All Topics Flashcards
(27 cards)
What is meant by the strength of an acid? (1)
The proportionation of dissociation
Place these in order of increasing strength (1) C6H5COOH - pKa of 4.19 CH3COOH - pKa of 4.76 CH3COCOOH - pKa of 2.39 CH3CHOHCOOH - pKa of 3.86
CH3COOH
C6H5COOH
CH3CHOHCOOH
CH3COCOOH
Calculate the pH of a 0.0150moldm-3 of an acid with pKa of 2.39 (4)
ka = 4.074X103 H+ = square roof of 6.11X10-5 pH = 2.11
Explain how a student could prove that 0.1 moldm-3 propanoic acid is a weak acid by taking one pH measurement and how Ka can be calculated (4)
- measured pH > 1
- hydrogen ion con = 10^negative pH
- equation for Kc
- kc = hydrogen ion conc squared / 0.1
Explain how the carbonic acid - hydrogencarbonate mixture acts as a buffer in control of blood pH (5)
- Equilibrium equation = H2C03 reversible arrow H+ + HCO3-
if alkali added - H+ reacts with them
- position of equilibrium moves to the right
if acid added - HCO3- reacts with added acid
- position of equilibrium moves to the left
Plan an experiment that a student should carry out to measure the enthalpy change of neutralisation (6)
- Acid and alkali mixed
- volume of acid and alkali stated
- Temperature taken at start and finish
- Energy Q=mcchangeT and meanings of m c and T given
- Energy scaled up to form 1 mole of water
- then need to do negative energy of this as this is an exothermic process
Suggest reasons for the difference between the enthalpy change of KF and RbF (4)
KF is -15kJmol-1
RbF is -24kJmol-1
- ionic radius of potassium ion is smaller
- lattice enthalpy of KF is more negative than RbF
- hydration of K+ is more negative than Rb+
- enthalpy of solution is affected more by lattice enthalpy than hydration enthalpy
What is a bidentate ligand? (1)
One which donates 2 electron pairs and form two coordinate bonds
Suggest why most reactions are unlikely to take place in one step (2)
- rate equation does not match overall equation
- collision is unlikely with more than one atom
Why does the rate of a reaction decrease over time? (1)
reactants concentration decreases leads to less frequent collisions
What is the rate determining step of a reaction? (1)
the slowest step
Which element has induced dipole-dipole interactions in its solid lattice? (1)
a) boron
b) magnesium
c) silicon
d) sulfur
d
In an experiment determining enthalpy change, which of these could have resulted in a more exothermic answer than expected? (1)
a) some methanol had evaporated before final weighing
b) the student used the molar mass of ethanol instead
c) incomplete combustion
d) the water boiled for 5 mins before the final temperature was taken
b
How could a sample of magnesium phosphate be obtained after reacting magnesium with phosphoric acid? (2)
- filter to remove solid
- dry solid to remove water
Explain the trend in boiling point with branching? (3)
- boiling point decreases with more branching
- more branching gives less surface contact and fewer/weaker induced DD interactions
- less energy is needed to break the intermolecular forces
What is an alkali? (1)
Something that releases OH- ions in solution
Explain why iodine is less reactive than bromine? (3)
- greater shielding
- larger atomic radius
- less nuclear attraction
Suggest 1 disadvantage of using chlorine for the purification of drinking water (1)
- toxic/poisonous
- forms carcinogenic compounds
Suggest whether the enthalpy change of vaporisation of bromine is endothermic or exothermic and why(1)
endothermic because energy needs to be put in to break the intermolecular forces
Draw a labelled diagram to show how you would safely set up apparatus for the preparation of bromobutane from butan-1-ol. Outline how a pure sample would be obtained (6)
- round - bottom/pear shaped flask
- heat source
- condenser
- separating funnel to separate organic and aqueous layers
- drying with an anhydrous salt
- redistillation
Why is benzoic acid difficult to nitrate? (1)
It is an electron withdrawing group
Explain the difference in melting point for elements Na and Mg (3)
Magnesium ions have a greater charge
Magnesium has more
(delocalised OR outer) electrons
Magnesium has greater attraction between ions and
electrons OR has stronger metallic bonds
Why should a minimum amount of solvent be used when disslving crystals? (1)
- the solution formed is saturated, meaning the maximum number of crystals form
Explain why the choice of solvent when dissolving crystals is very important? (1)
The solid needs to be very soluable in hot solvent and nearly insoluable when cold.
