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Tricks for remembering the names of organic molecules

A good way to remember the names of organic molecules is to make up a silly mnemonic where the first letter of each word matches the first letter of the organic molecules. For example the first 10 alkanes in order are , Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane and Decane. These can be memorised with “Many elephants prefer blue pinapples. However hungry orangutans never do.” This isn’t a very good mnemonic, but it is the one I made up for myself when I was at school, and you are best making up your own. The sillier, smellier and more colourful the better.

1:01 understand the three states of matter in terms of the arrangement, movement and energy of the particles

Solid

Arrangement: Particles are close together and regularly packed.

Movement: Particles vibrate around a fixed point.

Energy: Particles have less kinetic energy than both liquids and gasses.

Liquid

Arrangement: Particles are close together but irregular.

Movement: Particles are free to move.

Energy: Particles have less kinetic energy than gasses but more than solids.

Gas

Arrangement: Particles are far apart and there are no forces between them.

Movement: Particles are free to move.

Energy: Particles have more kinetic energy than liquids and solids.

 

1:02 understand the interconversions between the three states of matter in terms of: the names of the interconversions, how they are achieved and the changes in arrangement, movement and energy of the particles

Melting: When a solid is heated, the energy makes the particles vibrate fast enough so that the forces of attraction between the particles break. For example   H2O(s) –> H2O(l)

Freezing: When a liquid is cooled, the particles move slow enough so that the forces of attraction between them will hold them into a solid. For example   H2O(l) –> H2O(s)

Boiling: When a liquid is heated strongly, the energy makes the particles move fast enough so that all forces of attraction are broken. For example   H2O(l) –> H2O(g)

Condensing: When a gas is cooled, the particles move slow enough so that the forces of attraction between them will hold them as a liquid. For example   H2O(g) –> H2O(l)

Sublimation: A small number of substances have the ability to change directly from a solid to a gas when heated. For example   CO2(s) –> CO2(g)

1:03 understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained

Diffusion is the spreading out of particles in a gas or liquid. There is a net movement of particles from areas of high concentration to areas of low concentration until a uniform concentration is achieved.

 

i) dilution of coloured solutions

Dissolving potassium manganate(VII) in water demonstrates that the diffusion in liquids is very slow because there are only small gaps between the liquid particles into which other particles diffuse.

The random motion of particles cause the purple colour to eventually be evenly spread out throughout the water.

Adding more water to the solution causes the potassium manganate(VII) particles to spread out further apart therefore the solutions becomes less purple. This is called dilution.

 

ii) diffusion experiments

When ammonia gas and hydrogen chloride gas mix, they react together to form a white solid called ammonium chloride.

ammonia                  +              hydrogen chloride                 –>            ammonium chloride

NH3(g)                     +              HCl(g)                                     –>            NH4Cl(s)

A cotton wool pad was soaked in ammonia solution and another was soaked in hydrogen chloride solution. The two pads were then put into opposite ends of a dry glass tube at the same time.

The white ring of ammonium chloride forms closer to the hydrochloric acid end because ammonia particles are lighter than hydrogen chloride particles and therefore travel faster.

Even though these particles travel at several hundred metres per second, it takes about 5 min for the ring to form. This is because the particles move in random directions and will collide with air particles in the tube.

1:04 know what is meant by the terms: solvent, solute, solution, saturated solution

When a solid dissolves in a liquid:

  • the substance that dissolves is called the solute
  • the liquid in which it dissolves is called the solvent
  • the liquid formed is a solution
  • a saturated solution is a solution into which no more solute can be dissolved

 

1:05 (Triple only) know what is meant by the term solubility in the units g per 100g of solvent

Solubility is defined in terms of the maximum mass of a solute that dissolves in 100g of solvent. The mass depends on the temperature.

For example, the solubility of sodium chloride (NaCl) in water at 25⁰C is about 36g per 100g of water.

1:06 (Triple only) understand how to plot and interpret solubility curves

The solubility of solids changes as temperature changes. This can be plotted on a solubility curve.

Image result for solubility curve

The salts shown on this graph are typical: the solubility increases as temperature increases.

For example, the graph above shows that in 100g of water at 50⁰C the maximum mass of potassium nitrate (KNO₃) which will dissolve is 80g.

However, if the temperature were 80⁰C a mass of 160g of potassium nitrate (KNO₃) would dissolve in 100g of water.

1:07 (Triple only) practical: investigate the solubility of a solid in water at a specific temperature

At a chosen temperature (e.g. 40⁰C) a saturated solution is created of potassium nitrate (KNO₃) for example.

Some of this solution (not any residual solid) is poured off and weighed. The water is then evaporated from this solution to leave a residue of potassium nitrate which is then weighed.

The difference between the two measured masses is the mass of evaporated water.

The solubility, in grams per 100g of water, is equal to 100 times the mass of potassium nitrate residue divided by the mass of evaporated water.

 solubility (g/100g) = \frac{mass Of Solute}{mass Of Solvent} \times 100

1:08 understand how to classify a substance as an element, a compound or a mixture

Element: The simplest type of substances made up of only one type of atom.

Compound: A substance that contains two or more elements chemically joined together in fixed proportions.

Mixture: Different substances in the same space, but not chemically combined.

Note: elements such as oxygen (O2) are described as diatomic because they contain two atoms.

The full list of elements that are diatomic is:

  • Hydrogen (H2)
  • Nitrogen (N2)
  • Fluorine (F2)
  • Oxygen (O2)
  • Iodine (I2)
  • Chlorine (Cl2)
  • Bromine (Br2)

1:09 understand that a pure substance has a fixed melting and boiling point, but that a mixture may melt or boil over a range of temperatures

Pure substances, such as an element or a compound, melt and boil at fixed temperatures.

However, mixtures melt and boil over a range of temperatures.

Example: although pure water boils at 100⁰C, the addition of 10g of sodium chloride (NaCl) to 1000cm³ of water will raise the boiling point to 100.2⁰C.

Example: although pure water melts at 0⁰C, the addition of 10g of sodium chloride (NaCl) to 1000cm³ of water will lower the melting point to -0.6⁰C.

1:10 describe these experimental techniques for the separation of mixtures: simple distillation, fractional distillation, filtration, crystallisation, paper chromatography

Simple distillation

This method is used to separate a liquid from a solution. For example: separating water from salt water.

The salt water is boiled. The water vapour condenses back into a liquid when passed through the condenser. The salt is left behind in the flask.

Note: cold water is passed into the bottom of the condenser and out through the top so that the condenser completely fills up with water.

 

Fractional distillation

This method is used to separate a mixture of different liquids that have different boiling points. For example, separating alcohol from a mixture of alcohol and water.

Water boils at 100oC and alcohol boils at 78oC. By using the thermometer to carefully control of temperature of the column, keeping it at 78oC, only the alcohol remains as vapour all the way up to the top of the column and passes into the condenser.

The alcohol vapours then condense back into a liquid.

 

 

Filtration

This method is used to separate an insoluble solid from a liquid. For example: separating sand from a mixture of sand and water.

The mixture is poured into the filter paper. The sand does not pass through and is left behind (residue) but the water passes through the filter paper and is collected in the conical flask (filtrate).

 

 

Crystallisation

This method is used to obtain a salt which contains water of crystallisation from a salt solution. For example: hydrated copper sulfate crystals (CuSO4.5H2O(s)) from copper sulfate solution (CuSO4(aq)).

  • Gently heat the solution in an evaporating basin to evaporate some of the water
  • until crystals form on a glass rod (which shows that a hot saturated solution has formed).
  • Leave to cool and crystallise.
  • Filter to remove the crystals.
  • Dry by leaving in a warm place.

If instead the solution is heated until all the water evaporates, you would produce a powder of anhydrous copper sulfate (CuSO4(s)).

 

Paper chromatography

This method can be used to separate the parts of a mixture into their components. For example, the different dyes in ink can all be separated and identified.

The coloured mixture to be separated (e.g. a food dye) is dissolved in a solvent like water or ethanol and carefully spotted onto the chromatography paper on the baseline, which is drawn in pencil so it doesn’t ‘run or smudge’.

The paper is carefully dipped into the solvent and suspended so the baseline is above the liquid solvent, otherwise all the spots would dissolve in the solvent. The solvent is absorbed into the paper and rises up it as it soaks into the paper. The choice of solvent depends on the solubility of the dye. If the dye does not dissolve in water then normally an organic solvent (e.g. ethanol) is used.

As the solvent rises up the paper it will carry the dyes with it. Each different dye will move up the paper at different rates depending on how strongly they stick to the paper and how soluble they are in the solvent.

1:11 understand how a chromatogram provides information about the composition of a mixture

Paper chromatography can be used to investigate the composition of a mixture.

A baseline is drawn on the paper. The mixture is spotted onto the baseline alongside known or standard reference materials. The end of the paper is then put into a solvent which runs up the paper and through the spots, taking some or all of the dyes with it.

Different dyes will travel different heights up the paper.

The resulting pattern of dyes is called a chromatogram.

In the example shown, the mixture is shown to contain the red, blue and yellow dyes. This can be seen because these dots which resulted from the mixture have travelled the same distance up the paper as have the red, blue and yellow standard reference materials.

1:12 understand how to use the calculation of Rf values to identify the components of a mixture

When analysing a chromatogram, the mixture being analysed is compared to standard reference materials by measuring how far the various dyes have travelled up the paper from the baseline where they started.

For each dye, the Rf value is calculated. To do this, 2 distances are measured:

  • The distance between the baseline and the dye
  • The distance between the baseline and the solvent front, which is how far the solvent has travelled from the baseline

The Rf value is calculated as follows:

 R_f=\frac{distance\:of\:dye\:from\:baseline }{distance\:of\:solvent\:front\:from\:baseline}

If the Rf value of one of the components of the mixture equals the Rf value of one of the standard reference materials then that component is know to be that reference material. 

Note that because the solvent always travels at least as far as the highest dye, the Rf value is always between 0 and 1.

Dyes which are more soluble will have higher Rf values than less soluble dyes. In other words, more soluble dyes move further up the paper. The extreme case of this is for insoluble dyes which don’t move at all (Rf value = 0). The other aspect affecting how far a dye travels is the affinity that dye has for the paper (how well it ‘sticks’ to the paper).

1:13 practical: investigate paper chromatography using inks/food colourings

  1. A pencil line (baseline) is drawn 1cm from the bottom of the paper. Pencil will not dissolve in the solvent, but if ink were used instead it might dissolve and interfere with the results of the chromatography.
  2. A spot of each sample of dye is dropped at different points along the baseline.
  3. The paper is suspended in a beaker which contains a small amount of solvent. The bottom of the paper should be touching the solvent, but the baseline with the dyes should be above the level of the solvent. This is important so the dyes don’t simply dissolve into the solvent in the beaker.
  4. A lid should cover the beaker so the atomosphere becomes saturated with the solvent. This is so the solvent does not evaporate from the surface of the paper.
  5. When the solvent has travelled to near the top of the paper, the paper is removed from the solvent and a pencil line drawn (and labelled) to show the level the solvent reached up the paper. This is called the solvent front.
  6. The chromatogram is then left to dry so that all the solvent evaporates.

Common solvents are water or ethanol. The choice of solvent depends on whether most of the dyes are soluble in that solvent.

1:15 know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles

An atom consists of a central nucleus, composed of protons and neutrons.

This is surrounded by electrons, orbiting in shells (energy levels).

Atoms are neutral because the numbers of electrons and protons are equal.

 
MassCharge
Proton1+1
Neutron10
Electronnegligible (1/1836)-1

1:16a know what is meant by the terms atomic number, mass number and relative atomic mass (Aᵣ)

Atomic number: The number of protons in an atom.

Mass number: The number of protons and neutrons in an atom.

Relative atomic mass (Ar): The average mass of an atom compared to 1/12th the mass of carbon-12.

1:16 know what is meant by the terms atomic number, mass number, isotopes and relative atomic mass (Aᵣ)

Atomic number: The number of protons in an atom.

Mass number: The number of protons and neutrons in an atom.

Isotopes: Atoms of the same element (same number of protons) but with a different number of neutrons.

Relative atomic mass (Ar): The average mass of an atom compared to 1/12th the mass of carbon-12.

1:17 be able to calculate the relative atomic mass of an element (Aᵣ) from isotopic abundances

75% of chlorine atoms are the type 35Cl (have a mass number of 35)

25% of chlorine atoms are of the type 37Cl (have a mass number of 37)

In order to calculate the relative atomic mass (Ar) of chlorine, the following steps are used:

  1. Multiply the mass of each isotope by its relative abundance
  2. Add those together
  3. Divide by the sum of the relative abundances (normally 100)

    \[ A_r = \frac{( (35 \times 75) + (37 \times 25) )}{100} \]

    \[ A_r = 35.5 \]

 

Example question:

A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%.

Calculate the relative atomic mass (Ar) of bromine.

    \[ A_r = \frac{( (79 \times 50.7) + (81 \times 49.3) )}{100} \]

    \[ A_r = 79.99 \]

 

1:18 understand how elements are arranged in the Periodic Table: in order of atomic number, in groups and periods

The elements in the Periodic Table are arranged in order of increasing atomic number.

 

Image result for periodic table groups and periods

Columns are called Groups. They indicate the number of electrons in the outer shell of an atom.

Rows are called Periods. They indicate the number of shells (energy levels) in an atom.

1:19 understand how to deduce the electronic configurations of the first 20 elements from their positions in the Periodic Table

Electrons are found in a series of shells (or energy levels) around the nucleus of an atom.

Each energy level can only hold a certain number of electrons. Low energy levels are always filled up first.

Rules for working out the arrangement (configuration) of electrons:

Example – chlorine (Cl)

1) Use the periodic table to look up the atomic number. Chlorine’s atomic number (number of protons) is 17.

2) Remember the number of protons = number of electrons. Therefore chlorine has 17 electrons.

3) Arrange the electrons in levels (shells):

  • 1st shell can hold a maximum of 2
  • 2nd can hold a maximum of 8
  • 3rd can also hold 8

Therefore the electron arrangement for chlorine (17 electrons in total) will be written as 2,8,7

4) Check to make sure that the electrons add up to the right number

The electron arrangement can also be draw in a diagram.

Electron arrangement for the first 20 elements:

1:20 understand how to use electrical conductivity and the acid-base character of oxides to classify elements as metals or non-metals

Metals

  • conduct electricity
  • have oxides which are basic, reacting with acids to give a salt and water

 

Non – Metals

  • do not conduct electricity (except for graphite)
  • have oxides which are acidic or neutral

 

1:21 identify an element as a metal or a non-metal according to its position in the Periodic Table

Metals on the left of the Periodic Table.

Non-Metals on the top-right, plus Hydrogen.

1:22 understand how the electronic configuration of a main group element is related to its position in the Periodic Table

Elements in the same group have the same number of electrons in their outer shell.

This is why elements from the same group have similar properties.

1:23 Understand why elements in the same group of the Periodic Table have similar chemical properties

Elements in the same group of the periodic table have the same number of electrons in their outer shells, which means they have similar chemical properties.

1:25 write word equations and balanced chemical equations (including state symbols): for reactions studied in this specification and for unfamiliar reactions where suitable information is provided

Example:

Sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).

Word equation:

     sodium + water –> sodium hydroxide + hydrogen

Writing the chemical equation

A chemical equation represents what happens in terms of atoms in a chemical reaction.

Step 1: To write a chemical equation we need to know the chemical formulae of the substances.

     Na + H2O –> NaOH + H2

Step 2: The next step is to balance the equation: write a large number before each compound so the number of atoms of each element on the left hand side (reactants) matches the number on the right (products). This large number is the amount of each compound or element.

During this balancing stage the actual formulas for each compound must not be changed. Only the number of each compound changes.

     2Na + 2H2O –> 2NaOH + H2

If asked for an equation, the chemical equation must be given.

 

State symbols are used to show what physical state the reactants and products are in.

State symbolsPhysical state
(s)Solid
(l)Liquid
(g)Gas
(aq)Aqueous solution (dissolved in water)

Example:

A solid piece of sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).

     2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)

1:26 calculate relative formula masses (including relative molecular masses) (Mᵣ) from relative atomic masses (Aᵣ)

Relative formula mass (Mr) is mass of a molecule or compound (on a scale compared to carbon-12).

It is calculated by adding up the relative atomic masses (Ar) of all the atoms present in the formula.

Example:

The relative formula mass (Mr) for water (H2O) is 18.

Water                     = H2O

Atoms present      = (2 x H) + (1 x O)

Mr                           = (2 x 1) + (1 x 16) = 18

Select a set of flashcards to study:

     Terminology

     Skills and equipment

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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals

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