Wednesday, 19 December 2012
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
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+)
|
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
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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.
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