A ground state hydrogen atom absorbs a photon of λ = 94.91 nm, exciting the electron to a higher energy (quantum) level. The electron then decays to a lower, intermediate energy level, emitting a photon of λ = 1281 nm. From that intermediate energy level the electron decays back to the ground state, emitting another photon. a) What is the highest energy level attained by the electron?
b) What was the intermediate energy level of the electron?
c) What was the λ of the second photon?
In: Chemistry
Calculate the pH of the buffer formed by mixing equal volumes [C2H5NH2]= 1.68M with [HClO4]= 0.984M . Kb=4.3
In: Chemistry
Design a separation scheme for Cu2+, Fe3+, Mn2+, and Ni2+ include equations for all reactions.
In: Chemistry
The chemical formulae of some acids are listed in the first column of the table below, and in the second column it says whether each acid is strong or weak. Complete the table. List the chemical formula of each species present at concentrations greater than about 10^ -6 mol/L when about a tenth of a mole of the acid os dissolved in a liter of water.
* Weak or Strong? *Species present at 10^ -6 mol/L or greater when dissolved in water.
HBrO3
H2SO3
HClO2
HBr
In: Chemistry
Calculate the concentrations for all components of the following reaction at equilibrium:
PCl3 + Cl2 ⇄ PCl5
Equilibrium constant K=16
Initial concentration PCl5 = 0.5 M
In: Chemistry
why is substitution of a proline amino acid in the middle of an alpha-helix always disruptive?
In: Chemistry
Calculate the molar solubility of BaSO4 in a solution containing 0.70M SO42- ion.
_________ x 10 _______
In: Chemistry
Consider the reaction that converts pyruvic acid (CH3COCOOH) into gaseous acetaldehyde (CH3CHO) and gaseous CO2, which is catalyzed in aqueous solution by the enzyme pyruvate decarboxylase. Assume ideal gas behavior for CO2.
(a) Calculate delta-G (298 K) for this reaction at 160 bar.
(b) Calculate delta-G (298K) for this reaction at 100 bar. State any important assumption needed in addition to ideal gas behavior.
In: Chemistry
Pure solid NaH2PO4 is dissolved in distilled water, making 100.00 ml of solution. 10.00ml of this solution is diluted to 100.00 ml to prepare the original phosphate standard solution. Three working standard solutions are made from this by pipetting 0.8ml, 1.5ml and 3.0 ml of the original standard solution into 100.00 ml volumetric flasks. Acid and molybdate reagent are added and the solutions are diluted to 100.00 ml. You may assume that all these absorbance measurements have already been corrected for any blank absorbance. The absorbance of each is measured in the spectrophotometer. Mass of NaH2PO4 (mg) 512.2 Absorbance Standard 1 (0.8 ml) 0.1922 Standard 2 (1.5 ml) 0.3604 Standard 3 (3.0 ml) 0.7209 Calculate the following Concentration of original phosphate standard (mM) , Concentration of Standard 1(mM), Concentration of Standard 2(mM), Concentration of Standard 3(mM), Slope of calibration line?
In: Chemistry
Question 3
Sodium nitrite (NaNO2) is a commonly used meat preservative.
a. Knowing that the Ka of nitrous acid (HNO2) is 4.5 x 10-4 M, calculate the pH of a 0.25 M sodium nitrite (NaNO2) solution.
b. How many grams of sodium nitrite (NaNO2) must be added to 100.0 mL of 0.150 M nitrous acid (HNO2) to make a buffer solution with a pH of 3.50?
c. If 0.05 g of NaOH (s) are added to 100.0 ml of the buffer solution prepared in part (b), what is the new pH?
In: Chemistry
Use vibrational transitions and energy stored in the sulfur dioxide molecule to explain climate change
In: Chemistry
QUESTION 1
The half-life for a reaction that is
first-order in A is 15 minutes. How long will it take for the
concentration of A to change from 0.16 M to 0.040
M?
A(g) → B(g) + C(g)
|
60 min |
||
|
45 min |
||
|
30 min |
||
|
23 min |
||
|
15 min |
4 points
QUESTION 2
When a 0.100 mol of a pure compound is dissolved in 1.0 L of water, the solution pH changes from 7.00 to 4.24. Which of the following is most likely the identity of the substance?
|
A strong acid |
||
|
A strong base |
||
|
A weak acid |
||
|
A weak base |
||
|
A neutral salt |
4 points
QUESTION 3
Which of the following will NOT change if the temperature of a reaction system is changed?
|
Frequency of molecular collisions |
||
|
Average kinetic energy of reactant molecules |
||
|
Reaction rate |
||
|
Rate constant |
||
|
Activation energy |
4 points
QUESTION 4
Which of the following best describes any reaction system where Q < Kc?
|
The system will never be able to reach a state of equilibrium. |
||
|
The system is at equilibrium, and there are more products than reactants at equilibrium. |
||
|
The system is at equilibrium, and there are more reactants than products at equilibrium. |
||
|
The system is not at equilibrium, and the reaction will go in the reverse direction. |
||
|
The system is not at equilibrium, and the reaction will go in the forward direction. |
4 points
QUESTION 5
What is the equilibrium constant expression for
Kc for the following heterogeneous
equilibrium?
Ni(CO)4(g)
<----> Ni(s) + 4CO(g)
4 points
QUESTION 6
Which of the following occurs when the temperature of a contained gas is reduced at constant volume?
|
Pressure decreases |
||
|
Average molecular velocity decreases |
||
|
Average kinetic energy decreases |
||
|
Collision frequency decreases |
||
|
All of these |
4 points
QUESTION 7
Given a fixed amount of an ideal gas held at constant pressure, calculate the volume it would occupy if a 2.00 L sample were cooled from 60.0°C to 30.0°C.
|
1.00 L |
||
|
4.00 L |
||
|
0.20 L |
||
|
1.82 L |
||
|
0.455 L |
4 points
QUESTION 8
Which of the following properties of liquids generally is lower for substances with stronger intermolecular forces?
|
Viscosity |
||
|
Vapor pressure |
||
|
Boiling point |
||
|
Both viscosity and vapor pressure |
||
|
All of these |
4 points
QUESTION 9
Use the initial concentration and initial rate data in the table
to determine the rate law for the reaction:
A(aq) +
B(aq) → C(aq) +
D(g)
|
Experiment # |
[A] (M) |
[B] (M) |
Initial Rate (M/s) |
|
1 |
0.400 |
0.400 |
9.00×10-3 |
|
2 |
0.200 |
0.400 |
4.50×10-3 |
|
3 |
0.200 |
0.200 |
1.13×10-3 |
|
Rate = k[A] |
||
|
Rate = k[B]2 |
||
|
Rate = k[B] |
||
|
Rate = k[A]2[B] |
||
|
Rate = k[A][B]2 |
4 points
QUESTION 10
If the hydronium ion concentration, [H3O+], in a solution is 5.6×10−10M, what is the hydroxide ion concentration, [OH−], and the pH of the solution?
|
[OH−] = 1.8×109 M, pH = 4.75 |
||
|
[OH−] = 5.6×10−10M, pH = 10.56 |
||
|
[OH−] = 1.0×10−7M, pH = 5.60 |
||
|
[OH−] = 4.4×10−4M, pH = 9.25 |
||
|
[OH−] = 1.8×10−5M, pH = 9.25 |
4 points
QUESTION 11
Which of the following gases has the lowest average molecular velocity at the same temperature?
|
Ne |
||
|
Xe |
||
|
N2 |
||
|
F2 |
||
|
All of these have the same average molecular velocity. |
4 points
QUESTION 12
In the following 2-step mechanism, which is the
catalyst?
Step 1: A + B → C + D
Step 2: B + C → X +
A
|
A |
||
|
B |
||
|
C |
||
|
D |
||
|
X |
4 points
QUESTION 13
Which of the following substances has hydrogen bonding when in the pure liquid state?
|
CH3-O-CH3 |
||
|
NF3 |
||
|
CH3OH |
||
|
HBr |
||
|
All of these have hydrogen bonding in the pure liquid state. |
4 points
QUESTION 14
Consider the following endothermic reaction at equilibrium in a
1-liter container:
2Cl2(g)
+ 2H2O(g)
<----> 4HCl(g) +
O2(g)
ΔH
> 0
Which of the following will cause a decrease in
the equilibrium concentration of O2?
|
Increasing the temperature |
||
|
Adding Cl2 gas |
||
|
Adding HCl gas |
||
|
Adding O2 |
||
|
Increasing the volume of the container |
4 points
QUESTION 15
Consider the following exothermic reaction at a state of equilibrium: C(s) + O2(g) <----> CO2(g) . Which of the following changes will cause value of the equilibrium constant Kc to change?
|
Increasing the container volume |
||
|
Increasing the temperature |
||
|
Removing O2 |
||
|
Adding solid carbon |
||
|
All of these |
4 points
QUESTION 16
Which of the following increases the solubility of a gas in solution?
|
Increasing gas pressure and increasing temperature |
||
|
Increasing gas pressure and decreasing temperature |
||
|
Decreasing gas pressure and increasing temperature |
||
|
Decreasing gas pressure and decreasing temperature |
||
|
Adding more water |
4 points
QUESTION 17
When comparing a 1 m NaCl solution to that of pure water:
|
The 1 m NaCl solution has a higher boiling point and the higher freezing point. |
||
|
The 1 m NaCl solution has a higher boiling point and a lower freezing point. |
||
|
The 1 m NaCl solution has a lower boiling point and a higher freezing point. |
||
|
The 1 m NaCl solution has a lower boiling point and a lower freezing point. |
||
|
They both have the same boiling point and freezing point. |
4 points
QUESTION 18
Which of the following types of solids have relatively low melting points, because melting these solids requires breaking intermolecular forces, not real bonds?
|
Molecular solids |
||
|
Ionic solids |
||
|
Covalent-network solids |
||
|
Metallic solids |
||
|
Semiconductors |
4 points
QUESTION 19
Which of the following does NOT describe semiconductors?
|
Their band gaps are between metals and insulators. |
||
|
Doped p-type and n-type semiconductors are less conductive than semiconductor materials that are not doped. |
||
|
Their band gaps increase as particle size decreases in the 1-10 nm range. |
||
|
They can be a single element or a compound. |
||
|
They usually have an average number of 4 valence electrons per atom. |
4 points
QUESTION 20
If the average rate of appearance of NH3 in the
following reaction is 1.40 M/s, what is the average rate
of disappearance of H2 during the same time
period?
N2(g)
+
3H2(g) →
2NH3(g)
|
5.40 M/s |
||
|
2.80 M/s |
||
|
1.20 M/s |
||
|
0.700 M/s |
||
|
2.10 M/s |
4 points
QUESTION 21
Which of the following should be the most soluble in benzene, C6H6?
|
CH3OH |
||
|
H2O2 |
||
|
CCl4 |
||
|
HF |
||
|
CH3NH2 |
4 points
QUESTION 22
Which of the following best explains the relative boiling points for Cl2 and HCl?
|
Cl2 has the higher boiling point because liquid
Cl2 has stronger London-dispersion forces than liquid
HCl. |
||
|
Cl2 has the higher boiling point because liquid
Cl2 has stronger dipole-dipole forces than liquid
HCl. |
||
|
HCl has the higher boiling point because liquid HCl has
hydrogen-bonding interactions while liquid Cl2 |
||
|
HCl has the higher boiling point because liquid HCl has dipole-dipole forces while liquid Cl2 does not have dipole-dipole forces. |
4 points
QUESTION 23
What is the density (g/L) of H2 gas at a temperature of 283 K and 0.500 atm? (Hint: One approach is to assume a sample size of 1.0 L.)
|
0.0107 g/L |
||
|
0.0217 g/L |
||
|
0.0434 g/L |
||
|
93.7 g/L |
||
|
0.0899 g/L |
4 points
QUESTION 24
Given that the molar volume of Ne gas is 22.414 L/mol at STP
(1.00 atm of pressure and at a temperature of 273.15 K), predict
the volume of H2
gas when the number of moles is 2.50 mol under the same conditions
of temperature and pressure.
|
2.24 L |
||
|
56.0 L |
||
|
0.110 L |
||
|
5.60 L |
||
|
11.1 L |
4 points
QUESTION 25
Which of the following best describes a chemical reaction in a state of equilibrium?
|
Reactant molecules are forming products as fast as product molecules are reacting to form reactants. |
||
|
The rate constants of the forward and reverse reactions (kf and kr) are equal. |
||
|
The value of the equilibrium constant, Kc, is 1. |
||
|
The limiting reagent has been consumed. |
||
|
All chemical reactions have stopped. |
In: Chemistry
a)Consider an aqueous solution of ammonium chloride, NH4Cl. Neglecting the autoprotolysis of water, calculate the pH of NH4Cl for formal concentration of 0.10M.
b)Use the systematic treatment of equilibrium to derive an equation for an aqueous solution of NH4Cl that contains [H+], F, Ka and Kw. Do not neglect the autoprotolysis of water in this case.
In: Chemistry
On the same graph, sketch the pH titration curves for the titration of 91) a 0.1 M strong monoprotic a cid (e.g. HCL) with a NaOH and (2) a weak 0.1 M monoprotic acid (e.g. HCOOH) with the same strong base. Identify how the two curves differ with respect to each of the following and explain why:
a) Initial pH
b) The pH in the region between the start of the titration and the equivalence point
c) The pH at the equivalence point
d)The volume of base required to reach the equivalence point
e) The pH beyond the equivalence point
In: Chemistry
A stuent was assigned to work with the compound copper (II) sulfate pentahydrate. The student prepared a stock solution by weighing 0.817 grams of CuSO4.5H2O and diluting it with water to a final volume of 10.00mL. What is the concentration of this stock?
Answer:____________g/mL
From this stock solution, the student then took 1.00mL and diluted it to a final volume of 5.00mL with water. What is the final concentration of this diluted solution?
Answer:____________g/mL
In: Chemistry