Preliminary 2012 Chemistry Marathon (1 Viewer)

[bleakarcher]

maybe you guys didnt see it,

define the mole

 

[darkchaos51]

In ionic bonds, electrons are directly transferred from one atom, which becomes a positive ion (cation), to another atom, which becomes a negative ion (anion).
In covalent bonds, electrons are shared between the atoms in the bond.
Ionic bonds are involve the bonding of the atoms of a metal and a non metal where as covalent bonds are the bonding of the atoms of two non-metals.

define the mole.

A mole of a substance is that quantity which contains as many elementary units (atoms, ions or molecules) as there are atoms in exactly 12 grams of the carbon-12 isotope
A mole of an element is the mass that in grams is numerically equal to the atomic weight. A mole of a compound is the mass that in grams is mumerically equal to the molecular weight


Define the emipirical fomula (1 Mark)

 

[theind1996]

In ionic bonds, electrons are directly transferred from one atom, which becomes a positive ion (cation), to another atom, which becomes a negative ion (anion).
In covalent bonds, electrons are shared between the atoms in the bond.
Ionic bonds are involve the bonding of the atoms of a metal and a non metal where as covalent bonds are the bonding of the atoms of two non-metals.

define the mole.

The mole is a method of measuring quantities of reacting substances. (WE HAVEN'T LEARNT THIS AT ALL YET, SO I'M BASING THIS ON MY KNOWLEDGE FROM THE TEXTBOOK).

BTW, I answered your question in LaTeX.

Describe the limitations of models used to represent bonding between substances. (3 marks)

 

[skillstriker]

- copper is used in electrical wiring in households due to its high electrical conductivity
- aluminium is used as a construction material because it is strong, durable, lightweight
- tungsten is used in the filament in light bulbs because it's light, ductile and conducts electricity

 

[skillstriker]

empirical formula is the formula of a compound that states the ratio of the atoms/ions present in it (used for ionic compounds e.g. NaCl - for every 1 Na there is 1 Cl ion in the lattice)

 

[theind1996]

A mole of a substance is that quantity which contains as many elementary units (atoms, ions or molecules) as there are atoms in exactly 12 grams of the carbon-12 isotope
A mole of an element is the mass that in grams is numerically equal to the atomic weight. A mole of a compound is the mass that in grams is mumerically equal to the molecular weight


Define the emipirical fomula (1 Mark)

An empirical formula is the repeating ratio (e.g 1:2) used to express the composition of different elements within an ionic compound.

Identify 1 compound from each of the 4 spheres on Earth - The Biosphere, Lithosphere, Hydrosphere and Atmosphere (2 marks)

 

[darkchaos51]

An empirical formula is the repeating ratio (e.g 1:2) used to express the composition of different elements within an ionic compound.

Identify 1 compound from each of the 4 spheres on Earth - The Biosphere, Lithosphere, Hydrosphere and Atmosphere (2 marks)

Biosphere - silicon?
Lithosphere - oxgen, clay
hydrosphere - magnesium
atmosphere - water

State the total number of atoms in one molecule of chloric acid HCIO3 (2 Marks)

 

[theind1996]

Biosphere - silicon?
Lithosphere - oxgen, clay
hydrosphere - magnesium
atmosphere - water

State the total number of atoms in one molecule of chloric acid HCIO3 (2 Marks)

MY MARKING: You'll get 0.5/2 for that. The only compound mentioned was water. A Biosphere compound can be a protein or a carbohydrate or a fat, a Lithosphere compound can be Quartz or even Calcite, and a Hydrosphere compound can be Sodium Chloride or Water or even Magnesium Chloride.


FOR YOUR QUESTION: 1 Hydrogen atom, 1 chlorine atom, 1 iodine atom and 3 oxygen atoms?

Describe the limitations of models used to represent bonding between substances. (3 marks)

 

[planino]

An empirical formula is the repeating ratio (e.g 1:2) used to express the composition of different elements within an ionic compound.

Identify 1 compound from each of the 4 spheres on Earth - The Biosphere, Lithosphere, Hydrosphere and Atmosphere (2 marks)

Biosphere - Glucose
Lithosphere - Silicon dioxide
Hydrosphere - Water
Atmosphere - Carbon dioxide

Identify 4 metallic properties and explain them by referring to the metallic bond (8 marks)

 

[planino]

MY MARKING:

Describe the limitations of models used to represent bonding between substances. (3 marks)

Metallic bond: (Assuming a picture of a metallic bond is given) this model does not demonstrate the delocalised nature of the electrons, as in reality the electrons would be moving around the lattice
Covalent molecular: (Assuming a picture of e.g. two oxygen atoms w/ electron shells and two pairs of electrons being shared) This model doesn't show the 'electron cloud' that would be evident in reality, instead representing the electrons as distinct small dots.
Covalent lattice: (Assuming a ball and stick model of a tetrahedral diamond lattice) This model represents the covalent bonds as sticks, when in reality this is not the case. It also represents atoms as distinct spheres, also not the case in real life.

 

[theind1996]

Biosphere - Glucose
Lithosphere - Silicon dioxide
Hydrosphere - Water
Atmosphere - Carbon dioxide

Identify 4 metallic properties and explain them by referring to the metallic bond (8 marks)

- Lustre of metals is due to the high reflectivity of the delocalised electrons.
- Strength and hardness is due to the strong electrostatic forces between the poisitive ions and delocalised electrons.
- Malleability and ductility is due to the delocalised electrons acting as a "glue" and preventing the substance from cracking when bent or twisted.
- High melting and boiling point is due to the strong electrostatic forces requiring high levels of energy to break apart.


And 8 marks, a bit excessive?

And now everyone's favourite question. List the different ages of stone and metals throughout history in chronological order, identifying the years during which each age existed. (2 marks)

 

[planino]

^Yeah just realised, should have made it 4 marks instead, half a mark for a correct property and half a mark for a correct explanation with reference to the metallic bond. 8/8 btw

 

[theind1996]

^Yeah just realised, should have made it 4 marks instead, half a mark for a correct property and half a mark for a correct explanation with reference to the metallic bond. 8/8 btw

BTW, WTF, I haven't done the tetrahedral stuff in class.

My 3 points for that were just (4th point just in case):

- Bond strength and length is not indicated
- The lines representing the bonds have no physical reality, so they cannot be understood in terms of real life.
- Some exceptions always exist for each type of substance.
- Some physical properties cannot be properly shown using the models e.g sonority.

 

[planino]

BTW, WTF, I haven't done the tetrahedral stuff in class.

My 3 points for that were just (4th point just in case):

- Bond strength and length is not indicated
- The lines representing the bonds have no physical reality, so they cannot be understood in terms of real life.
- Some exceptions always exist for each type of substance.
- Some physical properties cannot be properly shown using the models e.g sonority.

My teacher touched on it just a little, but most of it was just what I thought of it

 

[planino]

And now everyone's favourite question. List the different ages of stone and metals throughout history in chronological order, identifying the years during which each age existed. (2 marks)

Stone Age
Copper Age
Iron Age
Bronze Age

don'yt know the time periods

 

[bleakarcher]

lol omg, I hate history.

 

[Kimyia]

Stone Age
Copper Age
Iron Age
Bronze Age

don'yt know the time periods

Post new question?

 

[planino]

Post new question?

When separating the components of a NaCl_(aq) solution, what would be a more effective technique, evaporation to dryness or distillation? Explain. (2 marks)

 

[theind1996]

When separating the components of a NaCl_(aq) solution, what would be a more effective technique, evaporation to dryness or distillation? Explain. (2 marks)

A solution would mean that it is dissolved in water. Therefore, to get rid of the water, evaporation to dryness should be first used. Then the NaCl crystals can be distilled, due to the differences in their boiling points.

Explain 4 reasons why there are more metals available for people to use now than there were 200 years ago (6 marks).

 

[theind1996]

Stone Age
Copper Age
Iron Age
Bronze Age

don'yt know the time periods

0/2 marks. Stone----> Copper----> Bronze----> Iron----> Modern Age

Stone - 5000 BC - 3000 BC
Copper - 3000 BC - 2300 BC
Bronze - 2300 BC - 700 BC
Iron - 700 BC - 1 AD
Modern - 1 AD - present day


Identify the 3 types of covalent bonds (NO EXPLANATION REQUIRED) (3 Marks)