Questions tagged [homework]
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900
questions
2
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1answer
15k views
How to calculate the mass of magnesium necessary to produce a certain volume of hydrogen gas?
How many grams of magnesium metal are required to produce 44.8 liters of hydrogen gas at STP according to the chemical equation shown below? (Answer: $48.6~\mathrm{g}$)
$$\ce{Mg(s) + 2 HCl(aq) -> ...
0
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2answers
42k 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. ...
2
votes
1answer
851 views
Equilibrium reaction ICE method to ideal gas law
The below equilibrium reaction takes place among the burnt exhaust gases still left inside the engine cylinder and being reused again for combustion. The author has specified the equilibrium between ...
1
vote
2answers
9k views
Air contain 20 % O2 by volume. How many cm³ of air will be required for oxidation of 100 cm³ of acetylene?
Air contain 20 % $\ce{O2}$ by volume. How many cm³ of air will be required
for oxidation of 100 cm³ of acetylene?
(a) 1064 cm³
(b) 212.8 cm³
(c) 500 cm³
(d) 1250 cm³
Answer: (d)
My ...
1
vote
2answers
8k 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 ...
3
votes
1answer
1k views
What is the standard heat of formation of the nitrate ion, based on the standard enthalpy of formation of silver nitrate?
Given the standard enthalpy of formation of $\ce{AgNO3(aq)} = -99 \text{ kJ/mol}$ and the standard enthalpy of formation of $\ce{Ag+(aq)} = +105 \text{ kJ/mol}$, what's the standard heat of formation ...
1
vote
3answers
4k 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
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2answers
17k 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
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2answers
1k 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
2k 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
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4answers
60k 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
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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 ...
3
votes
1answer
152 views
Nitration of aromatic compound with alkyl substituents
For 1,1,4,4-tetramethyl-1,2,3,4-tetrahydronaphthalene:
What would be the products following a standard nitration with $\ce{NO2+}$?
My reasoning is thus:
Since the substituent group is alkyl then it ...
3
votes
3answers
3k views
Which of the compounds give the same SN1 and SN2 products?
I think answer (b) is correct but correct answer is (c). I think so as it is the only compound where C is not chiral. While in others racemic mixture in $\mathrm{S_N1}$ and enantiomer in $\mathrm{S_N2}...
4
votes
2answers
453 views
How does sugammadex (a modified cyclodextrin) draw rocuronium into its lipophilic cavity?
Sugammadex is a modified cyclodextrin: 8 member sugar ring with carboxyl thioether extensions. Rocuronium is an aminosteroid, 4 steroid rings and one protonated amine group.
Sugammadex binds ...
3
votes
2answers
4k views
Ranking order of nucleophilicity
According to me the answer should be (c),(b),(a),(d). As we move left to right in a period the electronegativity increases and hence the tendency to donate electrons will decrease so nitrogen is ...
2
votes
2answers
29k views
Converting g/L to mol/L
I know I should divide $\mathrm{g~L^{-1}}$ by the molar mass of the substance, but I don't seem to find the specific answer on Google. So just to be sure:
If I have $10^{-5}~\mathrm{g~L^{-1}}~\ce{Cu^...
3
votes
1answer
17k views
dsp3 and sp3d hybridization — what is the difference and which applies to square pyramidal?
What is the difference between dsp3 and sp3d Hybridization?
Are they one in the same?
Also, I have a book that says that in compounds where the central atom is dsp3 hybridized, it's shape is square ...
1
vote
3answers
19k 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
193 views
Redox reaction terminology
In the case of this redox reaction:
$ \ce{ Cu SO_4 + Zn → 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?
...
1
vote
2answers
15k views
How does equilibrium change when the products are solid and gas?
$$\ce{CaCO3(s) <=> CaO(s) + CO2(g)}$$
How will the amount of each element change if the pressure is increased?
My guess is that the equilibrium will shift to the left, because the right side ...
0
votes
1answer
576 views
Effect of an inert gas on steam vapor pressure at equilibrium
Suppose we have a closed container with mobile walls, so it will change its volume in order to equal the external pressure(constant) to the internal pressure.
This container has inside it a liquid ...
3
votes
2answers
571 views
Confusion about the oxidation state of copper in copper cyanide redissolved with excess cyanide
$\ce{CuSO4}$ when reacts with $\ce{KCN}$ forms $\ce{CuCN}$ while it is insoluble in $\ce{H2O}$. It is soluble in excess of $\ce{KCN}$ due to the formation of the following complex:
a) $\ce{K2[Cu(...
2
votes
3answers
4k views
What is the pKa of the second ionizable group?
One compound contains an amino group with $\mathrm{p}K_\mathrm{a}$ of $8.8$, and one other ionizable group with a $\mathrm{p}K_\mathrm{a}$ of $5$ to $7$. To $100\ \mathrm{mL}$ of a $0.2\ \mathrm{M}$ ...
1
vote
4answers
1k views
Liquification of gas to liquid at critical temperature
The gas that liquifies first, when cooled from 500 K to its critical temperature given in parenthesis is
a) $\ce{CO2}$ (304.1 K)
b) $\ce{NH3}$ (405.5 K)
c) $\ce{O2}$ (154.3 K)
d) $\...
4
votes
1answer
87 views
Finding ppm getting too big of numbers
I have a question that is to find the concentration of magnesium ion in ppm for a $0.025\ \%$ solution of $\ce{MgCl2}$. I can use this formula:
$$\text{concentration in ppm} = \frac{\text{mass solute}...
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 $50.7\...
0
votes
2answers
83 views
Hydrolysis of Radiolabeled Esters
Hydrolysis of C$_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
1answer
935 views
Determine the isotope half-life?
A sample of $\ce{^{41}Ar}$, a radioisotope used to measure the flow of gases from smokestacks, decays initially at a rate of 34,500 disintegrations/min, but the decay rate falls to 21,500 ...
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
804 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
1k 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 ...
3
votes
1answer
3k views
Elimination of bromide and acetate under reducing conditions
Here is the reaction that I didn't find the mechanism of; maybe you can help:
The conditions is zinc dust, when the solvent is acetic acid at 110°C 1h. the reagents are Sodium acetate, 2,3,4,5-...
5
votes
3answers
5k views
Why do the trends in reactivity not apply for francium?
Why is francium not included in the reactivity series?
Why is potassium considered more reactive than francium?
I know that reactivity increases down the group! But why does it not apply here?
3
votes
1answer
549 views
I am confused about the stability of carbanion III and IV in the image
I am confused about the stability of carbanion III and IV in the image, I think III is more unstable because of electron donating effect (+R) of -OCH3 group but my book says III is more stable than ...
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
1k 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 $\ce{NH_{3}}$...
2
votes
2answers
3k views
Does 11.2 dm3 of nitrogen consist of 0.5 moles at STP?
Which of the following statements is true?
$11.2~\mathrm{dm^{3}}$ of nitrogen at STP
A: has a mass of $14\ \mathrm{g}$.
B: consists of $0.5\ \mathrm{mol}$ atoms.
My instinct was that the answer is ...
2
votes
2answers
2k views
Kinetic isotope effect in nitration of benzene
What is the effect of changing all the hydrogen atoms in benzene to deuterium? For example, which of the following reactions occurs at a faster rate?
2
votes
1answer
25k views
How to calculate the volume of a sodium hydroxide solution necessary to add to water, to raise the pH to a certain value?
What volume of 0.300N $\ce{NaOH}$ would be needed to bring $16.0~\mathrm{mL}$ of distilled water that has a pH of 7.00 to a new pH of 12.42?
This is my attempt at a solution:
$$\ce{NaOH + H2O-> ...
3
votes
2answers
12k views
Determining if reaction is endothermic or exothermic using equilbrium constant
For the following reaction:
$$\ce{W_{(s)} + 4 Br_{(g)} <=> WBr4_{(g)}}$$
At 900 K, $K_\mathrm{p}=100$ and at 2800 K, $K_\mathrm{p}=5$.
At higher temperatures, the equilibrium has shifted ...
1
vote
1answer
13k views
What does (heated) mean in a chemical equation?
I'm supposed to balance the following equation:
$\text{Potassium chlorate (heated) --> Potassium chloride + Oxygen}$
But I don't understand what the (heated) means in front of the first element. ...
3
votes
2answers
10k views
What happens when C17H35COO-, a soap, reacts with an acidic solution?
My book says that in acidic water, the negative fatty acid ions become fatty acids. However, they did not include a chemical equation to demonstrate this, so I made my own: $$\ce{C17H35COO- (aq) + HCl ...
2
votes
1answer
66k views
How do I find the final temperature using specific heat?
What is the final temperature of water and iron if a $30~\mathrm{g}$ piece of iron at $144~\mathrm{°C}$ was dropped into a calorimeter with $40~\mathrm{g}$ of water at $20~\mathrm{°C}$?
Specific heat ...
3
votes
1answer
7k views
Does solubility matter when measuring density with displacement method?
I thought I understood this, but I'm having some doubts now. My question is quite simple: Can the volume of a solid (specifically a granular crystal or powder) be accurately determined using the ...
2
votes
2answers
56k 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 but I ...
3
votes
1answer
446 views
Reactivity and transport safety of substituted methyl benzoates
This was a practice question from an MCAT book whose answer I didn't really understand:
The normal reactivity of methyl benzoate is affected by the presence of certain substituents. Which of the ...
0
votes
1answer
32k 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 ...
3
votes
1answer
541 views
What is the difference between these wave functions?
My chemistry textbook introduces the wave function as
$$\psi(x)= A \sin\left(\frac{2\pi x}{\lambda}\right)$$ Therefore, the Schrödinger Equation is:
$$\frac{d^2\psi(x)}{dx^2} = -~\left(\frac{...
4
votes
1answer
810 views
What is the structure of this molecule?
I need to find the Lewis structure of the ion $\ce{SCH^-}$.
I think the Lewis structure should be:
$\ce{S=C-H}$
with one lone pair on the carbon and two lone pairs surrounding the sulfur.
Is this ...
