Chemistry-Extra random information

When have oxygen,
Phosphate, Nitrate, Sulfate

When have one element only,
Sulfide, Chloride, Iodide, Bromide, Nitride, Oxide

Dissociation (examples)

Calcium+sulfuric acid --> calcium sulfate+hydrogen gas

Sodium carbonate+hydrochloric acid --> sodium chloride+carbon dioxide gas+water

Nitric acid+sodium hydroxide --> Sodium nitrate+water

Chemistry-Bases+Alkali

Bases

What a base is

Insoluble in water

A base is any metal oxide or hydroxide. Thus, it contains either oxide ions (O2-) or hydroxide ions (OH-).

A base is a substance that reacts with an acid to produce salt and water only.

base+acid --> salt+water

Basicity
1 hydrogen ion --> mono basic
2 hydrogen ion --> di basic
3 hydrogen ion --> tri basic

Alkalis (special class of bases)
An alkali is a base that is soluble in water.
Sodium oxide+water --> sodium hydroxide

Most bases are insoluble in water. (which is why alkalis are special)

Properties of alkali
1) Have a bitter taste and soapy feel
2) Turn red litmus paper blue
3) Produces hydroxide ions when dissolved in water
4) Can react with acids to form salt and water only. This reaction is called neutralisation.
In neutralisation reaction, hydrogen ions from the acid react with the hydroxide ions from the alkalis to form water.

5) When heated with ammonium salts, ammonium gas is produced:
alkali+ammonium salt --> ammonia+water+salt
ammonia can be recognised by its pungent smell. It also turns red litmus paper blue.

6) It can react with a solution of one metal salt to give metal hydroxide and another metal salt:
alkali+salt(of metal A) --> metal+salt(of metal B) hydroxide
The metal hydroxide will appear as precipitate if it is insoluble in water.

Uses of bases and alkali
Ammonia solutions: In window cleaning solution, in fertilisers
Calcium oxide: In neutralising acidic soil, to make iron, concrete and cement
Magnesium hydroxide: In toothpaste to neutralise acid on teeth, in antacids to relieve indigestion
Sodium hydroxide: In making soaps and detergents, in industrial cleaning detergent

Chemistry-Acids

Acids

Organic acids: naturally occurring acids such as citric acids, found in oranges.

Mineral acids: man-made (most of them), such as nitric and sulphuric acid.

What is an acid?

All acids produce hydrogen ions in aqueous solutions. Thus, an acid is a substance which produces hydrogen ions, H+, when dissolved in water.

All acids contain hydrogen but not all compounds that contain hydrogen are acids.

E.g. ammonia and methane contain hydrogen but are not acids because they do not produce hydrogen in the water. One of the properties of acids are that they produce hydrogen ions.

Properties of acids

1) Have a sour taste

2) Dissolve in water to form solutions which conduct electricity.

3) Turns blue litmus paper red.

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4) Reacts with reactive metals to form hydrogen and salt.

Metal+acid --> Salt+hydrogen

E.g. When magnesium ribbon is added to dilute sulphuric acid, bubbles of hydrogen gas is seen.

Magnesium+dilute sulphuric acid --> magnesium sulphate+hydrogen sulphate.

Magnesium sulphate: Salt produced from the reaction. (above)

Sulphates: Salt, but only referred to this name when formed from sulfuric acid. 

Nitrates when formed from nitric acid, chlorides when formed from hydrochloric acid.

Experiment: If a lighted splint is placed at the mouth of a test tube, a 'pop' sound can be heard and the lighted splint will extinguish. This shows that hydrogen gas has been produced.

Some acid and metal reaction DO NOT produce hydrogen.

(a) When unreactive metals (like copper and silver) are added to dilute acids.

(b) Concentrated nitric acid reacts with metals (like copper) but instead of hydrogen, a nitrate (salt), water and nitrogen dioxide gases are formed.

(c) Lead does not react with dilute sulfuric acid or dilute hydrochloric acid because a layer of lead chloride and lead sulphate is formed from the initial reaction between lead and dilute acid. The layer is insoluble in water and quickly forms a coating around the metal. This prevents the metal from further attack by the acid.

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5) Acids react with carbonates to form salt, carbon dioxide and water.

Carbonate+acid --> Salt+water+carbon dioxide

Sodium chloride and dilute hydrochloric acid produces sodium chloride, water and carbon dioxide.

Sodium carbonate+dilute hydrochloric acid --> sodium chloride+water+carbon dioxide

Test for carbon dioxide: Bubble carbon dioxide through lime water. Carbon dioxide forms a white precipitate with lime water.

6) Acids react with metal oxides and hydroxides to form salt and water only.

Metal oxide+acid --> salt+water

Metal hydroxide+acid --> salt+water

*All metal oxides and hydroxide react with acids in the same way.

Role of water in acidity

Hydrogen chloride exists as covalent molecules. In the absence of water, e.g. in organic solvents, they do not become acids.

Acids only display their properties when they are dissolved in water (aq), because acids dissociate in water to produce hydrogen ions which allow the acidic properties.

The hydrogen ions produced allow the acids to react with metals like magnesium:

hydrogen ions+magnesium --> hydrogen gas+magnesium ions

Dissociation does not occur when hydrogen chloride is dissolved in an organic solvent. Thus, it does not react with magnesium.

No reaction occurs as well when solid citric acid is mixed with anhydrous sodium carbonate. When a few drops of water is added to the mixture, bubbles of carbon dioxide is formed.

hydrogen ions+carbonate ions --> water+carbon dioxide

Uses of acids

Sulphuric acid: making detergent, making fertilisers, in car batteries

Ethanoic acid: to preserve food (in vinegar), in making adhesives such as glue

Hydrochloric acid: in leather processing, for cleaning metals


Examples of acids

Strong acids
-Hydrochloric acid, HCl
-Sulfuric acid, H₂SO₄
-Nitric acid, HNO₃
Weak acids
-Ethanoic acid, CH₃CO₂H
-Carbonic acid, H₂CO₃

Chemistry-Acids and Bases

Acids	Bases
Have a sour taste	Have a bitter taste and a soapy feel
Turns blue litmus paper red	Turns red litmus paper blue
Dissolve in water to form solutions which conduct electricity	Produce ammonia gas when heated with ammonium salts
React with reactive metals to form hydrogen and a salt. The general equation for the reaction is: Metal + acid → salt + hydrogen	Reacts with a solution of one metal salt to give metal hydroxide and another metal salt
pH less than 7
Hydrogen ions must be present (H+)

Concentration and strength
1. Concentration tells us how much a substance is dissolved in 1 cm3 of the solution.
2. Strength refers to how easily an acid or an alkali dissociates when dissolved in water.

The pH scale
1. The pH scale is used to determine if a given substance is acid, alkaline or neutral.
2. The pH of colourless solutions can be determined using the Universal indicator.
3. It is important to control the pH of soil. Most plants grow best when the pH is around 7.
4. Quicklime (calcium oxide) and slaked lime (calcium hydroxide) are commonly used to reduce the acidity of soil.

Universal indicator
pH value can be determined using the universal indicator. It gives different colours in solutions of different pH.
*The more hydrogen ions there are, the lower the pH value, the stronger the acid.
pH can be used to compare strengths of acids and alkalis of the same concentration.

Types of oxide
1. Metals react with oxygen to form basic oxides or amphoteric oxides.
2. Non-metals react with oxygen to form acidic oxides or neutral oxides.
3. Basic oxides that are soluble in water are called alkalis.
4. Basic oxides that are insoluble in water are called insolubles bases.

Sulphuric dioxide and sulphuric acid
1. Sulfur dioxide is used
-for manufacturing sulphuric acid
-as a bleaching agent
-as a food preservative

2. Sulphuric acid is used
-for manufacturing fertilisers
-for manufacturing detergents
-in car batteries

Chemistry-Chemical Bonding

Metallic bonding
-Metallic atoms are bonded together.
-Metal atoms lose their outer valence electrons and become positively charged in a metal lattice.
-These electrons which now do not belong to any metal atom are called 'delocalised'.
-The definition of a metallic bond is 'The force of attraction between positive metal ions and the free electrons'.

Key words concerning metallic bonding
-Delocalised
-Metallic bond
-Positive metal ions
-Sea of free electrons
-High boiling and melting points
-Lattice
-Force of attraction

Diagrams that effectively show metallic bonding

-Conduct heat, electricity

-Generally high melting and boiling points

-Strong

-Malleable

-Ductile

-Metallic lustre

-Opaque

-Insoluble

Covalent compounds	Ionic compounds	Metallic compounds
Formed between non-metals (generally)	Formed between metals and non-metals (generally)	Formed between metals
Low melting point, boiling point	High melting point, boiling point	High melting point, boiling point
Sharing pairs of electrons to obtain octet/ duplet structure	Gaining/Losing electrons to obtain octet/ duplet structure	Attraction between metal cation and shared electrons around it in a sea of delocalised electrons
Does not conduct electricity (generally)	Conduct electricity when dissolved in water	Conduct electricity in liquids
Insoluble in water	Soluble in water	Insoluble in water

Covalent compounds
Simple molecular structure
Giant molecular structure (e.g. diamond, sand ; high BP and MP
Low BP and MP: Bonding is weak as there are weak intermolecular forces. Little energy is needed to break the bonding, making the BP and MP low as less heat is needed to break the bonds.
Does not conduct electricity: There are no delocalised electrons as electrons are shared between the atoms.
Insoluble in water: Water is a polar solvent. Most covalent compounds are non-polar solvent. Hence, they do not dissolve in water.

Ionic compounds
Giant lattice structure
High BP and MP: Ions held together by strong electrostatic force. More heat is required to overcome this force, causing the BP and MP to be high.
Conduct electricity when dissolved in water: When ionic compounds dissolve, water break to their cations and anions. These delocalised ions allow the conducting of electricity.
Soluble in water: Water is a polar solvent. Water molecules surround the ionic compound when it is in water, giving enough energy to separate the ionic bond and allow the ionic compound to dissolve in water.

Metallic compounds
Giant lattice structure
High BP and MP: Metallic bonds (electrostatic forces of attraction)are very strong. Hence, more heat is needed to overcome the bonding, making the BP and MP higher.
Conduct electricity in liquids: In liquid, electrons in metallic bonds delocalised and allows the conducting of electricity.
Insoluble in water: They are insoluble in water unless they undergo a chemical reaction with it.

Chemistry-Atomic Structure

The proton number and the nucleon number
1. An atom is made up of three sub-atomic particles, neutrons, electrons and protons.
2. Sub-atomic particles differ in mass and electric charge.

Sub-atomic particle	symbol	Relative mass	Relative charge
Proton	P	1	+1
Neutron	N	1	0
Electron	E	1/840	-1

3. Proton number, Z=number of protons

4. Nucleon number, A= total number of protons and neutrons

5. Number of neutrons, A-Z

6. An atom is electrically neutral. This means that in an atom, the number of protons is the same as the number of electrons.

Isotopes

1. Isotopes are atoms with the same number of protons and electrons.

2. Isotopes have the same chemical properties, but slightly different physical properties.

3. Electrons are arranged in electron shells.

4. The first electron shell can hold up to 2 electrons, the second and third usually hold up to 8 electrons.

5. The way in which the electrons are arranged in electron shells is called the electronic structure or the electronic configuration of the atom.

6. Valence electrons are electrons found in the outer shell of the atom. They are important because they affect the chemical properties of an element.

Output:

1. Mass number = no. of protons+no. of neutrons

2. No. of proton = atomic number

3. Proton+neutron = mass number

4. electronic configuration shows the number of electrons

5. Valence is the outermost electron shell.

6. Isotopes --> same number of protons, different neutrons. different in mass number because mass number = no. of protons+no. of neutrons

7. Ion: atom/molecule in which total number of electrons is not equal to protons.

8. Positive ions: Less electrons compared to protons

9. Negative ions: More electrons compared to ions

Chemistry-Kinetic particle theory

States of matter
1. Matter is a substance that has mass and occupies space.
2. The three states of matter are solid, liquid and gas.
3. Changes in temperature and pressure can change the state of matter.

Kinetic particle theory
1. The kinetic particle theory states that all matter is made up of particles that are in constant, random motion.
2. The differences in the states of matter can be explained in terms of kinetic particle theory.

Properties	Solid	Liquid	Gas
Arrangement of particles	Orderly	Disorderly	Disorderly
Forces between particles	Very strong	strong	Very far apart
Kinetic energy of particles	Very low	Low	high
Particle motion	Vibrate and rotate about a fixed position	Slide over each other	More about at great speeds
Particles	Closely packed	Not really packed	Very far apart

Changes of state and the kinetic particle theory
1. Particles and solids, liquids and gases have different amounts of kinetic energy. Gases have the highest, followed by liquid then solid.
2. Changes of state occur when particles lose or gain energy.

Diffusion
1. Gases with a lower molecular mass diffuse faster than gases with higher molecular mass.
2. Diffusion is the movement of particles from a region of a higher concentration to a region of lower concentration until they are equal on both sides.
3. The relative rates of diffusion: liquid --> slow diffusion, gases --> fast diffusion

Factors affecting diffusion
1. The greater the difference of concentration between the two region, the greater the rate of diffusion.
2. The greater the resistance to diffusion, the lower the rate of diffusion. Resistance refers to anything that affects the rate of diffusion.
3. Temperature increases the rate of molecular movement, increasing the rate of diffusion.
4. Pressure increases the speed of molecules, increasing the rate of diffusion.

Kinetic particle theory
Shows how the particles interact with one another, there are a few assumptions.
1. Molecules are point masses. (no volume)
2. Gas molecules exert no forces on each other unless they collide.
3. Collision of molecules with each other on the walls of the container do not decrease the energy of the system.
4. The molecules of gas are in constant and random motion.
5. The temperature of a gas depends on its average kinetic energy, the energy of an ideal gas is entirely kinetic.

Chemistry-Separation Techniques

Simple distillation
Distillation involves two stages and both are physical state change.
Stage (1): The liquid or solution mixture is boiled to vaporise the most volatile component in the moisture. (liquid --> gas)
Stage (2): The vapour is cooled by water in the Liebig condenser to condense (gas --> liquid) it back to a liquid (the distillate) which is collected.

Crystallisation
-Crystallisation from solution is the most common method used to purify soluble solids.
-The seeding method allows you to grow a large single crystal, others allow you to grow many crystals at a time.
-By controlling the variables such as cooling rate and evaporation rate, the size and shape of the crystals can be controlled.
-Crystallisation is used to purify crystals and substances that decompose upon strong heating.

Decanting

Decanting is the process of pouring off a liquid leaving the precipitate(sediments) at the bottom of the container.

e.g. sugar solution

Decanting is used to separate a dense, insoluble solid from a liquid.

Filtration

-Filtration is used to separate a mixture of a solid and a liquid.

-Upon filtration, the solid that remains on the filter paper is called the residue. The liquid that passes through the filter paper is called the filtrate.

-Filtration can be used to separate two solids if only one of them is soluble in solvent.

-A magnet can be used to separate magnetic substances, from non-magnetic ones.

-Sublimation is used to separate a substance that sublimes from one with a high melting point.

Extra information

1. Substances that do not decompose on strong heating can be purified by evaporation to dryness.

2. A saturated solution can be produced by evaporation.

Chemistry-Elements, Compounds and mixtures

Element- An element is a substance that cannot be split into two or more simpler substances by chemical reaction. Elements are thus the simplest form of matter.

Compound- A substance made up of two or more substances chemically combined together. For example, water is made up of hydrogen(H) and oxygen(O).

Mixture- A substance that is made up of two or more substances that are not chemically combined together. The substances that make up the mixture may be elements, compounds or both. The substances may be solid, liquid or gas etc.