C3 Flashcards
Who was Newlands?
A chemist who noticed every 8th element had similar properties and created Newlands octaves
Why was Newlands work criticised?
- his groups contained elements that didn’t have similar properties
- he mixed up metals and non-metals
- he didn’t leave gaps for undiscovered elements
What did Mendeleev do?
arranged the elements in order of atomic mass (like Newlands) but left gaps so that elements with similar properties were in the same vertical column. He also predicted properties of undiscovered elements
elements in the same group have the same…
number of electrons on their outer shell
if the electron is far from the nucleus the force of attraction is…
weak, especially if the electron is shielded by other elctrons
the combination of increased shielding and distance means that…
an electron in a higher energy level is more easily lost as there’s less attraction from the nucleus.
This is why group 1 is more reactive as you go down the group
what are the properties of alkali metals (group 1 metals)?
low density and 1 outer electron
As you go down group 1:
- become more reactive
- lower melting and boiling points
What happens when group 1 metals form ionic compounds with non-metals?
produces white compounds that dissolve to form a colourless solution
What happens when group 1 metals react with water?
produce hydrogen gas, they float and fizz alot
What are the first 3 group 1 metals?
lithium, sodium, potassium
what are the properties of the halogens (group 7)?
non-metals with coloured vapours
Describe fluorine
very reactive, poisonous yellow gas
Describe chlorine
fairly reactive, poisonous dense green gas
Describe Bromine
dense, poisonous red-brown volatile liquid
Describe Iodine
dark grey solid or purple vapour
What happens as you go down group 7?
- less reactive
- higher melting point
- higher boiling point
What happens when halogens bond with metals?
they form 1- ions called halides
What are the properties of transition metals?
- good conductor of heat + elctricty
- very dense, strong and shiny (more than group 1 metals)
- less reactive than group 1 metals
- much higher melting points than group 1 metals
What is the reactivity of an element?
how easily its atoms lose or gain electrons
What is soft water?
it easily lathers with soap and contains dissolved sodium ions
What is hard water?
contains dissolved magnesium and calcium ions and produces scum and scale when ions react with soap or when the water is heated
What is scum?
formed when the calcium ions in hard water displace the sodium stearate to form calcium stearate
What is scale?
a thermal insulator and is formed when hard water is heated. it collects in pipes, boilers and kettles.
How is hard water formed?
when rainwater flows over rocks and calcium ions and magnesium ions dissolve into the water
Positives of hard water?
- good for teeth and bones
- helps prevent heart disease
Positives of soft water?
- fewer products are used up
- cheaper bills
Negatives of hard water?
- reduces efficiency of heating elements
- clogs pipes and costs money for plumbing
Negatives of soft water?
- contains alt which is bad for your heart
What is temporarily hard water?
caused by dissolved calcium hydrogen carbonate the hardness can be easily removed with heating. Calcium hydrogen carbonate thermally decomposes to form calcium carbonate, water and carbon dioxide
What is titration (water)?
it can be carried out to compare the hardness of water samples e.g. you can measure the amount of lather produced from water when soap is added
Explain how you can soften water using a ion exchange column
the column contains lots of sodium ions held in a resin which exchange for the calcium ions when water is run through it to make the water soft
Explain how you can soften water using sodium carbonate
the calcium ions in the water are displaced by the sodium leaving sodium ions in the water
What is the first stage of water treatment?
after the water leaves the reservoir it goes through screens to remove large objects
What is the second stage of water treatment? (settlement)
it is piped into the settlement tanks where soil and sand is removed
What is the Third stage of water treatment? (clumping)
aluminium sulphate and lime are added which causes small particles to clump together and sink
What is the fourth stage of water treatment? (sand)
The water i passed through a sand filter to remove any insoluble particles
What is the fifth stage of water treatment? (bacteria)
chlorine is added to kill bacteria
What is the sixth stage of water treatment? (pH)
The pH is checked so that is is neutral. water is then pumped to homes or stored in large tanks
What are the positives of water fluoridation?
- reduction in teeth cavities
- kills bacteria which causes heart disease
What are the negatives of water fluoridation?
- could cause learning disabilties
- causes fluorosis which can link to cancer
Why is water not totally pure?
because distillation is needed which is expensive
What is calorimetry?
the measure of heat transfers from a chemical reaction.
e.g. using a spirit burner to calculate the change in temperature of water
What is an exothermic reaction?
a reaction that gives out energy to the surroundings, usually in the form of heat and shown by a rise in temperature
What is an endothermic reaction?
a reaction that takes in energy from the surroundings, usually in the form of heat and shown by a drop in temperature
In any chemical reaction what happens?
old bonds are broken and new bonds are formed
What type of reaction breaks bonds (energy supplied)?
endothermic
What type of reaction makes bonds (energy released)?
exothermic
What happens when a catalyst is added?
activation energy is lowered
What is activation energy?
the minimum energy needed for reacting particles to break their bonds
What are the positives of using hydrogen as a fuel?
- very efficient
- very clean (no CO2)
What are the negatives of using hydrogen as a fuel?
- need a special & expensive engine
- hard to store safely
- need to use energy to make it
What is a fuel cell?
an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction to generate electricity
What colour does lithium turn the flame when burnt?
crimson
What colour does sodium turn the flame when burnt?
yellow
What colour does potassium turn the flame when burnt?
lilac
What colour does calcium turn the flame when burnt?
red/brown
What colour does Barium turn the flame when burnt?
green
Which metal causes a white precipitate when mixed with sodium hydroxide?
calcium, magnesium
Which metal causes a white precipitate which turns dissolves when mixed with sodium hydroxide?
aluminium
Which metal causes a blue precipitate when mixed with sodium hydroxide?
copper II
Which metal causes a green precipitate when mixed with sodium hydroxide?
Iron II
Which metal causes a brown precipitate when mixed with sodium hydroxide?
Iron III
How do you test for carbonates?
- add dilute acid then bubble collected gas through lime water, if it turns cloudy there is CO2 present
How can you test halides?
add nitric acid and silver nitrate solution
What colour precipitate does Chloride produce when mixed with nitric acid?
White precipiatate
What colour precipitate does Bromide produce when mixed with nitric acid?
Cream Precipitate
What colour precipitate does Iodide produce when mixed with nitric acid?
Yellow Precipitate
How can you test for sulphates?
add barium chloride, if a white precipitate forms the original compound was a sulphate
Why would a solution become more concentrated?
because more solute would dissolve in a give volume meaning they are more crowded
describe a titration experiment for neutralisation
- put alkali in a flask along with some indicator
- record the starting volume of acid and start adding acid until the alkali changes colour
- record the amount of acid needed to neutralise the alkali
What are the products and reactants of the Haber process?
Nitrogen + Hydrogen -> Ammonia
What conditions are needed for the Haber process?
200 atmospheres, 450 degrees celsius and an iron catalyst
Why are the conditions chosen for the Haber process?
high pressure and low temperatures favours the forward reaction (exothermic) however low temps mean a low rate of reaction so a balance is needed
What is a reversible reaction?
where the products of the reaction can themselves react to produce the original reactants.
What is equilibrium?
means that the amounts of reactants and products reach a certain balance and stay there: the reactions still take place but there is no effect as the reactions cancel each other out ( not effected by catalysts)
What happens if you change the temperature in a reversible reaction?
- if you raise the temperature the endothermic reaction will increase
- i you reduce the temperature the exothermic will increase
What happens if you change the pressure in a reversible reaction?
- if raise the pressure the reaction which produces less volume will increase
- if you reduce the pressure the reaction which produces more volume will increase
What is the functional group of alcohols?
- OH
What is the functional group of carboxylic acids?
- COOH
What is the functional group of esters?
- COO
What is the general formula of alcohols?
C²H²n+¹OH
What are the first three alcohols?
methanol, ethanol, propanol
What are the properties of alcohols?
- flammable
- dissolves in water to form neutral solutions
- react with sodium to make hydrogen and alkoxides
What are alcohols used for?
solvents and fuels
Why is carboxylic acid a weak acid?
they don’t dissolve in water properly
How can ethanoic acid be made?
oxidising ethanol
What are carboxylic acids used for?
food (vinegar and citric acid), making soap, solvents and esters
How are esters formed?
reacting alcohols and carboxylic acid
How do you name an ester?
alcohol-‘yl’ and acid-‘oate’
What are the properties of esters?
- nice smell
- flammable
- volatile
- don’t mix with water
What are esters used for?
perfumes, flavourings and solvents
what catalyst is used when making esters?
acid
why do group 7 elements become less reactive
the attraction between the nucleus and electron is weaker so it is less easily gained
why might you not be able to see the flame colour of two flame tests at the same time?
colours are masked by each flame colour
What did Mendeleev and Newlands arrange their periodic tables in order of?
atomic mass
Why is the start of group 7 more reactive than the end?
Because they need to gain an electron and the closer to the nucleus the stronger the attraction meaning its easier to gain 1 electron
Why is the end of group 1 more reactive than the start?
Because the electrons are further from the nucleus and more electron shielding means a weaker attraction and means its easier to lose the electron making them more reactive.
What does the resin in an ion exchange column contain?
sodium or hydrogen ions
Why is something exothermic in terms of bonds broken/ formed
because the energy released when bonds form is greater than energy used when bonds broken
Why can air not enter to Haber process?
because oxygen would oxidise the hydrogen
What happens to all the products after the Haber process?
they are cooled and the ammonia condenses and can be extracted and the hydrogen and nitrogen stay as gases and can be recycled for the next reaction
Why are the specific reaction conditions chosen for the Haber process?
The reaction is reversible
the forward reaction in exothermic so low temperatures mean a high yield of ammonia however it also means a slow rate of reaction so a medium temperature is used..
high pressure increases the yield because the forward reaction produces the least number of molecules however high pressures are also expensive.
How is a carboxylic acid formed?
A reaction between an alcohol and oxygen in a oxidation reaction
What is bad about adding chlorine to water?
its Toxic if there is too much and the user has no choice is chlorine is added or not.
number of moles =
volume x concentration
mass =
concentration x volume
