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Sian

Cards (42)

Why cant ionic compounds not be electrolysed when solid
Ions are in fixed positions and therefore cannot move freely in a solid
What is a mixture and how can it be separated
A mixture = two or more elements or compounds not chemically combined. It can be separated by physical process
How does distillation work ?
Solution is heated and boiled to evaporate solvent.
Vapour given off is collected in a condenser and the glass tube with water acts as a cooling jacket
Hot vapour is cooled and collected and condensed back to a separate liquid
How does distillation work ?
Solution is heated and boiled to evaporate solvent.
Vapour given off is collected in a condenser and the glass tube with water acts as a cooling jacket
Hot vapour is cooled and collected and condensed back to a separate liquid
How does fractional distillation work ?
Miscible liquid mixture has different boiling points and is heated using a Bunsen burner
Liquid with the lowest boiling point will vapourise and travel up the fractional column
The fractional column has a concentration gradient with higher temp being at the bottom and colder at the top
If the temp at the top of the column is higher than the liquid boiling point the vapour will stay in gaseous form and flow through the condenser and condensed into a liquid and collected in a conical flask
Describe the properties of ionic compounds
Have high melting and boiling points because they are giant structures with strong electrostatic force of attraction between oppositely charged ions so they need a lot of energy to break the strong ionic bonds
Can conduct electricity when the compound melts in an aqueous solution as ions are free to move and carry electrical charge
What is the history of the atom ?
Early 1800s - Daltons strong evidence substances made from tiny , hard spheres
End of 1800s - JJ.Thomson - the electron proposed the plum pudding model ( negative electrons ( plum ) embedded in a ball of positive charge ( plum pudding )
10 years later - Geiger and Marsden fired alpha particles ( dense positive charged particles at thin gold foil - some repelled = positive charge in centre
Rutherford - nuclear model with nucleus ( proton ) and electrons orbiting
1914 - Bohr electrons orbit in shells and 1932 - James Chadwick with neutron
What are ions and isotopes ?
Ion = charged atom or group of atoms, gain electron = negative charge , looses electron = positively charged
Isotopes are different forms of an element with same number of protons and electrons but different number of neutrons - they have same chemical properties but different physical properties
Describe the development of the periodic table
Early 19th century - Newlands - proposed law of octaves , it was arranged in order of atomic weight and claimed every eighth element had a similar property . However this was rejected as new elements being discovered didn't fit his table
1869 - Mendeleev placed known elements in order of atomic weight and changed the order so elements with same properties were in the same group. He used the table to predict properties of undiscovered elements and left spaces - his table was accepted
Explain group 1 - alkali metals
Group 1 reactivity increases going down the group - because the outer electron is less strongly attracted to the nucleus as energy levels increase as the atoms get bigger making It easier to loose the electron
Boiling and melting point decreased - as the larger atoms with more energy levels create a strong electron- electron repulsion making it easier to melt and boil
React with oxygen ( ionic ) - and form metal oxide
React with water - to produce metal hydroxide ( alkali ) and hydrogen
Describe the structure of metals and why it conducts electricity
Layers of atoms that form a regular lattice and atoms slide over eachother making it malleable
Atoms are held by strong electrostatic forces of attraction between positive nuclei and sea of delocalised electrons.
Electrons are free to move and carry a charge through the structure
Explain group 7 - halogens
Exist as small molecules and come in pairs with single covalent bond between them.
Reactivity decreases down the group - because more energy shells reduces the attraction of positive nucleus and negative electron making it harder to gain electrons as the atom increases in size
Boiling/ melting point increase - as the bigger the atom the stronger intermolecular forces - more energy is required to break the forces
At room temp - fluorine = yellow , chlorine = green , bromine = red brown , iodine = grey
Describe states of matter
Solid turns to liquid at melting point. Temp increases causes particles in the fixed position to vibrate faster. At melting point enough energy is transferred to the particles for the forces between particles break. So particles move around
Liquid to gas at boiling point temp increases gives particles more kinetic energy. More energy allows more particles to to escape from the surface of liquid (evaporating ) at boiling point bubbles of gas from and rise to the surface
Describe covalent bonding
When two non metals share electrons to get a full outer shell
Covalent bonds only act between 2 atoms it bonds to eachother so its small molecules
Some have double or triple covalent bonds ( 3 or 2 electrons are shared each )
What are the structure of simple molecules ?
Have low melting and boiling points as theres weak intermolecular ( attraction of molecules not atoms) between molecules so less energy is needed to overcome them
Intermolecular forces increase with size so larger the molecule, higher the melting and boiling point
What is the equation that links mass and moles and Mr
Mass= Moles * Mr
How do you find the empirical formula of products ?
Find the mass of both the reactants
Find the Mr ( use the periodic table )
Find the moles ( mass/Mr)
Find the ratio (divide each moles by the smallest moles eg: carbon - 0.6 moles and oxygen = 0.2 - therefore 0.6/0.2 = 3 to 1 )
How do you find reacting masses ? ( Have 50 grams of ... How much do you need for this )
Write down the mass you know
Find the Mr ( top number ) of both the reactants ( CaO = ...)
Find the moles ( mass/Mr)
The find the ratio of moles ( 2Cao = 2 OH= 1) - by big number ( if the ratio is 1:1 moles of both will be the same
Mass = moles *Mr
How do you calculate limiting reagents
Find the mass and Mr and divide to find the Moles
Smallest moles - the limiting reagents
What is concentration given in ?
(G/dm^3)
1dm^3 = 1000cm^3
What is the formula linking moles, concentration and volume ?
Number of moles = concentration ( mol/dm^3) *volume (dm^3)
How do you work out unknown concentration
Write down the volume
Write the known concentration
Work out moles ( concentration * volume )
Write the ratio ( big number in front of reactants )
Concentration - moles/ volume
How do you calculate percentage yield ?
(Mass of product produced / maximum mass of possible product) * 100
What is atom economy?
Measure of the amount of reactants that end up as useful products
Minimises waste and saves money
Increases sustainability by not wasting resources
How do you calculate atom economy
( Mr of desired products / Mr of all the reactants )*100
What is the removal and addition of oxygen called
Oxidised = oxygen added
Reduced = oxygen removed
What do metals and water produce ?
Group 1 metals ( most reactive ) - alkaline hydroxide solution and hydrogen gas
Other metals react slowly or have no reaction
How do metals and dilute acid react?
Group 1 - explode
Elements above hydrogen - form a salt and hydrogen gas
Produced from chlorides, sulfates and nitrates
Magnesium gives off more gas than zinc and iron so its more reactive
What is a displacement reaction ?
When a more reactive metal displaces a less reactive metal from one of its salts in an aqueous solution
What is the gain and loss of electrons
Oxidation = loss
Reduction = gain
(OILRIG)
What are the two ways of extracting metals
Metals less reactive than carbon ( zinc, iron, tin , lead, ..) extracted from their oxide when heated with carbon - carbon dioxide and metal
More reactive than carbon - aluminium above - electrolysis of molten metal in aqueous solution
What are the different ways to make salts ?
Acid + base = salt + water (metal oxide and hydroxide = bases)
Acid + alkali = salt + water ( neutralisation ) ( H+(aq) and OH-(aq) = H20 (l)
Acid + carbonate = salt + water + carbon dioxide
What is neutralising and pH scale ?
Neutral = pH 7
Acids produced H+ ions when added to water
Bases + water = neutralisation ( metal oxide + metal hydroxide)
Alkalis - soluble hydroxides that dissolve in water and form OH- ions
What are strong and weak acids ?
Strong acids ionise completely in aqueous solutions ( release higher concentration of H+ ions )
Weak acids that don't ionise completely in aqueous solutions = weak acids
Strong acids = LOWER pH as they loose H+ ions in water more acidic
Weaker acids = HIGHER pH as they don't loose H+ ions
What is electrolysis ?
Process using electricity to break down ionic compounds
Electrolyte - substance broken down
Where do ions go during electrolysis ?
Electrodes - inert substances and don't react
Positive electrode - anode (negatively charged ions - loose electrons )
Negative electrode - cathode ( positively charged ions - gain electrons )
Ions loose their charge and become atoms or molecules
Electrolysis of aqueous solutions
Water has OH- and H+ ions
At the cathode ( positive ions gain electrons) - positively charged metal ions and H+ are attracted ( 2H+( aq) + 2e- = H2(g) )
Hydrogen gas is formed as its less reactive
At anode - oxygen is formed (4OH- (aq) = O2(g) + 2H20(l) + 4e-
How and why is aluminium extracted ?
Aluminium is more reactive than carbon so it cant be displaced
Aluminium oxide needs lots of energy melts at 2000 - mixed with cryolite to lower at 850
At cathode - aluminium ions gain electrons and form atoms and molten aluminium metal is collected at the bottom of the cell
At anode oxide ions loose electrons to form oxygen atoms
What are exothermic reactions
Reaction transfers energy to surrounding and releases heat ( temp increase)
Energy released when new bonds for products is higher than energy needed to break reactant bonds
What are endothermic reactions ?
Energy being taken in from the surrounding during the reaction causes temperature decrease
Energy needed to break bonds is more than energy released when new bonds are formed