Formula, equations & amounts
What are considered concordant results in a titration?
Results that are within 0.10 cm3 of each other or +-0.05 cm3
+1
What is the trend for atomic and ionic radius down Group 1?
Give the equation to calculate energy transferred, Q.
Q = mc delta T
Give the unit for rate of reaction.
298 K & 100kPa
What is the oxidation number of nitrogen in the following compound: Ba(NO3)2
+5
What is the trend of solubility of Group 2 hydroxides and Group 2 sulfates in water?
Group 2 hydroxides increase in solubility down the group, Group 2 sulfates decrease in solubility down the group.
Name a main source of error in the experiment of burning fuel in a spirit burner and calculating enthalpy change from the temperature change of water.
Which five factors influence the rate of a chemical reaction?
Temperature, pressure, concentration, surface area, presence of a catalyst.
How many molecules are present in 100ml of water?
100ml = 100g
100 / 18 = 5.55 moles
5.55 x Avogadro's constant (6.02 x1023) = 3.35 x 1024
Explain the term disproportionation and show that this is a disproportionation reaction:
2Ca(OH)2(s) + 2Cl2(aq) --> CaCl2(aq) + Ca(ClO)2(aq) + 2H2O(l)
involves an element in a single species / same element being simultaneously oxidised and reduced.
Cl goes from 0 --> -1 in CaCl2 and from 0 --> +1 in Ca(ClO)2
Write a displacement reaction for bromine water, Br2(aq), added to a potassium iodide solution, KI(aq). What is the colour change you will observe?
Br2(aq) + 2I-(aq) --> 2Br-(aq) + I2(aq)
Colourless potassium iodide turns brown as bromine displaces iodine.
Give the definition of standard enthalpy change of formation.
enthalpy change when one mole of a compound forms from its elements under standard conditions in standard state.
Correct curve with labels:
vertical = number of particles with kinetic energy E
horizontal = kinetic energy E
OWTTE
A 25.0 cm3 sample of nitric acid was neutralised by 18.0 cm3 of 0.150 mol dm-3 sodium hydroxide solution. Calculate the concentration of nitric acid.
0.108 mol dm-3
Write the balanced half equation for the reduction of HOCl to chloride ions, Cl-, in acidic conditions.
HOCl(aq) + H+(aq) + 2e- --> Cl-(aq) + H2O(l)
Write the net ionic equation for the reaction between sodium carbonate and calcium chloride. Remember that all carbonates are insoluble and all nitrates are soluble. You must include state symbols.
Ca2+(aq) +CO32-(aq) --> CaCO3(s)
What does Hess's law state?
Enthalpy change in converting the reactants into products is the same regardless of the route taken.
Explain how a catalyst affects the rate of reaction (2 marks).
A catalyst changes the mechanism of the reaction by providing an alternative pathway. This lowers the activation energy and increases the rate of reaction.
Deduce the limiting reagent and calculate what mass of magnesium oxide is formed when 486 mg of magnesium reacts with 240 mg of oxygen:
Ar(Mg)=24.3, Ar(O2)=32, Mr(MgO)=40.3
2Mg + O2 --> 2MgO
Oxygen is the limiting reagent.
We can produce 0.015 mol MgO x 40.3 = 0.6045g = 605mg MgO
Use half equations to write the balanced ionic equation for the following redox reaction:
SO32- and Cl2 to give SO42- and Cl-
SO32- +H2O --> SO42- +2H+ + 2e-
Cl2 +2e- --> 2Cl-
SO32- +H2O + Cl2 --> SO42- +2H+ + 2Cl-
Explain what is meant by the term polarising power and how it affects the thermal stability of Group 2 carbonates.
Polarising power is the extent to which a positive ion is able to distort the electron cloud around a neighbouring negative ion.
It depends on two things: charge on the metal ion and the size of the ion (ionic radius). For these reasons, thermal stability decreases down Group 2 as ions get larger (charge is the same, +2).
What is meant by mean bond enthalpy?
mean value of the bond enthalpy for certain bond X-Y averaged across a wide range of compounds / different compounds. It takes into account that the bond enthalpy for a specific bond varies slightly from one compound to another and that successive bond enthalpies are not the same in compounds such as water and methane (energy to break first O-H bond in H-O-H requires 498 kJ/mol but the second 428 kJ/mol).
Explain the effect of temperature on the rate of reaction using collision theory (2 marks).
First of all, if temperature increases particles have more kinetic energy and move faster. There will be more frequent collisions / more collisions in the same amount of time. This increases the rate of reaction.
Secondly, in order for a reaction to take place, particles need to collide with sufficient energy to overcome activation energy. When temperature increases, more particles will have sufficient energy. This increases the rate of reaction.