general exam tips

Question 1

name the property of an element or compound that can enable it to react in two ways
or reacts with acids and bases

Answer 1

Amphoteric

Question 2

when can u distill a product from a reaction

Answer 2

-if it has a lower boiling point to the reactants

Question 3

why are some organic reactions heated under reflux

Answer 3

-can apply constant heat to a mixture without losing any of the liquid to evaporation - way of getting reaction to go to completion

-many organic reactions need to be heated as this supplies the Ea to break bonds and allow the reaction to occur

using a condsenser will allow this to happen whilst preventing the reagants from leaving the reaction vessel

Question 4

what do anti-bumping granules prevent

Answer 4

-bumping - obvs
-produce many bubbles instead of large ones - prevents uneven boiling

Question 5

what are some of the potential errors when using a gas syringe

Answer 5

-gas escapes before bung is inserted
-syringe sticks so cant move
-some gases (CO2 and SO2 etc) are soluble in water so the true amount of gas is not measured
-temp measured is less than temp in the syringe
-mass of liquid measured that is transferred to the syringe is less than actual mass

Question 6

what to do if reaction is slow and need to get accurate results

Answer 6

-take readings at regular intervals + extrapolate the temp line back to when reactants were added together becasue if reaction is slow the temp rise is hard to obtain as reaction is cooling quickly
-take readings for few mins before adding second reagant

Question 7

enthalpy practicle errors

Answer 7

• energy transfer to/from surroundings (usually loss)
• approximation in specific heat capacity of solution
• the method assumes all solutions have the heat capacity of water
• density of solution is taken to be the same as water
• some of the water could have evaporated
• reaction or dissolving may be incomplete or slow.

Question 8

how is bioethanol produced and what are the environmental impacts

Answer 8

-photosynthesis - natural process in plants that takes CO2 from the air
-6CO2 + 6H2O -> C6H12O6 + 6O2

-fermentation - the process used to make bioethanol that releases some CO2
C6H12O6 -> 2C2H5OH + 2CO2

-combustion is the process where bioethanol is burned and releases CO2
2C2H5OH + 6O2 -> 6H2O + 4CO2

-deforestation is used to provide raw materials and land is sacrificed that could be used for food
-there is a loss of biodiversity and habitat when trees are cut down and land used to build factories
-6CO2 in and 6CO2 out but it isnt actually carbon neutral as the fuel is used in production, distrubution etc

Question 9

what to remember when finishing a q=mcdeltaT question

Answer 9

final answer needs to be -ve - so just whack onto what ever answer u have - if combustion as its exothermic