Eleni N. GCSE Biology tutor, A Level Biology tutor, GCSE Chemistry tu...

Eleni N.

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Chemistry (Masters) - Edinburgh University

5.0
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9 completed lessons

About me

About Me: I am a Chemistry student at the University of Edinburgh, but I didn't always start out on this path. I spent my first two years at university persuing a Biochemistry degree and I took every opportunity to do more science subjects, such as Physics. From my childhood in Zimbabwe to my teen years in Cyprus, it was always obvious that I would pursue a career in a STEM subject, but I never believed I would be good enough. I hope that with my tutoring you will gain confidence, not only in the subject you are struggling with, but also in yourself. I am patient, understanding and will be supportive throughout the process.  I  have recently done research in a biology lab and in the 2016/2017 academic year I will be doing medical research at NTU in SIngapore. The Sessions The sessions will not have a rigid structure, as I believe everyone works differently and at their own pace. I will do my best to explain things in the way which best suits your needs.  I will emphasise understanding of the topic above else! Past paper questions are useless without understanding, I will not teach you how to answer questions, but how to analyse topics with the aim to aid your revision and best prepare you for exam questions. What Next? If you have any queries or concerns, do not hesitate to contact me! I am happy to get back to you as soon as possible. Please provide as much information as possible (level of study and examining body) in your emails xAbout Me: I am a Chemistry student at the University of Edinburgh, but I didn't always start out on this path. I spent my first two years at university persuing a Biochemistry degree and I took every opportunity to do more science subjects, such as Physics. From my childhood in Zimbabwe to my teen years in Cyprus, it was always obvious that I would pursue a career in a STEM subject, but I never believed I would be good enough. I hope that with my tutoring you will gain confidence, not only in the subject you are struggling with, but also in yourself. I am patient, understanding and will be supportive throughout the process.  I  have recently done research in a biology lab and in the 2016/2017 academic year I will be doing medical research at NTU in SIngapore. The Sessions The sessions will not have a rigid structure, as I believe everyone works differently and at their own pace. I will do my best to explain things in the way which best suits your needs.  I will emphasise understanding of the topic above else! Past paper questions are useless without understanding, I will not teach you how to answer questions, but how to analyse topics with the aim to aid your revision and best prepare you for exam questions. What Next? If you have any queries or concerns, do not hesitate to contact me! I am happy to get back to you as soon as possible. Please provide as much information as possible (level of study and examining body) in your emails x

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Ratings & Reviews

5from 1 customer review
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Ellie (Parent from Worthing)

February 22 2017

Qualifications

SubjectQualificationGrade
ChemistryA-level (A2)A*
BiologyA-level (A2)A*
PhysicsA-level (A2)A*
Pure MathematicsA-level (A2)A*

General Availability

Pre 12pm12-5pmAfter 5pm
mondays
tuesdays
wednesdays
thursdays
fridays
saturdays
sundays

Subjects offered

SubjectQualificationPrices
ChemistryA Level£20 /hr
BiologyGCSE£18 /hr
ChemistryGCSE£18 /hr
MathsGCSE£18 /hr
PhysicsGCSE£18 /hr

Questions Eleni has answered

Why does the solubility of Group 2 hydroxides in water increase down the group?

Firstly, we must consider the thermodynamics involved

It is known that a reaction is spontaneous due to thermodynamic favourability if the Gibbs Free Energy is negative. This is further broken down to entropy and enthalpy terms.

Upon dissolution of a salt, e.g. a hydroxide, the entropy increases (a favourable term) in all cases as the solid is separated into ions, which are free to move in solution.

However, in order for the ions to separate, the lattice must be broken. This requires breakage of the electrostatic forces of attraction between oppositely charged ions. Thus, energy must put in equal tot he lattice enthalpy - this is a very large positive term and so is unfavourable.

The above statements have only considered forced between the ions in the lattice, however, upon dissolution, the free ions interact with solvent molecules. In our example, we are using water. The polar water molecules can interact favourably with both types of ions and this introduces a further enthalpy term, known as the hydration enthalpy. If this interaction is favourable enough (large negative enthalpy) to overcome the energy required to break the lattice, the salt will dissolve.

Now we can consider the group 2 hudroxides and since the anion is identical in each case, we will only examine the cations. The early hydroxides, e.g. CaOH, are comprised of smaller cations (with a larger charge density) and thus have a very large lattice enthalpy. Interactions with water molecules are not great due to their relative sizes and so the hydration enthalpy is not large enough to overcome the electrostatic forces within the lattice and so the salt does not dissolve.

The opposite holds true for larger cations, e.g. Barium, and so later hydroxides are more readily dissolved in water

Note: HSAB theory has not been discussed as it is not taught at A Level (tot he best of my knowledge)

Firstly, we must consider the thermodynamics involved

It is known that a reaction is spontaneous due to thermodynamic favourability if the Gibbs Free Energy is negative. This is further broken down to entropy and enthalpy terms.

Upon dissolution of a salt, e.g. a hydroxide, the entropy increases (a favourable term) in all cases as the solid is separated into ions, which are free to move in solution.

However, in order for the ions to separate, the lattice must be broken. This requires breakage of the electrostatic forces of attraction between oppositely charged ions. Thus, energy must put in equal tot he lattice enthalpy - this is a very large positive term and so is unfavourable.

The above statements have only considered forced between the ions in the lattice, however, upon dissolution, the free ions interact with solvent molecules. In our example, we are using water. The polar water molecules can interact favourably with both types of ions and this introduces a further enthalpy term, known as the hydration enthalpy. If this interaction is favourable enough (large negative enthalpy) to overcome the energy required to break the lattice, the salt will dissolve.

Now we can consider the group 2 hudroxides and since the anion is identical in each case, we will only examine the cations. The early hydroxides, e.g. CaOH, are comprised of smaller cations (with a larger charge density) and thus have a very large lattice enthalpy. Interactions with water molecules are not great due to their relative sizes and so the hydration enthalpy is not large enough to overcome the electrostatic forces within the lattice and so the salt does not dissolve.

The opposite holds true for larger cations, e.g. Barium, and so later hydroxides are more readily dissolved in water

Note: HSAB theory has not been discussed as it is not taught at A Level (tot he best of my knowledge)

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2 years ago

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