Physical Flashcards Preview

A LEVEL CHEMISTRY PAPER 1 > Physical > Flashcards

Flashcards in Physical Deck (38):

Hydrogen is used in the chemical industry.
Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3)
State the role of hydrogen in this reaction (1 mark)

Reducing agent


State a risk of using hydrogen gas in metal extractions



State why the electrode potential for the standard hydrogen electrode is equal to 0.00 V (1 mark)

By definition


Give one reason, other than cost, why the platinum electrodes are made by coating a
porous ceramic material with platinum rather than by using platinum rods. (1 mark)

Increases surface area.


Suggest why the e.m.f. of a hydrogen– oxygen fuel cell, operating in acidic conditions,
is exactly the same as that of an alkaline fuel cell. (1 mark)

Overall reaction is the same (2H2 + O2 → 2H2O)


Other than its lack of pollution, state briefly the main advantage of a fuel cell over a
re-chargeable cell such as the nickel– cadmium cell when used to provide power for an
electric motor that propels a vehicle. (1 mark)

Hydrogen and oxygen supplied continuously
Can be operated without stopping to recharge


Hydrogen– oxygen fuel cells are sometimes regarded as a source of energy that is
carbon neutral. Give one reason why this may not be true. ( 1 mark)

Hydrogen may need to be made using an energy source that is not
‘carbon neutral’


Explain why the bond enthalpy of a Cl–Cl bond is greater than that of a Br–Br bond. (2 marks)

-Bond is shorter or bonding pair closer to nucleus

-So attraction (between nucleus and) (to) bond pair is stronger


Suggest why the electron affinity of chlorine is an exothermic change.

Net attraction between the chlorine nucleus and the extra electron
Allow Cl- ion more stable than Cl


Explain the meaning of the term perfect ionic model (1 mark)

Ions can be regarded as point charges (or perfect spheres)


Suggest why enthalpy lattice dissociated calculated from a born-haber cycle is GREATER than the theoretical value for enthalpy of lattice dissociation. (2 marks)

-AgCl has covalent character

-Forces in the lattice are stronger than pure ionic attractions


Give the meaning of the term DYNAMIC in the context of a dynamic equilibrium

-Forward and reverse reactions occur at the same time/all of the time


Effect on time taken to reach equilibrium if pressure is increased: (3 marks)

-Decrease in time taken
-More particles in a given space
-Therefore more successful collisions


What is the affect of doubling the pressure of a gas on the most probable energy in a maxwell-boltzmann distribution?

No effect


Write an overall equation to represent the decomposition of ozone into oxygen.



Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in
this test for iodide ions

-HCl would form a white ppt (which would interfere with test)


Give the formulas of the two different chlorine-containing compounds that are
formed when chlorine reacts with cold, dilute, aqueous sodium hydroxide




-Molecules with the same STRUCTURAL formula but with atoms and bonds arranged differently in space.


Why are you unable to measure enthalpy change using calorimetry for a hydrated salt reaction?

Not possible to prevent some dissolving so not accurate as it is soluble


Method to determine enthalpy of solution of an anhydrous salt (6);

-Measure 10-200cm^3 of water USING measuring cylinder
-Transfer into polystyrene cup
-Add known mass of salt,
-Weigh before and after

-Record a minimum of 2 INITIAL temps
-Record T at regular intervals until trend is seen and plot a T vs time graph
-Extrapolate line to when solid is added, to find initial and final t, getting /_\T. Use Q=MCAT. mol=mass/mr
Enthalpy of solution =-Q/mol


Why are major products formed in reactions:

Major product formed via more stable carbocation
-Due to positive inductive effect of alkyl groups (REASON: Due to having more alkyl groups than the minor)


Conc Sulfuric acid with NaCl observation:

White steamy fumes


Anti bumping granules purpose:

Prevents large bubbles from forming


Reason to use electric heater in reaction rather than bunsen



Why is sodium benzoate soluble in cold water but benzoic acid isnt

-Sodium benzoate soluble because ionic
-Benzoic acid has non polar benzene ring so not soluble


Method to purify benzoic acid (General purification):

-Dissolve crude product in hot water
-Of minimum volume
-Cool to recrystalise


In terms of electrostatic forces suggest why electron affinity of fluorine has a negative value (2 mark)

-Attraction from protons in nucleus to the (added) electrons
-Energy released/exothermic reaction (when the electron is gained)


A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical galue than the value calculated in the cycle:
explain (2)

-AgI contains covalent character
-Forces/bonds holding lattice together are stronger


Suggest a reagent used to indicate the presence of iodide ions in an aqueous solution, and describe the observation made: (2)


Would form a yellow ppt


Describe a test you could carry out in a test tube, to distinguish between SODIUM OXIDE and PHOSPHOROUS OXIDE (3)

-React with water

-Add litmus paper

-Litmus gives blue colour with NaO, red with P4O10


Reaction of sulfur trioxide with potassium hydroxide

SO3 + 2KOH ——> K2SO4 + H2O


Reaction with an excess of magnesium oxide with phosphoric acid

3MgO + H3PO4 —-> Mg3(PO4)2 + 3H2O


Draw the displayed formula of the undissociated acid formed when sulfur dioxide reacts with water:

H- O
S=O (SO3H)+
H - O


State the type of bonding between oxygen and hydrogen in

State why the chloride ions in this compound are not considered to be ligands


Cl- NOT donating a lone pair to the Cu2+


When Reagent D is added to [Cu(H2O)6]2+ , a yellow-green solution is formed. Identify D and write an ionic equation


[Cu(H2O)6]2+ + 4HCl —> [CuCl4]2- + 6H2O + 4H+


Explain why colorimetry cannot be used to determine the concentration of solutions containing [CuCl2]-
In your answer refer to electron configuration (2 marks)

-Full 3d orbital
-SO colourless


Describe how a student could distinguish between aqueous solutions of KNO3 and Potassium sulfate using one simple test tube reaction (3)

Reagent: BaCl2

Observation with KNO3: No reaction

Observation with K2SO4: White ppt formed


Describe how a student could distinguish between aqueous solutions of MgCl2 and AlCl3 using one simple test tube reaction (3)

Reagent: NaOH

Obs with MgCl2: White ppt

Obs with AlCl3: White ppt that dissolves in EXCESS NaOH