Chemistry C4 GCSE
Acids and Bases
Acids are substances pH less than 7
Bases are oxides and hydroxides of metals. If souble = alkalis (pH more than 7)
pH of solution can be determined by universal indicator solution
Acids and bases (alkalis) are chemical opposites. They cancel each other out if added together in the correct amounts. This is neutralisation because the pH remains a neautral pH 7.
As the acid is added to an alkali the pH of the solution decreases. acid neutralises the alkali to reach a pH of 7.
The opposite occurs if alkali is added to an acid. The pH increases to reach pH 7.
Carbonates neautralises acids to produce a salt, wayer and carbon dioxide.
The first name of the salt made from neutralisation comes from the base or the carbonate used.
- E.g. Sodium hydroxide = sodium salt
- Copper oxide = copper salt
- calcium carbonate = calcium salt
- ammonia = ammonium salt
The second name of the salt comes from the acid used
- hydrochloric acid = chloride salt
- sulfuric acid = sulfate salt
- nitric acid = nitrate salt
E.g adding potassium hydroxide to nitric acid to neutralise makes potassium nitrate
Some uses are - cleaning metals before painting or coating, NEUTRALISING FERTILISERS and car and motobike batteries.
Ionic equation of neutralisation
Neutralisation summerised by the ions in the solutions
alkalis in solution contain hydroxide ions
Acids in solution contain hydrogen ions
Acid + Base -----> Salt + Water
Ionic equation -
H+ (aq) + OH- (aq) ------> H2O (i)
Relative Atomic Mass Ar
Atoms are to small for their atomic mass to be useful. A useful measure is relative atomic mass, Ar. (The mass of a particular atom compared to the mass of an atom of hydrogen- lightest atom).
Each element has two numbers. Top left number is the larger number (and the Ar)
Relative formula mass Mr
Relative formula mass Mr = the Ar's of all its elements added together.
To calculate the Mr, need the formula of the compound and the Ar of all elements involved.
E.g. relative forumula mass of H2SO4
H - 2 x 1 = 2 (multiply the number of atoms in the formula by the Ar of the element)
S 1 x 32 =32
O 4 x 16 =64
Total = 98 (the Mr of H2SO4 is 98)
Reactants and Products
To calculate how much product a reaction will produce or how much reactant you need remember-
- Total mass of the starting materials (reactants) always equals the total mass of substances produced (products)
- the more reactant you start with the more product made
- substances react in simple ratios
Ratio used to calculate how much each reactant is needed i order to produce a certain amount of product.
E.g. Nitric acid + Ammonia --------> Ammonium nitrate
they react in a ratio 63:17 so.... 63g + 17g = 80g ammonia nitrate
calculate how much of each reactant you would need to make 80kg of product
63kg (nitric acid) + 17kg (ammonia) -------> 80kg
calculate how much of each reactant you woulod need to make 16g of product
12.6g (nitric acid) + 3.4g (ammonia) ----> 16g (ammonia nitrate)
Total mass of reactants equals the total mass of products. no atoms gained or lost during a chemical reaction. Results are the same number you started with, rearranged into different substances.
To work out how much substance is used up or produced in a reaction, know...
- Relative formula mass, Mr, of the reactants and products (or the relative atomic mass, Ar, of all the elements)
- The balanced symbol equation for the reaction.
By substituting the Mr's, into the balanced symbol equation you can work out the ratio of mass of reactant to mass of product and apply to question.
E.g. When calcium carbonate (CaCO3) is heated, it produces calcium oxide (CCaO) and carbon dioxide (CO2). How much calcium oxide can be produced from 50kg of calcium carbonate?
(write down the equation)
CaCO3 (s) -----heat----> CaO(s) + CO2 (g)
(work out the Mr of each substance)
40 + 12 + (3 x 16) ----> (40 + 16) + [12 + (2 x 16)]
(check that the total mass of reactants equals the total mass of products)
100 -----> 56 + 44
(since the question only mentions calcium oxide and calcium carbonate you can now ignore the carbon dioxide. This gives the ratio of mass of reactant to the mass of the product)
(apply this ratio the question)
If 100g of CaCO3 produces 56kg of Cao, then 1kg of CaCO3 produces 56/100kg of CaO and 56kg of CaCO3 produces 56/100 x 50 = 28kg of Cao.
When a reaction takes place the starting materials (reactants) produce new substances (products). The greater the amount of reactants used, the greater amount of product produced.
Percentage yield is a way of comparing the actual product made with the amount expected.
Percentage yield = actual yield/predicted yield x 100
A 100% yield means that no product was lost i.e. actual yield is the same as the predicted yield
- 0% yield means no product was made i.e. actual yield is 0.
Fertilizers are a chemical farmers use to provide their crops with the essential elements needed for growth. They make crops grow faster and bigger and they increase crop yield. Three main elements found in fertilizers are
- Nitrogen N
- Phosphorus P
- Potassium K
Fertilizers must be soluble in water so they can be taken in through the roots of the plants in solution. Urea can also be used as a fertilizer.
Fertilizers that can be made by neutralizing a acid with an alkali are....
- Ammonium sulfate (sulfuric acid and ammonia)
- Ammonium nitrate (nitric acid and ammonia)
- Ammonium phosphate (phosphoric acid and ammonia)
- Potassium nitrate (nitric acid and potassium hydroxide)
You need to be able to calculate the relative formula of a fertilizer if given chemical formula
E.g. Calculate the Mr of the fertilizer that is represented by the chemical formula NH4NO3
N 2 x 14 = 28
O 4 x 1 = 4
O 3 x 16 = 48 Mr = 80
Step 1) Measure out the alkali (e.g. potassium nitrate) into a basin using a measuring cylinder
Step two) Add acid (e.g. nitric acid) from a burette. Use a glass rod to put a drop of solution onto indicator paper to test the pH. Continue to add the acid a bit at a time until the solution is neutral. (pH 7)
Step three) Evaporate the solution slowly until crystals form on the end of a cold glass rod placed in the solution. Leave to cool and crystaliise.
Step four) Filter to seperate the crystals from the solution
Step five) Remove the crystals, wash them and leave to dry
This method is another example of producing a salt (a fertilizer) from neutralisation.
Fertilizers increase crop yield by replacing essential elements in the soil that have been used up by previous crop, or by increasing the amount of essential elements available. More importantly, they provide nitrogen in the form of soluble nitrates which are used by the plant to make protien for growth.
Factors surrounding cost
Effect of a Catalyst
Using a catalyst increases the rate of the reaction although it does not affect the percentage yield. However, although using a catalyst reduces cost, it increases intial costs by buying it.
- A low tempreture increases yield but the reaction is too slow
- A high pressure increases yield but the reaction is too expensive
- A catalyst increases the rate of reaction but does not change the percentage yield
- Tempreture = 450*
- Pressure = 200 atmospheres
- Catalyst = iron
A washing powder is a mixture, its components are....
- Detergent to do the cleaning
- Bleach to remove coloured stains
- Water softener to soften hard water (hard water contains soluble calcium and magenesium compounds that react with soap)
- Optical brightener to make whites appear brighter
- Enzymes to break up food and protein stains in low tempreture washes
When clothes are washed the water is the solvent (liquid that does the dissolving) and the washing powder is the solute (that solid that gets dissolved) because it is soluble (it dissolves) in water. The resulting mixture of solvent and solute is a solution.
Low tempreture washes are used to wash delicate fabrics i.e. the ones that would shrink in the wash or the dye would run and they do not denature enzymes in biological powders. Low tempreture washes save engergy.
Some stains will not dissolve in water; they are insolube. Dry cleaning solvents are used when a stain is insoluble in water. The clothes are still washed in a liquid but it does not contain water.
- ballpoint pen - methylated spirits (ethonal) then biological washing powder in water
- blood - biological washing powder in water
- show polish- white spirit then biological washing powder in water
- coffee - biological washing powder in water
- correcting fluid - white spirt
Washing up liquid
- detergent to do the washing
- water to dissolve and dilute the detergent so it pours out of the bottle
- water softener to soften hard water
- rinse agent to help water drain off the crockery so it dries quickly
- colour and fragerence so the product is attractive to buy
the detergent in washing-up liquid is often a salt made from neutralising a complicated organic acid with an alkali
acid + alkali ------> salt (detergent) + water
A detergent molecule is non polar i.e. the molecule has a balenced over all charge
However, when the molecule is dissolved in water, the sodium ion comes away from the 'head' of the molecule.
The sodium ion is postively charged, which leaves the 'head' of the detergent molecule negatively charged,
The charged head is atteacted to water molecules because of its polarity (electrical charge) so it is known as hydrophillic (water loving)
The hydrocarbon tail is non-polar and so it is not attracted to water molecules, therefore known as hydrophobic (water hating)
How detergents work:
Step one: The hydrophobic end of the detergent moleculen is repelled by the water causing it to stick to the oil droplet
Step two: As more and more detergent molecules are absorbed into the oil droplet, the oil is eventually lifted off the plate.
Step three: When is totally surrounded, the oil droplet can be washed away leaving the plate clean.
The molecules that make up a stain are held together by weak intermolecular forces. (attractive forces between the molecules). The stain substance will dissolve in a dry- cleaning solvent if the intermolecular forces that hold it together are overcome. The new intermolecular forces between the stain molecules and the solvent molecules are stronger than ones that were present before.
Batch and Continuous
In a batch process, the reactants are put into a reactor, the reaction happens and then the product is removed. Medicines and pharmaceutical drugs are often made in batches. Batch processess....
- Make a product on demand
- Make a product on a small scale
- Can be used to make a variety of products
- Are more labour intensive because the reactor needs to be filled, emptied and cleaned.
In a continuous process e.g. the Haber process, reactants are contunually being fed into a large reactor and the product is continually being produced at the same time (like a conveyor belt) continuous processes-
- operate all the time
- make a product on a large scale
- are dedicated to just one product
- can run automatically
The materials used to make a medicine can be manufactured (synthetic) or can be extracted from natural sources. Steps to extract are:
Step one: Crushing- the plant material is crushed using a motar and pestle
Step two: Dissolving- a suitable solvent is added to dissolve the matierial
Step three: Chromatography - a concentrated solution of the material is spotted onto chromatography paper and allowed to seperate
It takes a long time, over ten years to develop a medicine. From discovering the medicine to being able to use it on patients.
Research needs to be carried out into new pharmaceutical materials. This cannot be automated as important descions need to be made. Highly qualified staff are needed. This means labour costs are high.
Further research is carried out to develop the drug to increase effectivness before it is tested to ensure it work properly. It needs to be safe with no serious side effects. The medicine must then be approved for use and must satifsy all legal requirments set out from the government before it can be sold.
Medicines are expensive because the materials used could be rare or may require complex methords to extract the raw materials. Medicines are made in small quantities and it is not possible to totally autmoate the manufactoring process therefore, engery and staff costs are high. Marketing is also very expensive.
A pharmacutical company may invest hundreds of millions of pounds into making a new medicine and they only have a limited time to recoup their investment before their exclusive rights to the medicine runs out. It takes many years to carry out the research and development on the medicine but even longer to carry out safety tests around the strict legal rules.
There are three forms of carbon
- buckminster (buckyball)
Diamond has a ridgid structure-
- Does not conduct electricity
- Is insoluable in water
- Is used in jewllery because it is colourless, transparent and lustrous
- Can be used in cutting tools because it is very hard and has a very high melting point
Diamond is a giant molecule made of carbon atoms that are bonded by strong covalent bonds.
The large number of covalent bonds results in diamond having a very high melting point.
It doesnt have any free electrons so it doesnt conduct electricity
Unlike graphite it doesnt have any seperate layers and because there are strong covalent bonds between carbon atomsm it is very hard
Graphite has a layer structure...
- Is insoluble in water
- Is black, which is why it is used in pencils
- Is lustrous and opaque (light cannot travel through it)
- Conducts electricity and has a very high melting point so it used to make electrodes for electrolysis
- Is slippery so used in lubricants
Graphite is a giant molecule which exsists in layers of carbon atoms that are bonded to three other carbon atoms by strong covalent bonds. The layers are held together by weak intermolecular forces allowing each layer to slide easily so graphite can be used as a lube. The presence of free (delocalised) electrons in graphite results in it being an electrical conductor. It has a high melting point because it has many strong convalent bonds to break.
Diamond, graphite and the fullerences are allotropes of carbon. Allotropes are different forms of the same element where the atoms are arranged in different molecular structure
Nanochemisty deals with materials on an atomic scale, i.e. individual atoms. The properties of particles on this very small scale are very different to properties of bulk material
Fullerenes and nanotubes can be used to cage in other molecules because they are the perfect shape to trap other substances inside them. The caged substances could be...
- drugs - a major new HIV treatment uses buckyballs to deliver a material which disrupts the way the HIV virus works
- catalysts - by attaching a catalyst material to a nanotube a massive surface area can be achieved making the catalyst very efficent.
Fullerenes and nanotube molecules are manufcatures in a number of ways :
- Buckyballs first discovered in the soot of burnt hydrocarbons. hydrocarbon fuel is burned under low pressure and the hydrogen burns off leaving behind the carbon
- lasers can be used to vaporise carbon which then deposits onto a molecule and builds up the structure piece by piece
- matter can be removed from a big structure to produce nanoscale features
consists for 60 carbon atoms arranged in a sphere. It is a black solid and makes a res solution when dissolved in petrol
Discovery of buckminster led to chemists investigating similar structures.
Nanotubes conduct electricity and are very strong,
They reinforce graphite tennis rackets because of their strength
Make connectors and semiconductors in the most modern molecular computers because of their electrical properties
Develop new, more efficent industrial catalysts
Water has to be treated to purify it and make it safeto drink. Untreated water can contain..
- insoluble particles
- dissolved salt and minerals
Pollutants that may be found in water supplies include nitrates from the run-off of fertilizers, lead compounds from old pipes in the plumbing, pesticides from spraying crops near to water. Thrsr materials are diffcult to remove from water
The dissolved ions if some salts are easy yo identify as they will undergo precipitation reactions. A precipitation reaction occurs when a solid is made from mixing two solutions together.
Silver nitrate solution is used to detect halide ions. Halides are the ions made by halogens
With silver nitrate...
- Chlorides form white precipitate
- Bromides form cream precipiate
- iodies form a pale yellow precipaite