22a) x-axis: zinc conc, y-axis: absorbance, title need to be included
graph shape something like this with a line of best fit
https://imgur.com/a/04Qig
b) abs1/ppm1 = abs2/ppm2
0.58abs gives 3.45ppm (from drawing dotted lines on the graph roughly they will probably allow from 3.4 to 3.5ppm)
Therefore, it is not safe, as its above 2.80ppm
23a) As oxidation occurs at the anode (zinc), gradually there will be an excess of positive ions (Zn^2+) here. Similarly, at the cathode (Ag) due to reduction there will be an excess of negative ions (No3^-)
Without a salt-bridge, this would cause an imbalance of positive and negative charges in the system and the redox reaction ceases.
The salt bridge’s purpose is to complete the circuit and allow the migration of ions (Cations from the salt bridge flow towards the cathode, while anions flow towards the anode) to maintain electrical neutrality in both half cells. It must be soluble, one example is KNO3.
b)https://imgur.com/gallery/k2jfY
24a)https://imgur.com/gallery/hNYjY
b) Basic Salts: this is produced when a STRONG base and a WEAK acid react.
Dissociation of Salt Produced: NaCH3COO(aq) → Na+(aq) + CH3COO-(aq)
The Na+ is an extremely weak conjugate acid as it came from a strong base NaOH. This means it is too weak to react with water.
The CH3COO- is a weak conjugate base as it came from a weak acid CH3COOH. However, it is not as weak as Na+ and thus is able to react with water. Since it is a base, water will act as an acid.
Reaction (Hydrolysed) With Water: CH3COO-(aq) + H2O(l) ⇌ CH3COOH(aq) + OH-(aq)
Thus as OH- is produced it is a basic salt solution
25) Cellulose formed from the reaction of beta glucose monomers, which form a 1,4 -glycosidic linkage, n C6H12O6 (aq) → (C6H10O5)n (s) + (n-1) H2O(l), is a condensation polymer, that is a potential source of petrochemicals such as ethene because of its 6 carbon glucose monomer unit structure.
Conversion process:
1. Cellulose to glucose: (hydrolysis) using cellulase enzyme - (C6H10O5)n(aq) + nH2O(l) → nC6H12O6(aq)
2. Glucose to 15% v/v ethanol: In the fermentation of glucose, yeast is initially added to mashed grain and water. Any oxygen present will be absorbed by the growing and reproducing yeast cells and the conditions change to anaerobic. Upon this occurring yeast will respire and break down the glucose to obtain energy and in the process forms ethanol as a product of cellular respiration, as well as carbon dioxide gas (C6H12O6(aq) → 2 C2H5OH(aq) + 2 CO2(g) - write the catalyst on the arrow). When ethanol concentration reaches 15% v/v, the yeast die and fermentation stops.
3.15% v/v to 100% v/v ethanol: Fractional distillation and molecular sieving are required
4. Ethanol to ethene: dehydration using concentrated sulfuric acid catalyst. It works by breaking the C-OH bond and C-H bonds, allowing for the formation of a double bond and water. It is also a powerful dehydrating agent. (c2h5oh(l) ---> C2h4(g)+H2O(l)-write the catalyst on the arrow)
5. Ethene to polyethylene:
https://imgur.com/a/88e5n
26a) Reasons why it's a concern could be:
- Acid Rain: is formed when acidic oxides such as SO2 react with water molecules in the atmosphere to produce acidic solutions.
SO2 (g) + H2O (l) ⇋ H2SO3 (aq) or SO2 can be oxidised first to produce SO3 (So2 + 1/2O2--> So3),which forms sulphuric acid (So3 + H2O ----> H2SO4). Rainwater, snow and other forms of precipitation containing these acidic solutions fall to earth as acid rain.
Effects:
Erosion of limestone (CaCO3) structures CaCO3(s) + H2SO4(aq) → CO2(g) + CaSO4(aq) + H2O(l)
Acidification of waterways, leading to harm to marine animals → industries and environment affected.
It leaches essential metal nutrients from the soil → trace elements are important in biological processes.
Dissolves Al3+ ions from normally insoluble, non-toxic Al(OH)3 → toxic to plants, stunts root growth.
- Health Problems: Sulfur dioxide is a severe respiratory irritant and can cause breathing difficulties at concentrations of 1ppm. It can also trigger asthma attacks and aggravates conditions such as emphysema.
b) At the metal smelter: the extraction of metals from sulfide ores occurs as shown in the equation 3O2(g) + 2ZnS(s) → 2SO2 (g) + 2ZnO(s), this releases SO2 gas as shown in the black colour of the map portraying th high concentration of So2 above the metal smelter, as well as the dotted patches surrounding it showing the movement of the gas throughout the atmosphere.
Coal fire power stations: coal used in combustion is not completely pure and contains sulfur impurities which undergo combustion when the coal is burnt shown in S (s) + O2 (g) → SO2 (g) and this is displayed in the map in the black colour directly above the power station and dotted patches around it.
In the white areas: there is still some SO2 due to the movement of air molecules from the metal smelter and coal powered station, as well as due to natural causes such as volcanoes, geothermal springs and oxidation of H2S by bacteria (3O2(g)+ 2H2S(g) → 2SO2(g) + 2H2O(l)), however much less than the two other areas.
27) Firstly, acetic acid is an alkanoic acid, butan-1-ol is an alkanol and butyl acetate is an ester.
I recommend drawing their structures to show the different intermolecular forces that can occur
Boiling point is a direct measure of the intermolecular forces present. So this suggests that although these molecules have different molar masses, that they have quiet similar amounts of intermolecular forces.
Firstly, the one with the lowest molar mass is acetic acid, it is a polar molecule as it contains a COOH group and a OH group and thus are able to form twice as many hydrogen bonds (the strongest intermolecular forces) between molecules, compared to the second highest molar mass (button-1-ol) since this molecule only contains one polar group being the OH.
The difference in the degree of hydrogen bonding in these two molecules explains why acetic acid has the lowest molar mass than the alkanol, and can also be used to explain why butyl acetate has the highest molar mass, as ester molecules which are polar are only able to form dipole-dipole interactions (both other molecules have this too) and are not able to form hydrogen bonds with other ester molecules.
To account for these differences in intermolecular forces that arise from the hydrogen bonding differences, the higher molar mass compounds (butanol and butyl acetate (this has higher molar mass) have higher dispersion forces than acetic acid (the electrostatic force of attraction between fluctuating dipoles in atoms and molecules) as this is directly proportional to molecular mass, allowing the molecules to all have relatively similar boiling points.
28a) Possible answers could be
Advantages:
- Theoretically carbon neutral:
Photosynthesis: 6CO2(g) + 6H2O(l) → 6O2(g) + C6H12O6(aq) (consumes 6 moles of CO2)
Fermentation of Glucose: C6H12O6(aq) → 2CO2(g) + 2C2H5OH(aq) (releases 2 moles of CO2)
Combustion: 2C2H5OH(l)+ 6O2(g) → 4CO2(g) + 6H2O(l) (releases 4 moles of CO2)
Thus, from these equations there is no net release of CO2. However, in reality it is not as fuels are burnt in fractional distillation prior to step 3 (required as fermentation only produces 15% v/v), during growth and harvesting and also during transportation of fuels, but it is still much more environmentally friendly than octane.
- It burns cleaner than octane: due to its shorter carbon chain length and the fact it already contains an oxygen atom, so less oxygen is required per mole of fuel. Therefore, it more readily undergoes complete combustion which reduces toxic pollutants such as C (soot - carcinogenic) and CO (binds irreversibly with hemoglobin in red blood cells, restricting oxygen leading to hypoxia) produced from incomplete combustion.
- Also increases fuel efficiency as heat of reaction given by ∆H = bonds broken - bonds formed, reduces in incomplete combustion as CO is less stable than CO2, so less bonds are formed and thus it is less exothermic.
Ethanol Complete Combustion: C2H5OH(l)+ 3O2(g) → 2CO2(g) + 3H2O(l)
Octane Complete Combustion: C8H18(l)+ 252O2(g) → 8CO2(g) + 9H2O(l)
Octane Incomplete Combustion: C8H18(l)+ 6O2(g) → CO2(g) + 6C(s) + CO(g) + 9H2O(l)
- Renewable if from plant matter: explain the starch to ethanol dot point
Disadvantages:
- Engine modifications: When more than 15% v/v of ethanol is used as an additive to regular petrol known as gasohol is used in car engines, expensive engine modifications are required as ethanol is a polar molecule and thus attracts water causing corrosion.
- Large areas of arable land are required to grow crops: which has an ethical issue in the use of crops for fuel and also large environmental problems such as soil erosion, deforestation and salinity issues.
- Lower molar heat of combustion: produces less energy per mole than octane, so this means that more fuel is needed for same energy (i.e. to travel the same distance).
- Disposing large amounts of waste fermentation liquors: after ethanol removal can be environmentally damaging.
b)https://imgur.com/gallery/jdoyG
29)
Turbidity: is a measure of the clarity of water due to suspended matter.
Site X has low amount since it is coming from the limestone caves (however there is still some because of the farm).
Site y has a very high amount due to particles from the saw mill entering the water system. However, these particles are large and can easily be removed through the sedimentation and flocculation process.
Problems with high turbidity:
Decreases penetration of sunlight, limiting photosynthesis (dissolved oxygen decreases)
Small particles in upper layers can absorb infrared light raising water temperature which can lead to thermal pollution and further reduces the dissolved oxygen content.
Particles can clog fish gills.
pH: the PH of X is higher than 7 due to the limestone, while pH of Y is 6 due to natural co2 equilibrium. However, this isn't that much of an issue, as the town has pH control.
Calcium: At site X there is a high calcium concentration as limestone contains Ca^2+ in the formula. A contributor to water hardness (a measurement of the concentration of divalent metal ions such as Ca2+ and Mg2+ in water expressed as equivalent amount of dissolved CaCO3). Site Y has relatively low levels. The high count at site X is a large problem as this may lead to blockages in houses, affects water taste and also prevents soaps from lathering (potentially increasing bacteria amounts in the water).
Phosphate:At site X there is a high phosphate concentration due to the manure from the cows containing fertilisers which have a high amount of phosphate. this is a problem as this can lead to eutrophication, the process where water becomes enriched with nutrients such as PO43- and NO3-, primarily from fertilisers and detergents, to an extent that it promotes the formation of algal blooms.
PO43- is generally considered to be the growth limiting agent, recommended levels of P:N are 1:10 with 0.01-0.ppm and 0.1-1ppm, respectively (Site Y is in this range)
Effects:
Eutrophication increases the BOD and reduces the dissolved oxygen, reducing survivability of aquatic organisms.
Increases turbidity
Forms a layer that prevents any photosynthesis from plants, which reduces dissolved oxygen content.
Cyanobacteria produce poisons that can kill livestock and cause diseases in humans.
Assessment: Site Y is a better source for the town's water as the problems with the initial water supply can all be solved through the water purification steps
30)A scaffold that could be used to answer the q:
Balanced chemical equation (with the exothermic nature indicated + catalyst on arrow ) N2 (g) + 3H2 (g) ⇋ 2NH3 (g) ΔH = - 92 kJ/mol
Discussion of the equation (i.e. in terms of the exothermic nature and position of equilibrium at normal room temperatures and pressures)
Source of the reactants:
N2 is sourced from fractional distillation of liquefied air
H2 from the electrolysis of H2O, but it is more commonly sourced from the reaction of steam and methane (CH4(g) + 2H2O(l) ⇒ CO2(g) + 4H2(g))
Why we need to manipulate conditions:
The Haber process is an exothermic equilibrium reaction and is therefore subject it is subject to Le Chatelier’s Principle (M
UST DEFINE IT - When a system at equilibrium is disturbed, the system attains a new equilibrium by undergoing a chemical reaction which minimises the effect of the disturbance.) Due to this the reaction conditions must be manipulated in order to find a delicate balance between the rate of reaction as well as the yield of the reaction (crucial for an economically viable industrial process).
The strong covalent bonding between N2 and H2 atoms results in a high activation energy and thus at standard conditions causes the equilibrium to lie well to the left (i.e yield is very low).
Temperature:
Increase in temperature - increases reaction rate (describe why)
Increasing temperature speeds up the rate of reaction by providing kinetic energy through the conversion of thermal (heat) energy to kinetic energy increases to reactants and products, allowing more molecules to possess the correct collisional orientation and energy to overcome the EA (activation energy barrier) (therefore there is more successful collisions).
Increase in temperature - reduces yield (describe why in terms of LCP)
However, as the forward reaction is exothermic, increasing the temperature is a disturbance by Le Chatelier’s Principle. This causes the equilibrium to shift towards the endothermic reaction, the left, resulting in decomposition and decreases the yield of NH3.
Also, high temperatures are expensive to maintain and can damage the inorganic catalyst.
Compromise conditions
Therefore a compromise of 400-500℃ is used in conjunction with a heterogenous catalyst (Fe3O4).
Discussion of the use of the catalyst and what is done to it to enhance properties
Using a catalyst increases the rate of reaction by reducing the EA for the reaction by providing an alternate pathway (adsorption) for the reaction to occur, with a lower activation energy.
Thus allowing for a lower temperature to be used, which reduces the effects due to the use of higher temperatures which reduce the yield of ammonia.
The catalyst is finely grounded to produce a large surface area and thus this also further increases the rate of reaction. Additionally, adding potassium increases electron density and reactivity, while adding calcium allows magnetite to maintain its larger surface area.
Pressure:
Increase in pressure - increases the yield (describe why in terms of LCP)
According to LCP, increasing the pressure is a disturbance that will shift the equilibrium to the side with least gas moles, the right (LHS:RHS = 4:2), thus increasing the yield.
Increase in pressure - increases reaction rate (describe why)
It also has the added benefit of increasing rate of reaction as the concentration of reactants increases.
Disadvantages of this increase in pressure + compromise conditions
However, high pressures require expensive equipment and are dangerous to maintain and so a pressure of 250 atm is used.
3-4 Other Conditions important in monitoring:
The main monitoring required has been discussed in the above dot-points.
Other conditions also used include:
- A 1:3 mole ratio of N2 to H2 is used in line with the stoichiometric mole ratios.
- NH3 is removed via liquefaction, forcing the equilibrium right increasing yield.
- Unused reactants are recycled to save costs.
- Gases: no oxygen (system would become explosive), argon and methane (decreases efficiency) and CO which can poison catalyst.
Conclusion:
thus monitoring is essential to ensure efficiency, maximising yield, increasing rate of reaction and safety.
