General revision Flashcards by Charlotte Priday

What gives a violet colour if shaken with organic solvent

Iodine

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What are the conditions when chlorine reacts with sodium hydroxide to form bleach

Cold and dilute

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The reactivity of group 2 elements increases down the group, explain why (3 marks)

Increasing size:
Atomic radius increases
OR
more shells
OR
more (electron) shielding

Attraction
Nuclear attraction decreases
OR
(outer) electron(s) experience less attraction

Ionisation energy
Ionisation energy decreases
OR
less energy needed to remove electron(s)

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State 2 sources of nitrogen oxides in the stratosphere

Lightning/ thunderstorms
Aircrafts

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What type of reaction has the greatest atom economy
- Substitution
- Hydrolysis
- Elimination
- Addition

Addition

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Define stereoisomer

Same structural formula and different arrangement of atoms in space

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Suggest whether the enthalpy change of vapourisation of bromine is exothermic or endothermic. Explain your answer

Endothermic, Energy required to overcome induced dipole–dipole
forces/London forces

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Explain in terms of bonds breaking and bond forming, why a reaction can be exothermic

More energy is released by forming bonds
than energy required when breaking bonds

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Define the standard enthalpy change of combustion (3 marks)

-(enthalpy change that occurs) when one mole of a
substance
- completely combusts OR reacts fully with oxygen
- 298 K / 25 °C AND 1 atm / 100 kPa / 101 kPa / 105 Pa
/ 1 bar

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What is meant by the term average bond enthalpy (2 marks)

(Average enthalpy change) when one mole of bonds
✓
of (gaseous covalent) bonds is broken

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Explain the term stereoisomerism

Same molecular formula
AND
Different structural formulae

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What are the conditions when a carboxylic acid reacts with an alcohol to form an ester

Heat under reflux

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Describe in terms of orbital overlap the similarities and differences between the bonding in Kekule model and the delocalised model of benzene (3 marks)

Similarities
- Orbital overlap
(sideways) overlap of p orbitals

π bond
π bond/system/ring above and below (bonding (C)
atoms/ring/plane)

Difference
Kekule has: alternating π bonds OR 3 π bonds /
localised (π electrons) / overlap in one direction /
2 electrons in π bond
AND
Delocalised has: π ring (system) / all p orbitals
overlap OR (π electrons) spread around ring / overlap
in both directions / 6 electrons in π bond /

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Describe 2 pieces of evidence to support the delocalised model of benzene (2 marks)

Bond length
(C–C) bond length is between single (C–C) and
double bond (C=C)
OR all (C–C) bond lengths are the same
ΔH hydrogenation
∆H hydrogenation less (exothermic) than
expected
Resistance to reaction
Benzene is less reactive than alkenes
OR bromination of benzene requires a
catalyst/halogen carrier
OR benzene does not react with/decolourise
bromine (at room temperature)
OR benzene reacts by substitution
OR benzene does not (readily) react by addition

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What is meant by heterolytic fission

Heterolytic
one (bonded) atom/O receives both/2 electrons
Fission
Breaking of a covalent bond
OR breaking of C-O bond

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Define relative isotopic mass

The mass of an atom of the isotope compared with 1/12th the mass of an atom of carbon-12

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Define relative atomic mass of an element

The weighted mean mass of an atom of an element compared with 1/12th the mass of an atom of carbon-12

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Define relative molecular mass of a substance

The weighted mean mass of a molecule of that substance compared to 1/12th of the mass of an atom of carbon-12

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Define relative formula mass of a substance

The average mass of a formula unit of that substance compared to 1/12th of the mass of an atom of carbon-12

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Give chemical explanations for the following statements. The carbon–carbon bonds in benzene are all the same length

π bonds in benzene are delocalised

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The graph shows that rate of reaction decreases over time, explain why in terms of collision theory (2)

Reactant concentration decreases
So there’s less frequent successful collisions

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Explain how a catalyst increases the rate of reaction (2)

Catalyst lowers activation energy
Greater proportion of molecules have energy greater than the activation energy

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Describe and explain the effect of increasing the pressure on the rate of reaction(2)

(Increase in pressure) increases the rate
and because molecules are closer together… (1)
… so there are more collisions per unit time (1)

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Explain why use if catalyst reduces energy demands and benefits the environment (2)

Lower temperatures / less heat / less thermal energy
* Less fossil fuels / oil / coal / gas / non-renewable fuels
* Reduces CO2 emissions

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Explain why use of catakystcan reduce the demand for energy

Allows reactions to take place at lower temperatures

Explain how a concentration/ time graph shows zero order (1 mark)

- Constant gradient - Linear negative gradient - Constant rate - Rate independent of concentration - Decreasing half life

Explain how an initial rate/ concentration graph shows first order (1 mark)

- Straight line through (0,0) - Rate directly proportional to concentration - When the concentration doubles the rate doubles

How do you calculate the value of the pre-exponential factor A using a graph

The y-intercept is equal to lnA

Other than measuring volume of gas produced how else could the rate of reaction be followed

Measure mass loss

How do you calculate the initial rate when given concentration/ time graph

- Draw a tangent on graph at t=0 - Determine the gradient - Then remember to give units

How do you determine the order of a molecule when given a concentration/ time graph (2 methods)

- Determine half lives, 2 constant half lives indicate first order - Find 2 gradients = 2 rates, then sub into the Rate=k[x] equation

What is the equation to find k when you know the half lives

k = ln2/ half life

Explain how you could determine the activation energy for the reaction graphically using values of k and T (3 marks)

- Plot graph using lnk and 1/T - Measure gradient - Activation energy = -R x gradient

What is meant by the rate determining step

The slowest/ slow step

Explain why iodine is less reactive than bromine (3 marks)

- Iodine has larger atomic radius - Iodine has greater shielding / more shells -Iodine has weaker / less nuclear attraction (on electron gained than bromine)

Explain the trend in boiling points of the halogens (3 marks)

- Number of electrons increases - Number of London forces increase - More energy to break intermolecular forces

A student carries out test-tube experiments to prove the trend in reactivity of halogens. The student is provided with the following solutions: - Bromine water - Aqueous iodine - Aqueous barium chloride - Aqueous magnesium bromide - Aqueous calcium iodide Chlorine gas and chlorine water are NOT available. The student carries out the MINIMUM number of test-tube experiments using these solutions in the presence of cyclohexane - State the solutions that need to be added together in order to prove the trend in reactivity of halogens, using the minimum number of test-tube experiments - Describe the colour seen in the organic solvent at the end of each test-tube experiment - Write an ionic equation for one reaction that takes place (5 marks)

M1 Mixing of first pair of solutions Adding (aqueous) barium chloride to bromine (water) OR BaCl2 + Br2 M2 Mixing of second pair of solutions Adding (aqueous) calcium iodide to bromine (water) OR Cal2 + Br2 OR Adding aqueous magnesium bromide to aqueous iodine OR MgBr2 + I2 M3 Colours in cyclohexane Colour for M1 is orange OR yellow AND Colour for M2 is purple OR violet OR mauve OR pink OR lilac M4 Ionic equation mark Br2 + 2I− --> I2 + 2Br− M5 Use of M1 and one of M2 as only two experiments

When are solids and liquids emitted from the Kc equation

When it's a heterogeneous equation

What is total pressure

The sum of all pressures of the individual gases (partial pressures)

If change in temperature causes equilibrium to shift to the right, what happens to the Kp value

Increases

If temperature change causes equilibrium to shift to the left, what will happen to Kp

Decreases

If temperature change causes equilibrium to shift right, what happens to Kc

Increases

If temperature change causes equilibrium to shift left, what happens to Kc

Decreases

A student is provided with samples of 3 nickel compounds. - Nickel Bromide - Nickel Sulfate - Nickel carbonate Describe the tests that the student could carry out to identify the anion in each sample, and write equations for any reactions (6 marks)

- Carbonate test: Add HNO3 and fizzing -> carbonate identified 2H+ (aq) + CO32- (aq) -> CO2(g) + H2O(l) - Sulfate test: Add BaCl2 or Ba(NO3)2 and white precipitate Ba2+ + SO42- -> BaSO4 - Bromide: Add AgNO3 Ag+ + Br- -> AgBr Carbonate -> Sulfate -> Bromide

Describe simple tests that would identify the NH4+ and Br-, include reagents, expected observations and relevant equations (5 marks)

Br-: Add Silver nitrate and cream precipiate Ag+ + Br- -> AgBr NH4+: Heat with NaOH indicator paper turns blue NH4+ + OH- -> NH3 + H2O

Explain what is meant by the term enthalpy change of hydration (2 marks)

- 1 mole of gaseous ions react - gaseous ions dissolve in water

Predict how the enthalpy changes of hydration of F- and Cl- would differ (2 marks)

- Enthalpy change of hydration of F- would be more exothermic since F- has a smaller size then Cl- - F- being the smaller sized ion has greater attraction to H20

Explain what is meant by the term average bond enthalpy (2 marks)

- Breaking of one mole of bonds - In gaseous molecules

If the forward reaction is exothermic, and there are fewer gaseous moles on the right hand side, state and explain in terms of Kp, how you would expect the equilibrium position to change if the pressure was increased (3 marks)

- Equilibrium would shift to the right - Denominator of Kp expression would increase more than numerator - Numerator of Kp expression increases to restore Kp

What is the colour change of the end point of the titration when using starch

Blue goes to colourless

What is meant by the term isoelectric point

The pH at which the amino acid exists as a zwitterion

Explain how the chromatogram can be used to identify amino acids (2 marks)

- Measure the distance moved by spot and divide by distance travelled by solvent - Compare Rf value with data book values

How does gas chromatography separate the compounds in the mixture (1 mark)

Relative solubility in stationary phase

What is meant by the term average bond enthalpy (2 marks)

- Average enthalpy change when one mole of bonds - Of gaseous covalent bonds is broken

State and explain the features of hex-2-ene molecule that leads to E and Z isomers (2 marks)

- Carbon-carbon double bonds does not rotate - Each carbon atom of the double bond attached to 2 different groups/ atoms

Suggest why 2-methylbut-2-ene is less soluble in water than either of the structural isomers formed (2 marks)

- Does not contain OH group - Does not form hydrogen bonds with water

Describe how HCl is removed from waste gas produced (1 mark)

HCl gas is passed through alkali

State an advantage of using polymers made from natural foods

- Reduces the dependency on finite resources - Biodegradable - Photodegradable

Explain why the CF4 molecule has polar bonds but does not have an overall dipole (2 marks)

- F atom is more electronegative than C atom - CF4 is symmetrical so dipoles cancel

Explain why a small proportion of molecules in water have a relative molecular mass of 20 (1 mark)

Different O/H isotopes are present

Solid SiO2 melts at 2156 degrees, solid CO2 melts at -56 degrees. Suggest the type of lattice structure in solid SiO2 and in solid CO2 and explain the different in melting points in terms of the types of forces within each lattice structure (4 marks)

SiO2: Giant covalent lattice CO2: Simple covalent lattice In CO2 London forces Covalent bonds in SiO2 are stronger than the intermolecular forces in CO2

Describe a simple test which would confirm the presence of phenol (1 mark)

Indicator/ pH paper turns red/ orange and no reaction with Na2CO3