# Posts by DrBob222

Total # Posts: 55,883

Chemistry
Change radius of 7.0E5 km to cm; then (4/3)*pi*r^3 = volume of star. Change mass 1E36 kg to g. Density = mass/volume Post your work if you get stuck.

science
two? n-butane isobutane

chemistry
yes. coefficient.

chemistry
yes

Physical Science
right

Chemistry
You made a typo. Volume sphere = (4/3)*pi*r^3 Using the volume, calculate the volume of the sphere, then density = mass/volume Post your work if you get stuck.

chemistry
This is a limiting reagent (LR) problem. This procedure will find the LR as well as finish the stoichiometry. 1. Write and balance the equation. 2a. Convert 5.07 g butane to mols. mols = grams/molar mass = ? 2b. Do the same and convert g O2 to mols. 3a. Using the coefficients ...

Physical Science
yes.P1*V1 = P2*V2

Physical Science
one, not wone

Physical Science
I agree with this one. The wone about kinetic I agree with too but my answer won't post.

Physical Science
I agree

chemistry
I agree

chemistry
Is that 20% by mass (w/w) or 20% by volume (w/v)? I assume since it's 400 grams that 20% is 20% w/w. 2o% w/w means 20 g solute/100 g solution' therefore, 400 g will solution will be just 4 x that or 20 x (400/100) = ? Concentration in what units. I assume you mean % w/...

Chemistry
cc x M = cc x M 250 x 0.10 = cc x 2.0 Solve for cc, pipet that amount from the 2.0 M stuff into a 250 cc container, add water to the mark, shake, stopper.

CHEMISTRY
What is step 7? For that matter what are steps 1 through 6? And what does all that have to do with NH4Cl and SiO2? We aren't privy to the experiment you conducted.

Physical Science
I agree.

CHEMISTRY LAB 2
%C = 100% - %A - %B = ? g A = 25.0 x 0.335 = ? etc.

Chemistry
See above. NOTE. You will get better service if you stick to the same screen name.

Chemistry
NH3 + HCl ==> NH4Cl mols HCl = M x L = ? mols NH3 = the same. Look at the coefficients in the balanced equation. M NH3 = mols NH3/L NH3 = ? For percentage is that w/w, w/v, what? I will assume w/v (weight/volume). mols NH3 from above x molar mass NH3 = grams NH3. Then (g ...

Kate. Erin. Please stick to the same screen name. YOu get better service that way.

Chemistry - Chemical Kinetics
I don't see anything but numbers for concentrations; i.e., no numbers for rate constant or times. Nor anything about how the experiment was conducted.

Chemistry
Convert 35.01 pounds to kg. There are 2.204 pound/kg. 72.1 mg drug/kg x # kg = mg drug/day. Twice per day so divide by 2 for per dose. Your liquid is 126.0 mg drug/mL so 126.0/mL drug x # mL = per dose from above and solve for # mL. Watch the significant figures. Post your ...

Chemistry
You must balance the equation first. Fe2O3(s) + 3CO(g) --> 2Fe(s) + 3CO2(g) Now I see 3 mols CO2 per 1 mol Fe2O3.

Chemistry
Help us help you by answering the following. 1. How can the product be ONLY CO2 and H2O. Where is the Pb? And is that Pb, or PbO, PbO2, or Pb3O4? I suspect Pb but I don't know that because you don't list the temperature of the combustion. 2. Post your work for the ...

AP Chemistry
Follow the directions by Bunny and post your results. We will check it if you wish.

Chemistry
I don't see a question here.

AP Chemistry
This is done the same way as your other percent problem.

AP Chemistry
Cl2 + 3F2 ==> 2ClF3 mols F2 = g/molar mass = ? Using the coefficients in the balanced equation, convert mols F2 to mols Cl F3. Now convert mols ClF3 to grams. g = mols x molar mass = ? This is the theoretical yield (TY) assuming 100% of the product is formed.The actual ...

AP Chemistry
mols = g/molar mass

chemistry
NaOH + HCl ==> NaCl + H2O mols NaOH = ? Look at the reaction equation. 1 mol NaOH = 1 mol HCl; therefore, mols HCl = mols NaOH. Then mol/dm3 HCl = mols HCl/dm3 = ?

Chemistry
17 g x (16 oz/453.6 g) = ?

College Chemistry
I believe IUPAC recommends that be written as 273.15 K (without the degree symbol.)

Chem(net eq'n)
What is your basic question about net ionic equations. What is it you don't understand.

Chemistry
What's wrong with the response I gave to your original post at 11:53 yesterday?

Chemistry
PV = nRT

Chemistry
Fe2O3(s) + 2Al(s) ---> 2Fe(l) + AL2O3(s). Here are the steps to work any regular stoichiometry problem. 1. Write and balance the equation. You have that. 2. Convert 15.0 g Fe to mols. mol = grams/atomic mass Fe. 3. Using the coefficients in the balanced equation, convert ...

Ms Sue and other tutors https://www.jiskha.com/di
Again, thanks to all. Bob

message for Dr. BOB
Thank you Steve and Damon. I had not seen this. I looked for the original to see who posted this initially but didn't find it. Also, thanks to Marilynn for calling this to my attention or I never would have seen this. Bob

Science
Because gravity is not the same on each planet.

physical science
They have the same speed since speed is a scalar quantity. They do not have the same velocity since velocity is a vector quantity. They are moving at a constant speed. What do you thing the acceleration is?

Buffer
Well, that's tough. I didn't attend any of your classes and I don't have the supplemental readings. But here is what I would do. a is acid and b is base. pH = pKa + log (b)/(a) 4.6 = 4.76 + (a)/(b) Solve for a/b. That's equation 1. Then (a) + (b) = 0.15, That&#...

plus--Physical chemistry
For percent, multiply the above by 100.

Chemisty
I don't see a question here with any information.

Chemistry
cost/L of 0.5L bottle is 0.78/L x 1 L/0.5L = 0.??/l cost/qt for 24 oz stuff is 0.980/oz x 32 oz/24 oz = approx 1.30/qt but you need an exact number. Then we know 1 qt = 0.946 L so approx 1.30/qt x 1 qt/0.946 L = ?

Chemistry
The thiocyanate ion is the limiting reagent in the 1:1 rxn of iron(III) and SCN^-

Chemistry
Interesting but I don't see a question.

Chemistry
I just responded to your first post down below about the pH 6 thing. The absolute value is not the way to go.

Chemistry
I showed you how to do this for pH 7.5. You do it the same way for pH 6 and the answers are not the same. In instead of us working this again, why not show your work and let us find the error.

Chemistry
Surely you have a graph or a table showing/telling you the solubility at 100 C.You need to look that up; I haven't committed the solubility of thousands of chemicals to memory (yet).

Chemistry
NO. The M HCl = 0.24/40 = 0.006 and pH = -log (HCl). You're trying to put 0.24/40 as the pH into the HH equation. This is not a buffer solution anymore smf -/24/40 is (HCl) and not the pH. All of the base is gone. pH is about 2.2 or so isn't it?

Chemistry
Almost. The -0.263 (which I rounded to +0.24) is the excess HCl present (not HPO4^-). You have used all of the HPO4^- and the 0.24 mmols represents what is left of the 0.5 mmols HCl. So you need the pH of that M HCl. Then M = mmols/mL = 0.24/40 = ? and convert to pH. Obviously...

Chemistry
If you get a negative number it means there is more HCl added than the base can handle so that is excess HCl which is a strong acod. Then M HCl is millimols/mL and pH from there.

Chemistry
This is a little involved. I'll pick 7.5 and go from there. First, you have two equations to solve simultaneously. Here is how you get to equation 1. pH = pKa + log b/a 7.5 = 7.2 + log b/a 0.3 = log b/a b/a = 2 and b = 2a. Equation 1. Technically, one should work with M; ...

science {chemistry)
Use the Henderson-Hasselbalch equation. Post your work if you get stuck.

Chemistry
When 20 mols of WHAT decomposes.

Chemistry
2PbO(s) + 2NaCl(aq) + H2O(l) + CO2(g)==> Pb2Cl2CO3(s) + 2NaOH(aq) This is a limiting reagent problem(LR). mols PbO = grams/molar mass = ? mols NaCl = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols PbO to mols of your product. Do the same...

chemistry
You must have made a typo. 5.82% Sn is correct.

chemistry
% metal in sample = (mass metal/mass sample)*100 = ? mm stands for molar mass.am is atomic mass. mass Sn = mass SnO2 ppt x (am Sn/mm SnO2) = ? mass Zn2P2O7 in 1/2 sample is 0.2231 and x 2 = mass Zn2P2O7 in all of the sample. mass Zn = mass Zn2P2O7 x (2*am Zn/mm Zn2P2O7)*100...

chemistry
My best educated guess is c but I haven't been able to confirm that.

chemistry
I would call it 1-propanesulfonic acid.

chemistry
That isn't my choice.

chemistry
Define ionization. Does that change the identity of the substance? Define dissociation. Does that change the identity of the substance? Define dispersion. Does that change the identity of the substance? If you will define those three terms and see which one(s) change the ...

Chemistry
mols ZnCl2 = grams/molar mass = ? volume H2O = mass H2O/density H2O = ? M = mols/L. From the problem it sounds like you want molality.

Chemistry
Is this a low level or an advanced chemistry class? Assuming advanced, I would do this. H2SO4 is a strong acid for the first ionization but k2 for H2SO4 is 0.0102. H3PO4 has 3 k values but only the first one is large enough to matter. k1 is 0.00711. My rationale would be that ...

chemistry
wavelength = h/mv You have wavelength, h, and v (0.92*3E8 m/s). Calculate m. Post your work if you get stuck.

chemistry

Chemistry
Which of the recommendations do you not know how to do? Post the ones you know how to do and explain in detail the problem you have with the others.

chemistry
No, q high pH means it is basic.

chemistry
Note that you wrote potassium hydroxide but gave the formula of NaOH which is sodium hydroxide.

chemistry

Chemistry
You didn't give a number.

Science
They need to get the energy to the things they want to do. Food provides that. They need a liquid to move the nutrients around the system. Water provides that. Finally they need to rid the system of the materials not used in the food.

chemistry

Chemistry
a.Google electrolyte and electrode for definitions and examples. b. Solid NaCl is held by electrical forces in a solid network of Na^+ and Cl^-. They cannot move around. In solution the NaCl dissociates into the ions and are free to move.

Chemistry - half life
t1/2) = 1/k(A)

Chemistry - Rates
Use the Arrhenius equation. Post your work if you get stuck.

@Scott---CHEM
I see that now and thanks for pointing it out to me. I wondered at the time why you had agreed with 100. However, 100 still isn't right, is it? Technically, shouldn't the answer be 1E2 grams since there is only 1 sig fig in 100 g? Therefore,we should quote the answer ...

CHEM
The answer is not 100 g. If the answer key says it is 100 g then the answer key is not right. If you will post your work I will find the error you are making. And yes, I understand all about converting grams to mols and back to grams. I suspect what you have not done correctly...

CHEM
No, the answer is not 100 g. Look at what Scott asked about moles. And your response about grams appears that you think you can go from grams to grams without going through mol ratio. You can't.

chemistry
You read right. Gases are more soluble in cold water than in warm water.

chemistry
Right. But why not c ?

chemistry
No. Remember that like dissolves like.

chemistry
Probably b is the correct answer; however, please note that some substances are more soluble in cool water than in hot water.

Chemistry - van't Hoff factor
I don't get it. I can't figure out exactly what the question is (yes, I know they want i). What is the connection between the two statements? Are these two problems? What does "a salt solution" mean? Is that NaCl or some other salt. Is it the same salt as in ...

process chemical
Let x =kg of 1%. (100 kg*5) = (x*1) = (100+x)*4 Solve for x.

Science
Maybe I'm out of touch and need to go back to school.When I read this I consider rust (if Fe2O3) as a pure substance. Actually it isn't Fe2O3 either but a mixture of Fe2O3 and FeO. When I read nickel I read 5 cent piece and that isn't pure. I would chalk this up to...

chemistry
The error is you used H2 and not H. 6.6/1 = 6.6 so you have C = 5 H = 6.6 O = 2 Now multiply everything by 3 to get C 15 H 19.8 O = 6 Then round to whole numbers. I didn't divide by the smallest number, as I'm supposed to do, I just skipped that step since I had two ...

chemistry

Chemistry
This is a limiting reagent (LR) problem. Mg3N2 + 6HOH --> 3Mg(OH)2 + 2NH3 mols Mg3N2 = g/molar mass = ? mols H2O = g/molar mass = ? Using the coefficients in the balanced equation, convert mols Mg3N2 to mols Mg(OH)2 Do the same to convert mols H2O to mols Mg(OH)2. It is ...

Chemisty - Colligative properties/freezing point
First, the formula to use is delta T = Kf*m and delta T is 0.35 (not 0.34) Follow that through and you get about 292 for the experimental molar mass. None of the answers match. I think the freezing point of pure water at -0.58 C sounds fishy (it should be zero) BUI ...

oops--Chemistry
https://www.jiskha.com/display.cgi?id=1505246080

Chemistry
Here is a similar problem I worked.

chemistry
a is a better choice than c.

chemistry
C electronegativity isn't strong enough to pull the electrons from O So C and O share electrons.

Chem.
(V1/T1) = (V2/T2) Post your work if you still have questions.

Chemistry - Van't Hoff Factor
I suggest you post the problem with all of the details.

chemistry
yes

chemistry
CH3CH2CH2COONH4 + heat ==>CH3CH2CH2COOH + NH3 21.0 x (mm product acid/mm reactant) x 0.5 = ? whee mm stands for molar mass.

chemistry
dT = Kf*m or dT = Kb*m You know m, look up Kf and Kb, solve for dT in each case. For the new freezing point subtract from the normal freezing point. For the new b.p., add to the normal boiling point. Post your work if you get stuck.