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33 views

How to study chemistry effectively, quickly and enjoyably [on hold]

I'm not sure if this question belongs in the meta section or not, and if it does, do tell me and I'll repost it elsewhere, thanks! Basically, I have 40+ days to my final exam. I've been trying to ...
0
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1answer
39 views

calculate the amount of energy in KJ necessary to convert 346 g of liquid water from 0 C to water vapor at 182 C

Calculate the amount of energy in $\mathrm{KJ}$ necessary to convert $346~\mathrm{g}$ of liquid water from $0~^\circ\mathrm{C}$ to water vapor at $182~^\circ\mathrm{C}$. The correct answer is ...
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1answer
34 views

How to find out if ions are oxidised/ reduced based on half cell potentials

I have a hw question that I keep getting wrong and I need some help on? Assuming standard conditions, answer the following questions. (yes/no) Is $\ce{Fe^{2+}(aq)}$ capable of reducing ...
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2answers
440 views

is this statement always true? : The more -OH functional groups in the molecule, the more is its viscosity

Is the following statement always true? The more $\ce{-OH}$ functional groups in the molecule, the more is its viscosity? I think it is true, because it is known that weak intermolecular forces ...
2
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1answer
47 views

Electrochemistry question about equilibrium in half cell reaction

Given the following half-reactions: $\ce{Ce^{4+} + e− -> Ce^{3+}}$ E° = 1.72 V $\ce{ Fe^{3+} + e− -> Fe^{2+}}$ E° = 0.771 V A solution is prepared by mixing ...
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0answers
34 views

What is the white crystalline precipitate obtained when magnesium ions react with ammonium biphosphate in the presence of ammonium hydroxide? [closed]

What is the white crystalline precipitate obtained when magnesium ions react with ammonium biphosphate in the presence of ammonium hydroxide? Please give the formula as soon as possible.
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2answers
26 views

Find the color of the solution

The acid-base indicator methyl red has a $K_{a}$ = $1 \times 10^{-5}$. Its acidic form is red while its alkaline form is yellow. If methyl red is added in a colorless solution with a $pH = 7$, the ...
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3answers
38 views

What is the partial pressure of oxygen in this mixture of oxygen and argon?

A $19.3\:\mathrm{g}$ mixture of oxygen and argon is found to occupy a volume of $16.2\:\mathrm{L}$ when measured at $675.9\:\mathrm{mmHg}$ and $43.4\:\mathrm{^\circ{}C}$. What is the partial ...
0
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1answer
37 views

Equilibrium Graphs

What if I2 and H2 began at the same concentration - then do we start at the same point? ... or is it acceptable to start at different concentrations...
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1answer
19 views

Equilibrium Practical Discussion Help

I understand the theory, but am struggling to answer the following discussion questions: (i) Why isn't this represented by: Fe3+ (aq) + 3 SCN- (aq) <-> Fe(SCN)3 (aq) Why do we dilute the ...
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0answers
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Analytic Chemistry question [closed]

On being heated in oxygen 5.72 grams of red metal oxide 'A' was converted to 6.36 grams of black metal oxide 'B'. When 4.77 grams of 'B' was heated in a stream of H2(dihydrogen), 3.81 grams of metal ...
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1answer
15 views

A 1.00 L gas at 100. °C and 500. torr contains 70.0 % He and 30.0 % Ne by mass. What is the partial pressure of He?

A $1.00~\mathrm{L}$ gas at $100~^\circ\mathrm{C}$ and $500~\mathrm{torr}$ contains $70.0\%~\ce{He}$ and $30.0\%~\ce{Ne}$ by mass. What is the partial pressure of $\ce{He}$? My answer is ...
2
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1answer
52 views

What do the half-reactions need to be for balancing a redox reaction in an acidic medium?

Question: Balance the following reaction: $\ce{CuS + SO4^{2-} -> CuO + SO2}$ My Efforts: Number mentioned in the brackets oxidation number of S I have found out that the oxidation ...
2
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4answers
102 views

What is the proper Lewis structure for HCOOH?

I tried to draw the Lewis structure of $\ce{HCOOH}$ but I didn't get the correct representation. As you can see in the picture below, at no. 1, I put $\ce{C}$ as the central atom because it has less ...
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1answer
52 views

Does having constant pressure imply a temperature change? Why isn't the volume needed to calculate the final temperature and energy?

Calculate the final temperature and the change in internal energy when $500\:\mathrm{J}$ of energy is transferred as heat to $0.900\:\mathrm{mol}$ $\ce{O2(g)}$ at $298\:\mathrm{K}$ and ...
0
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1answer
31 views

Is Oxygen a Lewis acid?

As I recall a Lewis acid is a substance that can accept an electron pair from a donor substance and oxygen seems to be able to do that for example in $\ce{H2 + O -> H2O}$ so is oxygen a Lewis ...
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0answers
20 views

Came across an interesting question on titrations

What amount of substance containing 60% NaCl, 37% KCl should be weighed out for analysis so that after the action of 25 ml of 0.1 N AgNO 3 solution, excess of Ag+ is back titrated with 5 ml of NH ...
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2answers
45 views

Calculate the pH of acetic acid for a 0.02 M solution

We have a solution $\ce{CH3COOH}$ (acetic acid) with $c=0.02~\mathrm{mol/L}$ and the of acetic acid, $K_A = 1.8\cdot10^{-5}$. Calculate the $\mathrm{pH}$ of this solution. I tried everything ...
0
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1answer
13 views

Calculating the molar mass of a solute from freezing point

A 4.305-g sample of a nonelectrolyte is dissolved in 105 g of water. The solution freezes at -1.23C. Calculate the molar mass of the solute. Kf for water = 1.86C/m. My steps: 1.23=1.86 * x/1.05 ...
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1answer
76 views

Finding the Oxidation number

I have got the homework to balance the following redox reaction. $\ce{Cr(OH)3- + HO2- -> Cr2O7^{-2} + OH- }$(Basic medium) To balance this reaction first thing we need to do is to find the ...
2
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1answer
75 views

Can two positive ions be next to each other in a formula?

Lets say I want to find the oxidation numbers of a formula. For example: $\ce{H3AsO3}$ Oxygen has a 2- charge. They're 3 of them, so its 6- Hydrogen has a 1+ charge. They're 3 of them, so its 3+. ...
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1answer
42 views

When are we justified in making assumptions in questions

The density at $20^\circ\mathrm{C}$ of a $0.500~\mathrm{M}$ solution of acetic acid in water is $1.0042~\mathrm{g/mL}$. What is the molality of the solution? The molar mass of acetic acid is ...
3
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1answer
96 views

Is there an easy way to remember charges on ions?

I have a chemistry test coming up and I might need to know the charge that goes with the different ions like $\ce{SO4}$ has $-2$, $\ce{NO2}$ is $-1$ and $\ce{PO4}$ is $-3$. Is there an easy way to ...
2
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1answer
43 views

Why is oxygen absorbed in a colorless alkaline solution of pyrogallol and why does it turn dark brown?

I'm reading about recognition and identification of gases. My book says: Oxygen is absorbed in colorless alkaline solution of pyrogallol and turns dark brown? I'd like to know why and how. ...
2
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1answer
44 views

Wavelength of X-rays

What will be the wavelength of X-ray if we apply a potential difference of , say 20 KV across the ends of the x-ray tube ? Alright, i started with the modified de-broglie equation ...
1
vote
1answer
42 views

What is the difference between a bond, force, and interaction?

I am trying to explain why some solids are more soluble in water than others: So the energy released from the formation of bonds between the solid solute molecules and water molecules compensate the ...
4
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0answers
44 views

Determine the ΔH for the reaction in kJ/mol of ethanol?

A $1.000~\mathrm{g}$ sample of ethanol, $\ce{C2H5OH}$, was burned in a bomb calorimeter whose heat capacity had been determined to be $2.71~\mathrm{kJ/C}$. The temperature of $3.000~\mathrm{kg}$ of ...
1
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0answers
34 views

Neutralisation of HCl with NaOH - generated heat and excess concentration [closed]

If you have $75\:\mathrm{mL}$ of $M(\ce{HCl}) = 4\:\mathrm{M}$ at $25\:\mathrm{^\circ C}$ and $100\:\mathrm{mL}$ of $M(\ce{NaOH})=5\:\mathrm{M}$ at $27\:\mathrm{^\circ C}$ with a final temperature ...
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2answers
25 views

Calculate the second ionization energy for the Mg from the following data?

here is a problem : What I did " as shown in the picture below " I rewrote the information given in terms of reactants and products ( equations )// in Part 1 Then I used the Hess law to obtain ...
2
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1answer
28 views

Thermodynamic question - Work during a reversible compression

I have a short multiple choice question that I have already solved. The question is The work done during a reversible compression (Vi (initial) = V1; Vf = 1/6V1) of an ideal gas is? I chose ...
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1answer
40 views

Determining covalent bond strengths without hybridisation

Assuming pure $\ce{2s}$ and $\ce{2p}$ orbitals of carbon are used in forming $\ce{CH4}$ molecule, which of the following statements is false? (single choice question) Three $\ce{C-H}$ bonds ...
0
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1answer
18 views

Calculate the Molarity of a soln

Having ethanol with its mole fraction equal to $0.040$, assume the density of water to be 1. I used this method, is it correct? Moles of $\ce{H2O} =0.96$ Therefore mass is equal to $0.96\cdot18 ...
3
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3answers
202 views

How can metals like magnesium and sodium burn underwater?

I can't find the answer anywhere else and I need it for an essay (I'm in 8th grade). Please answer with as much detail as possible (though any help is appreciated). Any websites I have found have ...
0
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1answer
41 views

Moles to Moles question for my online homework

Online homework problem: How many moles of water vapor react to yield 151.52 moles of hydrogen? I did, $$x \text{ mol } \ce{H2O} = 151.52 \text{ mol }\ce{H2} \frac{1 \text{ mol } \ce{H2O}}{3 ...
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0answers
25 views

Supercritical Steam Expansion

Ten $\mathrm{kg}$ of steam at $500~\mathrm{bar}$ is expanded at constant pressure until its volume increases to seven times its initial value of $0.01~\mathrm{m^3}$. (a) Calculate the initial and ...
4
votes
1answer
34 views

Differentiating between Titration, Buffer, diluted buffer, Deionized H₂O

I had a chemistry lab where we had to titrate three solutions with HCl, a buffer, a diluted buffer and deionized water. My partner and I didn't label the charts we made, so now I have to figure out ...
4
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3answers
61 views

Why is CaCl2 called Calcium chloride?

Doing a first year chem class. Just read through the molecular naming of compounds and now I'm confused as to why CaCl2 is called calcium chloride and not calcium dichloride?
2
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1answer
39 views

…If the final temperature of the combined liquids is 28.5 C and heat capacity of the calorimeter is 19.3J/C determine the specific heat of methanol?

A question in the book says : A $25.95 g$ sample of methanol at $35.6 °C$ is added to a $38.65 g$ sample of ethanol at $24.7 °C$ in a constant pressure calorimeter If the final temperature pf the ...
3
votes
1answer
116 views

Kinetics of Interstellar Chemistry — Applying steady state to formation of H₂

I am trying to solve problem 2 from the 2009 International Chemistry Olympiad (IChO), which is as follows: If two atoms collide in interstellar space the energy of the resulting molecule is so ...
1
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1answer
32 views

What total energy (in kJ) is contained in 1.0 mol of photons, all with a frequency of 2.75 • 10¹⁴ Hz?

There is a question, that says: What total energy (in $\mathrm{kJ}$) is contained in $1.0~\mathrm{mol}$ of photons, all with a frequency of $2.75 \cdot 10^{14}~\mathrm{Hz}$? My answer was: The ...
3
votes
2answers
133 views

Help with identifying an unknown substance?

I have the following IR and NMR of an unknown substance. Can someone tell me what is a possible structure of the compound or point me in the correct direction. So far I am thinking of a benzene ring ...
2
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3answers
162 views

Identifying an unknown compound(w/ NMR/IR)?

I need some help identifying the following unknown compound. Any suggestions or hints regarding the possible compound would be highly appreciated. So far I am thinking the broad peak on the IR is an ...
1
vote
1answer
37 views

How do I find a concentration from a sample tested on a spectrophotometer?

I have an assignment to calculate the concentration from a sample. The assignment is: You have 100 µL of RNA. You take 10 µL from the sample and put it in 990 µL of water in the cuvette. The OD is ...
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0answers
51 views

I need help with this exercise i need to find all chem elements

White solid A water insoluble cleaved hot to solid gas B and C. B is insoluble in water and in $\ce{HCl}$ but soluble to $\ce{HNO3}$ the react gives solution D and E colorless gas which becomes red ...
2
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2answers
29 views

How many mL of solution will result when 15.0 g of H₂SO₄ is dissolved to make a 0.200 M solution?

How many $\mathrm{mL}$ of solution will result when $15.0~\mathrm{g}$ of $\ce{H2SO4}$ is dissolved to make a $0.200~\mathrm{M}$ solution? Here's what I have so far: First, I converted ...
2
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0answers
54 views

Interpreting the Infrared Spectroscopy(IR)?

I have already attempted to interpret some of the peaks. Please tell me if they are correct/incorrect and anything that I have missed. Thanks !
1
vote
1answer
45 views

Is this Hess's Law Electrochemistry question incorrect?

It is my understanding that to apply Hess' Law to this equation the top equation sign would be reversed and the outcome would be +0.65 V. Often the system produces incorrect answers. I was looking ...
2
votes
1answer
47 views

Figuring out the pH

So, I'm refreshing my college chemistry a bit. Could someone give me a pointer on the following practice exercise? What is the pH @ 25 degrees Celcius in a bucket with 10liter pure water in which a ...
0
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1answer
39 views

Relationship between Van der Waals forces and the boiling point

Choose the right answers in the following statement: The boiling point of a liquid substance is higher as the Van der Waals forces (in/between) the molecules of the substance are (lower/higher). I ...
0
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1answer
34 views

Carbonate Equilibrium Question: Finding concentration using concentration ratio and number of moles of acid

Lake water contains dissolved sodium carbonate and sodium hydrogen carbonate. The following equilibrium exists: $\ce{HCO3- <=> H+ + CO3^{2-}}$ $\frac{\ce{[CO3^{2-}]}}{\ce{[HCO3-]}} = 0.958$ ...