Thursday
October 2, 2014

Posts by ana


Total # Posts: 981

Chemistry
Calculate the number of moles in 2.65x1015 atoms of 14C.
October 1, 2014

Maths
Find the highest common factor of 693 and 1365?
October 1, 2014

MATH HELP
arthur wants to model 758 using the fewest blocks possible. how many tens should he use? A. 8 B.5 C.7 D.4
September 29, 2014

math problem solving
arthur wants to model 758 using the fewest blocks possible. how many tens should he use? A. 8 B.5 C.7 D.4
September 29, 2014

Chemistry
Aluminum sulfate reacts with calcium hydroxide (from lime) to form aluminum hydroxide and calcium sulfate. Write the balanced formula unit equation for the reaction.
September 28, 2014

Physics College - Circular motion
At time t1 = 2.00 s, the acceleration of a particle in counterclockwise circular motion is (6.00 m/s2) i^+ (4.00 m/s2) j^. It moves at constant speed. At time t2 = 5.00 s, its acceleration is (4.00 m/s2) i^+ (-6.00 m/s2) j^. What is the radius of the path taken by the particle?
September 21, 2014

Spanish
2.¿Quién le recomendó ese plato? (su tío) I have to answer this using the double object pronouns. these are the anwers I tried so far: Mi tío me lo recomendó. Su tío se lo recomendó. it is saying that the se lo recomendo...
September 18, 2014

spanish two
directions: answer the questions using the double object pronouns. example quien te compro esos zapatos? mi tio is the person buys. this is for my question.
September 16, 2014

spanish
quien le recomendo ese plato? su tio Su tio se lo recomendo. is the answer i first did. Mi tio me lo recomendo was the second. i am on the last allowed attempt and i am not sure what else to do.
September 16, 2014

Algebra
A motorboat left a harbor and traveled to an island at an average rate of 18 knots. The average speed on the return trip was 10 knots. If the total trip took 14.0 hours, how far is the harbor from the island?
September 14, 2014

Math
6m by 5m by 4m , rectangular tank How do you know which one is the height?
September 14, 2014

Math
Thanks!
September 14, 2014

Math
Mrs lim bought apples at a cost of $150 from the wholesaler. If she sells 1 pace of 5 apples at $2.40, what is the least number of apples she must sell in order to make a profit? I am kind of sure I need to use HCF(highest common factor) in this question.. I might be wrong ...
September 14, 2014

Math7
You download 12 new songs to ur MP3 player then u delete 5 old songs write each amount as an integer
September 8, 2014

12th Grade Physics
Ben pulls a rope that is attached to a wagon with a magnitude of 300N. He pulls it in a way that te rope is at an angle of 30 degrees from the horizontal. The mass of the wagon is 2kg and the mass of Mike, who sits on the wagon, is 20kg. While the wagon moves to the right, the...
August 28, 2014

Chem
1.00 * 10^26 molecules of Tl to moles
August 26, 2014

Economics
Production Possibilities Curve (PPC) Worksheet All PPC’s Reflect Increasing Opportunity Costs For Numbers 1-10, think the change affects all markets. On all graphs, place “Consumer Goods” on the X Axis and place “Capital Goods” on the Y. 1) Hurricane ...
August 21, 2014

AP Statistics
For a, I have lie still after embryo transfer for control and acupuncture for randomization. I'm not sure what to put for replicate but i think it's the same as the control...?
August 20, 2014

AP Statistics
A study sought to determine whether the ancient Chinese art of acupuncture could help infertile women become pregnant. 160 healthy women undergoing treatment for infertility were recruited for the study. Half of the subjects were randomly assigned to receive acupuncture ...
August 20, 2014

science
Unit 33 discusses a natural way to reinforce science process skills and introduces the scientific method. This strategy, especially appropriate for primary grades, is to have children do which one of the following?
July 13, 2014

Physics
A boat is moving 24.4m/s, 35 degrees North of East against the 10m/s water current that flows towards south. What would be the speed of the boat as it crosses the river
July 10, 2014

PHYSICS
a girl weighing 620 n sits in the middle of a 2.8 m long hammock which sags 1.2m below th e point of support. What force is exerted by each of the two ropes supporting the hammock
July 3, 2014

statistics
predict the score in statistics for a student whose score in mathematics is 30
May 21, 2014

(2-8) Chemistry - Science (Dr. Bob222)
Thank you for your explications. Could you tell me if the expansion of a gas into the vacuum would be considered zero work?
May 11, 2014

(2-8) Chemistry - Science (Dr. Bob222)
Also, could you tell me please what processes would result in work=0 (beside the constant volume)?
May 11, 2014

(2-8) Chemistry - Science (Dr. Bob222)
Ahhhh, I got it now. I should have been more careful on my reading. Thank you
May 11, 2014

(2-8) Chemistry - Science (Dr. Bob222)
Thank you for your answers. Dr.Bob, you said that "q changes with T", thus dE changes with T, then why the answer D in the problem below is not true. IT is just a bit confusing, thank you. In heating an ideal gas, A) It takes more heat to raise T by one degree K in ...
May 11, 2014

(2-8) Chemistry - Science (Dr. Bob222)
Which of the following statements is correct? A) The internal energy of a system increases when more work is done by the system than the heat that flows into the system. B) The system does work on the surroundings when an ideal gas expands against a constant external pressure...
May 11, 2014

Chemistry - Science (Dr. Bob222)
Liquid chloroform (CHCl3) is placed in a closed container and allowed to equilibrate with chloroform vapor. With the temperature held constant, additional chloroform is introduced into the system, and the vapor-liquid equilibrium is reestablished. Following this, the ...
May 10, 2014

(1-22)Chemistry - Science
True. Will do so
May 10, 2014

(1-22)Chemistry - Science
Thank you Dr.Bob222 for clarification. I am reviewing all the information for Gen Chem 2 for a big exam next week; and as you know the information is quite vast and it takes a bit to recall how to solve the problems correctly. I do not seek for mere answers to these problems, ...
May 10, 2014

(1-22)Chemistry - Science
Consider the following reaction: C(s) + H2O (g) ⇌ CO (g) + H2 (g) (Kp = 0.45 at 900 K) What is the equilibrium partial pressure of H2O when the initial partial pressure of water is 1.00 atm? a) 0.43 atm b) 0.58 atm c) 0.22 atm d) 0.52 atm e) 1.16 atm
May 10, 2014

(1-17)Chemistry - Science
Consider the reaction: SO2 (g) + NO2 (g)  SO3 (g) + NO (g) At T = 1000 K, where the reaction is exothermic with an equilibrium constant K = 9.00 If the reaction vessel is instead charged initially with SO3(g) and NO(g), each at a partial pressure of 0.500 atm, the ...
May 10, 2014

(1-16)Chemistry - Science
Consider the reaction: SO2 (g) + NO2 (g) ==> SO3 (g) + NO (g) At T = 1000 K, where the reaction is exothermic with an equilibrium constant K = 9.00 The reaction vessel is charged initially with all four gases, each at a pressure of 0.5 atm. After equilibrium is achieved, ...
May 10, 2014

(1-15) Chemistry - Science
The answer is C but not sure why so
May 10, 2014

(1-15) Chemistry - Science
Assume a gas of molecular mass M g/molecule obeys the Maxwell Boltzmann distribution of speeds at temperature T. If u2> u1, the ratio of the number of molecules at speed u2 to the number at speed u1 a) is always less than one. b) is always greater than one. c) can be either...
May 10, 2014

(1-13) Chemistry - Science
Which of the following effects will make the ratio (PV) / (nRT) less than 1 for a real gas? a) The gas molecules are large enough to occupy a substantial amount of space. b) A large number of molecules have speeds greater than the average speed. c) The gas molecules have a ...
May 10, 2014

1-12. Chemistry - Science
At STP, 3.0 L of D2 reacts completely with 3.0 L of E, producing 1.5 L of a product. What is the formula of the product?
May 10, 2014

(1-11) Chemistry - Science (Dr. Bob222)
Will the Le Chatelier's principle work here? Because pure liquid has no effect on the equilibrium position, it will not move towards products; thus, chloroform vapor will not form.
May 10, 2014

(1-11) Chemistry - Science (Dr. Bob222)
Liquid chloroform (CHCl3) is placed in a closed container and allowed to equilibrate with chloroform vapor. With the temperature held constant, additional chloroform is introduced into the system, and the vapor-liquid equilibrium is reestablished. Following this, the ...
May 10, 2014

Chemistry - Science (Dr. Bob222)
Nitrogen gas has values of Cv and Cp of 20.8 and 29.1 J K-1 mol-1, respectively. When a certain amount of nitrogen is heated at constant pressure, what fraction of the heat Q is used to increase the internal energy of the gas, and how is the remaining energy used? A) 3/2 of Q ...
May 8, 2014

Chemistry - Science (Dr. Bob222)
Hydrazine is used as a rocket fuel because its reaction with oxygen is extremely exothermic: N2H4(liquid) + O2(g)  N2(g) + 2H2O(liquid) ΔH(reaction) = -615 kJ mol-1 What is the enthalpy of this reaction if water were produced in the gaseous rather than the liquid ...
May 8, 2014

(12)Chemistry - Science (Dr. Bob222)
This problem is quite confusing. Thank you for your contribution and elucidation!
May 8, 2014

(12)Chemistry - Science (Dr. Bob222)
...not sure how to derive it
May 8, 2014

(12)Chemistry - Science (Dr. Bob222)
I have solved it this way too and I got answer A: -7740 J, but the correct answer is actually C :(
May 8, 2014

(12)Chemistry - Science (Dr. Bob222)
Thank you Devron for this clarification.
May 8, 2014

(12)Chemistry - Science (Dr. Bob222)
Calculate delta E for a process in which 88.0 g of nitrous oxide gas (N2O) is cooled from 165 ˚C to 65 ˚C at a constant pressure of 5.00 atm. The molecular weight of nitrous oxide is 44.02 g/mol, and its heat capacity at constant pressure, Cp, is 38.70 J/molK. A) - ...
May 8, 2014

(23.Chemistry - Science (Dr. Bob222)
This Q. seemed too easy to me, and I though it must be a trick question or something, nonetheless thank you for explaining.
May 8, 2014

(23.Chemistry - Science (Dr. Bob222)
Thank you Devron for explication.
May 8, 2014

(23.Chemistry - Science (Dr. Bob222)
The correct answer is D. But my question is how is it possible to have an initial voltage of 1.1V for the cell is with concentration of 1M, if E standard for the cell is 0.48. I am sure I am missing something here.
May 8, 2014

(23.Chemistry - Science (Dr. Bob222)
An electrochemical battery made from Sn and Cu electrodes under standard conditions shows an initial voltage of V= 1.1 V. If the concentration of both Cu2+ and Sn2+ solutions is increased to 2 M from 1 M, the observed voltage will: (Hint: use the Nernst equation) A. increase ...
May 8, 2014

(19) Chemistry - Science (Dr. Bob222)
Good morning, Could you please let me know how did you calculated K for answer D and C. Thank you.
May 8, 2014

(19) Chemistry - Science (Dr. Bob222)
Use the following information to answer this question: Cu+(aq) + e- → Cu(s) E° = 0.521V Cu2+ (aq) + e- → Cu+ (aq) E° = 0.153 V. Given these half cell reactions, an aqueous solution of Cu+ ion in the absence of O2(g) : A. will be thermodynamically stable B. ...
May 8, 2014

(11) Chemistry - Science (Dr. Bob222)
Yes, A! Thank you for making it easy to understand.
May 7, 2014

(11) Chemistry - Science (Dr. Bob222)
The correct answer is A, which I got it right, but I was torn between A & B. could you please explain why B is incorrect. Thank you.
May 7, 2014

(11) Chemistry - Science (Dr. Bob222)
In the following hypothetical reaction A + B → C + D, the equilibrium constant, Keq is less than 1.0 at 25°C and decreases by 35% on changing the temperature to 45°C. What must be true according to this information? A. The ΔH° for the reaction is ...
May 7, 2014

Chemistry - Science (Dr. Bob222)
Thank you!
May 7, 2014

Chemistry - Science (Dr. Bob222)
Hello, how are you? The correct answer to this Q is E. but I have chosen B. Could you please explain why all of them cannot be true? Thank you
May 7, 2014

Chemistry - Science (Dr. Bob222)
The following reaction has a positive value of ΔG°. 2H2O(g) → 2H2(g) + O2(g) Which of the following statements must be true? A. The reaction is slow. B. The reaction will not occur. That is, when H2O(g) is introduced into a flask, no O2 or H2 will form even over...
May 7, 2014

(5) Chemistry - Science (Dr. Bob222)
aha very interesting, thank you so much for this detailed explanation, now I get it.
May 6, 2014

(5) Chemistry - Science (Dr. Bob222)
Also, could you tell me please how you have solved for X?
May 6, 2014

(5) Chemistry - Science (Dr. Bob222)
P.S. I just found out that our calculation were right all along for Zn/Cu cell problem... indeed the answer is 1.09V =) Thank you!
May 6, 2014

(5) Chemistry - Science (Dr. Bob222)
This is a beautiful way of thinking, thank you for sharing. The problem is that at the test I am not given the Ka value for the acid. I solved it this way: I used HH equation, then since we are dealing with the same acid the value of Ka would not change (i thought of it as ...
May 6, 2014

(5) Chemistry - Science (Dr. Bob222)
Consider a buffer made from 0.13 M sodium acetate and 0.10 M acetic acid in 1L. What amount of KOH must be added to cause an increase of the pH by 0.14? A) 0.048 mol B) 0.038 mol C) 0.028 mol D) 0.018 mol E) 0.008 mol
May 6, 2014

Chemistry - Science (Dr. Bob222)
Ammonia is a weak base with a Kb of 1.8 x 10-5. A 100.0 mL sample of 0.13 M aqueous solution of ammonia (NH3) is mixed with 87 mL of 0.15 M solution of the strong acid HCl, calculate the pH of the final solution. A) 2.9 B) 11.1 C) 8.8 D) 5.2 E) None of the above
May 6, 2014

Chemistry - Science (Dr. Bob222)
Thank you! I finally have solved it
May 6, 2014

Chemistry - Science (Dr. Bob222)
the correct answer is 5.2 mmol; however, I get lost in the calculations. It seems easy to solve: I have pH, pKb, and HH eq, but then I get stuck to derive x correctly
May 6, 2014

Chemistry - Science (Dr. Bob222)
How many mmol ( millimoles) of HCl must be added to 130.0 mL of a 0.40M solution of methyl amine (pKb = 3.36) to give a buffer having a pH of 11.59? Thank you for your help!
May 6, 2014

Chemistry - Science (Dr. Bob222)
Posted by Ana on Saturday, May 3, 2014 at 11:23am. A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The ...
May 5, 2014

Math
If a navigation error puts a plane 2 degrees off course, how far off course is the plane after flying 121 miles? Round to the nearest tenth of a mile. Just explain how to solve, please.
May 5, 2014

Math
A boat travels 74 miles on a course with direction 34 degrees and then changes its course to travel 58 miles at 53 degrees. How far north and how far east has the boat traveled on its 132-mile trip? A 87.7 miles east and 44.3 miles north B 35.7 miles east and 96.3 miles north ...
May 5, 2014

Math
An airplane, after 1 hour in the air, arrives at a point 350 miles south of its departure point. There was a steady wind of exactly 25 mph from the northwest during the entire flight. Which represents the airplane's average air speed?
May 5, 2014

Chemistry - Science (Dr. Bob222)
thank you!!
May 3, 2014

Chemistry - Science (Dr. Bob222)
Ammonium metavanadate reacts with sulfur dioxide in acidic solution as follows (hydrogen ions and H2O omitted): xVO3^–^ + ySO2 → xVO^2+^ + ySO4^2–^ What is the ratio of x : y? A. 1 : 1 B. 1 : 2 C. 2 : 1 D. 1 : 3 E. 3 : 1
May 3, 2014

Chemistry - Science (Dr. Bob222)
Thank you for such a great response! You are a legend!
May 3, 2014

Chemistry - Science (Dr. Bob222)
the correct answer is D, but i am confused on the rational here. Not sure what the professor wants me to understand here, the concept behind...
May 3, 2014

Chemistry - Science (Dr. Bob222)
Use the following information to answer this question: Cu+(aq) + e- → Cu(s) E° = 0.521V Cu2+ (aq) + e- → Cu+ (aq) E° = 0.153 V. Given these half cell reactions, an aqueous solution of Cu+ ion in the absence of O2(g) : A. will be thermodynamically stable B. ...
May 3, 2014

chemistry - Science
Disregard of 1M solution, it's a typo. The volume of 1.00L is relevant
May 3, 2014

chemistry - Science
A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The mass of each electrode is 200 g. Each half-cell ...
May 3, 2014

chemistry - Science
A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The mass of each electrode is 200 g. Each half-cell ...
May 3, 2014

Chemistry - Science
A fuel cell designed to react grain alcohol with oxygen has the following net reaction: C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) The maximum work that 1 mol of alcohol can yield by this process is 1320 kJ. What is the theoretical maximum voltage this cell can achieve?
May 3, 2014

chemistry - (Dr. Bob222)
Thank you so much! This makes much more sense now. Indeed a great tool to know
April 21, 2014

chemistry - (Dr. Bob222)
Thank you very much! The formula is very useful,but if it's no trouble for you could you please explain the concept?
April 21, 2014

chemistry - (Dr. Bob222)
A student attempted to synthesize malonic acid which has a molecular weight of 104 g/mol by the same method used to synthesize aspirin. A titration was performed to find the equivalent weight. 0.125 g of malonic acid product was used for a titration that required 24 mL of 0.10...
April 21, 2014

College Chemistry (DrBob222)
Thank you! You are legendary!
April 16, 2014

College Chemistry (DrBob222)
The decomposition of HCO2H follows first-order kinetics. HCO2H(g) CO2(g) + H2(g) The half-life for the reaction at a certain temperature is 44 seconds. How many seconds are needed for the formic acid concentration to decrease by 73%?
April 16, 2014

chemistry - (Dr. Bob222)
No, they did not provide any reaction for this problem. If I'll find the solution, I'll post it here. Thank you for your help.
April 16, 2014

chemistry - (Dr. Bob222)
I did that and but I got 1.52 mol/L rather 0.97 (as the answer key provides it)
April 16, 2014

chemistry - (Dr. Bob222)
The rate constant for a second order reaction has the value of 2.5 x 10–3 L·mol–1·s–1. If the initial concentration of reactant is 3.5 mol·L-1, what will be the molar concentration of the reactant after 2.5 minutes?
April 16, 2014

Chemistry - Science (Dr. Bob222)
I have calculated K1 and K2 by dividing initial rate to initial concentration [A2], and I solved for Ea but for some reason I don't get the right answer, (which is 10.2KJ)
April 16, 2014

Chemistry - Science (Dr. Bob222)
Consider the kinetic data given in the table below for the first order reaction: What is the value of the activation energy? A_2_--> 2A Expt. Initial [A2] Temp. Initial Rate mol/L (°C) [A2]·s–1 1 0.10 100 1.2 x 10–3 2 0.20 200 4.8 x 10–3 3 0.15 ? 4...
April 16, 2014

Chemistry - Science (Dr. Bob222)
Consider the kinetic data given in the table below for the first order reaction: What is the value of the activation energy? A_2_--> 2A Expt. Initial [A2] Temp. Initial Rate mol/L (°C) [A2]·s–1 1 0.10 100 1.2 x 10–3 2 0.20 200 4.8 x 10–3 3 0.15 ? 4...
April 16, 2014

chemistry
a 0.0500 mol sample of a nutrient substance is burned in a bomb calorimeter containing 2.00 x 10^2g H2O. If the formula weight of this nutrient substance is 114g/mol, what is the fuel value (in nutrient Cal) if the temperature of the water increased 5.70C
April 15, 2014

Math
Use synthetic division to determine which pair of integers provide both a lower and an upper bound for the zeros of f(x)= x^5-2x^4-25x^3+50x^2+144x-290 PLEASE SHOW WORK!!!
April 9, 2014

Subtracting Fractions with like Denominators
If Lori's neighbor gave her sixths eighths cup of milk, would she then have enough milk to make her 2 pancakes?
April 8, 2014

french
Do this sentence is direct or indirect je vais voir mes cousins
March 26, 2014

Physics
if you throw a 0.2 kg ball straight up at 8 m/s how high will it go
March 23, 2014

physics
What are the principles behind seatbelts and air bags that make passengers safer in a collision?
March 23, 2014

physics
If a motorboat travels 25km/h towards the sea, down a river whose velocity is 4km/h what is the boats velocity related to the shore? A, 21 km/h B, 29km/h C, 25 km/h D, 4 km/h
March 21, 2014

physics
if an airplane is traveling at 550 km/h into a head wind with a velocity of 40km/h what is the airplanes velocity relative to the ground
March 21, 2014

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