What are the two obvious ways to categorise elements?
- Their physical and chemical properties
- Their relative atomic mass
Why could scientists in the 1800s only rely on elements physical characteristics and atomic mass to classify them?
They had no idea of atomic structure (electrons, neutrons, protons) and relative atomic mass was the only characteristic they could measure
What was Newlands’ law of octaves?
Newland tried to arrange elements in a useful order in 1864, he noticed that every 8th element had similar properties to he listed the known elements in rows of seven.
Why were Newlands’ octaves criticised? (4)
- The pattern broke down on the third row due to transition metals
- His groups contained elements that didnt have similar properties (eg. carbon and titanium)
- He mixed up metals and non-metals (oxygen and iron)
- He didn’t leave any gaps for elements that hadn’t been discovered yet
How did Dmitri Mendeleev order elements in 1869?
He put them in order ot atomic mass and left gaps in order to keep elements with similar properties in the same vertical gaps. These gaps predicted the properties of undiscovered elements.
How is the modern periodic table arranged?
In vertical groups, with the group number being equal to the number of electrons in the outer shell of the element.
How does the distance between a nucleus and an electron affect an atoms reactivity?
The further away the electron is (the more ‘shells’/energy levels are present), the more distance and therefore the less attraction there is between the electron and the nucleus. This means the electrons in the outer shell are more easily lost and the element is more reactive.
As you study down Group 1 of the periodic table, how are reactivity and boiling/melting points impacted?
The alkali metals become more reactive (the electron is more easily lost because it’s further from the nucleus) and the elements will have lower melting and boiling points.
Name the 6 alkali (group 1) metals and their chemical symbols
What do all the group 1 metals have in common?
They have one electron in their outer shell and are very reactive
What do alkali (group 1) metals form when reacted with non-metals?
Explain why ionic compounds are formed from group 1 metals and a non metal and what is produced from this reaction
The electron in the highest energy level of the group 1 metal atom is weakly bonded to the nucleus, this means that covalent bonding can’t occur because the atom needs to form a 1+ ion.
A white compound that dissolves in water to form a colourless solution is the product.
Give atleast one symbol equation example of a group 1 metal reacting with chlorine
- lithium + chlorine → lithium chloride
- 2Li(s) + Cl2(g) → 2LiCl(s)
- sodium + chlorine → sodium chloride
- 2Na(s) + Cl2(g) → 2NaCl(s)
- potassium + chlorine → potassium chloride
- 2K(s) + Cl2(g) → 2KCl(s)
What happens when lithium, sodium or potassium are reacted with water?
- They will float and move around on the surface, fizzing
- They produce hydrogen (remember the “squeaky pop” splint test)
- They form hydroxides that dissolve in water to make an alkaline solution
What is the balanced equation for sodium reacting with water?
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2 (g)
What is the commonly used name for the Group 7 elements?
List the 5 elements in Group 7 and their symbols
- Fluorine F
- Chlorine Cl
- Bromine Br
- Iodine I
- Astatine At
As you study down Group 7 how do the characteristics of the elements change?
- They become less reactive
- Their melting and boiling points increase
Describe each of the halogens physical characteristics (colour etc) and molecular structure
- Fluorine is a reactive, poisonous yellow gas
- Chlorine is a fairly reactive, poisonous dense green gas
- Bromine is a dense, poisonous, red-brown volatile liquid
- Iodine is a dark grey crystalline solid or a purple vapour.
They are all non-metals that exist as molecules which are pairs of atoms.
What do halogens form when they are reacted with metals?
Ionic bonds, 1 - ions called halides
Fill in the gaps in this sentence:
A more reactive halogen will ……. a less reactive halogen from an …………. solution of its salt eg. Chlorine can displace ……… and iodine from an aqueous solution of its salt (a ……….. or ………..)
A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt eg. Chlorine can displace bromine and iodine from an aqueous solution of its salt (a bromide or iodide)
What is the balanced symbol equation for the reaction of chloring and potassium iodide?
Cl2 (g) + 2KI (aq) → I2 (aq) + 2KCl (aq)
Give the 5 main properties of transition metals
- Good conductors of heat and electricity
- They’re very dense, strong and shiny
- Transition metals are much less reactive than Group 1 metals
- They’re denser, stronger and harder than Group 1 metals
- Transition metals and their compounds all make good compounds,
Transition metals often have more than one ion (eg. Fe2+ and Fe3+). What do these usually form?
Different coloured compounds (eg. Fe2+ ions give green, whereas Fe3+ make a red/brown compound, such as rust)
Colours in gemstones such as blue sapphires and green emeralds are due to transition metals.
Name 3 transition metal catalysts and how they are used
- Iron is the catalyst used in the Haber process for making ammonia
- Manganese (IV) oxide is a good catalyst for the decomposition of hydrogen peroxide
- Nickel is useful for turning oils into fats for making margarine
When you lather hard water and soft water with soap, what is the difference in what happens?
With soft water, you get a nice lather but hard water creates a nasty scum - unless you’re using a soapless detergent.
Why does hard water create scum when mixed with soap, rather than a lather as soft water does?
There are dissolved calcium and magnesium ions in the water that react with the soap to make scum which is insoluble.
What happens when hard water is heated?
It will form a scale (mostly calcium carbonate)
How does scale impact on heating systems?
Badly scaled up pipes and boilers reduce the efficency of heating systems, and may need to be replaced - all of which costs money.
How does scale reduce the efficency of a kettle?
It acts as a slight thermal insulator, meaning that if scale builds up on the heating element of a kettle, the water will take longer to boil that a non-scaled up kettle. This reduces efficency.
How might rainfall become hard water?
It falls on some types of rocks (e.g. limestone, chalk and gypsum) and can dissolve in compounds like magnesium sulfate (soluble) and calcium sulfate (slightly soluble).
Give two positive health effects of hard water
- Ca2+ ions are good for healthy teeth and bones.
- Studies have found that people who live in areas of hard water are less at risk of developing heart disease than those living in soft water areas. This could be due to the minerals in the water.
What is the difference between the causes of ‘temporary hardness’ and ‘permanent hardness’?
Temporary hardness is caused by the hydrogencarbonate ion, HCO3- in CA(HCO3)2
Permanent hardness is caused by dissolved calcium sulfate (amongst other things)
How might temporary hardness be removed? Give the symbol and word equation
Why doesn’t this method work for removing permanent hardness?
By boiling - when heated the calcium hyrogencarbonate decomposes to form calcium carbonate, which is insoluble (this is the ‘limescale’ in your kettle)
Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2
Calcium hydrogencarbonate → Calcium carbonate + Water + Carbon dioxide
(This doesn’t work for permanent hardness because heating a sulfate has no significant effect)
How can both forms of hard water be softened? Explain how this works and give the symbol equation
By adding washing soda (sodium carbonate, Na2CO3). The added carbonate ions react with the Ca2+ and Mg2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The Ca2+ and Mg2+ ions are no longer dissolved in the water so they can’t make it hard.
Ca2+(aq) + CO32-(aq) → CaCO3(s)
How can both temporary and permanent hardness be removed by exchanging ions? Give the symbol equation
Both types of hardness may be removed by running water through ‘ion exchange columns’, these have lots of sodium ions (or hydrogen ions) and will ‘exchange’ them for calcium or magnesium ions in the water.
Na2Resin(s) + Ca2+(aq) → CaResin(s) + 2Na+(aq)
Describe the process by which titration is used to compare the hardness of water samples
- Fill a burette with (50cm3 of) soap solution
- Add (50cm3 of) the first water sample into a flask
- Use the burette to add (1cm3 of) soap solution to the flask
- Put a bung in the flask and shake
- Repeat steps 3 and 4 until a good lasting lather is formed (where the bubbles cover the surface lasts for atleast 30 seconds)
- Record how much soap was needed to make this lather
- Repeat all steps with other water samples
What must water be free of in order for it to be safe for human consumption? Name two diseases that can be caused by polluted water
Poisonous salts (eg. phosphates and nitrates) and harmful microbes
Chloera and dysentry can be caused by microbes in water
What are reservoirs?
A reservoir is a large natural or artificial lake used as a water supply, water will flow into it from rivers and ground water to then be treated so it is free of pollution.
Describe the process of water treatment
- It will pass through a mesh screen to remove bits of debris (like twigs)
- Chemicals will be assed to make solids and mircrobes stick together and fall to the bottom
- The water is filtered through gravel beds to remove all solids
- Water is chlorinated to kill off any harmful microbes left
How might people treat their water at home?
- Filters containing carbon or silver can be bought to remove substances from tap water (carbon removes the chlorine taste whilst silver is supposed to kill bugs)
- Water softeners which contain ion exchange resisn might be bought by people who live in hard water areas
What is distillation and why is it not used to purify water in homes?
Distillation is the process of boiling water to make steam and then condensing the steam to create totally pure water with nothing dissolved in it.
It is too expensive to boil water for home use but this method is often used in chemistry labs.
Why might fluoride be added to drinking water?
To prevent tooth decay
Why do some people disagree with chlorine being added to our water supplies?
Studies have shown that chlorine can react with other natural substances in water to prodice toxin by-products which are said to increase the risk of cancer by as much as 93%. Some people also have objections to the odour/taste.
Why is adding fluoride to drinking water disputed? (3)
- Consumption at higher levels over time has been proven to cause painful bone disease.
- Can cause dental fluorosis, or browning and pitting of the teeth, in young children.
- Some studies suggest that fluoride does not significantly reduce tooth decay
A + B ⇔ C + D
What is this an example of?
A reversible reaction
What happens when a reversible reaction takes place in a closed system?
A state of equilibrium will be reached
What does the term equilibrium mean?
The amount of reactants and products will reach a certain balance and stay there. The reactions are still taking place in both directions but the overal effect is nil becaus ethey cancel each other out and will be taking place at exactly the same rate in both directions.
What two factors does the ‘position of equilibrium’ depend on?
Temperature and pressure
All reactions are exothermic in one direction and endothermic in the other. What happens if you raise/reduce the temperature of a reversible reaction?
If you raisse the temperature, the endothermic reaction will increase to use up the extra heat.
If you reduce the temperature, the exothermic reaction will increase to give out more heat.
Many reactions have a greater volume on one side either of products or reactants (greater volume more there are more gas molecules and less volume means there are fewer gas molecules). How will raising/lowering the pressure of a reversible reactionchange
When pressure is raised it will encourage the reaction which produces less volume
If you lower the pressure it will encourage the reaction which produces more volume
How will adding a catalyst change the equilibrium position?
It does because it will speed up both the forward and backward reactions, meaning it will happen quicker but you will be left with the same amount of product.
Which two substances are needed to make ammonia? Give the balanced symbol equation
What type of reaction is this?
Nitrogen and Hydrogen
N2(g) + 3H2(g) → 2NH3(g)
What industrial conditions are used to make ammonia? (3)
Pressure = 200 atmospheres
Temperature = 450ºC
Catayst = Iron
Where is the nitrogen and hydrogen used to make ammonia sourced?
Nitrogen from the air and hydrogen from natural gas or crude oil
Why is the pressure for making ammonia industrially 200 atmospheres when an even higher pressure could increase yield?
Higher pressure favours the forward reaction (four gas molecules on the left hand side of the equation, two on the right). So a higher pressure means more product. The pressure is set as high as possible to give the best %yield without making the plant too expensive to build.
The forward reaction in making ammonia is exothermic. What will happen when temperature is increased?
The temperature will move the equilibirum towars the N2 and H2 side of the reaction, meaning that the yield of ammonia would be lower.
Why is 450°C used in the industrial production of ammonia if more would be made in a lower temperature?
It is a compromise between maximum yield and speed of reaction because a lower temperature would increase the time it takes for the reaction to take place.
What is the general formula for alcohol?
Name the first three alcohols in the homologous series
(Homologous is a group of chemicals that react in a similar way because they have the same functional group - eg. in alcohols its the -OH group)
List 3 properties of the first three alcohols
- They are flammable and burn in air to produce Carbon Dioxide and water
- They all dissolve completely in water to form neutral solutions
- THey react with sodium to gve hydrogen and alkoxides eg. Ethanol gives sodium ethoxide and H2
What is the most common use for ethanol?
It is the main alcohol in alcoholic drinks (not as toxic as methanol, which causes blindness if drunk but still damages the liver and brain)
Why are alcohols used as solvents?
They can dissolve most compounds that water dissolves as well as substances water cannot dissolve - eg. hydrocarbons, oils and fats.
What particular purpose does ethanol have as a solvent?
It is used in perfume and aftershave because it can mix with the oils (which give it the smell) and water, which makes up the bulk.
What is methylated spirit and what is it used for?
It is ethanol with chameicals like methanol added to it, used to clean paint brushes and as a fuel. Poisonous to drink.
Give 3 examples of ethanol being used as a fuel
- Ethanol is used as a fuel in spirit burners (burns fairly cleanly and isn’t smelly)
- Ethanol can be mised with petrol and used as fuel for cars
- Countries that have little or no oil deposits but plenty of land and sunshine grow loads of sugar cane, which they ferment to form ethanol (an advantage as sugar cane is a renewable resource)
What is the functional group of Carboxylic acids?
Name three carboxylic acids and their symbol formula if possible
Methanoic acid HCOOH
Ethanoic acid CH3COOH
Propanoic acid C2H5COOH
How do carboxylic acids react with carbonate? Give an example in word equation form
With carbonates they react like any other acid to make carbon dioxide and a salt which will end in -anonate.
ethanoic acid + sodium carbonate → carbon dioxide + sodium ethanoate
What happens when carboxylic acids dissolve in water?
They create acidic solutions. When they dissolve they ionise and release H+ ions which are responsible for making the solution acidic but because they don’t ionise completely they are weak acidic solutions, which have a higher pH than aqueous solutions of strong acids with the same concentrration
How can ethanoic acid be made and what is it used in?
Ethanoic acid can be made by oxidising ethanol (microbes can cause it to ferment or oxidising agents can be used). It can then be dissolved in water to make vinegar, which is used for flavouring and preserving food.
Where is citric acid found and how is it used?
Citric acid is present in oranges and lemons, it is manufactured in large quantities to make fizzy drinks and is also used to get rid of scale.
Give three examples of how carboxylic acids are used in industry
- Those with longer chains of carbon atoms are used in soaps/detergent
- They are used in the preparation of esters
- Ethanoic acid is a very good solvent for many organic molecules but isn’t usually used because it makes the solution acidic
What are esters made from and what is theirfunctional group?
alcohol + carboxylic acid → ester and water (an acidic catalyst is often used eg. sulfuric acid)
Functional group: -COO-
How is the name of an ester formed? Give an example
They end in ‘oate”. the alcohol makes the first part of the name and the acid forms the second part
eg. ethanol + ethanoic acid → ethyl ethanoate + water
List 4 properties of esters
- They have pleasant smells (often sweet and fruity)
- They can be very flammable
- They don’t mix with water well (aren’s as soluble as carboxylic acids or alcohols)
- They mix well with alcoholc and other organic solvents
Give some examples of how esters are used
- Flavourings and aromas (eg. rum, apple, orange, banana)
- Ointments (they give Deep Heat its smell)
- They are used as solvents for paint, ink glue and in nail varnish remover
What four things might you need to consider when using an ester?
- Inhaling the fumes can irritate mucous membranes in the nose and mouth
- Ester fumes are heavier than air and very flammable
- Some esters are toxic (there are worries about health problems assosciated with synthetic food additives like esters)
- However, hey arent as volatile or toxic as some other organic solvents and are now used in paints and varnishes