Flashcards in EMPA Deck (23)
Why is nitric acid used in the silver nitrate test to test for halide ions?
To remove any ions that may interfere with the results of the test
What are the positive results of the silver nitrate test for 1. Chloride ions 2. Bromide ions 3. Iodide ions?
1. White ppt 2. Cream ppt 3. Yellow ppt
Why does the silver nitrate test produce no visible change for fluoride ions?
Silver fluoride is soluble in water
Describe the test you can do to further determine the halide ions in a solution that may contain chloride, bromide or iodide ions?
If the ppt dissolves in dilute NH3-chloride ions are present.
If the ppt dissolves in conc. NH3-bromide ions are present.
If the ppt doesn't dissolve in conc. NH3-iodide ions are present.
Describe the trend in electronegativity down group 7
Give a reason for the trend in electronegativity down group 7
Larger atomic radius as you go down the group + more electrons provide shielding to the nucleus
Describe the trend in reducing power down group 7
Give a reason for the trend in reducing power down group 7
Larger atomic radius means electrons are further away from the nucleus so are easier to lose + more electrons provide more shielding so the attractive force of the nucleus is weaker down the group
Describe the general trend in ionisation energies down group 2
Explain the general trend in ionisation energies down group 2
Each element down group 2 has an extra inner electron than the previous element which provides extra shielding
Explain the reactivity in group 2 elements
When group 2 elements react they lose electrons forming positive ions. Elements further down group 2 have more inner electrons so the electron that is lost is further away from the nucleus and is therefore easier to remove. This makes it more reactive.
Explain the general trend in melting points down group 2
Decreases- as you go down the group the positive ions in the metallic structure increase in size but the number of delocalised electrons around them stays the same. Therefore the delocalised electrons are further away from the nucleus. These two factors reduce the attraction and therefore less energy is needed to break the bonds.
Give the general equation for the reaction between group 2 metals and water.
M(s) + 2H20 --->M(OH)2(aq) + H2
What are the two equations for calculating moles
N=Mass/Molecular Mass & N=conc x volume in dm-3
What equation involves the gas constant?
How do you calculate atom economy?
%atom economy = (mass of desired product / total mass of reactants) x 100 (useful note, if no masses are given, use the relative mass of the atoms but make sure to take into account the number of moles of the atoms or compounds)
How do you calculate percentage yield?
%yield = (actual yield / theoretical yield)x 100
State Hess' law
The total enthalpy change of a reaction is always the same no matter which route is taken. (or words to that effect)
What is the definition of standard enthalpy of combustion?
The total enthalpy change of one mole of substance completely burned in oxygen in its standard states and conditions.
What is the definition of standard enthalpy of formation?
The total enthalpy change of one mole of substance formed completely from its elements in its standard states and conditions.
What are the two equations for enthalpy change?
q=mc(delta)T and Hc=q/n (combustion only)
What are the constituents of q=mc(delta)T and Hc=q/n
q = heat lost or gained in J. The same as enthalpy change if the pressure is constant.
m = mass of solution in the container being heated.
c = specific heat capacity of the solution being heated.
(delta)T = the change in temperature of the solution in K or degrees C
n = number of moles of fuel burnt