1.What is true about sample preparation for NMR?
a. Samples for 13C NMR should be concentrated, and for 1H NMR should
d for 1H NMR should be dilute.
b. Samples for 13C NMR should be dilute, and for 1H NMR should be concentrated.
c. Samples for 13C NMR and 1H NMR should both be concentrated.
d. Samples for 13C NMR and 1H NMR should both be dilute.
3. What is the proper way to dispose of an NMR sample that had deuterated chloroform (CDCl3) as the solvent?
a. Placement down the drain.
b. Placement in the non-halogenated organic waste container.
c. Placement in the halogenated organic waste container.
d. Placement in the oven for evaporation.
4. Which feature of a 1H NMR spectrum can provide information about the number of inequivalent kinds of hydrogen in the structure?
a. chemical shift
d. None of the above.
5. Which feature of a 1H NMR spectrum can provide information about the number of neighboring hydrogens that a given hydrogen in the structure has?
a. chemical shift
d. None of the above.
6. Which feature of a 1H NMR spectrum can provide information about the number of hydrogens responsible for each signal?
a. chemical shift
d. None of the above
7. An unknown has a specific rotation (i.e., a rotation unequal to 0°) as measured with a polarimeter. What is true about the unknown?
a. The structure contains at least one chirality center.
b. The structure contains no chirality centers.
c. The structure has a plane of symmetry.
d. None of the above.
8. True or False: Conjugation increases the wavenumber of absorption in the IR spectrum.
9. What group classification does a solid unknown most likely belong to if its melting point is greater than 250 °C?
a. carboxylic acid
b. amino acid
d. acid derivative
10. True or False: If a liquid unknown freezes when placed in an ice-water bath for 10 minutes, the melting point of the unknown is between 0 °C and 25 °C.
2.a) Carbon tetrachloride is an organic compound with the chemical formula CCl4. It is a
colorless liquid with a “sweet” smell.
quid with a “sweet” smell.
i. Using the ground state electron configuration and excited state electron
configuration explain the hybridization of the central Carbon (C) atom. (7 Marks)
ii. Identify the orbitals that overlap to form the C-Cl bond. Draw a diagram to show
the orbital overlap. (3 Marks)
iii. What is the bond angle of CCl4? (1 Mark)
b) Consider a Fluorine atom (F) and a Fluorine anion (F-). Which of these two species would
you expect to have a larger radius? Explain your answer. (5 Marks)
c) Explain why the first ionization energy of Aluminum (Al) is less than that of Magnesium
(Mg). (4 Marks)
d) Assume the atom Oxygen(O) can form both cationic(O+) and anionic(O-) species. Place
the following species in order of increasing first ionization energy, starting with the lowest.
O+, O, O-
a) Sea water contains roughly 28.0 g of NaCl per liter. (NaCl molar mass = 58.44 gmol-1).
i. Calculate the number of moles of NaCl in a liter of sea water. (2 Marks)
ii. Calculate the molarity of NaCl in sea water. (4 Marks)
iii. Calculate the mass by volume percent (W/V) of NaCl in sea water. (4 Marks)
4.AP Chem AB FRQ
A sample consisting of 50. mL of 0.400 M solution of the acid, HClO4, is titrated
titrated with a 0.200 M solution of the base, LiOH.
Write the balanced chemical reaction for neutralization reaction:
HClO4 (aq) + LiOH (aq) → LiClO4 (aq) + H2O (l)
Write the NET ionic equation for the neutralization reaction.
OH⁻ (aq) + H⁺ (aq) → H2O (l)
Compute the pH of the titration solution. Show your work
i) before any of the base is added
ii) after 25. mL of base is added
iii) after 50. mL of base is added
A student performs the titration with the same chemicals but with smaller volumes of each chemical . Which of the following titration curves could represent the titration. Explain
A because this entails a strong acid and a strong base.
A student performs a titration of an unknown acid with a strong base and gets the following titration curve:
a) The student consults the list of pKa of acids shown below. If the acid is listed in the table below, which is the most likely identity of the unknown acid? Explain.
7.2 x 10-4
1.8 x 10-5
4.3 x 10-7
2.0 x 10-9
The unknown acid is HBrO because the calculated Ka is in between 50^-4 and 50^-6 and 2.0 x 10^-9 lies in between them.
b) What is the initial molarity of the acid?
10^-3 = 0.001M
a) Describe the components and the composition of an effective buffer solution. Explain how the components of the buffer allow the buffer to maintain its pH.
An effective buffer solution has a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer solution is most effective when the ratio of its component concentrations is close to 1, also when the pH is equal to the pka of the acid.; The components of the buffer allow the buffer to maintain its pH because buffers can absorb excess H+ions or OH– ions.
An employer is interviewing four applicants for a job as a laboratory technician and asks each how to prepare a buffer solution with a pH of 5.0. The following constants may be helpful: hydrazoic acid, pKa = 4.74 Boric acid, pKa = 9.23
Archita A. says she would mix equal molar solutions of hydrazoic (HN3) and sodium azide (NaN3) solutions.
Bradley B. says she would mix equimolar Boric acid (H3BO3) and HCl solutions.
Carlos C. says he would mix equimolar Boric Acid (H3BO3) and sodium dihydrogen borate (NaH2BO3) solutions.
Delia D. says he would mix equimolar hydrazoic Acid (HN3) and NaOH solutions.
b) Which of these applicants has given an appropriate procedure? Explain your answer
Delia because she is using Sodium hydroxide which results in a pH of 5. NaOH is a strong base and in order to have an effective buffer a weak acid must be incorporated which is the HN3.
c) Explain what is wrong with the erroneous procedures.
The rest all incorporate a strong acid and a strong base or a weak acid and a weak base which don’ result in an effective buffer.
d) The applicants have access to the 1 Liter volumes of each of the solutions listed above. They have access to graduated cylinders. In order to make 1.0 Liter of the correct 5.0 buffer solution, what volumes of the two chemicals must be mixed?
5.(a) A 20.0 L container at 303 K holds a mixture of two gases with a total pressure of 5.00
here are 2.00 mol of Gas A in the mixture, how many moles of Gas B are present? (R = 0.0821 L • atm/(K • mol))
(b) The gas in a 250. mL piston experiences a change in pressure from 1.00 atm to 2.80 atm. What is the new volume (in mL) assuming the moles of gas and temperature are held constant?
(c) Small quantities of Oxygen can be produced by the decomposition of mercury(II) oxide as shown below. Typically, the oxygen gas is bubbled through water for collection and becomes saturated with water vapor. Atomic weight of HgO = 216.6 amu, Atomic weight of Oxygen = 32.00 amu)
2 HgO(s) → 2 Hg(ℓ) + O₂(g)
(i) Assuming that 3.05 grams of HgO was used in this reaction, determine the number of moles of oxygen gas formed.(According to the above chemical equation)
(ii) Assuming 310. 0 mL of Oxygen gas was collected at at 29°C, calculate the pressure of the Oxygen gas that was collected. (R = 0.0821 L • atm/(K • mol)
(iii) If the vapor pressure of water at this temperature equals to 0.042 atm, calculate the pressure reading of this experiment.
12.1) A hypothetical element exists as two isotopes: I = 42.00 amu and II = 49.00 amu. If the percent
bundance of isotope I is (1.94x10^1)%, what would be the calculated atomic mass (in amu)?
2) A hypothetical element exists as two isotopes: I = 78.00 amu and II = 84.00 amu. If the atomic mass of this element is found to be 80.33 amu, which isotope must be more abundant?
3) If the hypothetical polyatomic ion ThOM2- is called "thomite", what would be the formula and name of the acid formed by this ion?
4) How many atoms of hydrogen are there in a sample of (4.00x10^2) grams of NH3(g)?
5) How many O (oxygen) atoms are there in (6.40x10^2) grams of H3PO4?
6) How many moles of fluorine atoms are there in (5.80x10^2) grams of SF4?
7) When 3.50 g of titanium (Ti) reacts with oxygen, the resulting oxide compound weighs 5.84 g. What is the empirical formula of this oxide?
8) How many moles of molecules are there in (6.70x10^2) grams of CH4?
9) A chemical is found to be 80.0% C and the rest is H. If the molar mass of this chemical is known to be 90.2 g/mol, what is the molecular formula?