Paper 1 content

• The transfer of electrons requires a lot of energy.

  Groups 1, 2, 6 and 7 form ions very easily. This is because they only need to gain or lose a small number of electrons, and so less energy is required. 

  Those in groups 3, 4 and 5 do not form ions very easily, because they need to gain or lose a larger number of electrons, and therefore more energy is required. 
• 1. Hydroxide:  OH-
  2. Sulphate:  SO42-
  3. Nitrate:  NO3-
  4. Carbonate:  CO32-
  5. Ammonium:  NH4+
• 'A compound is found to contain 50.05% sulfur and 49.95% oxygen by weight. What is the empirical formula for this compound?'

  1)Assume 100 g of the compound is present. This changes the percentages given in the question into grams

  2) Convert these masses to moles (moles = mass ÷ Mr)

  3) Divide both the mole values you just calculated by the lower number of the two, this gives you the smallest whole-number ratio between the two elements

  So now you know the ratio of sulfur to oxygen in this compound is 1 : 2

  4) Use this ratio to write out the empirical formula for the compound:

  so the answer: SO2
• Properties of simple molecular substances:

  1. Strong covalent bonds between the atoms of each molecule. 
  2. Weak intermolecular forces between molecules. 
  3. Low melting and boiling points (so normally gaseous as room temperature).
  4. Cannot conduct electricity. 
• Properties of giant covalent structures:

  1. Every atom is connected by strong covalent bonds 
  2. No weak intermolecular forces as there is only one structure
  3. High melting and boiling points
  4. Cannot conduct electricity (except graphite)
• Two substances made from the same element, that are in the same physical state, but that have different structures, are called allotropes.
• Graphite is a lot softer than diamond. 

  This is because the 2D layers of graphite stack on top of each other with only weak intermolecular forces holding them together.

  This means the layers can slide over each other, making graphite easier to break.

  Graphite is able to conduct electricity.

  This is because each carbon atom has one delocalised electron, which can move freely, and so is able to carry charge.
• Graphene can be found naturally within graphite.

  The sheets can be folded into two types of 3D structure: tubes and spheres, which are known as fullerenes.

  Graphene is just a single layer of graphite, which consists of carbon atoms arranged into flat hexagons. 

  Each carbon has one delocalised electron, so graphene can conduct electricity.
• Fullerenes are allotropes of carbon, made by bending sheets of graphene into hollow structures.

  Nanotubes made from these are useful in electronics. This is because each carbon atom has one delocalised electron which can carry charge. They also have a high strength to weight ration and this means that they can make the tennis racket frame a lot stronger without making them much heavier. Fullerenes are useful because they have a high surface area to volume ratio and are used as catalysts and delivery of medicine within the body(such as Buckminsterfullerene).
• In metallic bonding, each metal atom becomes an ion with a positive charge. 

  It does this by giving up its outer shell electrons. 

  These electrons are said to be 'delocalised', and are shared across all the ions in the structure.
• Alloys tend to have a higher strength than pure metals. 

  This is because the atoms/ions of the different elements are different sizes, which disrupts the regular layered structure and so means the layers can no longer slide over one another. 
• The particle model (sometimes also called the kinetic model) has 3 main assumptions.

  These are that the particles are:

  Small

  Inelastic 

  Spheres
• 1000cm^3= 1 dm^3
• volume (in dm^3) = moles x 24

  THIS IS ONLY FOR GASES
• $Atom economy=$$(Mr of desired products/ Mr of all reactants) *$$100$
• %(percentage) yield = (actual yield (g) ÷ theoretical yield (g)) x 100
• Why percentage yield of a chemical reaction may be less than 100%:

  The reactants may not all react (e.g. because the reaction is very slow or reaches equilibrium)

  There may be side reactions, meaning that other products are produced instead

  Some of the products may be lost (e.g. gases may float off, or some solids may be left on the filter paper)
• Select two reasons why using a probe may be more reliable than using an indicator.

  Determining the colour of an indicator is subjective

  A probe produces a more accurate result
• Titration required practical(EQUIPMENT):

  1. A pipette to accurately measure a certain volume of acid or alkali (normally 25 cm3)
  2. A conical flask to contain the liquid from the pipette
  3. A burette to add alkali or acid to the the conical flask
  4. A white tile to place the conical flask on
• Titration procedure

  1. Use the pipette to add 25 cm3 of alkali to a clean conical flask

  2. Add a few drops of indicator and put the conical flask on a white tile

  3. Fill the burette with acid and note the starting volume

  4. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix

  5. Stop adding the acid when the end-point is reached (this is when the acid has neutralised the alkali and the indicator changes colour)

  6. Note the final volume reading, and calculate how much acid you added in total

  7. Repeat the titration until you get 'concordant results', which means volumes of acid that are within 0.10 cm3 of each other

  8. Use the concordant results to calculate the mean volume of acid required to neutralise the alkali
• It is important to swirl the conical flask as you add the acid from the burette in order to evenly distribute it, and ensure that the colour change occurs as soon as neutralisation takes place.

  It's also important that you place the conical flask on a white tile, so you can more easily see when the colour change takes place.
• There are 3 different type of indicators (and their respective colour changes) you should know:

  Litmus is red in acidic solutions and blue in alkaline solutions

  Phenolphthalein is colourless in acidic solutions and pink in alkaline solutions

  Methyl orange in red in acidic solutions and yellow in alkaline solutions 
• titrations can also be done the other way around, with the acid in the flask, and the alkali in the burette.
• For a weak acid, does the position of equilibrium lie to the left or the right?

  Left
• pH is a measure of the hydrogen ion (H+) concentration of the solution. 
• Every change of 1 on the pH scale represents a 10 fold change in the H+ concentration. 
• Acid + metal oxide ➔ salt + water
• What type of reaction is it when an acid and a base react together? 

  Neutralisation reaction
• During a neutralisation reaction, the positive hydrogen ions from the acid react with the negative hydroxide ions from the alkali to form molecules of water.
• Acid + metal hydroxide ➔ salt + water
• Acid + metal carbonate ➔ salt + water + carbon dioxide
• How to obtain soluble salt crystals from an acid base reaction:

  1. Place dilute acid in a beaker and heat gently.
  2. Add the solid base bit by bit until it stops reacting, which means it's in excess.
  3. Isolate the salt solution by filtering out the excess solid base using filter paper and a funnel.

  4. Heat the salt solution gently in a water bath until crystals start to form.

  5. Let the solution cool further, which will cause more crystals to precipitate.

  6. Filter out the soluble salt crystals using filter paper and funnel.
• When a soluble salt is formed from an acid and an insoluble base, how do you know when an excess of base has been added?

  Some of the reactant will be left unreacted
• Metal + acid ➔ salt + hydrogen
• Pure metals can be extracted from metal oxides using the element carbon.

  The carbon causes the metal to lose its oxygen, so the metal becomes reduced.

  This produces CO2, and can only work for metals less reactive than carbon.
• Why do we find pure gold in the ground, but not pure iron?

  Gold is unreactive, so doesn't react with any other elements

  Iron is reactive enough to react with oxygen so is oxidised to iron oxide 
• Ca  ➔  Ca2+  +  2e-

  example of oxidation
• When a metal reacts with an acid, a redox reaction takes place.
• A spectator ion is an ion that doesn't take part in the reaction and so keeps the same charge.
• What is the name of the substance that is mixed with aluminium oxide to lower its melting point? 

  Cryolite