Questions tagged [homework]

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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 ...
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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 ...
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1answer
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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 ...
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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 ...
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1answer
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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 : $...
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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.
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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-...
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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 ...
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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 ...
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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?...
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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: $$\ce{Cu -> Cu(NO3)2 + 2e-}$$ $$\ce{3e- + HNO3 -> NO}$$ $$\...
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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. ...
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2answers
11k 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 solution: equation:...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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2answers
215 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? ...
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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 ...
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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 $0.2\ \mathrm{M}$ ...
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4answers
2k 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) $\...
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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\ \...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $\ce{NH_{3}}$...
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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. ...
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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 ...
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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 ...
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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 ...
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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)}\\ \...
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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 ...
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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 ...
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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 ...
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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 ...
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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/...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $...
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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 ...
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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 ...

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