stuff to remember for paper one Flashcards
How do you find out number of molecules?
Mol X Avogardo constant (6.022x10^23)
When a dilution occurs, what changes and what stays the same?
The more H2O added, the lower the concentration.
Concentration and volume change, but mol and mass of solute stays the same.
Why is it hard to predict enthalpy change of solution down a group?
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.
What happens if a titration is read from the top of the meniscus instead of the bottom?
Nothing as the volume is measured as a difference.
Why should the burette only be washed with the substance in it?
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,
How can you reduce an error in a titration?
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
What effect will increasing temperature, pressure and using a catalyst have on inital rate?
Increases rate
How do you calculate activation energy via the Arrhenius equation?
-(The gradient) x gas constant (8.314) which will provide answer in J.
To convert to KJmol-1 you divide by 1000
What is enthalpy change of solution?
When one mol of compound dissolves.
Will a change in temperature occur if the mol of reactants are doubled and why?
No because double the moles= double the energy spread over double the volume
How do we know a buffer solution has formed?
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
What is the equation for dilution?
ConcxVol before solution = ConcxVol after solution
Where does the change fro metals to non metals occur in the periodic table?
What do the elements near the divide show? Give examples.
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.
Why can do metals have electrical conductivity?
They have delocalised electrons which are mobile carriers of change.
Describe the structure of graphite
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.
Why does the MP increase then have a sharp decrease across Period 2 and 3
Because there is a change from giant structures to simple molecular structures.
Why is haemoglobin an example of a ligand substitution reaction?
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
How do you oxidise Fe2+ to Fe3+?
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
How do you reduce Fe3+ to Fe2+?
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
How do you reduce Cr2O7 2- to Cr3+?
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+
How do you go from Cr3+ to CrO4 2-?
By using hydrogen peroxide
3H2O2 + 2Cr3+ + 10OH- -> 2CrO4 2- + 8H2O
How can you use electrode potentials to explain why redox reactions take place, including equilibrium reasons.
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+.
How do you convert from dm3 into cm3?
x1000
or cm3 into dm3 is dividing by 1000
How do you go from m3 into cm3?
Multiply by 1000000
cm3 into m3 is dividing by a million
How do you go from m3 into dm3?
Divide by 1000
or dm3 into m3 = x1000
What is the equivalence point in a pH curve?
The centre of the vertical section which is the volume of one solution that reacts exactly with another
What effect will using a strong acid or base have on a titration curve?
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.
What is the endpoint of a titration and how can you tell?
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.
Why may the enthalpy change of combustion not always be fully accurate when recorded?
Heat loss to the surroundings
Non standard conditions
Incomplete combustion
Evaporation of methanol
What is gdm-3?
The mass concentration, which is concentration x mr
What does mass x avogardo constant tell us?
mass x 6.022x10^23 = relative formulae mass/mr
What does a high pKa indicate?
The higher the pKa, the stronger the acid.
The higher the Ka, the weaker the acid.
How do you prepare a standard solution?
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
What is a shell, orbital and subshell?
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
Define lattice enthalpy
Lattice enthalpy is the enthalpy change that occurs when one mol of an ionic compound is formed from its gaseous ions.
How do you find the concentration of the original?
New concentration x New volume/Original volume
How do you calculate initial rate using a concentration/time graph ?
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)
What does it mean by weighted mean mass?
Taking into account the contribution of all the isotopes to the overall mass of the element
What is the bond angle of square planar complexes?
90*
In terms of Kc, Kp etc.. equilibrium, why does the equilibrium shift?
Increasing or decreasing a condition will decrease the ratio of Kp or Kc.
Therefore the equilibrium will rebalance to restore the ratio
Define electronegativity
The attraction of a bonded atom for a pair of electrons in the covalent bond
Why do the solubilities of hydroxides increase down the group?
Because the atomic radius increases, attraction between outer electrons and nucleus decreases so water molecules are able to dissolve the compound more accessibly
What are the benefits of using catalysts in processes?
Reduce the temperature requirement as they increase the rate of the reaction
Reduce the need to use fossil fuels
What effect will using a higher temperature and a catalyst have on a boltzman distribution graph and why?
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
How would you use the iodine clock procedure to determine the rate order of a reaction?
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
In an iodine thiosulphate titration, what is S2O3 oxidised to?
S2O3 is oxidised to S4O6 and iodine is reduced to 2I- ions
What are the limitations of predictions using E* values?
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*
How can Barium nitrate be used to check for a sulphate group?
Formation of a white precipitate in the form of BaSO4 shows that there is a SO42- group present
Why is the change that produces lattice enthalpy spontaneous but has a negative entropy change?
Because the enthalpy change is more negative than temperature x entropy
What happens when Cr3+ reacts with excess Naoh?
Forms Cr(OH)6 3- which is dark green
Other than gas collection, what is another way to measure rate of reaction?
Mass loss/time
