-made acids (e.g. nitric acid, sulfuric acid)
Properties of Acids
– Have a sour taste
– Conduct electricity when aqueous (dissolved in WATER). This is because the acid’s
molecules are separated into free-moving ions when aqueous.
– Turns blue litmus paper red (red litmus paper stays red).
1. Metal (s) + acid (aq) -> SALT (aq) + hydrogen (g) (E.g. Magnesium + sulfuric acid)
Test if a liquid is acid with this concept: Add a metal to the liquid and test for hydrogen gas by bringing a lighted splint above the mixture. If the burning splint extinguishes with a ‘pop’ sound, hydrogen gas is present and the liquid is an acid.
Note: Some metals, like lead and barium, appear not to react with some dilute acids. Lead
appears not to react with dilute sulfuric acid and dilute hydrochloric acid. Barium appears not to react with dilute sulfuric acid. This is because a layer of barium sulfate is formed from the initial reaction between the barium and the dilute sulfuric acid. This layer is insoluble in water and quickly forms a coating around the metal. The coating protects the metal from further attack by the acid. The same applied to lead.
2. Carbonate (s, except NH4+ and group I elements) + acid (aq) -> SALT (aq) + water (l) + carbon dioxide (g) (E.g. Sodium carbonate + hydrochloric acid)
Test if a liquid is acid with this concept: Add a carbonate to the liquid and test for carbon dioxide gas by bubbling the gas produced through limewater. If the gas forms a white precipitate with the limewater, it is carbon dioxide and the liquid is an acid.
3. Bases/alkalis (s) (any metal hydroxides/oxides) + acid (aq) -> SALT (aq) + water (l)
(E.g. Zinc hydroxide + nitric acid) (This is called neutralization.)
Solubility rules:
· Metal hydroxides are already in aqueous form (except some like zinc hydroxide and caesium hydroxide). Thus, they are UNABLE to be soluble.
· Metal oxides are insoluble, thus they are in solid state.
· All carbonates, except and group I elements, are insoluble.
· Metals are insoluble.
Bases and Alkalis
A base is any metal oxide or hydroxide. A base can be defined as a substance that reacts with an acid to give a salt and water only. The oxide or hydroxide ions from the bases react with the hydrogen ions from the acids to form water. All bases are insoluble except alkalis, which are a special class of bases.
An alkali is a base that is soluble in water (e.g. sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, barium hydroxide, aqueous ammonia).
Properties of Alkalis and Bases
– Have a bitter taste and soapy feel
– Turns red litmus paper blue (blue litmus paper stays blue).
– All alkalis produce hydroxide ions when dissolved in water.
– [All] Alkalis (aq) + acids (aq) -> SALT (aq) + WATER (l) [only]. This process is called neutralization. However, neutralization would not have taken place if a new substance is to be observed.
– (Alkalis heated with ammonium salts, which are for example ammonium chloride,
ammonium carbonate and ammonium nitrate, give off ammonia gas.) Alkali (aq) +
ammonium salt (s) -> AMMONIA (g) + WATER (l) + SALT (aq) . The presence
of ammonia can be tested for by holding a moist red litmus paper over ammonia gas.
Ammonia also has a characteristic pungent smell. The hydroxide ions and the ammonium
ions react to produce ammonia gas.
– (Alkalis can react with a solution of one metal salt to give metal hydroxide and another
metal salt.) Alkali (aq) + Salt (metal A) (aq) -> METAL HYDROXIDE (s) + SALT
(METAL B) (aq)
E.g. Sodium hydroxide + iron (II) sulfate -> iron (II) hydroxide + sodium sulfate.
NOTE: The metal hydroxide appears as a precipitate if it is insoluble in water.
INFO: Hydroxides can be used to identify cations. A hydroxide can react with a metal cation
and the resulting compound has a characteristic colour. Hence, hydroxides can be used to
identify the cations present.
Concentration and Strength
The concentration of an acid or an alkali can be changed by adding water or more
concentrated solution. However, the strength of an acid or an alkali cannot be changed.
The term strength refers to how easily an acid or an alkali dissociates when dissolved
in water. A strong acid/alkali dissociates fully in water while a weak acid/alkali only
dissociates partially in water. The stronger the acid/alkali, the higher the concentration
of hydrogen/hydroxide ions in water as there are more hydrogen/hydroxide ions that are
able to dissociate.
pH can be determined by:
1. chemical compound called an indicator (e.g. Universal Indicator)
2. a pH probe attached to a data logger
Less than 7 on pH scale is more acidic (has more hydrogen ions) and more than 7
on pH scale is more alkaline (has more hydroxide ions). 7 is neutral. pH can be used to
compare the strength of acids and alkalis of the same concentration.
pH is important as blood is slightly alkaline (pH of 7.4) and a fluid that is injected into
someone’s bloodstream needs to have a pH of around 7.4. If not, the person could die.
pH is also important in soil as the pH of the soil affects plant growth. Plants grow best
in slightly acidic to neutral soil. The optimum pH range of soil for crops to grow is 5.5-
8.5. Plants would not grow if the pH is not within that range. Chemicals can be added to
control the acidity of the soil. Treating the soil with bases (e.g. Quicklime [calcium oxide]
or slaked lime [calcium hydroxide]), known as ‘liming’ the soil, can reduce the acidity
of the soil. The bases react with the acids in the soil (neutralization) and raise the pH so
that the plants can grow healthily. However, adding too much base will make the soil too
alkaline and unsuitable for plant growth.
Types of oxides
Most oxides can be grouped into four types: acidic oxides, basic oxides, amphoteric oxides and neutral oxides.
Acidic oxides: Non-metals form acidic oxides. MOST, not all, are soluble in water. Most acidic oxides dissolve in water to form an acid (this is a chemical change, a chemical reaction occurs). For example, an acidic oxide, sulfur trioxide (SO3(g)) dissolves in water. A chemical reaction takes place and sulfuric acid is formed.
ACIDIC OXIDE + ALKALI/BASE -> SALT + WATER
Basic oxides: These are alkalis. Metals form basic oxides, especially alkali metals and
alkaline earth metals. MOST are insoluble in water but some are sparingly soluble in water (exceptions: sodium oxide and potassium oxide, which are soluble in water). Basic oxides react with water to form hydroxides.
Amphoteric oxides: These behave as both basic and acidic oxides. They react with both acids and bases to form a salt and water. Metals form amphoteric oxides. They are insoluble in water. (Note: Lead forms plumbate , not “leadate”. Lead (II) oxide, an amphoteric oxide, and sodium hydroxide, a base, does not form “sodium leadate”, it forms sodium plumbate .)
Neutral oxides: Non-metals form neutral oxides. Neutral oxides behave as neither basic nor acidic oxides. They are insoluble in water. An unknown oxide can be classified using the flow chart below:
Sulfur Dioxide and Sulfuric Acid
Sulfur dioxide is an acidic oxide. It can be used to:
· Manufacture sulfuric acid.
1. SO2(g) + O2(g) -> 2SO3(g)
Sulfur dioxide (made by burning sulfur in oxygen) is further reacted with oxygen to form sulfur trioxide (SO3).
2. SO3(g) + H2SO4(l) -> H2S2O7(l)
It is then dissolved in concentrated sulfuric acid (H2SO4) to give a fuming liquid called oleum (H2S2O7).
3. H2S2O7(l) + H2O(l) -> 2H2SO4(l)
Water is then added to oleum to form concentrated sulfuric acid (Thus there is one more molecule of sulfuric acid created through this method).
· Bleaching agent.
It decolourises coloured compounds, causing them to turn pale or white by removingoxygen from them.
· Food preservative
Sulfur dioxide is poisonous to all organisms, especially bacteria. It is added to food in small amounts to prevent the growth of mould or bacteria The minute concentrations of sulfur dioxide added is sufficient to kill bacteria but not humans. Sulfuric acid is the cheapest and most readily available acid. Other than being used to make synthetic fibres, paints and pigments, it is also used to:
· Manufacture fertilisers.
Sulfuric acid can be used to manufacture fertilisers like ammonium sulfate (salt formed when sulfuric acid + ammonia) and superphosphate (calcium dihydrogen phosphate + calcium sulfate made from calcium phosphate + concentrated sulfuric acid).
· Manufacture detergents.
It is used to treat organic compounds called hydrocarbons to form an organic acid, which is then neutralized with sodium hydroxide solution to produce the detergent. (Note: Acid
+ alkali -> salt and water)
Word equations:
1. Hydrocarbon + concentrated sulfuric acid -> organic acid
2. Organic acid + sodium hydroxide -> detergent
· As battery acid in cars.
Lead and lead (IV) oxide plates are fitted in the batteries that contain dilute sulfuric acid. Electrical energy, used to start the car engine running, is produced when the lead, lead(IV) oxide and sulfuric acid react.
Valency Table Of Ions or Radicals
Cations Anions
VALENCY 1 (+) VALENCY 1 (-)
Group I ions:
- Lithium
- Sodium
- Potassium
- Rubidium
Group VII ions:
- Fluoride
- Chloride
- Bromide
- Iodide
- Caesium
- Francium
- Transition metals followed by (I)
- Hydrogen ion
- Silver ion
- Ammonium ion
- Hydroxide
- Nitrite
- Nitrate
VALENCY 2 VALENCY 2
Group II ions
- Magnesium
- Calcium
- Strontium
- Barium
- Radium
- Transition metals with (II)
- Mercury
- Zinc
Group VI ions
- Oxygen
- Sulphur
- Selenium
- Tellurium
- Polonium
- Sulfite
- Sulfate
- Carbonate
- Oxide
- Sulphide
VALENCY 3 VALENCY 3
Group III ions:
- Boron
- Aluminium
- Gallium
- Indium
- Thallium
Transition metal with (III)
Group V ions:
- Nitrogen
- Phosphorus
- Arsenic
- Antimony
- Bismuth
- Nitride
- Phosphate
VALENCY 4 VALENCY 0
Group IV elements:
- Carbon
- Silicon
- Germanium
- Tin
- Lead
NB: elements are much more likely to form covalent compounds than to form ions
Group VII atoms:
- Helium
- Neon
- Argon
- Krypton
- Xenon
- Radon
NB: elements with stable electronic
configuration does not tend to form ions
Final Notes: Diamond and Graphite
http://images.tutorvista.com/content/carbon-compounds/diamond-structure-graphitestructure.jpeg
Biology Journal 
