The periodic table
… Newlands structured his periodic table using his ‘law of …?…’ (he noticed that every eighth element had similar …?…).
He put the elements in order of …?… …?… However, after calcium their …?… did not match very well with the groups, so other scientists did not accept his ideas.
… Mendeleev ordered the elements in a similar way to Newlands, except he left …?… for unknown elements and …?… their properties. The discovery of these elements confirmed his predictions and his ideas were more readily accepted by other scientists. His table became the basis for the modern periodic table today.
… The modern periodic table is ordered by…?
… The number of …?… in the outermost shell (the highest …?… level) determines the element’s …?… properties (e.g. reactivity).
(Physical properties are characteristics like boiling and melting points)
… The group number of each element tells us..?
… Using ideas of distance between nucleus and outer electrons, and the number of occupied inner shells, explain the trends in reactivity as you move down a group.
for the metals
for the non-metals
The Alkali Metals
… Group 1 metals all react with water to produce …?… and an a…?… solution containing the metal hydroxide.
… Alkali metals form …?… ions with a charge of …?… to make ionic compounds, which are usually w…?… or colourless crystals that …?… in water to form colourless solutions.
… The reactivity of the alkali metals …?… going down the group. This is because…?
… Here is a link to an interesting video on the history of the periodic table:
‘Chemistry – a volatile history’: http://youtu.be/nsbXp64YPRQ
… The density of the alkali metals …?… as you go down the group. This is because as the atoms increase in size, the added mass of the extra protons and neutrons has a larger effect than the increased volume of the atom.
The Transition Elements
… Compared with the alkali metals, transition elements have much higher m…?… and b…?… points and also have higher d..?…
They are also stronger, h…?… (difficult to scratch) and t…?… (difficult to crack) but are chemically much less r…?…
… Transition metals are useful as building and structural materials, often mixed with other metals to form a…?…
… The transition elements generally have a much lower reactivity compared to the group 1 and 2 metals, so they do not react vigorously with o…?… or w…?…
… Transition elements can form ions with different c…?…, in compounds that are often brightly …?… (This is because they have complicated electron shell arrangements)
… Transition elements and their compounds have an important use in industry as c…?… , which speed up the r…?… of reactions (without being changed by the reaction).
Group 7 elements – the Halogens
… Halogens (meaning ‘salt formers’) form ions with a single …?… charge and react with metals to produce i…?… compounds.
… Compounds of metals with non-metals are called ‘salts’.
… Why does the reactivity of group 7 elements (the ‘…?…’) decrease going down the group?
… What is the trend in melting and boiling points for group 7 elements (why is this?)
… The halogens form c…?… – bonded compounds with other non-metals by s…?… electrons.
… A more reactive halogen can displace a less reactive halogen from a solution of one of its salts. For example, KBr + Cl2 —-> ? + ?
Chemistry of hard water:
… Hard water contains c…?… and m…?…. ions
… Hard water reacts with soap to form s…?… which is a precipitate (an insoluble solid)
… The are two types of hard water: t…?… and p…?… The dissolved ions in both of these two types of hard water are …?
… What reaction occurs when you boil temporary hard water (write a word equation and a balanced chemical equation)?
Why can this be a problem?
… What happens when you boil permanent hard water?
… Both types of hard water can be softened by either using an i…?… e…?… column or by adding s…?… c…?… (‘washing soda’), which results in a precipitate that can befiltered.
… Why is it better to drink hard water rather than soft water?
… What is the difference between scum and scale?
… Titration of hard water can be done using using …?… solution – from this we can work out how ‘hard’ the water is compared to other sources.
Purifying water to produce potable (drinking) water
… Water can be purified from a fresh water source (a reservoir, river or lake) by f…?… using reed beds and then by adding a small amount of c…?… or o…?… to kill bacteria/microbes.
… When water is scarce in a country, coastal areas can use sea water which can be processed in d…?… plants. This involves distillation of the sea water, but this process requires a lot of e…?… and so can be very expensive to run.
… F…?… ions are sometimes added to water supplies for dental health reasons. However, too much of this can damage teeth. This can be an ethical problem as some people think that they should have a choice whether to fluoridate their water.
… Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the e…?….
… Sewage and agricultural waste water require removal of o…?… matter and harmful m…?….
… Industrial waste water may require removal of organic matter and harmful ch..?….
… Sewage treatment to produce potable (drinking) water includes:
• screening and grit removal
• sedimentation produces sewage sludge and effluent (liquid waste)
• anaerobic digestion of sewage sludge
• aerobic biological treatment of effluent.
• disinfection by adding small amounts of chlorine.
Here’s a useful video to give you an idea of how water is processed to create drinking water:
https://youtu.be/PDeiRlQvWnM
Using hydrogen as a fuel
… To reduce the effects of global warming and air-pollution in cities, alternatives to fossil feels need to be found soon.
… Using hydrogen as a fuel is one alternative. It can be burned in combustion engines or used in fuel cells to power vehicles.
… Hydrogen can be produced from renewable sources. The disadvantages of using hydrogen include supply, storage and safety problems.
… Vehicles that use fuel cells or combust hydrogen need to match the performance, convenience and costs compared to petrol and diesel vehicles – otherwise society will not adopt this new technology.
Testing for positive (metal) ions
… The colours observed in a flame test for positive ions Li+, Na+, K+, Cu2+ and Ca2+ are…?
… Describe how you would test for the positive ions of Al3+, Ca2+, Mg2+, Cu2+, Fe2+ and Fe3+ ions using a chemical method? How could you distinguish Al3+ ions?
… Write a balanced ionic equation to show the reaction of one of the positive ions that you have described (remember to include the state symbols).
–
Testing for negative (non-metal) ions
… Describe how you would test for the following negative ions:
carbonate ions?
Halide ions (Cl-, Br- and I-)
Sulfate ions
… When testing for halides, you must first add dilute …?… acid to remove any …?… ions already present (which would ruin the test). Why must you use this particular acid and not any other dilute acid?
… What are the balanced symbol equations for the carbonate, halide and sulfate tests?
… A compound gave a lilac colour in a flame test. Nitric acid and silver nitrate solution was added to the solution of the compound and a yellow precipitate was formed. Name the compound.
Chemical Analysis
… Scientists working in e…?… monitoring, medicine and f…?… science all need to analyse substances.
… The results of their analysis are often matched against existing d…?… to identify substances (or suspects!)
… What is the difference between quantitative and quantitative analysis methods? Can you give some examples of both?
Uses of titration analysis:
… Titration is used to determine unknown concentrations of chemicals of interest, for example, in blood and urine.
Pharmacists also use titration in the development of new pharmaceuticals, for example, to check that a new drug has a high level of purity.
Titration can also be used to determine the amount of a certain chemicals in food.
Titration calculations and method
… First write the balanced symbol equation for the reaction. For example:
HCl + NaOH ——-> NaCl + H2O
… Use an “MVC” table with the acid and alkali as the column headings. Enter the information given in the question (remember to convert cm3 into dm3)
Note that the ‘M’ can either stand for Moles or Mass, depending on the units that the question gives you for concentration (g/dm3 would be Mass, mol/dm3 would be Moles):
HCl NaOH
Moles (or Mass):
Volume:
Concentration:
Fill in the blanks remembering that ‘Down’ is ‘Divide’ and ‘UP’ is ‘mUltiply’.
… Once you have found the moles of added acid or alkali, use the RATIOS in the balanced chemical equation to find the number of moles of the solution under test that must have reacted.
… To convert your answer to g/dm3 (a measure of density), multiply the concentration by the relative formula mass:
g/dm3 = Concentration (mol/dm3) x Mr
… Describe a method for carrying out a titration, e.g. to find the concentration of an unknown acid using an alkali of known concentration…
1) Add the unknown concentration of acid in a (conical) flask. Measure the volume of acid using a pipette (usually 25cm3)
2) Add drops of indicator solution in (conical) flask… or use a pH meter
3) Add the alkali of known concentration to the burette
4) Put a white tile under flask (easier to see colour change)
5) Add the alkali slowly, especially near the ‘end point’ where colour starts to change (or the pH approaches 7) and swirl to mix the reactants.
6) Stop adding the alkali at the colour change
7) Measure the volume of alkali added (from the burette scale)
Reversible Reactions and Equilibrium
… A reversible reaction has two reactions going on at the same time – the forward reaction to make the products, and the backwards reaction where the products decompose back into the reactants.
… After some time, the rate of making products (the forwards reaction) will become equal to the rate of making reactants (the backwards reaction). At this point, we say that the reaction has reached ‘dynamic equilibrium’.
… The ‘equilibrium position’ of a reversible reaction is the relative amounts of reactants vs. products once the reaction has reached equilibrium.
… In a closed system (where substances cannot e…?… or e…?…) equilibrium is achieved when the rate of the forward reaction is e…?… to the rate of the reverse reaction.
Changing the Temperature
… If the forwards reaction is endothermic, then the backwards reaction will be …?…. Increasing the temperature will favour the …?… reaction
ammonium chloride <—-> ammonia + hydrogen chloride
The forward decomposition of ammonium chloride is endothermic… So if you HEATED ammonium chloride, which direction would be favoured? Would the equilibrium move to the left or to the right?
Changing the Pressure
… If the forwards reaction REDUCES the number of gas molecules (check the balanced equation), then increasing the pressure will favour the …?… reaction.
… The Haber process is a classic example of changing temperature and pressure to favour the forwards reaction – moving the dynamic equilibrium position ‘to the right’ which produces more ammonia.
… Describe and explain the reaction conditions used for producing ammonia in the Haber process.
… Le Chatelier’s principle helps us to predict the effect of changing the reaction conditions on the equilibrium position (The amounts of products and reactants at equilibrium)
“If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.”
… Increasing the concentration of one of the reactants will favour the forwards direction, shifting the equilibrium position to the right and increasing the yield.
The Haber process
… As the production of ammonia is a reversible reaction we can favour the forward exothermic direction by:
- lowering the …?… (but not too much so that we maintain the overall …?… of reaction), and
- increasing the pressure to as …?… as possible given c…?… and safety factors.
… The Haber process requires an …?… catalyst to speed up the rate of reaction. This does NOT affect the y…?… but does mean that the equilibrium position will be achieved …?…. So if you remove some ammonia, then more will be produced quickly.
… Note that if ammonia could be removed immediately from the products formed, then the yield would also increase. This is because the forward reaction rate would increase when products are removed.
This doesn’t happen in practice because it is difficult to remove the ammonia immediately after it has been produced (it is separated by condensing the product mixture some time afterwards).
NPK Fertilisers
… Ammonia is used to make fertlisers. The three numbers on fertiliser represents the value of the three macro-nutrients used by plants. These macro-nutrients are nitrogen (N), phosphorus (P) and potassium (K) or NPK for short. The higher the number, the more concentrated the nutrient is in the fertilizer.
… Potassium chloride, potassium sulfate and phosphate rock are obtained by m..?…, but phosphate rock cannot be used directly as a fertiliser because it is insoluble and difficult for plant roots to absorb.
… Phosphate rock is treated with nitric acid or sulfuric acid to produce soluble salts that can be used as fertilisers.
… What are the names of the salts produced when phosphate rock is treated with nitric acid, sulfuric acid and phosphoric acid?
… What are the main differences between the industrial production of fertlisers compared with laboratory preparations of the same compounds?
The Contact Process
… Used to make sulfuric acid
… The First stage is when Sulfur dioxide is made by burning sulfur in air (or roasting sulfide ores):
S + O2 —-> SO2
… The second stage is a reversible reaction to make sulfur trioxide:
2SO2 + O2 <—-> 2SO3
The forward reaction is exothermic, so a lower temperature would increase the yield. However, a lower temperature would also reduce the overall rate of reaction. So 450 degrees Celsius is used (same as in Haber process) as a compromise.
There are more moles of reactants that products, so in increasing the pressure will also increase the yield.
In practice, a pressure of only 2 atmospheres is used, 450C temperature with a catalyst of vanadium (V) oxide. This gives a yield of 99% which is pretty good :).
… The third stage is to dissolve the sulfur trioxide in sulfuric acid to form liquid ‘oleum’:
SO3 + H2SO4 —-> H2S2O7
… The final stage is to dilute the oleum with a little water to form contracted sulfuric acid:
H2S2O7 + H2O —-> 2H2SO4
… Sulfuric acid is used to make fertilisers, detergents and paints.
Energy Change Calculations
… When fuels and food react with oxygen, energy is released to the surroundings in an e…?… reaction.
… The apparatus used to compare the energy released by different fuels or different foods is called a c…?… The fuel or food is burned and heats a known mass of w..?… What two measurements would you take before and after burning the fuel?
… Energy transferred (to the water) = water mass (g) × 4.2 (J/g°C) × temp rise (°C)
This equation is also used in physics:
Energy transferred = mass × specific heat capacity × temp rise
You won’t need to learn the specific heat capacity of water (4.2J/g°C) as this will be given to you in the question.
… 1 kilojoule (1 kJ) = …?… joules
… The energy released can be calculated in kJ/g by dividing by the mass of fuel used up.
… The energy released can be calculated in kJ/mol by dividing by the number of moles of fuel used up (find this using moles = mass ÷ Mr)
… The specific heat capacity equation can also be used for reacting solutions. Note that the volume of water is the total volume of the solutions together. We also assume that the specific heat capacity is the same as for water (4.2J/g°C)
… Energy level diagrams (energy reaction profiles) show the relative difference in the energy of the reactants compared to the products. Endothermic changes go UP and exothermic changes go DOWN. Remember to label the activation energy and the overall energy change of the reaction.
… The minimum energy needed for a reaction to happen is called the ‘a…?… energy’. How does this idea explain why catalysts increase the rate of reaction…?
Calculations using bond energies
… C-H means a single covalent bond (one pair of shared electrons) between a carbon atom and a hydrogen atom.
… O=O means a double covalent bond (two pairs of shared electrons) between two oxygen atoms
… The displayed formula is useful for showing the individual bonds between atoms. For example, the displayed formula for water is H-O-H
… When bonds are broken, energy must be put IN (+) = endothermic
Remember “BREAK IN!”
… When bonds are formed, energy is given OUT (-) = exothermic
Remember “OUT perFORM!”
… Reactions happen when individual atoms rearrange themselves to form different combinations. For this to happen, the atoms must first break their existing bonds and then form new bonds.
… In an EXOthermic reaction the energy released when you bonds are FORMED is …?… than the energy absorbed when bonds are BROKEN.
… In an endothermic reaction the energy released when you bonds are formed is …?… than the energy absorbed when bonds are broken.
… To calculate the overall energy change (sometimes called “enthalpy change of reaction”) in a chemical reaction, use the balanced chemical equation to:
- Add up all of the bond energies required to BREAK the existing bonds (in the reactants). This will be a POSITIVE value.
- Then add up all of the energy released when the new bonds are FORMED (in the products). This will be a NEGATIVE value.
- Finally, add these two numbers together (a negative value + a positive value) to give the energy change for the reaction.
You will be given the relevant bond energies for the reaction.
… Do use brackets so that you can see clearly how many bonds there are in the equation. For example:
H-H + F-F —— > 2 ( H-F )
Or if a product is 2 moles of carbon dioxide, then you could write: 2 ( O=C=O ) … It’s then easier to see that there are 4 x C=O bonds.
Rules for the Solubility of Salts in Water
- Most nitrate (NO3)- salts are soluble.
- Most salts containing the alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4)+ are soluble.
- Most chloride, bromide, and iodide salts are soluble. Notable exceptions are salts containing the ions Ag+ and Pb2+ and (Hg2)2+
- Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, HgSO4, and CaSO4.
- Most hydroxide salts are only SLIGHTLY soluble. The important soluble hydroxides are NaOH and KOH. The compounds Ba(OH)2, Sr(OH)2, and Ca(OH)2 are marginally soluble.
- Most sulfide (S)2-, carbonate (CO3)2-, chromate (CrO4)2-, and phosphate (PO4)3- salts are only slightly soluble