Title: CHE2FCA Pre-lab quizzes

CHE2FCA Pre-lab quizzes

Q: At the point in the titration where [H_3PO_4] = [H_2PO_4^– ], the slope of the titration curve ...
- ... is at a minimum.
- ... at a maximum.
- ... exactly 1.
- ... mathematically undefined.
A: ... is at a minimum.

Q: Which solution has the greater nominal ionic strength: 5 mol/L NaOH or 5 mol/L NH_4OH?
- Both have the same ionic strength.
- sodium hydroxide
- ammonium hydroxide
A: Both have the same ionic strength.

Q: Which of the following hazards apply to concentrated ammonia solution (approx. 30 % in water)?
- toxic
- flammable
- carcinogenic (i.e, cancer-causing)
- corrosive
A: toxic; corrosive

Q: A solution containing 1 mmol/L each of compounds 1 and 2 is analysed by UV/vis spectroscopy at the wavelength of 510 nm.  The absorbances of the individual compounds at 1 mmol/L are A1_ and_ A2.  What is the abAsorbance of the mixture?
- A1 x A2
- A1 + A2
- A1 - A2
- A1 or A2, whichever is greater
A: A1 + A2

Q: In the test for chloride with silver nitrate in this experiment, the initially formed AgCl precipitate is first immersed in an ammonia solution (step 1) before nitric acid is added (step 2). What do you expect to observe in these steps?
- Step 1: The silver chloride precipitate disappears. Step 2: The precipitate forms again.
- Step 1: The silver chloride precipitate disappears. Step 2: Nothing happens.
- Step 1: Nothing happens. Step 2: The silver chloride precipitate disappears.
- Step 1: The silver chloride precipitate turns black. Step 2: The black precipitate disappears.
- Step 1: Nothing happens. Step 2: Nothing happens
A: Step 1: The silver chloride precipitate disappears. Step 2: The precipitate forms again.

Q: The persulfate ion has the structure shown below.

[Image: Structure of the persulfate ion]

What is the formal oxidation number of the oxygen atoms a, b and c?
- a) -2, b) -2, c) -1
- a) -2, b) -2, c) -2
- a) -1, b) -2, c) -1
- a) -1, b) -2, c) -2
- a) -3, b) -2, c) -1
A: a) -2, b) -2, c) -1

Q: What is the oxidation number of chromium in (a) potassium dichromate and (b) the bis(oxalato)chromium complex that will be synthesised in this practical?
- (a) +6, (b) +3
- (a) +6, (b) +6
- (a) +3, (b) +3
- (a) +3, (b) +6
- (a) +6, (b) +4
A: (a) +6, (b) +3

Q: A solution containing 1 mmol/L each of two compounds (1 and 2) is analysed by UV/vis spectroscopy at the wavelength of 510 nm.  The absorbances of the individual compounds at 1 mmol/L are A1 andA2.  What is the absorbance of the mixture?
- A1 x A2
- A1 + A2
- A1 - A2
- A1 or A2, whichever is greater
A: A1 + A2

Q: A thin-layer chromatography of benzoic acid (see structure below) on a silica TLC plate and with ethyl acetate as eluent gives an R_f value of 0.5. What would you need to add to the solvent mixture to lower the R_f value?

[Image]
- a base
- an acid
- methanol
A: a base

Q: At the point in the titration where [H_3PO_4] = [H_2PO_4^– ] (compare the titration plot in the instruction), the slope of the titration curve ...
- ... is at a minimum.
- ... at a maximum.
- ... exactly 1.
- ... mathematically undefined.
A: ... is at a minimum.

Q: A stock solution of ammonium chloride is prepared by dissolving 5.3503 g of ammonium chloride (M=53.49 g/mol) in 100 mL of water. What is the resulting ammonium concentration (in mol L^-1)?
A: 1 (± 0.005)

Q: Thomas and Elena each calibrated a certified 100 mL volumetric flask by filling it with water to the mark and weighing it. They repeated the measurement five times and calculated the average volume measured and the standard deviation of their measurement. The results are:
Thomas 100.9 mL +/- 0.7 mL
Elena 99.8 mL +/- 1.3 mL

Which measurement is the most accurate and which one is the most precise?
- Thomas is most precise, Elena most accurate.
- Thomas is most precise and most accurate.
- Elena is most precise and most accurate.
- Thomas is most accurate, Elena most precise.
A: Thomas is most precise, Elena most accurate.

Q: In the AnSk2 exercise, what is the dilution factor required to dilute the Allura Red stock solution (0.010 mol L^-1) to 10^-5 mol L^-1?
A: 1000

Q: In the AnSk2 exercise, your task is to prepare dilutions of the Allura Red AC stock solutions (concentration: 0.010 mol L^-1) that fall within the target range (between 5·10^-5 mol L^-1 and 2·10^-6 mol L^-1), using the available glassware (5 mL volumetric pipettes, volumetric flasks: 3 x 50 mL, 3 x 25 mL)

If 5 mL of the stock solution are pipetted into a 50 mL volumetric flask, which is then filled to the mark, what is the resulting concentration of Allura Red (in mol L^-1)?
A: 0.001
Feedback ("0.001"): What is the ratio of the volume before dilution to volume after dilution? Multiply with the concentration of the stock solution.
  Hint: What is the ratio of the volume before dilution to volume after dilution? Multiply with the concentration of the stock solution.

Q: How will addition of sodium hydroxide to phosphoric acid affect the temperature of the acid solution?
- The temperature will increase.
- The temperature will not be affected.
- The temperature will decrease.
A: The temperature will increase.

Q: What is the pH of a 0.1 mol L^-1 solution of sodium hydroxide (assume complete dissociation of NaOH)?
A: 13 (± 0.05)

Q: One cubic centimetre (cm^3) equals how many millilitres (mL)?
- 1
- 1.043
- 0.1
- 100
A: 1

Q: Disposable nitrile gloves are generally more resistant to polar solvents than to non-polar ones. How would you classify toluene?
- Toluene is comparatively polar (similar to methanol).
- Toluene is of medium polarity (similar to acetone).
- Toluene is comparatively non-polar (similar to hexane).
A: Toluene is comparatively non-polar (similar to hexane).

Q: What is the boiling point of toluene?
A: 111 (± 3)

Q: What are the roles of potassium permanganate and hydrogen peroxide in the titration reaction (multiple correct answers)?
- Permanganate acts as an oxidising agent.
- Permanganate is being oxidised.
- Permanganate is being reduced.
- Hydrogen peroxide acts as an oxidising agent.
- Hydrogen peroxide is being oxidised.
- Hydrogen peroxide is being reduced.
A: Permanganate acts as an oxidising agent.; Permanganate is being reduced.; Hydrogen peroxide is being oxidised.

Q: What are the bubbles that form when pipetting hydrogen peroxide solutions?
- Oxygen
- Water vapour
- Hydrogen
- Carbon dioxide
A: Oxygen

Q: How does addition of the iron chloride catalyst change the parameters of the Arrhenius equation?
- The rate constant k increases because the activation energy E decreases
- The rate constant k increases because the activation energy E increases
- The rate constant k increases because the the reaction temperature T decreases
- The rate constant k does not change.
A: The rate constant k increases because the activation energy E decreases

Q: Which type of phosphates can be quantified without digestive sample treatment?
- orthophosphates
- condensed phosphates
- organic phosphates
A: orthophosphates

Q: Which of the following half-reactions of persulfate is correct (under the conditions in experiment WQ11)?
- (S2O8)2- + 2e- --> 2 (SO4)2-
- (S2O8)2- + 2H+ --> (S2O7)2- + H2O
- (S2O8)2- + 2e- --> 2 (SO3)2- + O2
A: (S2O8)2- + 2e- --> 2 (SO4)2-

Q: The solution used to spike the shell sample in the standard addition method contains which acid?
- sulfuric acid
- nitric acid
- hydrochloric acid
A: sulfuric acid

Q: What is the electron configuration of cadmium?
- [Kr] 4d10 5s2
- [Ar] 3d10 4s2
- [Kr] 5s2
A: [Kr] 4d10 5s2

Q: What is the approximate temperature of the flame in an AAS instrument?
- 400-500 K
- 900-1150 K
- 2000-3000 K
- 3600-4000 K
A: 2000-3000 K

Q: What is the boiling point of phenol?
A: 182 (± 3)

Q: The pK_a of phenol is 10.0.  At pH 7.9, the majority of the phenol molecules are:
- protonated
- deprotonated
- positively charged
- negatively charged
A: protonated

Q: Bromocresol green has a pKa of 4.7.  What functional group(s) is responsible for its acidity?
- sulfonic acid
- aromatic bromo substituents
- phenolic hydroxyl groups
- ammonium groups
A: phenolic hydroxyl groups

Q: Which of the following hazards apply to boric acid?
- toxic
- teratogenic (i.e., harmful to the foetus)
- carcinogenic (i.e, cancer-causing)
- flammable
A: teratogenic (i.e., harmful to the foetus)

Q: The absorption of visible light is primarily due to which process?
- The excitation of molecular rotations
- The excitation of molecular vibrations
- The excitation of electrons into higher energy levels
- The expulsion of electrons from atoms
A: The excitation of electrons into higher energy levels

Q: How many protons, neutrons and electrons does a hydrogen atom consist of?
- one proton, one neutron, one electron
- one proton, no neutrons, one electron
- two protons, no neutrons, two electrons
- no proton, one neutron, one electron
A: one proton, no neutrons, one electron

Q: Light of which colour has the highest energy?
- yellow
- red
- green
A: green

Q: What happens to the pH when carbon dioxide dissolves in water?
- Carbon dioxide does not dissolve in water.
- The pH increases.
- The pH decreases.
- The pH remains unchanged.
A: The pH decreases.

Q: The catalytic converter in modern cars converts carbon monoxide, nitrogen oxides (NO_x) and hydrocarbons to what?
- carbon dioxide, oxygen and nitrogen
- carbon, ammonia and water
- carbon dioxide, water and nitrate
- carbon dioxide, nitrogen and water
A: carbon dioxide, nitrogen and water

Q: Which of the following statements about carbon monoxide are true?
- Carbon monoxide is poisonous.
- Carbon monoxide is denser than air.
- Carbon monoxide is flammable.
- Carbon monoxide smells of burnt coal. (CO is an odourless gas.)
A: Carbon monoxide is poisonous.; Carbon monoxide is flammable.

Q: Which of the following statements about carbon dioxide are true?
- Carbon dioxide is poisonous.
- Carbon dioxide is denser than air.
- Carbon dioxide is flammable.
- Carbon dioxide smells of burnt coal.
A: Carbon dioxide is denser than air.

Q: Match the hazards below with the four chemicals in the menu.
- Flammable. Causes severe burns. | acetic acid
- Extremely flammable. May form explosive peroxides. Vapours may cause drowsiness and dizziness. | diethyl ether
- Highly flammable. Toxic: danger of very serious irreversible effects through inhalation, in contact with skin and if swallowed. | methanol
- Highly flammable. Possible risk of harm to the unborn child. Harmful: danger of serious damage to health by prolonged exposure through inhalation. Vapours may cause drowsiness and dizziness. | toluene

Q: What is the oxidation state of tin in stannous chloride?
- +2
- +3
- +4
- +1
A: +2