paper 1 Flashcards
(39 cards)
A student is supplied with 100.0 cm3 of a solution of 0.400 mol dm–3 magnesium iodide, MgI2.
A student plans to dilute this solution so that the iodide concentration is 0.250 mol dm–3.
What volume of water, in cm3, does the student need to add?
220cm3
The enthalpy changes of solution of the magnesium halides show a trend from MgF2 to MgI2.
Explain why it is difficult to predict whether the enthalpy change of solution becomes more exothermic or less exothermic down the group from MgF2 to MgI2.
Ionic radius:
Halide ion gets larger down the group
Lattice enthalpy:
Lattice enthalpy is less exothermic down group
OR halide ion has less attraction for Mg2+
Hydration enthalpy:
Hydration enthalpy is less exothermic down group
OR halide ion has less attraction for H2O
Enthalpy of solution
Difficult to predict whether lattice enthalpy or
hydration enthalpy has bigger effect
Explain whether calculated percentage mass of copper from titration would be higher, lower, or the same if the burette readings were read from the top of meniscus.
The same AND burette measures by difference
State one important of a fuel cell that is different from a conventional storage cell
Fuel reacts with oxygen/oxidant to give electrical energy/voltage
Zinc reacts with copper(II) sulfate solution, CuSO4(aq).
What apparatus could be used to determine the effect of the concentration of CuSO4(aq) on the rate of reaction?
Colorimeter
How would the lattice enthalpies of magnesium chloride and calcium chloride differ? Explain your answer
Lattice enthalpy of MgCl2 is more exothermic than CaCl2
because magnesium ion/Mg2+ is smaller (than calcium
ions/Ca2+) OR Mg2+ has a greater charge density
therefore the attraction between Mg2+ and Cl is greater (than between Ca2+ and Cl)
Describe and explain the relative reactivity of the halogens, chlorine, bromine and iodine, in their redox reactions with halides, using reactions on a test-tube scale.
Include reaction equations and observations in your answer.
Trend in reactivity
* More shells or increasing radius down the group
* Increased shielding down the group
* More difficult to gain an electron
Observations
* Reaction of Cl2 or Br2 with I– : orange/brown solution OR purple in organic
* Reaction of Cl2 with Br– : yellow solution OR orange in organic
Reaction equations
* Cl2 + 2Br– → Br2 + 2Cl–
- Cl2 + 2I– → I2 + 2Cl–
OR Br2 + 2I– → I2 + 2Br– - Order of reactivity linked to observations
Describe how a heterogenous catalyst works
Reactants adsorbed onto surface of catalyst and form bonds to surface (AW)
Bonds within reactants weaken and break
New bonds form (AW)
Products formed desorb/leave from catalyst
Describe and explain the steps in the purification of an organic solid by recrystallisation
- The organic solid / desired product should be less soluble than the soluble impurities in the chosen solvent.
- Solubility is greater in hot solvent than cold solvent, so the organic solid should be insoluble in cold solvent but soluble in hot solvent
- A minimum volume of hot solvent is added to dissolve the impure product
- Cool the resulting solution and the solid recrystallises
- Sold crystals then cold filtered out under reduced pressure in Buchner funnel/flask and solid is washed with cold solvent to remove soluble impurities
- Pure crystals then dried in an oven at a lower temperature than the melting point to obtain pure solid.
What is (i) homolytic and (ii) heterolytic fission?
i) Homolytic = breaking of a covalent bond with one of the bonded electrons going to each atom, forming 2 radicals
ii) Heterolytic = breaking of a covalent bond where one of the bonding atoms receives both electrons, forming a cation (positive ion) and an anion (negative ion)
Give the 2 approximations that can be made for the Ka equation of a weak acid.
- [H+] at equilibrium = [A-] at equilibrium. Dissociates to produce equal conentrations.
- [HA] at equilibrium = [HA] at start, as dissociation of weak acids is small, you can assume that [HA]»_space; [H+] and you can neglect any decrease in the conc of HA from dissociation
What is graphene?
Single layer of graphite
What happens to solubility as you go down the G2 hydroxides?
Solubility increases - so solutions become more alkaline as they contain more OH- ions
Give the reaction of chlorine and water. What is it used for?
Cl2(g) + H20(l) —> HCl(aq) + HClO(aq)
Disinfectant for drinking water. Acids produced kill harmful bacteria.
Chloric (I) acid also acts as a weak bleach - test by adding indicator - first turns red (acid) then disappears (bleach)
Give the reaction of chlorine with cold, dilute sodium hydroxide. What is it used for?
Cl2(g) + NaOH(aq) —> NaCl(aq) + NaClO(aq) + H2O(l)
Sodium chlorate (I) = household bleach
What is the test for ammonium ions?
Add aqueous sodium hydroxide + warm. Test for gas with damp red litmus paper - turns blue from ammonia if NH4+ was present.
NH4+(aq) + OH-(aq) —> NH3(g) +H2O(l)
What is enthalpy (H)?
Measure of heat energy in a chemical system.
Enthalpy change = difference in enthalpies (products - reactants)
Enthalpy change of reaction of gases, using BOND ENTHALPIES:
reactants - products
Suggest one reason, other than a high activation energy or slow rate, why the enthalpy change of formation of pentane cannot be obtained directly
Carbon reacts with hydrogen to form many different hydrocarbons
What happens when you increase / decrease the concentration of a reactant in terms of Kc?
Increase:
[products]/[reactants] is now less than Kc (no longer in equilibrium). [products] must increase and [reactants] must decrease to restore Kc. So p.o.e shifts right
Decrease: [products]/[reactants] is now greater than Kc (no longer in equilibrium). [reactants must increase and [products] must decrease to restore Kc. So p.o.e shifts left
What happens when you increase pressure in terms of Kp?
Side with more gas molecules increases more in pressure, so p(products)/p(reactants) adjusts to restore Kp, so p.o.e shifts to the side with fewer gas molecules
What is the acid dissociation constant (Ka)?
Equilibrium constant that measures the extent of acid dissociation. Larger Ka = greater dissociation so stronger acid.
Give the buffer system that maintains pH in the human body. Give the weak acid and conjugate base in this.
Carbonic acid-hydrogencarbonate buffer system. Weak acid = H2CO3 (carbonic acid). Conjugate base = HCO3 - (hydrogencarbonate)
What is enthalpy change of hydration?
What is enthalpy change of solution?
Hydration:
Enthalpy change when 1 mole of gaseous ions dissolve in water to form 1 mole of aqueous ions under standard conditions
Solution:
Enthalpy change when 1 mole of a solute completely dissolves in a solvent under standard conditions
Give the factors affecting lattice enthalpy and enthalpy of hydration
- Ionic radius: smaller = greater attraction between oppositely charged ions / ions and water molecules = more exothermic lattice and hydration enthalpy
- Ionic charge: greater = greater attraction between oppositely charged ions / ions and water molecules = more exothermic lattice and hydration enthalpy
