Saturday
August 30, 2014

Posts by drbob222


Total # Posts: 43,405

chemistry
71 mass number has abundance of 39.892 let x = mass number of other isotope. % abundance is 100-39.892 = 60.108 Then 71(0.39892) + 0.60108x = 69.723 (from periodic table) 28.32 + 0.60108x = 69.723 x = (69.723-28.32)/0.60108 = 68.9 which I would round to 69 as the probable ...
August 29, 2014

sig figs
I don't obtain that answer at all. 1.277E5 which I would round to 1.3E5
August 29, 2014

Chemistry
What ppt do you want. If you wand PbCl2 then Pb(NO3)2(aq) + 2HCl(aq) --> PbCl2(s) + 2HNO3(aq) Pb^2+(aq) + 2Cl^-(aq) ==> PbCl2(s)
August 29, 2014

chemistry
Follow my directions to get the answer or explain in detail what you don't understand about the directions. Retyping the question won't get it.
August 29, 2014

chemistry
2H2 + O2 ==> 2H2O mols H2 = grams/molar mass Using the coefficients in the balanced equation, convert mols H2 to mols O2. Now convert mols O2 to grams. That's grams mols O2 x molar mass O2.
August 29, 2014

is it correct algebra 2
20 is correct.
August 29, 2014

is it correct algebra 2
I was just showing you how I got the +3. The second term is -[4(-9)/2(6)] The numerator is 4*-9 = -36 and the denominator is 2*6 = 12 so the term is -(-36/12) = -(-3) = +3
August 29, 2014

is it correct algebra 2
When a - sign precedes a set of parentheses, the sign inside is changed. So -(-9-6). Adding inside the parentheses gives -9-6 = -15 and -(-15) = +15
August 29, 2014

is it correct algebra 2
That last term is -(-9-6) = -(-15) = +15
August 29, 2014

is it correct algebra 2
I use parentheses to keep from getting confused and what part goes with what part. (3b)-(4c/2b)-(c-b) but if you used (3b-4c/2b) - (c-b) of course you will get two different answers. [3(6)]-[4(-9)/2(6)]-[(-9-6)] = 18+[(36/12)]+15 = 18+3+15 = 36
August 29, 2014

is it correct algebra 2
- x - = +
August 29, 2014

is it correct algebra 2
2ac-12b 2(-4)(-9)-12(6) -8(-9)-72 72-72 0right ac/b + 2b/a -4(-9)/6 +2(6)/-4 36/6 +12/-4 = 6-3 = 3 =48/2 =3/2 3b-4c/2b-(c-b) 3(6)-4(-9)/2(6)-(-9-6) = 18+(36/12)+15 = 18+3+15 = 36 18-36/12-(-15) 18-36/12+15 -18/27
August 29, 2014

is it correct algebra 2
3ab-2bc a=-4 b=6 c=-9 3(-4)(6)-2(6)(-9) -12(6)-12(-9) -72- -108 = -72+108 = +36 -180
August 29, 2014

Chemistry
molar mass approx 9*12 + 8*1 + 4*16 = 108 +8 + 64 = about 180 mols = grams/molar mass = ?
August 29, 2014

Chemistry
You have 0.1 mol NaCl. That's correct. So there is 1 mol Na/1 mol NaCl and 1 mol Cl/1 mol NaCl. Right?
August 29, 2014

Chem Help
And the lower temperature is important because many compounds decompose at higher temperatures where they might normally boil.
August 28, 2014

Physical sciences
Another one is H2SO4 + NaOH ==> NaHSO4 + H2O Both equations are correct.
August 28, 2014

pmdc
1. mols CO2 = grams/molar mass 2. Using the coefficients in the balanced equation, convert mols CO2 to mols Mg. That will be mols CO2 x (2 mol Mg/1 mol CO2) = mols CO2 x (2/1) = ? 3. Now convert mols Mg to grams. g = mols x atomic mass.
August 28, 2014

Rounding nearest numbers
47,005 rounds to 47,000 to the nearest 1000. 49,904 rounds to 50,000 to the nearest 10,000
August 28, 2014

chemistry
3.7 mg/mL x (1000 ug/mg) x ? mL = 20 ug Solve for ?mL.
August 27, 2014

chemistry
How many mols do you want? That's M x L = 0.35 x 0.500 = 0.175 mols. Then grams = mols x molar mass = 0.175 x 58.44 = approx 10.3 grams NaCl but you need to get a more accurate number. b. There are 0.175 mol and that x 1E6 to give micromoles. c. % what? w/w; w/v; ? I will ...
August 27, 2014

Chemistry
It depends upon how big the fire is and what it is? Almost all labs are equipped with a CO2 fire extinguisher and in general I would use that being careful that the force of the CO2 out of the nozzle did not blow the flames off the bench.
August 27, 2014

Question
http://www.rosamondgiffordzoo.org/assets/uploads/animals/pdf/NakedMoleRat.pdf
August 27, 2014

Haley
If you draw the triangle and label the sides a,b,c and the angles A, B, C, then c^2 = a^2+b^2-2*a*b*cos C I labeled them arbitrarily and worked the cos law three times and came up with angles of 76.4, 57.7 and 45.9 and all of that adds up to 180 degrees.
August 27, 2014

chemistry
mols primary std = g/molar mass = 0.4125/HgO = approximately 0.002 but you need to do that more accurately. Convert mols HgO to mols OH^- = approx 0.004 (again redo all of this). HClO4 + OH^- ==> H2O + ClO4^- 0.004 mols OH will consume 0.004 mol HClO4 M HClO4 = mols HClO4/L...
August 27, 2014

Liz
The answer to a question is 564.90 what? If that is meters, then to the nearest 1 m is 565 and to the nearest 10 is 560 if you are rounding 5s to the nearest even number.
August 27, 2014

Liz
Would you check the numbers? The area of the lawn is 800 x 400 cm which is larger than the flower bed so the flower bed can't surround the lawn. Or am I missing something?
August 27, 2014

Chemistry Help!!!!!!!!!!!!!!
1. You don't have a picture in your book/experiment manual that gives you this information? 2. Many compounds decompose at normal boiling points under atmospheric pressure but under reduced pressure the boiling point is much lower where decomposition doesn't occur. ...
August 27, 2014

chemistry
On second thought if there were no other products the reaction must be 100% so the only question is how much Zn reacts with the 156g Br2.If just 35.6g Zn is provided, the product will be the same as with 87.1g Br2; therefore, 35.6/65.38 = 0.544 mols and that x 225.2 (molar ...
August 27, 2014

chemistry
Too many unanswered questions in this question. 156 g Br2 and how much Zn? Was the yield 100%.
August 27, 2014

Algebra
Doesn't (1,-4) mean x = 1 and y = -4? So -4 = -2(1) and I agree it isn't.
August 27, 2014

Chemistry
symmetry
August 27, 2014

Chem
Nope. That's not it. There are 6.02E23 molecules in a mol; therefore, mols in 1E26 molecules = 1E26/6.02E23 = ?
August 26, 2014

Chemistry
The bottom of the cap stopper is wet and if placed down it will pick up and be contaminated with anything on the table top.
August 26, 2014

chemistry
Here is the titration curve for glycine. https://www.google.com/search?q=titration+amino+acids&client=firefox-a&hs=ha9&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=jjr9U9jcKdH9yQTljIH4Dw&ved=0CCYQsAQ&biw=1024&bih=609#facrc=_&imgdii=_&imgrc=...
August 26, 2014

chemistry
This tutorial may help. http://www.chem.uiuc.edu/CLCtutorials/104/AminoAcidTitrations/SeeIt.html I would use the Henderson-Hasselbalch equation and substitute into the log term either 1/100 or 100/1 depending upon which way you want to write it.
August 26, 2014

Chemistry
Don't you have a set of safety tips in your course. Read that to answer these.
August 26, 2014

Chemistry
You don't want to contaminate the experiment.
August 26, 2014

Chem Help Please!!!
Na is in group I. F is in group VII (or 17 depending on the system your instructor is using) so F is -1. So the formula is NaF. NaF is ionic. N and H. N is in group V so it needs three electrons. H is in group I so it has 1 e. So the formula is NH3. NH3 is covalent.
August 26, 2014

Chemistry Help!!!!!!!!!!!!!!
I don't understand your trouble here. 6C is 1s2 2s2 2p2. If you want boxes with electrons in them we can't draw that on this forum.
August 26, 2014

chemistry
Let's call fluoroacetic acid HFAc. Then .........HFAc ==> H^+ + FAc^- I.......1.11......0......0 C.....-0.055....0.055...0.055 E......you do it..0.055..0.055 Ka = (H^+)(FAc^-)/(HFAc) Substitute the E line into Ka expression and solve for Ka, then convert to pKa. Note: ...
August 26, 2014

chemistry
delta T = i*Kb*m delta T = 20 Kb = 0.512 i for NaCl = 2 m = ?
August 26, 2014

Chem Help Please!!!
The lanthanides fill the 4f orbital. There are 7 4f orbitals, two electrons to each, 7*2 = 14.
August 26, 2014

chemistry
That looks ok to me BUT you have too many significant figures. If the 0.79 is density you are allowed only two so you should round the answer to 12. If the density is given as 0.790 you can have three and round to 12.2.
August 26, 2014

chemistry
m = mols/kg solvent. You know m and kg solvent, solve for mols. mols = grams/molar mass. You know mols and grams, solve for molar mass.
August 26, 2014

Science
I think B is the best answer there but note that the "old" experiment may not be appropriate for testing the revised hypothesis.
August 26, 2014

chemistry
Here is how you work the problem BUT I don't believe the molar mass is as small as you have it. Check your numbers. mol pepsin = grams/molar mass = 0.400/? = ? M = mols/0.055L = ? pi = MRT pi in atm. M = from above R = 0.08206 T = 273 + 30 = ? K. Convert atm to mm Hg; atm ...
August 26, 2014

Science
I agree, too, but I don't like any of the answers. D is the best answers there.
August 26, 2014

Chemistry
Cl2 has two atoms of Cl in the molecule. Each atom will have the same radius. If each atom had the same nucleon number it would be 35 and 35 or 37 and 37 but of course it could be 35 for one and 37 for the other and they would not be the same. The isotopic mass will differ for...
August 26, 2014

chemistry
delta P = 54.68-53.60 = 1.08 mm delta P = 1.08 = Xchlor*Posolvent 1.08 = Xchlor*54.68 Solve for X chlorophyll Then Nc = mols chlorophyll and Netoh = mols ethanol (Nc)/(Nc+Netoh) = X chlorophyll from above. Solve for Nc Then convert to grams. g chlorophyll = mols chlorophyll x ...
August 26, 2014

Analytical Chemistry
millimols HNO2 = M x mL = 0.300 x 500 = 150 mmols NaNO2 = 0.2 x 500 = 100 mmols HCl added = 6 x 1 = 6 ---------------------------- .........NO2^- + H^+ ==> HNO2 I.......100......0........150 add..............6.................. C........-6.....-6........+6 E........94.........
August 26, 2014

A lev chem
A. highly solbule. I2 dissolves easily in CCl4. Both are covalent compounds. "The components are both nonpolar and therefore have the capability of mixing." B. Almost insoluble. "One component is polar and the other is nonpolar, and therefore they don't have...
August 26, 2014

Physical Science
The density of gasoline is about 0.7 g/mL. What's the density of the wood? And is it a block or has it been shaped to displace enough gasoline to be able to float.
August 25, 2014

Math
177/88 - 564/88 = (177-564)/88 = ?
August 25, 2014

science
q = mass H2O x specific heat x (Tfinal-Tinitial) YOu know mass, specific heat, Tfinal and Tinitial. Solve for q.
August 25, 2014

ap chemistry
density = mass/volume Assuming that the powder doesn't dissolve and that all of it is submerged (none floats), d = 40/15 = ? g/mL
August 25, 2014

chemistry
What's the temperature? 0.78/0.0053 doesn't give a number that agrees with the literature.
August 25, 2014

chemistry
This appears not to be the complete question. It makes no sense as is.
August 25, 2014

physicsal science
9E18 (or 0.9E19) is 1 s.f. 9.1234E18 is 5 s.f.
August 25, 2014

chymistry
DO you have a question?
August 25, 2014

Chemistry
Do this in steps. Within a single phase use q = mass x specific heat x (Tfinal-Tinitial). For example. For ice at -22.0C to ice at 0C, it will be q = 43.0g H2O x specific heat ice x [0-(-22] = ? At a phase change use q = mass x heat fusion (at melting point) or q = mass x heat...
August 25, 2014

Chemistry
Au
August 25, 2014

AP Chemistry
This is a limiting reagent (LR) problem. I work these the long way because I think this way is easier to explain. Step 1. Write and balance the equation. 2Na3PO4 + 3Ba(NO3)2 ==> Ba3(PO4)2 + 6NaNO3 Step 2. Convert grams to mols. mols Na3PO4 = grams/molar mass = ? mols Ba(NO3...
August 25, 2014

electrical circuit
a is right on both accounts but I don't get your answer for b. P = E*I 90/115 = I R = E/I = 115/I from above. I get about 147 ohms and subtract 72 from that.
August 24, 2014

chemistry
All of that looks ok to me. Here is a good picture of ClF3. http://employees.csbsju.edu/hjakubowski/classes/ch123/Bonding/vsepr.gif
August 24, 2014

biochemistry
Use the Henderson-Hasselbalch e4quation and solve for base/acid ratio. 2.00 = pKa + log b/a b/a = ? Then a + b = 0.1M Solve the two equations simultaneously and obtain (base) and (acid). Convert to volume HCl and g alanine. You will need the concn of HCl you have available; I ...
August 24, 2014

Physical Science
In addition to the site provided by Ms. Sue the following information may help. Oxygen is an element and hydrogen is an element. If you combine oxygen with hydrogen the compound, water, is produced. Water, the compound, has different properties than either hydrogen or oxygen.
August 24, 2014

chemistry
mol ethylene glycol = 35.00/molar mass = ? mol H2O = grams/molar mass Xethylene glycol = n eth/total mols psoln = Xethyl gly*PoH2O
August 24, 2014

chemistry
See your post on O2 in the lungs. If you can't find k for CO2 perhaps I can help with that.
August 24, 2014

chemistry
http://www.rapidtables.com/convert/electric/ev-to-volts.htm
August 24, 2014

chemistry
That number, if eV, looks ok to me.
August 24, 2014

chemistry
p = kC partial pressure = k*C (in molarity) k = 769.2 L*atm/mol Plug in 40 mm O2 (convert to atm first) and k and solve for C (in mols/L). Convert to grams.
August 24, 2014

Chemistry
This is a two equation and solve simultaneously. Al reacts with 8-hydroxyqinoline (Q) to form Alq3. Mg reacts similarly to form Mgq2. Let X = weight Alq3 and Y = weight Mgq2, then -------------------- equation 1 is X + Y = 1.0843 The second equation is obtained from the Al2O3 ...
August 24, 2014

Chemistry
You must have a table or a graph showing solubility of CsCl at various temperatures. I don't think very many people have all of the solubility tables memorized. http://chemicals.etacude.com/c/more/cscl.html
August 24, 2014

Physical Science
This site gives the current definition but also the history before. http://dictionary.reference.com/browse/meter
August 23, 2014

Physical Science
From the first set, use mass = volume x density to determine the mass of the bread. Then use that with the second set and mass = volume x density to calculate density (with the new volume of 2400 cm3)
August 23, 2014

chemistry
A can't be right but check out the others.
August 23, 2014

Chemistry
You know mass ppt is 0.7121g and that is the piperazine diacetate (pipd). Calculate the molar mass of ppd. Then calculate the molar mass of the piperzine (pip). Convert 0.7121g pipd to g pip this way. 0.7121g x (molar mass pip/molar mass pipd) Then mass% = (mass pip/mass ...
August 23, 2014

thermodynamics
Did you not type in the value of the number of mols, n?
August 23, 2014

add note---thermodynamics
Don't forget to convert C (after you've converted F to C) to Kelvin. K = 273.15 + C If this is an engineering problem you can use Rankin
August 23, 2014

thermodynamics
Convert 80 F and 120 F to C. Convert 40 psig to psia. 40+14.7 = ? psia. Then (P1/T1) = (P2/T2) and solve for P2. P2 will be in psia.
August 23, 2014

Math percentage (Money problem tax, discount)
Let x = price of the book before discount x-0.15x = 26 1x-0.15x = 26 0.85x = 26 x = 26/0.85 Punch in 26 on the calculator, hit the divide button, type in 0.85 and hit the enter = button.
August 22, 2014

chemistry
% w/w = (grams solute/g solution)*100 % = [grams solute/(g solute + g solvent)] % = [5 g urea/5 g urea + g solvent)]*100 = 16.2
August 22, 2014

AS Chemistry
http://www.chemguide.co.uk/mechanisms/elim/dhethanol.html
August 22, 2014

chemistry
1.06E-6 M/mm x 760mm = ? mols/L. ? mols/L x molar mass = g/L and convert to g/mL.
August 22, 2014

Chemistry
http://en.wikipedia.org/wiki/Noble_gas#Occurrence_and_production Scroll down to "occurrence and production". The table gives you the data.
August 22, 2014

chemistry
I may have missed something but I don't think this problem has been posted correctly. If I start with 20 mL CO and no mL CO2 it will form 20 mL CO2. If I start with no CO and 20 mL CO2 it will have 20 mL CO2 after the spark. I don't see how you can get less than 20 if ...
August 21, 2014

chemistry
40% w/w HCl means 40g HCl in 100 g solution. That is 40g HCl in (40g HCl + 60g H2O). mols HCl in 40 g = 40/about 36.5 = about 1.1 but you need a more accurate number. Then m = mols/kg solvent = 1.1mol/0.060kg solvent = ?m. I think you need density to determine the molarity but...
August 21, 2014

chemistry
? means I assume you can do what comes before the ? g = mols x molar mass. You want to know grams Co(NO3)2. You know mols Co(NO3)2. You can look up the molar mass Co(NO3)2. So to obtain grams (which you must do to solve the problem) you take mols (0.471) from above and ...
August 21, 2014

chemistry
0.471 m means 0.471 mols Co(NO3)2 in 1 kg solvent. How many g Co(NO3)2 is 0.471 mols? That's g = mols x molar mass = ? = approx 86 grams Co(NO3)2 Total mass of the solution then is approx 86 + 1000 = approx 1086g total. % = (g solute/total grams solution)*100 = ?
August 21, 2014

chemistry
Didn't you understand the NaOH answer? Wouldn't this be answered the same way.
August 21, 2014

Chemistry
1.50 g NaHCO3 in 17.1 g H2O. So in 100, there is 1.50 g NaHCO3 x (100/17.1) = approx 9 but you need to do it more accurately. % NaHCO3 = (g NaHCO3/total g)*100 = (9/109)*100 = ? %H2O = (gH2O/total g)*100 = (100/109)*100 = ?
August 21, 2014

chemistry
7.06% w/w NaOH means 7.06g NaOH in 100 g solution. So in 187 g there will be 7.06g NaOH x (187/100) = ? or if you want to do it by the factor method it is 187 g solution x (7.06g/100g) = ?
August 21, 2014

physical science
When each is acting on the same line in the same direction then the forces will add to be 5N + 7N = 12 N.
August 21, 2014

chemistry
I do limiting reagent problems the long way. There are shorter ways to work this problem but I think they are more difficult to explain. H2 + Cl2 ==> 2HCl mols H2 = grams/molar mass = 3.56/2 = 1.78 mols Cl2 = 8.94/71 = 0.126 Using the coefficients in the balanced equation, ...
August 21, 2014

science
We need more information. Are the resistors in series or parallel. How many resistors.
August 21, 2014

General Physical Science
volume in cc = 65 cm x 45 cm x 80 cm = ? Assuming the density of the water is 1.00 g/cc, then mass = volume x density There are 1000 g in 1 kg.
August 21, 2014

oops--physical science
That's 1024 km/11.5 = ? km/hr which works out to be about 55 mph. No speeding ticket today. :-)
August 21, 2014

chemistry
if heated produces iron (II) sulfide
August 21, 2014

chemistri
5.20% w/w means 5.20 g Cu(NO3)2 in 100 g solution. 1. Convert 5.20g to mols. mols = grams/molar mass. 2. Convert 100 g solution to mL using density. mass = volume x density or volume = mass/density = 100g/1.48 and convert mL to L. 3. Then M = mols from step 1/L from step 2
August 20, 2014

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