Hard questions from past papers Flashcards
What does .XH2O represent in the formula Al2(SO4)3(aq).xH2O
Number of water of crystallisation
Suggest formula of the ion responsible for bleaching when chlorine reactions with NaOH (aq)
ClO-
Why is Na3PO4 described as a salt of H3PO4
Hydrogen ions are replaced by the sodium ions
Why is it unnecessary to refer to carbon as either diamond or graphite in a table pf 1st ionisation energies
Diamond and graphite form gaseous atoms of carbon when they are ionised
Particles between which the force of the bond is acting in fluorine
Between molecules
Suggest formulae of the ions present in H4N2O3
NH+ NO3-
Describe and explain the electrical conductivity of Na
Sodium conducts in the solid and molten states. Sodium has delocalised electrons (in both solid and
liquid state)
State conditions for the reaction of aqueous sodium hydroxide and chlorine
Cold and dilute NaOH
How to find formula of solid product formed after SrCl2.6H2O is heated and water is lost
- Find moles of SrCl2.6H2O
- Find moles of water lost
- Divide moles of water lost by moles of SrCl.6H2O to find moles of water lost from 1 mol of SrCl2.6H2O
- Take this number away from the number of moles of water to start with (6) to get your final formula
Write reaction between Barium nitride and water to form an alkaline solution and an alkaline gas
Ba3N2 + 6H2O → 3Ba (OH)2 + 2NH3
Draw dot and cross diagram of BaO2 which contains Barium and peroxide ions
Ba 2+ in one bracket
2 oxygen bonded together with one electron from each Ba on each oxygen. This is in brackets with a 2- round the side.
State one type of a biodegradeable alternative to CFCs
HCFCs
Give an everyday use for infrared spectroscopy
Breathalysers and to monitor air pollution
Describe and explain using equations how the concentration of ozone in the stratosphere is maintained
O3→02 +O
O + O2→ O3
Rate of ozone decomposition equals rate of ozone formation
Cyclopropane undergoes an addition reaction with bromine in the absence of UV. Suggest the structure of the organic product produced
1,3-dibromopropane
Suggest one advantage of adding cyclohexane to petrol
It will burn more efficiently
Suggest a reactant other than a different acid that could be used to imporve the atom economy of making 1-bromobutane
Add NaBr directly instead of KBr and H2SO4
Suggest one other method of CCS apart from reacting CO2 with a metal oxide
- Store deep in the oceans
2. React to make carbonates
How do you get from a alkene to an alcohol
Add KOH (aq)
Suggest 2 properties that make CF2CL2 suitable for use as an aerosol
- Low reactivity/ will not burn
- Volatile/ low boiling point
- Non poisonous
What happens to molecules when infrared radiation is absorbed
The bonds vibrate
What is the general formula of the homologous series that has CH2=CHCH2Br as a member
CnH2n-1Br
Suggest reasons for the difference in the calculated value for deltaHc and the value from data books
- Heat loss
- Incomplete combustion
- Non- standard conditions
- evaporation of alcohol/water
- Specific heat capacity of beaker
Write the state of hexane
liquid
Why is it difficult to determine the standard enthalpy change of formation of hexane directly
- Many different hydrocarbons would be produced
2. activation energy too high/ reaction too slow/ they don’t react
State two reasons why there is still concern about ozone depletion
- CFCs take many years to reach the ozone
- CFCs are still being used
- There are other ozone depleting substances
Outline 2 ways waste polymers are processed usefully
- Separation into types and recycling
- Combustion for energy generation
- Used for cracking or feedstock for plastics or chemicals
Suggest with the aid of an equation, how NO is formed within an aeroplane engine
N2 + O2→ 2NO
Explain the advantages of the manufacture of H2O2 from hydrogen and oxygen, compared to using BaO2 with H2SO4 and forming BaSO4
- Oxygen comes from the air
- No poisonous materials formed
- No waste products formed
Explain why some reactions are exothermic
- Bond breaking absorbs energy and bond making releases energy
- More energy is released than absorbed
Do graphs showing change in temp and levels of CO2 provide reliable evidence that an increase in atmospheric carbon dioxide concentration will result in global warming
- There are times when there is a high concentration of CO2 and the temperature is also high
- It is impossible to measure with certainty the temperature years ago
- There are other gases that may cause a greenhouse affect
- There are very few anomalous results
Suggest why some scientists are more concerned about CO2 as a greenhouse gas than methane
- Greater concentration of CO2
2. C=O absorbs carbon dioxide more readily than CH
Write equations or reaction of chlorine with dilute and concentrated NaOH
- Dilute: Cl2 + 2NaOH → NaClO + NaCl + H2O
2. Concentrated: 3Cl2 + 6NaOH → NaClO3 + 5NaCl +3H2O
Describe one difference you might observe if strontium instead of magnesium reacted with dilute HCl
- Quicker/ more vigorous/ gets hotter
What apparatus should a student use to measure acid solution to 250cm3
Volumetric flask
What apparatus should be used to measure the 25cm3 of acid
Pipette
Suggest what the student could do to reduce the effect of any random error in a titration
- Repeat until two results are concordant
2. Calculate mean titre from the concordant results
Explain the difference in melting point for the elements Na and Mg
- Magnesium has a greater charge
- Magnesium has more electrons
- Magnesium has greater attraction between ions and electrons
Remember metallic bonding
State two factors that affect the contribution of a greenhouse gas to global warming
- Atmospheric concentration
- Ability to absorb infrared radiation
- Residence time- how long it stays in atmosphere
Suggest ways in which the use of catalysts helps chemical companies to make their processes more sustainable
- Not used up in reaction
- Reactions take place at lower temperatures with lower energy demands/ activation energy so fossil fuels last longer
- Different reactions can be used with better atom economy with less hazardous waste
Draw a diagram to show metallic bonding
- Need regular arrangement of labelled ions at least two rows.
- Electrons dotted in between the lattice structure labelled as delocalised
Suggest why second ionisation energy of oxygen has a greater value than the first
- The O+ ion is smaller than the O atom
2. The electron shielding is smaller
Describe ways that research chemists are trying to minimise climate change caused by release of greenhouse gases
- Developing carbon capture and storage e.g bury deep in ocean or react to form carbonates
- Monitoring atmospheric change
- Develop alternative energy sources e.g solar panels
- Develop more efficient engines for transport
- Find uses for CO2
