Chemistry Task 3 Flashcards
Summarise all the info needed for Chemistry Task 3
What is step 1 through to 4 of the titration experiment?
- The equipment was thoroughly cleaned, until no droplets were left on the inside of the equipment.
- The stopcock was closed and the burette overfilled with titrant. It was then clamped to a retort stand.
- The stopcock was then opened, and titrant allowed to flow out, until the burette’s tip was full, and the titrant was below the zero mark.
- The burette was tapped to remove any bubbles.
How was the equipment cleaned?
The burette was rinsed three times with a small volume of the titrant.
The pipettes and conical flask used were all thoroughly cleaned, and free from any residual substances.
What are steps 5 through to 8 of the titration experiment?
- Take the reading on the burette, taking care to avoid parallax error, and reading the level of the meniscus.
- A pipette was used to measure an aliquot of analyte.
- Position the conical flask containing a measured amount of analyte below the tip of the burette.
- An appropriate pH indicator was added.
What is an aliquot?
sample of a solution with an accurately known volume
What are steps 9 through to 13 of the titration experiment?
- The stopcock was repeatedly opened and closed with one hand, allowing the titrant to slowly drain into the conical flask. With the other hand, continuously swirl around the conical flask.
- Titrant was allowed to flow quickly at first, then in single drops, when there were signs that it was nearing the end point, i.e. the colour change was more significant and remains for longer.
- The stopcock is opened and a drop allowed to form on the tip of the burette. The drop is wiped on the edge of the conical flask and allowed to flow in.
- Once the end point is reached, the reading on the burette was taken. The endpoint is reached when the colour changes, and has remained changed for at least 10 seconds.
- The pH of the analyte was calculated from the measurements taken.
What is a standard solution?
a solution of specific volume containing a precisely known amount of solute.
What is a secondary standard solution?
solution of known concentration determined by titration with a primary standard.
What are the first five steps of the preparation of 100mL of a primary standard solution?
- Rinse all beakers, volumetric flasks and spatulas to be used.
- Calculate the required amount of salt to prepare the standard.
- Place a sheet of paper on electronic scales, and zero the scales.
- Using a spatula, weigh the required amount of salt onto the sheet of paper.
- The salt was transferred into a beaker.
What are the last 4 steps of the preparation of 100mL of a primary standard solution?
- Distilled water was added to the beaker, and stirred with a stirring rod to dissolve the salt. Care was taken to not exceed 100mL.
- The solution was transferred into a 100mL volumetric flask, with the beaker washed out with distilled water into the volumetric flask.
- The volumetric flask was topped up with distilled water until the meniscus of the solution was at exactly 100mL.
- The flask was inverted 10-20 times in order to fully dissolve any salt.
Typically, primary standards are made from a salt which is: (4)
- anhydrous
- stable
- AR grade; extremely pure
- high formula mass, as this minimises the percentage error during the weighing.`
What is a titration curve?
A titration curve is a graphical representation of the changing pH of the solution in the conical flask during a titration. For different combinations of acids/bases, titration curves have different characteristics.
What does the titration curve for a strong base and weak acid look like?
Ph of the y axis, volume of titrant on x-axis. A sort of sideways S, beginning at fourteen, and plateauing at around 7.
What does the titration curve for a strong base and strong acid look like?
Ph of the y axis, volume of titrant on x-axis. A sort of sideways S, beginning at fourteen and plateauing at around 1.
What does the titration curve for a strong acid and weak base look like?
Ph of the y axis, volume of titrant on x-axis. A sort of sideways S, beginning at 12, dropping significantly at 7, beginning to plateau at 3, and actually plateauing at 1.
What does the titration curve for a weak acid and weak base look like?
Ph of the y axis, volume of titrant on x-axis. A sort of sideways S, beginning at 12 and going down pretty steadily until 7, where there is a slightly faster drop and plateauing at around 5.
What is the equivalence point?
When equal amounts of H- and OH- ions have been added i.e. a complete neutralisation has occurred.
When does a complete neutralisation occur?
At the equivalence point.
What is the pH of an equivalence point?
Not necessarily 7, depends on the salt formed from the neutralisation.
What is the endpoint?
When the titration is finished, and a colour change has been observed, lasting for more than 10 seconds.
How is the pH indicator chosen?
Chosen such that the endpoint s close enough to the equivalence point, i.e. lies on the point of inflexion.
What is the point of inflexion?
Sharp fall (or rise) on the curve near equivalence point
With what formula is the pH calculated
-log(10)[H+]
Where,
[H+] - concentration of hydrogen ions (mol L–1)
What is the aim of the reflux experiment?
To prepare an ester by reflux.
Outline steps 1-4 of the reflux method?
- 10mL each of an alkanoic acid and alkanol and 5 drops of concentrated sulfuric acid were measured into a pear bottom flask. Boiling chips were also placed in.
- A hot plate was used to set up a water bath, and keep it at a temperature near boiling.
- The entire setup was placed into the water bath. This was left for about an hour, to allow the reaction to progress.
- The mixture in the flask was taken out of the water bath and allowed to cool to room temperature.
Outline steps 5-8 of the reflux method?
- A sodium bicarbonate paste was prepared.
- The mixture was placed into a separating funnel, and the bicarbonate paste was added, along with water.
- A cork was placed over the top, and the funnel inverted to mix it in, neutralising the sulfuric acid. The cork was periodically removed to allow the produced carbon dioxide to escape.
- The bottom layer of water was removed using the separating funnel, to leave the top layer of ester.
Discuss the safety of the reflux method
A hot plate was used instead of a naked flame, as the products and reactants are volatile.
Boiling chips were placed inside the pear bottom flask, to stop it from boiling over.
The top was kept open so that pressure did not build up.
The cork was always kept on to prevent volatile substances from evaporating.
Water was added to absorb the heat produced by the neutralisation.
What is the Haber process?
A process for producing ammonia, developed during WW1 by Fritz Haber.
How did the Haber process work?
Ammonia was used as a starting material for the synthesis of nitric acid.
Ammonia could be reacted with nitric acid to form the fertiliser ammonium nitrate.
Nitric acid was used as a raw material for the synthesis of explosives.
What were nitrates originally used for?
Manufacture these important chemicals (nitrogen compounds)
What changed, resulting in other avenues for the production of nitrogen compounds
being explored?
Increased demands for nitrates, coupled with the supplies of naturally occurring saltpetre (NaNO3) being cut off
Industrial synthesis of ammonia through the Haber process had a _________ impact on the war
Profound
How did the synthesis of ammonia have a profound impact on the war?
Germany’s dwindling pool of naturally occurring nitrates was of no consequence, with the Haber process supplying all the ammonia required for the war effort. Without this process, Germany would have quickly lost the war due their inability to produce food on a large scale and their lack of ammunition/explosives. Helped sustain the war effort, prolonging the conflict
The Haber process also had a great global impact as it
Diminished the threat of worldwide famine, by producing a fertiliser
Outline the method for testing for the presence of certain ions. (4)
- Hold a platinum wire to a Bunsen flame. If the flame does not change colour, the wire is clean and ready to be used. If the flame changes, dip the wire into hydrochloric acid, and then hold the wire to the Bunsen flame. Repeat until the flame doesn’t change colour.
- Concentrate the sample by heating it, causing a portion of the water to evaporate.
- In a fume cupboard, dip the wire into the sample solution, and then hold the wire to the Bunsen flame.
- Alternatively, use a spray bottle to spray the solution into the flame.
When heated, electrons in a metal ion ______
Gain energy and move into higher energy states
Metal ions gaining energy and moving into higher energy states is (a) so (b).
(a) energetically unstable
(b) so the electrons fall back quickly into a lower energy level
In what form is energy emitted when the metal ions move into a higher energy state then lower energy level?
Photon
