Production of Materials Practicals

Question 1

what should i always include in a chem prac?

Answer 1

• safety
• balanced equations with correct states
• tabular data which include all raw data
• discussing reliablity, accuracy and validity
• 1 sentence conclusion
• diagrams if necessary with a ruler
• in the method and materials state what had been used not what had been said in the textbook
• diagram should be 2D not 3D

Question 2

why did the alkene react but the alkane didnt?

Answer 2

because of the carbon double covalent bond present within the alkene. this region of the molecule is of high electron density and is very unstable, and readily attracts electronegative species such as halogens to that region which readily react in addition reactions. the alkane does not have a double bond, is more saturated and more stable

Question 3

what variables needed to be controlled when comparing the reactivity of alkanes and alkenes?

Answer 3

• size of test tube used
• amount of alkene/alkane and bromine water added in each test
• the time taken to agitate the rxn mixture in each test

Question 4

what safety was considered when comparing the reactivity of alkenes and alkanes?

Answer 4

• vapours from bromine water and oraganic liquids were toxic = fume cupboard used to peform experiments
• cant expell waste down sink, and so small amounts of chemicals used in order to ensure no massive build up of waste = used small test tubes
• organic fluids used were volatile and flammable, and as such were kept in stock bottles which were stoppered appropriately and stored well away from any sources of heat or flames.

Question 5

what happened during the fermentation of glucose?

Answer 5

there was bubbling and mass had been losed

Question 6

why did it bubble?

Answer 6

carbon dioxide was being produced

Question 7

why was the mass lower?

Answer 7

because carbon dioxide gas was free to leave the vessel through a rubber tube in limewater

Question 8

how did you know it was co2?

Answer 8

the limewater turned milky

Question 9

what where the conditions like for fermentation to occur?

Answer 9

• anaerobic
• glucose was in solution
• yeast present
• temp at 37 degrees

Question 10

why did the glucose breakdown?

Answer 10

the yeast could not use oxygen to respire and thus requred the energy in the glucose to survive

Question 11

what had to be controlled during the fermentation practical?

Answer 11

-electronic balance used was kept the same

Question 12

what affected the validity of the fermentation?

Answer 12

• stopper tube had been wet with limewater during final weighing, even though attempts were made to dry the tube, this would have definitely cause some innaccuracies
• some yeast may have been lost when the packet was opened

Question 13

what is the overall word equation for the fermentation of glucose?

Answer 13

glucose ——> carbon dioxde + ethanol

Question 14

whats ethanol?

Answer 14

ethanol is an alknanol with two carbon atoms and an hydroxyl group

Question 15

what occured during the heat of combustio of alkanols practical?

Answer 15

-three spirit burners had been weighed and used to heat a vessel containing 100ml to a 20 degree celcius increase.

Question 16

what had been performed prior to the alkanols experiment to support safety?

Answer 16

consulting a MSDS

Question 17

what materials had been used in the alknaols investigation?

Answer 17

-spirt burner x3 for methanol, ethanol and propan-1-ol
-matches
- bosshead and clamp
-retort stand
vessel
thermometer
electronic balance

Question 18

how had the validity of the alkanol experiment be put under jeopardy?

Answer 18

• without using the aluminium foil shielding, a considerable amount of heat had been lossed to the surroundings
• the spirt burner had not been placed close enough to the vessel, leading to more heat loss
• blowing out the wick on the spirit burner would have led to a loss of contents and hence the final weight would have been inaccurately measured

Question 19

what things could have been done to better the accuracy of the alkanol experiment?

Answer 19

using a digital thermometer over a standard one

Question 20

under what conditions is a galvanic cell produced?

Answer 20

• must have an anode and cathode, each with their respective electrolyte solution and seperated
• a conducting pathway must be present which can fascillitate the flow of electrons
• a salt bridge must be present

Question 21

whats the purpose of a salt bridge in a galvanic cell?

Answer 21

to maintain electric neutrality by allowing ions to migrate into each half cell. if it was not present a build of charge would occur resulting in the formation of a potential difference directly opposite to the one provided by the reaction

Question 22

whats the procedure for comparing reactivities between alkanes and alkenes experiment?

Answer 22

1. Pour 2mL of bromine water each into two small test tubes
2. Using a dropper bottle, place a few drops of cyclohexane into one of the test tubes, noting its effect.
   shake gently with thumb over the top of the tube
3. Repeat with a dropper bottle of cyclohexene. shake for same amount of time

ALKANE REACTION
1. With solutions that alkanes have
been added to, place them near a bright window and observe the effect over time.

Question 23

what materials where needed during the heat fo combustion of alkanols experiment?

Answer 23

• Copper can
• Retort stand and ring clamp
• Glass rod
• 3 spirit burners filled with methanol, ethanol and 1-propanol
• 100mL measuring cylinder
• Thermometer
• Balance

Question 24

whats the procedure for the heat of combustion of alkanols experiment?

Answer 24

1. Light the first spirit burner.
2. Adjust the height of the can so that the tip of the flame just touches the can.
3. Replace the cap on the spirit burner to extinguish the flame. Do not blow out the flame in
   order to extinguish it.
4. Weigh the burner with its liquid contents and record.
5. Add 200 mL of cold water to the copper can using a measuring cylinder. Place the thermometer
   in the water and record its initial temperature.
6. Light the wick and stir the water gently with the stirring rod to ensure uniform heat.
7. Monitor the temperature and extinguish the flame by replacing the cap when the temperature
   has risen by 10◦C. The thermometer should be kept halfway in the water.
8. Reweigh the burner.
9. Remove soot from the bottom of the can and replace the water in the copper can before testing
   the next alcohol.

Question 25

whats the procedure for the fermentation of glucose prac?

Answer 25

1. Place warm water, glucose, and yeast in a flask and stopper the top with either a cork, or
   cotton wool.
2. Weigh the flask and its contents and record the results.
3. Place the flask in a warm area such as the window sill, and allow to sit. Ideally, set this
   experiment up in the morning, and take measurements regularly (In hourly intervals) over four
   hours, recording the weight at each observation.
4. Reweigh the flask and its contents, and record the results along with the difference in weight.