stuff to remember for paper one

Question 1

How do you find out number of molecules?

Answer 1

Mol X Avogardo constant (6.022x10^23)

Question 2

When a dilution occurs, what changes and what stays the same?

Answer 2

The more H2O added, the lower the concentration.

Concentration and volume change, but mol and mass of solute stays the same.

Question 3

Why is it hard to predict enthalpy change of solution down a group?

Answer 3

Because as you go down the group, the ionic radius will increase which will make both the lattice enthalpy and the enthalpy changes of hydration less negative, and they both determine enthalpy change of solution.

Question 4

What happens if a titration is read from the top of the meniscus instead of the bottom?

Answer 4

Nothing as the volume is measured as a difference.

Question 5

Why should the burette only be washed with the substance in it?

Answer 5

It could react with other substances or be diluted by H2O which would lead to a lower concentration and therefore a higher titre than expected,

Question 6

How can you reduce an error in a titration?

Answer 6

Repeating titres to allow for anomalies to be detected and calculate a mean.

Use an apparatus with greater resolution or increase the size of measurements

Decrease the concentration of the substance in the burette

Titre a larger volume by increasing the vol and concentration of the substance in the conical flask

Question 7

What effect will increasing temperature, pressure and using a catalyst have on inital rate?

Answer 7

Increases rate

Question 8

How do you calculate activation energy via the Arrhenius equation?

Answer 8

-(The gradient) x gas constant (8.314) which will provide answer in J.
To convert to KJmol-1 you divide by 1000

Question 9

What is enthalpy change of solution?

Answer 9

When one mol of compound dissolves.

Question 10

Will a change in temperature occur if the mol of reactants are doubled and why?

Answer 10

No because double the moles= double the energy spread over double the volume

Question 11

How do we know a buffer solution has formed?

Answer 11

Buffer solution can be either made by reacting an excess weak acid with a strong base via partial neutralisation or reacting a weak acid and a salt.
The conjugate base of the weak acid is provided by the salt or formed in situ

Question 12

What is the equation for dilution?

Answer 12

ConcxVol before solution = ConcxVol after solution

Question 13

Where does the change fro metals to non metals occur in the periodic table?
What do the elements near the divide show? Give examples.

Answer 13

From the top of Group 13 to the bottom of Group 17.

Elements near the divide such as boron and silicon show in between properties.

Question 14

Why can do metals have electrical conductivity?

Answer 14

They have delocalised electrons which are mobile carriers of change.

Question 15

Describe the structure of graphite

Answer 15

Graphite has parallel of hexagonally arranged carbon atoms where the layers are linked by weak intermolecular forces but the carbons are linked by strong covalent bonds.

Question 16

Why does the MP increase then have a sharp decrease across Period 2 and 3

Answer 16

Because there is a change from giant structures to simple molecular structures.

Question 17

Why is haemoglobin an example of a ligand substitution reaction?

Answer 17

Haemoglobin has four polypeptide chains, each which contain a Fe2+ ion that can bind to oxygen and release it where required in the body.
CO can replace oxygen via ligand substitution, and will bind more strongly, which prevents haemoglobin from transporting oxygen

Question 18

How do you oxidise Fe2+ to Fe3+?

Answer 18

Using maganate ions MnO4- which becomes reduced to Mn2+
The colour will change from purple to colourless
This is done under acidic conditions

MnO4- + 8H+ + 5Fe2+ -> 5Fe3+ + Mn2+ + 4H2O

Question 19

How do you reduce Fe3+ to Fe2+?

Answer 19

The use of iodide ions which become oxidised to iodine.
The pale green formation of Fe2+ is obscured by brown of iodine forming.

2Fe3+ + 2I- -> 2Fe2+ + I2

Question 20

How do you reduce Cr2O7 2- to Cr3+?

Answer 20

Use of zinc ions
Zinc are oxidised to Zn2+ under acidic conditions
The colour will change from orange to green
Cr2O72- + 14H+ + 3Zn -> Cr3+ + 7H2O + 3Zn2+

With further zinc, Cr3+ can be further reduced to Cr2+

Question 21

How do you go from Cr3+ to CrO4 2-?

Answer 21

By using hydrogen peroxide

3H2O2 + 2Cr3+ + 10OH- -> 2CrO4 2- + 8H2O

Question 22

How can you use electrode potentials to explain why redox reactions take place, including equilibrium reasons.

Answer 22

The more positive the E* value, the equilibrium is more likely to gain electrons and therefore will shift to the right (the direction to gain electrons)
For example, MnO4-/Mn2+ equilibrium has a higher E* value than the equilibrium for Fe3+/Fe2+ and therefore will become reduced while Fe2+ becomes oxidised to Fe3+.

Question 23

How do you convert from dm3 into cm3?

Answer 23

x1000

or cm3 into dm3 is dividing by 1000

Question 24

How do you go from m3 into cm3?

Answer 24

Multiply by 1000000

cm3 into m3 is dividing by a million

Question 25

How do you go from m3 into dm3?

Answer 25

Divide by 1000

or dm3 into m3 = x1000

Question 26

What is the equivalence point in a pH curve?

Answer 26

The centre of the vertical section which is the volume of one solution that reacts exactly with another

Question 27

What effect will using a strong acid or base have on a titration curve?

Answer 27

pH curve could start off or end off earlier depending on what is being added to what

The stronger the substance you are using, the larger the vertical section will be unlike weak-acid and weak-base which will not produce any vertical section at all.

Question 28

What is the endpoint of a titration and how can you tell?

Answer 28

An end point of a titration is when there are equal amounts of the substance, for example an acid and base. The colour will present as half way between them.

Question 29

Why may the enthalpy change of combustion not always be fully accurate when recorded?

Answer 29

Heat loss to the surroundings
Non standard conditions
Incomplete combustion
Evaporation of methanol

Question 30

What is gdm-3?

Answer 30

The mass concentration, which is concentration x mr

Question 31

What does mass x avogardo constant tell us?

Answer 31

mass x 6.022x10^23 = relative formulae mass/mr

Question 32

What does a high pKa indicate?

Answer 32

The higher the pKa, the stronger the acid.

The higher the Ka, the weaker the acid.

Question 33

How do you prepare a standard solution?

Answer 33

1) Weigh solid accurately
2) Solid is dissolved in a beaker and then transferred to a volumetric flash
3) Filled to the graduation line using distilled water until the bottom of the meniscus line
4) Volumetric flash is inverted several times to mix solution thoroughly or else results may not be consistent

Question 34

What is a shell, orbital and subshell?

Answer 34

Shell is the big circle, the energy level
Atomic orbitals are what make up shells, can be s, p, d or f
Subshells are orbitals of the same group, for example 2s or 3p are subshells

Question 35

Define lattice enthalpy

Answer 35

Lattice enthalpy is the enthalpy change that occurs when one mol of an ionic compound is formed from its gaseous ions.

Question 36

How do you find the concentration of the original?

Answer 36

New concentration x New volume/Original volume

Question 37

How do you calculate initial rate using a concentration/time graph ?

Answer 37

Calculate the k constant = In2/half life

Then substitute into Rate= Kx concentration of reactants in order (at the start of the reaction if inital)

Question 38

What does it mean by weighted mean mass?

Answer 38

Taking into account the contribution of all the isotopes to the overall mass of the element

Question 39

What is the bond angle of square planar complexes?

Answer 39

90*

Question 40

In terms of Kc, Kp etc.. equilibrium, why does the equilibrium shift?

Answer 40

Increasing or decreasing a condition will decrease the ratio of Kp or Kc.
Therefore the equilibrium will rebalance to restore the ratio

Question 41

Define electronegativity

Answer 41

The attraction of a bonded atom for a pair of electrons in the covalent bond

Question 42

Why do the solubilities of hydroxides increase down the group?

Answer 42

Because the atomic radius increases, attraction between outer electrons and nucleus decreases so water molecules are able to dissolve the compound more accessibly

Question 43

What are the benefits of using catalysts in processes?

Answer 43

Reduce the temperature requirement as they increase the rate of the reaction

Reduce the need to use fossil fuels

Question 44

What effect will using a higher temperature and a catalyst have on a boltzman distribution graph and why?

Answer 44

Higher temperature: More molecules will exceed the activation energy, a greater proportion of collisions and therefore will be more frequent.
The graph will look lower and move more to the right

Catalyst: Lowers the activation energy s a higher portion of molecules can exceed the activation energy

Question 45

How would you use the iodine clock procedure to determine the rate order of a reaction?

Answer 45

Separate concentrations of one reactant is used , other concentrations are kept constant
Sodium thiosulfate will delay the reaction
The solution is colourless at first and the time is measured to determine for the blue-black colour to appear of iodine
A graph of 1/T is plot against concentration
The rate can be determine via the shape of the graph, a rate concentration graph

Question 46

In an iodine thiosulphate titration, what is S2O3 oxidised to?

Answer 46

S2O3 is oxidised to S4O6 and iodine is reduced to 2I- ions

Question 47

What are the limitations of predictions using E* values?

Answer 47

A reaction may have a very large activation energy and therefore a slow reaction rate

Many reactions often do not take place in standard conditions where concentration is 1.00 moldom-3, the electrode potential will then be different from the standard value.

Standard conditions may be different from the ones used to measure E*

Question 48

How can Barium nitrate be used to check for a sulphate group?

Answer 48

Formation of a white precipitate in the form of BaSO4 shows that there is a SO42- group present

Question 49

Why is the change that produces lattice enthalpy spontaneous but has a negative entropy change?

Answer 49

Because the enthalpy change is more negative than temperature x entropy

Question 50

What happens when Cr3+ reacts with excess Naoh?

Answer 50

Forms Cr(OH)6 3- which is dark green

Question 51

Other than gas collection, what is another way to measure rate of reaction?

Answer 51

Mass loss/time