Concentration Definition and 550 Threads

I have a homework on Solid state device the question is :"If a Si sample is doped with 10^14 boron atoms per cm3 then determine the carrier concentration in the Si sample at 300K."[/b] I thought that the concentration is calculate by n = 2[(2pi*un*kT/h^2)]^(3/2) is this right formula ...

Homework Statement At a height of 300km above the Earth's surface, an astronaut finds that the atmospheric pressure is about 10-8 mmHg and the temperature 500 K. How many molecules are there per milliliter at this altitude? Homework Equations The Attempt at a Solution I first...

Hi everyone. I was doing a past paper. I got some of the question wrong about finding out Volumes and Concentrations Could you please Help me with these Question. I have enclosed the question sheet that has all the work done on it. If you can't see image properly then use this link...

Homework Statement 0.00116 moles of a weak monoprotic acid was dissolved in 25.0 mL in water. This solution was titrated with 10.0 mL of 0.0633 M NaOH. What are the concentrations of HA and A- at this point in concentration? Homework Equations The Attempt at a Solution

Homework Statement The problem can be found here: http://alex.fangsoft.net/math.pdf I have completed Task #2, it is Task #1 that I am very lost on. Our teacher has really thrown us head first into the water with this one, I am very unfamiliar with differential equations and their...

Homework Statement This is the lab I did: http://chemistry.depaul.edu/wwolbach/205_207/11.pdf only steps 1,2, & 3 was performed Homework Equations MV1=MV2The Attempt at a Solution I need help finding the concentration of Ca 2+ and Mg 2+. I already know the basics of it, but I really don't...

This might be a stupid question, but it has me kind of confused. In diffusion, molecules will flow from high concentration to low concentration, and the explanation typically given is that in the laws of thermodynamics there is a net increase in entropy over time. But I am trying to think of...

I did a lab using an electrochemical cell to establish a relationship between cell potential and concentration. I derived two equations from lines of best fit. One is Cell potential of Ag vs. Cu Concentration: y = -0.04520x+0.5515. The other is cell potential of Zn vs. Cu concentration: y =...

Hey guys, looking for some advice from some more experienced engineers and students. I'm currently a junior in the Mechanical Engineering program at my university, but I've recently begun to think that this may have been the wrong choice. I don't know if this is how it is in other programs...

I have a project in my grade 11 biology class to design a controlled experiment showing how some factor affects plant growth, specifically radishes. I have decided to add urea as a nitrogen fertilizer to one group and do nothing to the other leaving all other factors the same between the two...

Homework Statement show the calculation for [HT-] in your saturated solution for part 2. titration- 14.30ml 0.04M sodium hydroxide i used. 2.005g KHT and 8.5g NaNO3 i diluted the NaNO3 to 100ml and added 2g KHT. filtered it then titrated with sodium hydroxide. Homework Equations...

A 40 ml volume of iron nitrate (1.8M) is mixed with 21.5ml of iron nitrate (0.808M) calculate the molar concentration of the final solution. what would be the steps to solve this problem. I am assuming i have to find the number of moles of each given the data but from there I am unsure.

Homework Statement Hello, I'm creating a Michealis/Menten curve and need to find the X values for the graph. Homework Equations These are the instructions given to find the X values: To obtain the X value, plot the molar concentration (molarity) of substrate used in each well...

hello everyone, i need to do a beers law plot. i got the percent transmittance which i converted to absorbance but I am not sure how to get the molar concentration. i found the max wavelength to be 515 nm. I prepared three 8-10ml diluted solutions by mixing a standard solution x (0.100M) and...

Homework Statement When 38 mL of 0.1250 M H2SO4 (sulfuric acid) is added to 100 mL of solution of PbI2 (Lead(II) Iodide) a precipitate of PbSO4 forms. The PbSO4 (Lead(II) Sulfate) is then filtered from the solution, dried, and weighed. If the recovered PbSO4 is found to have a mass of 0.0471...

Homework Statement Suppose the concentration of phosphate in Phoenix tap water is 7.3 ppm (mass based), then what is the concentration of selenium in milligrams per liter? The density of water is 1 g/mL. Homework Equations Phosphate: PO4-3; 7.3 parts/million The Attempt at a Solution...

What actually happens to concentration of species at neutral point of an indicator (say that of a weak acid)? HIn----> H+ + In- (In=indicator)

Homework Statement Why don't we take into consideration the concentration of pure solids and pure liquids in equilibrium constant expression? I read that their concentration per unit volume does not change. If the concentrations (moles per litre) don't change then it won't undergo any...

Homework Statement Nitric acid is commercially available as a 72% ( w/ w) solution ( density, 1.42 g/cm3). How many milliliters of this reagent are needed to prepare 2.00 L of a 1.00M HNO3 solution? Homework Equations C%= (g HNO3/ g Solution) * 100 The Attempt at a Solution So...

Hello people, I'm needing help in calculating data or treating the data. I get measures of counts vs channel, using a silicon detector for detecting radon progeny. These peaks are Po218 and Po214, now how obtain or how understand... obtaining the concentration of radon...

Hello, everyone! I could not imagine what force makes this convection under concentration gradients , no matter how hard I thought. Maybe we can use principle of entropy increase to explain it, but that is not vivid to me. anyone can help me? Thans!

Homework Statement The arsenic in a 1.42 g sample of pesticide was converted to AsO43- by suitable chemical treatment. It was then titrated using Ag+ to form Ag3AsO4 as a precipitate. If it took 33.7 mL of 0.113 M Ag+ to reach the equivalence point in this titration, what is the mass...

Hello i have a problem with my homework and i hope someone can help me? because i really don't know how to calculate this so its translated with google translate :blushing: Major customer PCB (polychlorinated biphenyls, a hazardous substance used in manufacture of transformers and...

calibration curve and concentration?? The following is all of the data I have from a AAS/FES for water analysis. I need to make the calibration curves for calcium and sodium. and then I have to find the concentration. can someone please help me with this? i know that the Abs values will be one...

Homework Statement A 0.0450 M solution of para-aminobenzoic acid had an absorbance of 0.844 at 267 nm in a 1.00 cm cuvet, and an absorbance of 0.034 at 240 nm. A 0.0366 M solution of nicotinic acid had absorbances of 0.010 and 0.755 at 267 and 240 nm, respectively. A MIXTURE of PABA and...

Hey guys, just a quick question: If you have a solution of nitric acid, and if you were asked to find the concentration of H+ ions in the solution, would you find the concentration of H+ ions in the acid plus in the water? Re-wording of question: you find the moles of H+ ions in acid +...

Alright guys, I am a little bit confused on how to find the concentration of ions in a reaction. In a solution, it is relatively easy. Are the number of ions in the beginning the same they are in the end? Please give me some general guidelines: i know to begin with a balanced equation ...

Homework Statement At a certain temperature, the reaction 2NO2(g) --> 2NO(g) + O2(g) progresses in a 4.00 liter vessel at a rate of 0.88 mol · L−1· s−1. What is \Delta[NO2] \Deltat under these conditions? Answer in units of mol · L−1· s−1. Homework Equations C = n/v ...

Suppose i have a spherical volume of 100nm with a solution 30mM. How many solute molecules it corresponds to? My answer is about 6400...is that correct? im just not sure i did some conversion correctly... Thanks Alfio

Hello everyone, This a question related to ATP pump that uses electrochemical gradient to provide energy to make ATP. I have few questions about this. 1. In an electrochemical gradient there are more positively charged ions on one side of the membrane(In proton gradient case). So why do...

Question: A voltaic cell is constructed with two silver-silver chloride electrodes, each of which is based on the following half-reaction: AgCl(s) + e- = Ag(s) + Cl-(aq). The two cell compartments have [Cl-]= 1.41×10−2 M and [Cl-]= 2.70 M, respectively. What is the emf of the cell for the...

What exactly is the difference between a concentration cell and galvanic/voltaic cell? How do you know what are the half reactions? Also, is the ion and electron flow the same found in voltaic cells or is it the opposite? My biggest question of electrolysis has to do with Cl species...

Hope you can give me a hand here guys. I'm finding the whole carrier concentration thing a bit confusing! Si doped with say 10^17 P (/cm3). At 300K, calculate n, p, E_F (Fermi energy). Now I know the relations such as n=(N_c)exp[(E_c-E_F)/kT], N_c given I just can't figure out...

Homework Statement You have a solar cell with a constant electron density n, and known dimensions. I am looking for the change in density due to diffusion, so basically the diffusion current. All other relevant parameters are also known (temperature, D diffusion constant, etc.) To summarize...

Huge concentration of energy! 1.It's told that before the big bang everything was comressed in a very small space (as small as an atom, some say as small as a coin). My point is even if matter was not created at that time, there should be some limit to the concentration of energy (or...

Tomorrow I have an exam and my teacher gave us a hint to understand why the concentration to volume curve looks like the formula x2 but I can't find it anywhere's can someone take a quick second to explain. C = mol/L

I'm trying to find PhD programs in math that offer number theory as a focus. Where do I find this sort of information besides looking at each individual school? Is there some sort of catalogue or list that readily offers this information?

Homework Statement A sample of air was collected to assess the safety level of nitrogen trichloride in the air around a swimming pool. It was found that the air contained 0.0025% by mass of nitrogen trichloride. Calculate the molar concentration of nitrogen trichloride in the sample collected...

I am really confused about how to approach the following question. Can someone please help me out? A buffer is made by mixing CH3COO- and CH3COOH of the same concentration of 0.5M. If the volume of the former is v1 and the latter is v2, show algebraically that the following will always hold...

How do you get from a concentration to an effective dose? For example, if you have 10-9 Ci/cm3 of tritium in a human body, then how do you get the effective dose to that body? Thanks

There is a tank that contains 10,000 gallons of a weak salt solution. The salt concentration is 1300 parts per million. Now we start adding 130 gallons per minute of water and also remove 130 gallons per minute of salt solution. Thererore the salt solution concentration gradually decreases to...

Solution A: is a dilute soultion of potassium iodate, KIO3 which is the source of iodate, IO2(1-) Solution B: contains some starch and the other reacting species, the hydrogen sulfite ion, HSO3(1-) 1. In a small beaker obtain about 50mL of solution A (0.02 M IO3(-)) and in another small...

Homework Statement I'm doing my best to figure out how these answers were worked out. We discussed it as a class but then moved on to another topic and after that, I just lost it because of the topic I'm doing right now. I basically need to explain how these answers can be worked out...

In what general way could I go about finding out M of Ca 2+ given a standard calcium carbonate solution and after the addition of 3 X 10 ^ -4 M of sodium carbonate at 25 degrees Celsius. I haven't done chemistry in years and would appreciate any help getting started.

Homework Statement How many grams of NaCl (molecular weight=58.5g mole^-1) would you dissolve in water to make a 0.5M NaCl solution with 500mL final volume? Homework Equations The Attempt at a SolutionSince, 1 L of 58.5g NaCl is equal 1M I used this to firstly convert 500ml into...

Hello everyone. Just a quick question: Could somebody explain to me what atomic concentration is, and whether there is a list of all the atomic concentration of the elements somewhere in the internet. The 1st time I heard the term, I typed it on wikipedia and google, surprisingly the...

Hello, I have a rod of two different diameters and I'm trying to find the stress concentration at the chamfer between the two diameters. I understand how to find the stress concentration factor, K, if the joint was a fillet (using r/d and D/d to find K in the appropriate table). However I can't...

Upon some calculation I arrive to the expression: d2DPn(x)/dx2 = DPn(x)/Lh2 Where: DPn(x) = Pn(x) + Pno - excess minority carriers (holes) concentration in the n-type part of the pn junction. Now the roots to the characteristic equation are +/- 1/Lh where Lh is the length of the...

I'm currently finishing up my third semester in Civil Engineering. Recently a couple of my friends switched from standard "Civil Engineering" to "Civil Engineering with Concentration in Management" So this got me thinking if I should switch.. If i switch, I would not be taking...

This may not even be a valid question, as I may have misunderstood; but here goes... At 25C, the KW of water is 1 x 10-14 If you increase the amount of hydogen ions present, why does the concentration of hydroxyl ions present alter in such a way that the KW is maintained (i.e. the product of...