Archive for July 2019

In an open end manometer, one end of a U-tube filled with mercury is attached to a gas-filled container and the other end is open to the atmosphere. If the gas pressure in the container is less than atmospheric pressure

In an open end manometer, one end of a U-tube filled with mercury is attached to a gas-filled container and the other end is open to the atmosphere. If the gas pressure in the container is less than atmospheric pressure



Answer: the Hg level will be higher in the arm connected to the container

In the following reaction, Cl2 is

In the following reaction, Cl2 is



Answer: 2 Rb(s) + Cl2(g) → 2 RbCl(s)


the oxidizing agent

A student dissolved 3.00 g of Ca(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the solution then diluted it with water to give 275 mL of a final solution. How many grams of NO3- ion are there in the final solution?

A student dissolved 3.00 g of Ca(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the solution then diluted it with water to give 275 mL of a final solution. How many grams of NO3- ion are there in the final solution?



Answer: 0.0906g

Which statement about diluted solutions is false? When a solution is diluted

Which statement about diluted solutions is false? When a solution is diluted



A) the concentration of the solution decreases.
B) the molarity of the solution decreases.
C) the number of moles of solute remains unchanged.
D) the number of moles of solvent remains unchanged


Answer: D) the number of moles of solvent remains unchanged

Which of the following statements is false?

Which of the following statements is false?




(a) If a molecule contains one polar bond then the molecule must be polar.
(b) Nitrogen contributes five electrons to the Lewis dot structure of ammonia
(c) The molecular shape of the water is bent.
(d) The bond angle in NF3 is smaller than that in NH3.
(e) If a molecule has no dipole moment the molecule must be non-polar.


Answer: If a molecule contains one polar bond then the molecule must be polar.

One of the following questions is false, the rest are true. Please identify the false statement in the enumeration below.

One of the following questions is false, the rest are true. Please identify the false statement in the enumeration below.



(a) A pi bond restricts rotation about the sigma bond axis.
(b) Hybridization of atomic orbitals is required to explain molecular geometry.
(c) Bonds between atomic s orbitals are always sigma bonds.
(d) A double bond consists of a sigma bond and a pi bond.
(e) A triple bond consists of two sigma bonds and a pi bond.


Answer: A triple bond consists of two sigma bonds and a pi bond.

Which of the following is incorrect:

Which of the following is incorrect:



(a) sigma bonds can result from the overlap of two p-orbitals
(b) pi bonds are stronger than sigma bonds.
(c) pi bonds can result from the overlap of two p-orbitals.
(d) a double bond is less than twice as strong as a single bond.
(e) double bonds are stronger than single bonds.


Answer: pi bonds are stronger than sigma bonds.

Consider the following molecule: CH3−CO−CH−−CH2. Which of the following statements is an outright lie? (Hint: it will help if you draw its Lewis structure, first).

Consider the following molecule: CH3−CO−CH−−CH2. Which of the following statements is an outright lie? (Hint: it will help if you draw its Lewis structure, first).



(a) There are some H-C-H bond angles around 109 degrees.
(b) The central carbon atoms are both sp2 hybridized.
(c) The molecule contains 28 valence electrons.
(d) There are 10 sigma and 2 pi bonds.
(e) Oxygen is sp3 hybridized.


Answer: oxygen is sp3 hybridized

What is the bond order (BO) in He2, He2+? Which one is stable?

What is the bond order (BO) in He2, He2+? Which one is stable?



(a) He2: BO = 0, stable, He2+: BO = -1, unstable.
(b) He2: BO = 0, unstable, He2+: BO = 1, unstable.
(c) He2: BO = 0, unstable, He2+: BO = 1, stable.
(d) He2: BO = 2, stable, He2+: BO = 1, unstable.
(e) none of the above.


Answer: none of the above

Use the provided molecular orbital diagram to calculate the bond order and the number of unpaired electrons for the molecular ion N2+.

Use the provided molecular orbital diagram to calculate the bond order and the number of unpaired electrons for the molecular ion N2+.



(a) 0 unpaired electrons, bond order = 3
(b) 1 unpaired electron, bond order = 2
(c) 2 unpaired electrons, bond order = 1.5
(d) 1 unpaired electron, bond order = 2.5
(e) 3 unpaired electrons, bond order = 2.


Answer: 1 unpaired electron, bond order = 2.5

What does a bond order of zero represent?

What does a bond order of zero represent?



(a) single bond.
(b) no bond exists.
(c) double bond.
(d) triple bond


Answer: no bond order

What is the molecular geometry of SbCl3?

What is the molecular geometry of SbCl3?



(a) trigonal pyramidal
(b) tetrahedral
(c) trigonal planar
(d) T-shaped


Answer: trigonal pyramid

One of the following questions is true; the rest are false. Please identify the true statement in the enumeration below.

One of the following questions is true; the rest are false. Please identify the true statement in the enumeration below.



(a) Lone pairs are an exception to the rules for Lewis dot structures.
(b) A double bond consists of two sigma bonds.
(c) Tetrahedral molecules are more stable than other molecular geometries.
(d) A pi bond allows rotation about the sigma bond axis.
(e) None of the above.


Answer: None of the above.

What is the direction of the net dipole moment of the H2S molecule?

What is the direction of the net dipole moment of the H2S molecule?



(a) H2S has no net dipole moment.
(b) Pointing up and to the left.
(c) Pointing down, towards the bottom of the page.
(d) Pointing up, towards the top of the page.
(e) Pointing down and to the right.


Answer: Pointing up, towards the top of the page.

Classify CF4, NH3, Na3P, and CO2 as polar or nonpolar:

Classify CF4, NH3, Na3P, and CO2 as polar or nonpolar:




(a) Polar: NH3, Na3P. Nonpolar: CF4, CO2
(b) Polar: NH3, Na3P, CF4.Nonpolar: CO2
(c) Polar: CO2, Na3P, CF4. Nonpolar: NH3
(d) Polar: CO2 NH3.Nonpolar: CF4, Na3P
(e) Polar: CO2, Na3P. Nonpolar: NH3, CF4


Answer: Polar: NH3, Na3P. Nonpolar: CF4, CO2

Predict the electron group geometry and molecular structure for boron trichloride, BCl3

Predict the electron group geometry and molecular structure for boron trichloride, BCl3



(a) molecular structure: trigonal planar; electron group geometry: tetrahedral.
(b) molecular structure: trigonal planar; electron group geometry: trigonal planar.
(c) molecular structure: bent; electron group geometry: tetrahedral.
(d) molecular structure: trigonal planar; electron group geometry: bent.
(e) molecular structure: bent; electron group geometry: tetrahedral.


Answer: molecular structure: trigonal planar; electron group geometry: trigonal planar.

Select the correct order of sizes for the different types of electron regions in a molecule:

Select the correct order of sizes for the different types of electron regions in a molecule:



(a) lone pair < triple bond < double bond < single bond
(b) lone pair> triple bond> double bond> single bond
(c) lone pair < single bond < double bond < triple bond
(d) they vary according the elements involved and there is no simple way to order them.


Answer: lone pair> triple bond> double bond> single bond

Use the following bond energies to estimate the enthalpy change for the combustion of one mole of methane (CH4). Hint: You will need to write a balanced equation and draw Lewis structures to solve this problem.

Use the following bond energies to estimate the enthalpy change for the combustion of one mole of methane (CH4). Hint: You will need to write a balanced equation and draw Lewis structures to solve this problem. 


Bond Bond energy (kJ/mol)
C−H 414
O−O 142
O−−O 498
C−−O 736
C−O 360
O−H 464


(a) 388 kJ
(b) 676 kJ
(c) - 676 kJ
(d) - 388 kJ
(e) - 776 kJ


Answer: -676 kj

Which of the following is(are) false?

Which of the following is(are) false?



The wavefunction Ψ,
(a) is used to obtain the electron trajectory as it orbits in an atom around the nucleus.
(b) is a solution of the Schr¨odinger equation.
(c) can be used to calculate the probability of finding the electron at any given location.
(d) can be used to calculate the quantized energies of a bound electron.
The wavefunction Ψ,


Answer: (a) is used to obtain the electron trajectory as it orbits in an atom around the nucleus.

Carbon has how many lone pairs, single bonds, double bonds, and triple bonds in the most plausible Lewis structure for CO2 ?

Carbon has how many lone pairs, single bonds, double bonds, and triple bonds in the most plausible Lewis structure for CO2 ?



(a) 0 triple bonds, 2 double bonds, 0 single bonds, 0 lone pairs.
(b) 1 triple bond, 0 double bonds, 1 single bond, 0 lone pairs.
(c) 0 triple bonds, 1 double bonds, 0 single bond, 1 lone pair.
(d) 0 triple bonds, 0 double bonds, 2 single bonds, 2 lone pairs.
(e) 0 triple bonds, 2 double bonds, 0 single bonds, 2 lone pairs.


Answer: 0 triple bonds, 2 double bonds, 0 single bonds, 0 lone pairs.

A molecular compound with a molar mass of about 28.05 g/mol contains ∼ 85.56% carbon and ∼ 14.4% hydrogen, by mass. How many double bonds, single bonds, and lone electron pairs are in the molecule?

A molecular compound with a molar mass of about 28.05 g/mol contains ∼ 85.56% carbon and ∼ 14.4% hydrogen, by mass. How many double bonds, single bonds, and lone electron pairs are in the molecule?



(a) 1 double bond, 2 single bonds, 2 lone pairs.
(b) 1 double bond, 4 single bonds, 0 lone pairs.
(c) 0 double bonds, 1 single bond, 1 lone pair.
(d) 0 double bonds, 1 single bond, 2 lone pairs.
(e) 1 double bond, 2 single bonds, 0 lone pairs


Answer: 1 double bond, 4 single bonds, 0 lone pairs.

Using the electronegativity values in the periodic table below, arrange the following covalent bonds - all commonly found in amino acids - in order of increasing polarity:

Using the electronegativity values in the periodic table below, arrange the following covalent bonds - all commonly found in amino acids - in order of increasing polarity:



C−H, C−N, C−O, N−H, O−H


(a) C−H, C−N, N−H, C−O, O−H
(b) C−H, C−N, C−O, N−H, O−H
(c) C−N, C−H, C−O, O−H, N−H
(d) O−H, C−N, N−H, C−O, C−H
(e) C−H, N−H, C−N, C−O, O−H


Answer: (a) C−H, C−N, N−H, C−O, O−H

Select from the list below the correct formal charges for the atoms in the Lewis structure of NO3-(nitrate ion).

Select from the list below the correct formal charges for the atoms in the Lewis structure of NO3-(nitrate ion).




(a) 0 on all atoms
(b) -1 on doubly bonded O atom(s), 0 on singly bonded O atom(s), 0 on N.
(c) +1 on the N atom, -1 on singly bonded O atom(s), 0 on doubly bonded O atom(s).
(d) 0 on the N atom, -2 on singly bonded O atom(s), 1 on doubly bonded O atom(s).
(e) 0 on the N atom, 1 on singly bonded O atom(s), -1 on doubly bonded O atom(s).


Answer: +1 on the N atom, -1 on singly bonded O atom(s), 0 on doubly bonded O atom(s).

Which of the following combinations would make an ionic compound?

Which of the following combinations would make an ionic compound?



(a) silicon and oxygen
(b) phosphorus and chlorine
(c) magnesium and sulfur
(d) sodium and oxygen
(e) silver and copper


Answer:


(magnesium and sulfur) and
(sodium and oxygen)

Predict the charge on the monatomic ions formed from the following atoms in binary ionic compounds: i) P, ii) Mg, iii) Al, iv) O, v) Cl

Predict the charge on the monatomic ions formed from the following atoms in binary ionic compounds: i) P, ii) Mg, iii) Al, iv) O, v) Cl



(a) P2-; Mg2+; Al2+; O-; Cl-
(b) P3-; Mg2+; Al3+; O2-; Cl-
(c) P3+; Mg2+; Al3-; O2+; Cl-
(d) P3-; Mg2+; Al3-; O2+; Cl-
(e) P5+; Mg2+; Al2-; O2+; Cl-


Answer: (b) P3-; Mg2+; Al3+; O2-; Cl-

An acid base equilibrium system is created by dissolving 0.50 mol CH3CO2H in water to a volume of 1L. What would be the effects of adding 0.50 mol of CH3CO2- to the solution?

An acid base equilibrium system is created by dissolving 0.50 mol CH3CO2H in water to a volume of 1L. What would be the effects of adding 0.50 mol of CH3CO2- to the solution?



Answer: Adding conjugate base to the equilibrium, will cause some CH3CO2- to react with H3O increasing the concentration of CH3CO2H increasing the pH

Compare 2dimensional motion to 1dimensional motion.

Compare 2dimensional motion to 1dimensional motion.



Answer: When motion is on a firm surface (eg. a road) it is one dimensional because the motion is only horizontal. But when the motion is through the air (as in the case of a projectile or off a cliff) it is 2 dimensional because there is both a horizontal component and a vertical component (and they can be handled separately/not related)

Describe negative acceleration and give an example using gravity.

Describe negative acceleration and give an example using gravity.




Answer: If acceleration is in the direction opp to the velocity, then there is negative acceleration (or deceleration). The sign is negative. For example y acceleration is always g and pointing towards the earth and it is never 0. So if a ball is going up then the action of g is pointing in the direction opp to the velocity and hence a is -g.

Who is credited with discovering the atomic nucleus?

Who is credited with discovering the atomic nucleus?



a) Dalton and his atomic theory
b) Millikan and the oil drop experiment
c) Thomson and cathode ray tubes
d) Chadwick using beryllium sheets
e) Rutherford and the gold foil experiment


Answer: e) Rutherford and the gold foil experiment

Consider the Bohr model of the hydrogen atom. When an electron moves from the n = 1 orbit to the n 1 orbit to the n = 6 orbit, which of the following statements is true?

Consider the Bohr model of the hydrogen atom. When an electron moves from the n = 1 orbit to the n 1 orbit to the n = 6 orbit, which of the following statements is true?




a) light is emitted
b) energy is absorbed
c) the electron can have a continuous range of energies in between those of the n=1 and 6 orbits
d) all of the above
e) none of the above


Answer: b) energy is absorbed

How many atoms are in 31.3 g of nickel, Ni?

How many atoms are in 31.3 g of nickel, Ni?



a) 1.13 × 1024 atoms
b) 1.48 × 1025 atoms
c) 2.44 × 1022 atoms
d) 3.21 × 1023 atoms
e) 6.98 × 1021 atoms


Answer: d) 3.21 × 1023 atoms

What is the electron configuration of Fe2+?

What is the electron configuration of Fe2+?



a) [Ar]3d44s2
b) [Ar]3d54s1
c) [Ar]3d6
d) [Ar]3d64s2
e) [Ar]3d64s1


Answer: c) [Ar]3d6

Lithium forms compounds which are used in dry cells and storage batteries and in high-temperature lubricants. It has two naturally occurring isotopes, 6Li (isotopic mass = 6.015121 amu) and 7Li (isotopic mass = 7.016003 amu). Lithium has an atomic mass of 6.9409 amu. What is the percent abundance of lithium-6?

Lithium forms compounds which are used in dry cells and storage batteries and in high-temperature lubricants. It has two naturally occurring isotopes, 6Li (isotopic mass = 6.015121 amu) and 7Li (isotopic mass = 7.016003 amu).  Lithium has an atomic mass of 6.9409 amu. What is the percent abundance of lithium-6?



(1A)
a) 92.50%
b) 86.66%
c) 46.16%
d) 7.503%
e) 6.080%


Answer: d) 7.503%

Which of the following metric relationships is incorrect?

Which of the following metric relationships is incorrect?



a) 1 liter = 1000 milliliters
b) 1 kilogram = 103 grams
c) 1 microgram = 106 grams
d) 1 centimeter = 10-2 meters
e) 1 nanometer = 10-9 meters


Answer: c) 1 microgram = 106 grams

What is the concentration of a solution?

What is the concentration of a solution?



Answer: a measure of the amount of solute is a specified quantity of solvent

Rank each set of ions in order of decreasing size and explain your ranking

Rank each set of ions in order of decreasing size and explain your ranking



A) Ca+2, Sr+2, Mg+2
B)K+, S2-, Cl-
C) Au+, Au+3,


Answer:


A) Mg+2 < Ca+2 < Sr+2 All these ions are from group 2A so size increases down the group
B) K+ < Cl- < S2- These ions are isoelectronic, so size decreases as nuclear charge increases
C) Au+3 < Au+ Cation decreases as charge increases

Which of the following is paramagnetic

Which of the following is paramagnetic



A) Zn [Ar]3d10 4s2
B) V [Ar] 3d3 4s2
C) Sr [Kr]5s2
D) Kr [Ar] 3d10 4s2 4p6
E) Ca [Ar] 4s2


Answer: B) V

Use condensed electron configuration to write the reaction for the formation of each transition metal ion, and predict whether the ion is paramagnetic or diamagnetic.

Use condensed electron configuration to write the reaction for the formation of each transition metal ion, and predict whether the ion is paramagnetic or diamagnetic.



A) Mn+2 (Z =25) B) Cr+3 (Z = 24) C) Hg+2 (Z = 80)
A) Since there are 5 unpaired electrons = paramagnetic
B) Since there are 3 unpaired electrons = Paramagnetic


Answer: C) Since they are filled diamagnetic

When comparing the successive ionization energies of an element, an unusually big increase in ionizations is seen when?

When comparing the successive ionization energies of an element, an unusually big increase in ionizations is seen when?



When the first core electron is removed

Mettalic Behavior
Increases Left and Down

Ionization Energy
increases Up and Right

Atomic Size
Increases Left and Down

Electron Affinity
Increases Up and Right (with several exceptions)

Give the full and condensed electron configurations, partial orbital diagrams showing valence electrons only and number of inner electrons for the following elements

Give the full and condensed electron configurations, partial orbital diagrams showing valence electrons only and number of inner electrons for the following elements




K (Z = 19)
Tc (Z = 43)
Pb (Z = 82)


K = 1s1 2s2 2p6 3s2 3p6 4s1 ([Ar] 4s1) 1 valence electron, 18 inner electrons

Tc = 1s1 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 d5 ([5s2 4d5]) 7 valence electrons and 36 inner electrons)

Pb = [Xe] 6s2 4f14 5d10 6p2 4 valence and 78 inner electrons

Give the name, magnetic quantum numbers and number of orbitals for each of the sub-levels with the following quantum numbers.

Give the name, magnetic quantum numbers and number of orbitals for each of the sub-levels with the following quantum numbers.



a) n = 3 l = 2
b) n = 2 l = 0
c) n = 5 l = 1
d) n = 4 l = 3


Answer:

a) sub-level 3d (m = -2, -1, 0, 1, 2), orbitals =5
b) sub-levels 2s (m = 0) orbitals 1
c) sub-levels 5p (m = -1, 0, 1) orbitals 3
d) sub-levels 4f (m = -3-+3) orbitals 7
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