past Paper 2021: 1,2 And 3 Flashcards
Magnesium chloride dissolves in water. Give an equation giving state symbols to represent the process that occurs when the Enthalpy of solution of magnesium chloride is measured
MgCl2 (s) —> Mg2+ (as) + 2Cl-(aq)
SUGGEST WHY THE ENTHALPY OF HYDRATION of Ca2+ is less exothermic than Mg2+
Ca2+ ion bigger , there is a lower charge to size ratio, weaker attraction to Od- in water
Define the mass number of an atom
Number of protons and neutrons in the nucleus of an atom
Give an equation including state symbols for the reaction of sodium with water, suggest why it is dangerous to react a similar piece of sodium with a lot more water in a boiling tube
2Na(s) + 2H2O(l) —> 2NaOH(aq) + H2(g)
Temperature will go up more causing reactants to shoot out or explode
Give an equation foe the reaction of phosphorous oxide with water and suggest a pH for this
P4O10 + 6H2O —> 4H3PO4
1
Explain in terms of crystal structure and bonding, why silicon oxide has a higher melting point than phosphorous oxide
SiO2 is macromolecular with strong covalent bonds between atoms or covalent bonds need a lot of energy to be overcome
P4O10 is molecular or simple covalent with weak induced dipole dipoles between molecules- require little energy to overcome
Am element in period 3 forms an oxide that is insoluble in water- it reacts with sulfuric acid and aqueous potassium hydroxide, give the formula of this oxide and an equation for its reaction with sulfuric acid
Al2O3
Al2O3 + 3H2SO4 —> Al2(SO4)3 + 3H2O
Give the formula of a hydroxide ion of an element in period 3 using in medicine
Mg(OH)2
identity the element in period 3, from sodium to chlorine, that has the largest atomic radius
Na
2SO2 + O2 = 2SO3
State and explain the effect of a decrease in overall pressure of the equilibrium yield of SO3
Decrease, equilibrium shifts to the left to oppose decrease in pressure
Explain why the value of Kw increases as temperature increases
Forward reaction is endothermic, equilibrium shifts to the right to oppose increase in temperature so concentration of H+ increases
Suggest why the ph probe is washed with distilled water
Different solutions must not contaminate each other
Explain why the volume of sodium hydroxide added between each pH measurement is smaller as the end point of titration is approached
To avoid missing the endpoint
How to determine if a an indicator is suitable
Changes pH within the vertical region
Explain why the standard entropy for CO2 is greater than that of carbon
CO2 is a gas so there is more disorder
Name the type of compound shown by formula RCOOK ans state its use
Carboxylic salt- soap
Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH, give a safety precaution used when heating the mixture
It dissolves both oil and KOH
Use a water bath as ethanol is flammable
State the meaning of fraction as used in the term petrol fraction
Group of hydrocarbons with similar boiling point
Give a reason why carbon dioxide absorbs infrared radiation
Vibrate at the same frequency as IR
Bioethanol is used as an alternative to fossil fuels
Evaluate the statement: “the fact that bioethanol is a carbon-neutral fuel outweighs the environmental disadvantages of producing bioethanol”
Photosynthesis: 6CO2 + 6H2O —> C6H2O6 + 6O2
Fermentation: C6H12O6 —> 2C2H5OH + 2CO2
Combustion: 2C2H5OH + 6O2 —> 6H2O 4CO2
Environmental impacts: deforestation, loss of biodiversity, 6CO2 in and 6CO2 out isn’t carbon neutral as fuel is used in production
The student considered using a glass beaker on a tripod and gauze instead of the clamped copper calorimeter
Suggest two disadvantages of using a glass beaker beaker on a tripodd gauze
Tripod and gauze so reduced heat transfer
Doesn’t conduct heat as well as copper
Suggest two reasons why the value of Enthalpy of combustion for this experiment is less exothermic than the data value
Heat lost, incomplete combustion may have occured
Suggest one addition to apparatus to improve accuracy
Use a lid to prevent heat loss
Explain why benzene is more thermodynamically stable
Electrons delocalised
Suggest the importance of fewer steps and higher percentage atom economy in experiments
Fewer steps-better yield
Less waste
State why the ozone layer is beneficial for living organism
Prevents harmful UV
State how chlorofluorocarbons form chlorine in the upper atmosphere
C-Cl bonds broken homolytically
Suggest why the 1cm portions of the reaction mixture are added to an excess of NaHCO3 solution
The sodium Hydrogencarbonate solution neutralises the acid so stops the reaction
Suggest why the order of this reaction in respect to propanone can be ignored
Concentration is almost constant
The concentration is much larger than the concentration of iodine
Explain how the graph shows 0 order
Has a constant gradient so the rate of reaction does not change as the concentration of iodine changes
Describe how the crystalline solid is separated and purified
Filter, dissolve in minimum volume of hot solvent cool and filter under reduced pressure, wash with cold solvent and dry
Suggest a reason why KCN is used rather than HCN
KCN dissociates to provide the CN- nucleophile
1.dilute nitric acid is added to the solution
2.aqueous silver nitrate is added to the solution
3. A pale yellow ppt forms
Excess dilute aqueous ammonia is added to the mixture
Some of the precipitate dissolves and a darker yellow ppt remains
Give a reason for the use and explain the observations using equation
HNO3 to remove hydroxide ions that may give other pts with AgNO3
AgNO3 produces pts with ions
Ag+ + Cl- —> AgCl
NH3 dissolves AgCl
AgCl + 2NH3 —> Ag(NH3)2+ + Cl-
