EMPA

Question 1

Why is nitric acid used in the silver nitrate test to test for halide ions?

Answer 1

To remove any ions that may interfere with the results of the test

Question 2

What are the positive results of the silver nitrate test for 1. Chloride ions 2. Bromide ions 3. Iodide ions?

Answer 2

1. White ppt 2. Cream ppt 3. Yellow ppt

Question 3

Why does the silver nitrate test produce no visible change for fluoride ions?

Answer 3

Silver fluoride is soluble in water

Question 4

Describe the test you can do to further determine the halide ions in a solution that may contain chloride, bromide or iodide ions?

Answer 4

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.

Question 5

Describe the trend in electronegativity down group 7

Answer 5

Decreases

Question 6

Give a reason for the trend in electronegativity down group 7

Answer 6

Larger atomic radius as you go down the group + more electrons provide shielding to the nucleus

Question 7

Describe the trend in reducing power down group 7

Answer 7

Increases

Question 8

Give a reason for the trend in reducing power down group 7

Answer 8

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

Question 9

Describe the general trend in ionisation energies down group 2

Answer 9

Decreases

Question 10

Explain the general trend in ionisation energies down group 2

Answer 10

Each element down group 2 has an extra inner electron than the previous element which provides extra shielding

Question 11

Explain the reactivity in group 2 elements

Answer 11

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.

Question 12

Explain the general trend in melting points down group 2

Answer 12

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.

Question 13

Give the general equation for the reaction between group 2 metals and water.
M=metal

Answer 13

M(s) + 2H20 —>M(OH)2(aq) + H2

Question 14

What are the two equations for calculating moles

Answer 14

N=Mass/Molecular Mass & N=conc x volume in dm-3

Question 15

What equation involves the gas constant?

Answer 15

pV=nRT

Question 16

How do you calculate atom economy?

Answer 16

%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)

Question 17

How do you calculate percentage yield?

Answer 17

%yield = (actual yield / theoretical yield)x 100

Question 18

State Hess’ law

Answer 18

The total enthalpy change of a reaction is always the same no matter which route is taken. (or words to that effect)

Question 19

What is the definition of standard enthalpy of combustion?

Answer 19

The total enthalpy change of one mole of substance completely burned in oxygen in its standard states and conditions.

Question 20

What is the definition of standard enthalpy of formation?

Answer 20

The total enthalpy change of one mole of substance formed completely from its elements in its standard states and conditions.

Question 21

What are the two equations for enthalpy change?

Answer 21

q=mc(delta)T and Hc=q/n (combustion only)

Question 22

What are the constituents of q=mc(delta)T and Hc=q/n

Answer 22

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

Question 23

What is the definition of the standard enthalpy change of reaction?

Answer 23

The enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all the products and reactants in their standard states.