Questions tagged [homework]
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587
questions
0
votes
2answers
35k views
Difference between an absorbance, emission, and excitation spectrum for uv-visible spectroscopy
The exam paper answer is 500, because we need the wavelength of "maximum absorbance." But this graph shows two curves, and the absorbance curve is omitted.
But what is the difference between an ...
-4
votes
0answers
21 views
Artificial Ripener [closed]
Artificial Ripener through natural agents (Citrus Peel) any idea? Typically Ethephon is used as fruit ripening however i want to use natural fruits dehydrated powder with some other natural product ...
1
vote
1answer
3k views
What to do when there is an odd number of valence electrons left on the the central atom?
For example, I'm trying to write the formula for $\ce{NO}$, and $\ce{ClO2}$. The steps my teacher gave me always assume that the central atom has a full valence, or more than full, after the outer ...
1
vote
2answers
8k views
Help balancing reaction between Iron (II) chloride and potassium phosphate
Very rusty with chemistry and looking to review some basics. Came across the following:
Iron(II) chloride and potassium phosphate react. Write and balance the molecular, ionic, and net ionic ...
0
votes
1answer
3k views
Unit conversion of Molar Conductivity
I know this might be a silly question but I am confused with different answers of internet. My question is:
Molar conductivity is given as:
Molar conductivity = $\frac{\kappa}{M}$.
S.I. unit of :
$...
1
vote
2answers
452 views
What liquid substance impedes cellular respiration?
I'm doing a biology assignment and need to identify a clear liquid substance that impedes cellular respiration. It needs to be toxic and either absorbed through the skin or inhaled.
1
vote
2answers
26k views
How to calculate the concentration of all relevant species in a buffer of a given pH?
You prepare $1.0~\mathrm{L}$ of a $0.25~\mathrm{M}$ acetic acid solution with a final $\ce{pH}$ of $6.0$. What are the molar concentrations of all relevant acetic acid species ($[\ce{HA}]$ and $[\ce{A-...
1
vote
1answer
136 views
Finding moles of different compounds using balancing
$$\ce{K2Cr2O7 + $x$\,H2SO4 + $y$\,SO2 -> Cr2(SO4)3 + K2SO4 + $z$\,H2O}$$
For $\ce{Cr}$ change in oxidation number is: $+12$ becomes $+6$
For $\ce{S}$ change in oxidation number is: $+4y$ becomes ...
1
vote
3answers
9k views
How can metals like magnesium and sodium burn underwater? [closed]
Please answer with as much detail as possible. I can't find the answer anywhere else and I need it for an essay.
Any websites I have found have conflicting answers.
One said that they don't actually ...
2
votes
4answers
79k views
How many valence electrons do elements in the d block have?
I just noticed that on the periodic table it doesn't say how many valence electrons there are for each column in the d block.
How do I find out how many valence electrons elements in the d block have?...
1
vote
3answers
478 views
How to balance this redox reaction
How to balance this redox reaction (using half reaction method):
$$\ce{Cu + HNO3 -> Cu(NO3)2 + NO + NO2 + H^2O}$$
My attempt:
$$\ce{Cu -> Cu(NO3)2 + 2e-}$$
$$\ce{3e- + HNO3 -> NO}$$
$$\...
0
votes
2answers
48k views
How to calculate the number of atoms of each element in a urea?
I have a stoichiometry question which I answered incorrectly and I am not sure where I went wrong. The question is as follows:
Urea, $\ce{(NH2)2CO}$, is used for fertilizer and many other things. ...
1
vote
2answers
11k views
Air contain 20āÆ% O2 by volume. How many cm³ of air will be required for oxidation of 100 cm³ of acetylene?
Air contain 20āÆ% $\ce{O2}$ by volume. How many cmĀ³ of air will be required
for oxidation of 100Ā cmĀ³ of acetylene?
(a) 1064Ā cmĀ³
(b) 212.8Ā cmĀ³
(c) 500Ā cmĀ³
(d) 1250Ā cmĀ³
Answer: (d)
My solution:
equation:...
1
vote
2answers
11k views
Is methyl orange acidic or basic?
It has been saying that if adding too much indicator in solution, the ph value of solution would be changed. From this, it can be saying that indicators have a pH value. Methyl orange is the indicator ...
1
vote
3answers
6k views
Find the maximum temperature attained by the gas during the change
The main question is:
2 moles of an ideal gas is changed from its initial state $(16\ \mathrm{atm},\ 6\ \mathrm L)$ to final state $(4\ \mathrm{atm},\ 15\ \mathrm L)$ in such a way that this change ...
3
votes
2answers
18k views
How to calculate the percentage of calcium carbonate in sea shells in an experiment [closed]
We have a investigation in my chemistry class in which we must calculate the amount of calcium carbonate in sea shells. We can have as many sea shells as we wish, lab equipment, and hydrochloric acid ...
0
votes
2answers
2k views
Temperature Dependent Specific Heat of Nitrogen
Calculate the change in enthalpy as 1kg of nitrogen is heated from 1000K to 1500K, assuming the nitrogen is an ideal gas at a constant pressure. The tempreature dependent specific heat of nitrogen is ...
1
vote
2answers
3k views
Balancing a REDOX reaction using the oxidation number method, in acidic solution
I am trying to balance the REDOX equation shown below, but I got stuck after balancing the major atoms. Where can I go from here? I know I need to balance the H and O atoms, and make sure the charges ...
1
vote
2answers
4k views
How to Prepare a Buffer Solution?
Problem
I am given the task of preparing three buffer solutions at pH 10, 9.5, and 9.0. I have available concentrated ammonia and 3M hydrochloric acid.
Attempt at Solving
By adding HCl to a ...
1
vote
3answers
21k views
Filling a buret tip before an experiment
I have a question that asks if the buret tip is not filled before the experiment what would happen (effect on molarity for acid/base titration). The way I'm thinking about it, it's not like you're ...
2
votes
2answers
215 views
Redox reaction terminology
In the case of this redox reaction:
$ \ce{ Cu SO_4 + Zn ā Zn SO_4 + Cu} $
Is it correct to say that the sulfate reduces to the zinc? Or is it the whole molecule that is reducing? Or just the copper?
...
0
votes
1answer
743 views
Effect of an inert gas on steam vapor pressure at equilibrium
Suppose we have a closed container with mobile walls, so it will change its volume in order to equal the external pressure(constant) to the internal pressure.
This container has inside it a liquid ...
2
votes
3answers
5k views
What is the pKa of the second ionizable group?
One compound contains an amino group with $\mathrm{p}K_\mathrm{a}$ of $8.8$, and one other ionizable group with a $\mathrm{p}K_\mathrm{a}$ of $5$ to $7$. To $100\ \mathrm{mL}$ of a $0.2\ \mathrm{M}$ ...
1
vote
4answers
2k views
Liquification of gas to liquid at critical temperature
The gas that liquifies first, when cooled from 500Ā K to its critical temperature given in parenthesis is
a) $\ce{CO2}$ (304.1 K)
b) $\ce{NH3}$ (405.5 K)
c) $\ce{O2}$ (154.3 K)
d) $\...
0
votes
1answer
1k views
How do I calculate the enthalpy change when a gas is being used to heat water?
The question I'm trying to answer is:
Calculate the mass of butane gas that would be needed to heat $724\ \mathrm{cm^3}$ of water from an initial temperature of $7.44\ \mathrm{^\circ C}$ to $50.7\ \...
0
votes
2answers
98 views
Hydrolysis of Radiolabeled Esters
Hydrolysis of C$_6$H$_5$COO$^{18}$CH$_3$ with aqueous NaOH produces what final product.
(a) CH$_3$$^{18}$OH
(b) CH$_3$CO$^{18}$ONa
(c) CH$_3$C$^{18}$OONa
(d) CH$_3$$^{18}$ONa
(e) CH$_3$OH
The ...
1
vote
2answers
2k views
Magnesium powder mixed with CuSO4 solution
$\ce{Mg}$ powder is stirred into $\ce{CuSO4}$, what is the balanced molecular equation for this reaction ? I have $\ce{Mg + CuSO4 -> Mg2SO4 + Cu}$. Also, is the ionic equation the same as the net ...
0
votes
2answers
1k views
Understanding how electrons are counted for lone pairs vs. bonds especially when understanding resonance?
This is taken from the book Organic Chemistry as a Second Language from page 35.
In the following image:
It is seen that when the electrons from the double bond are pushed into the lone pair ...
1
vote
2answers
2k views
Distinguishing pentanol isomers in 13C DEPT NMR spectroscopy
Pentanol has eight isomers as shown below. The circles represent carbon atoms that I think are equivalent.
Below there are eight DEPT-spectra that should represent these eight substances.
As you can ...
0
votes
2answers
4k views
How to calculate the molar mass of a protein from its osmotic pressure?
I am unsure how to go about solving this question. I know how to get the osmotic pressure, but where do I go from there?
I can't use the gas law since the protein is not a gas.
$\pu{2.38 g}$ of a ...
1
vote
2answers
2k views
How are reactivity and dipole moment related?
Recently, I came across a question: which of the two compounds has a greater reactivity; $\ce{NH_{3}}$ or $\ce{NF_{3}}$?
It is known that despite the same structure the dipole moment of $\ce{NH_{3}}$...
1
vote
1answer
15k views
What does (heated) mean in a chemical equation?
I'm supposed to balance the following equation:
$\text{Potassium chlorate (heated) --> Potassium chloride + Oxygen}$
But I don't understand what the (heated) means in front of the first element. ...
0
votes
1answer
36k views
Metal vs. Styrofoam cup calorimeter?
For a metal cup as opposed to a styrofoam cup calorimeter, do you expect the enthalpy of the reaction to be higher, lower, or the same?
I think the enthalpy of the reaction would be the same in the ...
1
vote
1answer
3k views
When the heat is absorbed by the ice then ice will melt to form liquid water
My new try:
Given data
Energy given by reaction =1690 kJ
Initial temperature = 0 oC
Final temperature = 50 oC
C water = 4.18 Jmol-1 K-1
?Hfus ice = 6.01 kJ*mol-1
Calculate Mass of ice = ?
Ice ...
0
votes
1answer
4k views
Galvanic cell using NaCl, Cu and Zn, why does it work?
Got a paper due tomorrow in chemistry, and my friends and I are totally stuck on this:
Basically we mixed some regular salt (NaCl) into a glass of water and stuck a zinc nail and a copper nail into ...
2
votes
1answer
2k views
Finding the enthalpy of formation of magnesium oxide
I have the following reactions:
$$\begin{align}
\ce{Mg(s) + 2HCl(aq) &-> MgCl2(aq) + H2(g)}\\
\ce{MgO(s) + 2HCl(aq) &-> MgCl2(aq) + H2O(aq)}\\
\ce{H2(g) + 1/2O2(g) &-> H2O(l)}\\
\...
2
votes
1answer
3k views
How to calculate the bond energy of C-Cl?
$$\ce{C(s) + 2 Cl2 (g) -> CCl4 (g)}$$
\begin{align}
\Delta H^\circ_\mathrm{f} (\ce{C(g)}) &= 121~\mathrm{kJ/mol}\\
\Delta H^\circ_\mathrm{f} (\ce{Cl(g)}) &= 716~\mathrm{kJ/mol}\\
\Delta ...
2
votes
1answer
3k views
Reaction of sodium dihydrogen phosphate and ammonium chloride
I have a homework question that says
Write an equation when $\ce{NaH2PO4}$ and $\ce{NH4Cl}$ are mixed.
I assume that this is an acid base neutralization and will probably also give a salt due to ...
1
vote
1answer
295 views
What is the result of this elimination reaction?
$$\ce{(R)-2-Bromooctane + alcoholic~KOH -> E2~reaction}$$
My answer is that this reaction will have a minor and a major product. In relation to the regiochemistry, the major product is the one ...
1
vote
2answers
2k views
Plot Binary Eutectic from Temperature of Melting and Enthalpy
I'm a little confused about plotting a binary eutectic diagram (temperature vs mole fraction), and finding the eutectic point. I understand the eutectic point is the lowest temperature that a mixture ...
1
vote
1answer
34k views
Calculating the molar mass of a solute from freezing point
A $\pu{4.305 g}$ sample of a nonelectrolyte is dissolved in $\pu{105 g}$ of water. The solution freezes at $\pu{-1.23^\circ C}$. Calculate the molar mass of the solute. $k_f$ for water is $\pu{1.86 C/...
1
vote
4answers
439 views
Balancing the oxidative decomposition of FeS2
Doing some practice for the GRE next year.
Please could you look at my working for this and tell me why I'm wrong?
$$\ce{? FeS2 + ? O2 + ? H2O = ? Fe(OH)3 + ? H2SO4}$$
My working so far is:
There ...
1
vote
2answers
917 views
How does an anode metal come into solution if it cannot react with an electrolyte?
From what I understand, an anode material is chosen so that it does not react with the anode electrolyte solution.
I was just wondering, then, that when you have a galvanic cell which has a Mg metal ...
1
vote
1answer
3k views
What does being an “elementary substance” mean?
Which of the following isn't an elementary substance?
Ozone
Sulfur
diamond
quartz
I don't get what elementary substance means.
By seeing the options and the word elementary, I guess it means ...
1
vote
1answer
5k views
Calculating the pH of the endpoint in a titration of weak acid and strong base
Show that the pH at the endpoint in the titration of $\mathrm{0.100\ mol\ dm^{-3}}$ ethanoic acid with $\mathrm{0.100\ mol\ dm^{-3}}$ sodium hydroxide is 8.72. The dissociation constant Ka of ethanoic ...
1
vote
2answers
147 views
Should the anode potential be increased or decreased to generate current?
I am taking a course on fuel cells and we were talking about the activation energy needed to start a chemical reaction.
I would think that the answer to this question is that the anode potential ...
0
votes
1answer
2k views
Relation between number of equivalents of reactants
Consider the reaction $\ce{Sb2S3 + F2 -> SbF5 + SF6}$. If the milliequivalents of antimony, sulfur and fluorine are x, y and z respectively, then prove that $x+y=z$.
This is what I know: Number of ...
2
votes
1answer
3k views
Stability by using charge/radius rule
I found a question
Which is more stable among the following?
(a) $\ce{CaCO3}$
(b) $\ce{MgCO3}$
Answer : (a)
Explanation was given as:
"$\ce{Mg^2+}$ has smaller radius than $\ce{Ca^2+}$ and thus $...
2
votes
1answer
1k views
Bond length comparison between sulfur tetrafluoride and thionyl tetrafluoride
I'm comparing sulfur tetrafluoride and thionyl tetrafluoride. The lone pair has more s character compared to a double bond. Therefore, sulfur in $\ce{SF4}$ should have a greater s character compared ...
2
votes
1answer
276 views
How to prove this formula of extent of reaction?
We've a solution of $\ce{HCOOH}$ and Water $\ce{H_2O}$,
I want to prove that the extent of this reaction is equivalent to :
$$\xi=\frac{K_a}{K_a+10^{-\mathrm{p}H}}$$
Could you help try to figure that ...
