SC5: separate chemistry 1 Flashcards
where are the transition metals?
middle, groups 3-12
typical transition metals properties
-high melting and boiling points
-good conductors of electricity and heat
-high densities
-form coloured compounds
-they (and their compounds) can act as catalysts
iron (Il) hydroxide
pale green compound
iron (III) hydroxide
orange-brown compound
iron (III) oxide
reddish brown compound
catalyst
substances that speed up the rate of reaction without being used up in the reaction.
corrosion
when a metal continues to oxidise in air & weakens
rusting
when iron or steel reacts with oxygen and water (oxidation)
how the rusting of iron or steel is prevented
-oxygen can be excluded by storing the metal in an atmosphere of unreactive nitrogen or argon
-water can be excluded by storing the metal with a desiccant (a substance that absorbs water vapour)
physical barriers to oxygen and water
-painting
-oiling and greasing
-coating with plastic
why is a bike chain is protected from rusting by oiling it, rather than by painting it
the oil also lubricates the chain, helping it to move smoothly, paint flakes off when the bike is ridden, exposing the steel chain to air and water again
electroplating
uses electrolysis to put a thin layer of metal on the object (improves appearance)
sacrificial protection
a metal is coated with another metal which is more reactive than it so the more reactive metal oxidises
galvanising
the protection of iron or steel by coating it with a layer of zinc (works even when zinc layer is scratched
alloy
a mixture of two or more metals
why are alloys stronger than pure metals?
-solid metals have a regular lattice structure, when a force is applied to a metal, layers of atoms can move past each other
-the more difficult it is for the layers to move, the more force is needed and the stronger the metal
-alloy atoms have different sizes
-this distorts the lattice structure, so layers of atoms cannot slide over each other so easily
mild steel
iron & carbon
uses of mild steel & why
-can be used for car body parts
-is malleable, ductile & can be easily pressed into shape
-is protected by galvanising & painting
tool steel
tungsten and iron
uses of tool steel and why
-used for making drill bits
-hard, resistant to high temperatures
stainless steel
iron and chromium
uses of stainless steel and why
-washing machines and dishwashers
-hard, resistant to high temperatures
magnalium
aluminium and magnesium
uses of magnalium and why
-magnalium is stronger than aluminium alone but still has a low density
-used to make aircraft parts
uses of aluminium and why
window frames
-does not react with water
-its surface is protected by a natural layer of aluminium oxide that allows the metal to resist corrosion
aluminium foil is used in the home for wrapping and storing food
-does not react to substances in food
-malleable, so it is easily folded into shape around the food
electricity cables
-good electrical conductor
-low density prevents the wires from sagging too much or breaking under their own weight
brass
copper and zinc
uses of brass
-resist corrosion, good electrical conductor
-musical instruments, door knobs, locks and taps
-pins in electrical plugs
jewellery gold
-gold and copper
-nice appearance but stronger
-hard, brittle, ductile, resistant to corrosion
bronze
copper and tin
uses of bronze and why
-statues, bells, coins
-hard, brittle, ductile, resistant to corrosion
structure of a metal
-lattice of positive ions
-delocalised electrons which flow snd carry change
-attraction between electrons and positive ions is electrostatic
what is theoretical yield?
the maximum possible mass of a product that can be made in a chemical reaction
what is actual yield?
the mass of product that is actually obtained in a reaction
why is actual yield usually less than theoretical yield?
-incomplete reactions, some of the reactants do not react to form the product
-practical losses during the experiment, such as during pouring or filtering
-side reactions (unwanted reactions that compete with the desired reaction)
percentage yield
actual yield/theoretical yield × 100
atom economy
a measure of the amount of starting materials that end up as Useful products
atom economy equation
mr of desired product/mr of all products ×100
titration steps
- use a pipette and pipette filler to add 25 cm of dilute sodium hydroxide solution to a clean conical flask
- add a few drops of phenolphthalein indicator and put the conical flask on a white tile
- fill the burette with dilute hydrochloric acid and note the starting volume
- slowly add the acid from the burette to the conical flask, swirling to mix
- stop adding the acid when the end-point is reached (when the colour first permanently changes from pink to colourless). note the final volume reading
- repeat steps 1 to 5 until you get concordant titres
concentration
a measure of the mass or amount of solute dissolved in a given volume of solvent or solution
mol/dm³ to g/dm³
multiply by the mr
equation for concentration in mol/dm³
amount of solute in mol/volume in dm³
cm³ to dm³
divide by 1000
what unit must volume be in for concentration calculations
dm³
how to calculate a concentration with titration
- write down the mass, volume and concentration for each of the substances mentioned in the question
- convert any volume from cm³ to dm³
- with the substance you have a volume and concentration for, multiply the volume and concentration to find the amount of solute
- use the mole ratio to find out if both substances in the question have the same mass, if not multiply to get the correct amount of solute
- with the volume provided in the question for the required substance, divide the found mass of solute by the volume to find the concentration
avogadro’s law
equal volumes of different gases contain an equal number of molecules when the temperature and pressure stay the same
molar gas volume
the volume occupied by one mole of any gas, at room temperature and pressure (24,000cm³ or 24dm³)
how to calculate the volume of a gas
amount in mol × molar volume (24dm³)
go look at higher calculations involving molar volume because it’s hard to explain
!!!
calculating volume of gas from mass
step 1: calculate the mass in mol of the substance you have an amount in g for (mass in g/mr)
step 2: find the amount of the substance that you are asked for in the question (mole ratio)
step 3: calculate the volume of the substance you are asked for in the question (amount in mol × molar vol)
calculating a mass of a gas from a volume
step 1: calculate the mol of the substance which’s volume you’re given (vol/molar vol)
step 2: calculate the mol of the mass of the substance you are asked to find (mole ratio)
step 3: calculate the mass of the substance you’re asked to find (mr × amount in mol)
what happens to plant minerals as they grow?
-as plants grow, they absorb mineral ions from the water in the soil through their root hair cells
-over time, the concentration of these ions decreases, so farmers and gardeners add fertilisers to the soil
fertilisers
-provide mineral ions needed for healthy growth in plants
-must be soluble in water so they can be absorbed by the root hair cells
NPK fertilisers
fertilisers with nitrogen, phosphorus & potassium
ammonium nitrate
a salt used as a fertiliser, a source of soluble nitrogen
how is ammonium nitrate made?
by reacting ammonia solution with nitric acid
how is ammonia made?
through the haber process:
-temperature of 450°C
-a pressure of 200 atmospheres
-an iron catalyst
how is nitric acid made?
ammonia + oxygen → nitric acid + water
making ammonium sulfate in the lab
- put some dilute sulfuric acid into a beaker
- add a few drops of methyl orange indicator
- add dilute ammonia solution drop by drop, stirring in between
- continue step 3 until the colour permanently changes from red to yellow
- add a few more drops of dilute ammonia solution
- pour the reaction mixture into an evaporating basin, and heat carefully over a boiling water bath
- stop heating before all the water has evaporated, leave aside for crystals to form
- pour away excess water and leave the crystals to dry in a warm oven (or pat dry with filter paper)
batch process
a small amount of product is made slowly at any one time, and the apparatus cleaned ready to make another batch
what happens in a reversible reaction at equilibrium
-the forward and backward reaction are still happening
-the forward and backward reactions have the same rate of reaction
-the concentrations of all the reacting substances remain constant (they do not change)
how quickly an equilibrium is reached depends upon:
-the pressure of a reacting gas
-the concentration of a reacting solution
-the temperature of the reaction mixture
-the presence of a catalyst
what happens to equilibrium when pressure increases?
-equilibrium position moves towards the fewest molecules of gas
-time to reach equilibrium decreases
what happens to equilibrium when concentration increases?
-equilibrium position moves away from that reactant
-time to reach equilibrium decreases
what happens to equilibrium when temperature increases?
-equilibrium position moves in the direction of the endothermic reaction
-time taken to reach equilibrium decreases
what happens to equilibrium when a catalyst is added
-no change in equilibrium position
-time to reach equilibrium decreases
what are the conditions used for industrial reactions related to?
the availability and cost of:
-raw materials
-energy supplies
factors involved in choosing between manufacturing hydrogen by reacting natural gas with steam or the electrolysis of water
raw materials:
gas & steam = natural gas is non-renewable
electrolysis of water = water is readily available
energy supplies:
gas & steam = strong heating using natural gas, coal or fuels from crude oil
electrolysis of water = electricity can be generated using renewable resources
what is a reaction pathway
the sequence of reactions needed to produce a desired product
what does the reaction pathway depend on?
-percentage yield
-atom economy
-rate of reaction
-equilibrium position
-usefulness of by-products
which two ways can ethanol be made?
-fermentation of plant sugars
-hydration of ethene (obtained from crude oil) using steam:
fermentation of sugars facts
yield = 15%
atom economy = 51.1%
reaction rate = low
-lots of labour needed
-avg temp & low pressure needed (low energy)
-renewable
hydration of ethene facts
yield = 95%
atom economy = 100%
reaction rate = high
-non renewable (crude oil)
-high temp and pressure (high energy)
-few workers needec
what type of reaction is hydration if ethene?
-reversible
-the equilibrium position lies to the left, so only about 5% of the ethene supplied is converted to ethanol
-the overall yield of 95% is achieved by recirculating unreacted ethene through the reactor
by products of fermentation of sugars
-carbon dioxide is a by-product of the fermentation of plant sugars
-it may be sold to fizzy drinks manufacturers to provide the bubbles in lemonade and cola
-this makes it a desirable product as well, so the atom economy can be increased to 100%.
chemical cells/batteries
-use chemical reactions to transfer energy by electricity
-include the familiar batteries used in torches and mobile phones
-produce a voltage until one of the reactants is used up
-when this happens, the battery goes flat
fuel cells
-produce a voltage continuously, as long as they are supplied with a fuel & oxygen from the air
hydrogen-fuel cell
-hydrogen and oxygen are used to produce a voltage
hydrogen + oxygen → water
strengths of hydrogen-oxygen fuel cells used in spacecraft
-they have no moving parts to maintain
-they are small for the amount of electricity they produce
-the water they produce is useful as drinking water
how will a hydrogen-fuel cell continue working in space
-hydrogen-oxygen fuel cells must be supplied with hydrogen fuel and oxygen
-spacecrafts in orbit have solar cells
-these convert light into electricity, so the hydrogen and oxygen can be replaced by the electrolysis of water
-solar cells only work when they are in the light, so the fuel cells allow electricity to be produced even when the spacecraft is in the dark
strengths of fuel cells & petrol/diesel for cars
fuel cells:
quiet in use; only waste product is water; fewer moving parts
petrol/diesel:
petrol and diesel are easier to store; thousands of filling stations
weaknesses of fuel cells & petrol/diesel for cars
fuel cell:
hydrogen is more difficult to store; few filling stations
petrol/diesel:
noisy in use; carbon dioxide is a waste product; many moving parts
suggest a reason that explains why the quietness of fuel cell vehicles may be a weakness
pedestrians may not hear the vehicle coming, and so they may be more likely to be run over when crossing the road
