Questions tagged [homework]

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When two moles of an ideal gas (C p,m. = 5/2R) is heated from 300 K to 600 K at constant pressure, the change in entropy of the gas (ΔS) is [closed]

Is this the right way to solve it ? In the final answer , it will be R(f+2)/300.Answer for change in entropy.
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1answer
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confusion regarding stereoisomers [closed]

I am a high school student and I am very confused in optical isomerism My confusions are: 1)Is the carbon shown in the image is a chiral carbon or pseudo-chiral carbon? 2)will this compound show ...
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0answers
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Why is Tyrian purple called 6,6'-dibromoindigo if all carbons are numbered differently? And the bromines are at opposite ends?

If the two bromines are attached at opposite ends of the molecule, why are they both labelled with a 6? Also, why is 6,6'-dibromoindigo not called 1,1'-dibromoindigo if carbons in a ring are numbered ...
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1answer
485 views

Lab test to compare the reactivity of liquid 1-heptene and liquid heptane

Describe how you would carry out a lab test to compare the reactivity of liquid 1-heptene and liquid heptane. State clearly what the possible results of the test are and what they would indicate. ...
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2answers
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How does the polarity of the eluent and sample affect the Rf value in thin layer chromatography?

A three-component mixture (X, Y, Z) was separated using normal phase TLC. Three eluents of varying polarity were used. Select the TLC plate that was developed using the least polar eluent (click on ...
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1answer
976 views

Mg and Cu Reaction in HCl

When a solid piece of Mg is attached to a solid piece of Cu and is placed into HCl(aq), why does it appear that the Cu slowly starts to bubble?
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1k views

Osmotic pressure of a solution of a protein?

A small protein molecule, code-named "sloth", has a MM of $\mathrm{1.50 x 10^4}$ g/mol. What is the osmotic pressure exerted at $\mathrm{24.0^oC}$ by 25.0 mL of an aqueous solution that contains $\...
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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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1answer
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Relationship between a temperature increase of an exothermic reaction, Keq, and kf (forward rate constant)

I'm currently stuck on #30 for Chemistry Olympiad 2015 local exam which reads as: For a reversible exothermic reaction, what is the effect of increasing temperature on the equilibrium constant (Keq) ...
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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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652 views

Simple Distillation of Unknowns

Can an identification experiment (using acetonitrile, isopropyl, and cyclohexane) using simple distillation and boiling point be improved by using a digital thermometer? Can simple distillation be ...
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1answer
525 views

Do cycloalkanes have open chain Alkene isomers?

I've been trying the get the number of isomers of bromocyclohexane and 1,2-dibromocyclohexane.I was taught that every cycloalkane should have an isomer that's an open chained alkene. I searched ...
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1answer
375 views

Nucleophilicity of alcoxy groups

I found a nucleophilicity order as $\ce{HO-} > \ce{CH3-O-} > \ce{(CH3)2CH-O-} > \ce{(CH3)3C-O-}$ The reason was given that bulky groups reduce nucleophilicity. But why? The order of the $+...
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2answers
279 views

Why do substances ionise in water to turn into charged species? Wouldn't they prefer to stay as uncharged molecules?

Wouldn't this be more stable if they stayed as neutral molecules? I've learnt that they will seek to reach the ratio of $[A]^a[B]^b/[C]^c$ that matches the $\ce{Ka}$ or $\ce{Kb}$ value. But I do ...
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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 : $...
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1answer
10k views

Solubility order for alcohols [closed]

Order for solubility of isomeric alcohols in a book was given as: Primary alcohol >Secondary alcohol >Tertiary alcohol After this I found a question as : 1) Which is more soluble in water? (a) 3-...
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1answer
132 views

Is Nuclear Spin Isomer a kind of allotrope?

In my book there's a question: Does $\ce{H2}$ shows allotropy ? Enlist its allotropes and their application? I pondered over different way Hydrogen can be arranged(I don't know but I have weak ...
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2answers
7k views

How to calculate what temperature change in entropy for the reaction equal to the change in entropy for the surroundings given Enthalpy and entropy

A reaction has $\Delta H_{rxn} = -107$ kJ and $\Delta S_{rxn} = 285$ J/K. At what temperature is the change in entropy for the reaction equal to the change in entropy for the surroundings? My ...
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2answers
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When pH increases, does the effect of increased [OH-] or reduced [H+] control precipitation of CaC2O4

The image below shows how oxalic acid dissociates and forms calcium oxalate ($\ce{CaC2O4}$ or $\ce{Ca(OOC-COO) as written below}$). When the pH increases, does this result in more or less $\ce{Ca(OOC-...
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1answer
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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
436 views

Acidity of primary and secondary amines

I was reading a book on organic chemistry by David Klein and I came across this question, but I wasn't able to understand why one amine is more acidic than the other.
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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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2answers
3k views

What happens to acids/bases left out overnight?

I conducted a titration experiment a few days back and was unable to neutralize the solution in time, so I had to leave the solutions of HCl and NaOH out overnight in order to use them the next day. ...
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1answer
2k views

Stoichiometry Chemistry Lab: Copper (II) Sulphate Pentahydrate and Iron Single Displacement Reaction?

In my grade 11 chemistry class, we performed a lab in which we added 1.00g of iron to 6.00g of copper (II) sulphate which was dissolved in water. Using stoichiometry, we predicted that if the iron was ...
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2answers
3k views

Help with determining the rate constant of a reaction

The question asked was, The initial concentration of $\ce{N2O5}$ in the first order reaction $$\ce{N2O5 -> 2NO2 + 1/2O2}$$ is $1.24\cdot 10^{-2}~\mathrm{mol\,L^{-1}}$ at 318K. The concentration of ...
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2answers
7k views

Why and how carboxylate ion has greater stability than carboxylic acid?

I found it written in my textbook. I think it's a misprint, I can't think of any logic behind this statement. I've only learned that ion is less stable specie so carboxylate ion cannot be more stable ...
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1answer
412 views

Stability order of octahydrobiphenylenes

I am facing trouble in the following question What is the stability order of the following compounds? In my view cis is less stable than trans. So if prior groups are on the same side of the ...
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2answers
258 views

A metal, M, forms two fluorides containing 40.43% F and 50.44% F by mass. Identify the metal

A metal, $\ce{M}$, forms two fluorides containing 40.43 % $\ce{F}$ and 50.44 % $\ce{F}$ by mass. Identify the metal. I get that you can find out how much of the metal reacts with 1 mole of fluorine ...
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1answer
115 views

Arranging different oxygen-containing organic compounds by decreasing acidity

I am facing difficulty in the following problem. Arrange the following compound in decreasing order of acidity. It is clear that conjugate base of (Q) is more stable.hence it is most acidic.in R) ...
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2answers
810 views

When finding hybridisation of atoms, why are double bonds and triple bonds only considered once?

To figure out what hybridization an atom has is to just count the number of atoms bonded to it and the number of lone pairs. Double and triple bonds still count as being only bonded to one atom. (...
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40k views

How to determine which aqueous solution has the largest freezing point depression

Question This is more of a conceptual question. Let's say that we are given different aqueous solutions and we are asked to choose the one with the highest freezing point depression, which do we ...
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2answers
1k views

How can I derive whether the methyl cation or anion is planar?

According to VSEPR theory, in which species do all the atoms lie in the same plane? $\ce{CH3+}$ $\ce{CH3-}$ (A) 1 only (B) 2 only (C) both 1 and 2 (D) neither 1 nor 2 My try: ...
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1answer
853 views

Finding the molarity of an acid in a titration

I was doing a question that asks the molarity of a 10 mL of tartaric acid that is titrated to phenolphthalein endpoint with 20 mL of 1.0 M NaOH. I worked it out by equating the molarity of the NaOH ...
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2answers
2k views

How to determine which of two similar compounds has the larger dipole moment?

I am solving some problems involving the order of dipole moments of some compounds. I could solve most of them but the following. The question is to find out which has greater dipole moment $\ce{...
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1answer
155 views

Arrow pushing: why does the O become positive when its lone pair becomes a double bond?

In the following image: The oxygen's top pair of electrons forms a double bond. But in a covalent bonds, aren't the electrons shared? So won't the oxygen still have these $2$ electrons (that it ...
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2answers
3k views

When is rotation around double bonds to form cis-trans isomers allowed?

The Rhodopsin molecules in the retain contain a derivative of vitamin A called cis-retinal (Figure 6). On exposure to light, cis-retinal becomes an isomer called trans-retinal (Textbook Question). ...
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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
88 views

Heat exchange between tin and ethanol

This is a pretty straightforward heat/energy exchange problem, but I can't figure the answer out. A constant-pressure calorimeter contains $250.0\ \mathrm{mL}$ of ethanol (density = $7.89\ \mathrm{...
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1answer
577 views

What are the reactions occurring during the titration of a carbon dioxide contaminated water sample with diluted sodium hydroxide solution?

During estimation of dissolved $\ce{CO2}$ in water, we took a water sample, added few drops of phenolphthalein and titrated it against dil $\ce{NaOH}$. Questions What are the reactions that happen: ...
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127 views

Fe/Ga cell has a negative potential?

In the following homework problem, the answer says: "$E ^{o}_{cell}$ is negative, which makes the $\ce{Fe}$ and $\ce{Ga}$ half-reactions non-spontaneous." But I found $E ^{o}_{cell}$ to be positive ...
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1answer
908 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
464 views

Why does bromide not react with water when methyl ammonium bromide is dissolved in water?

In the following reaction, the salt $\ce{CH3NH3Br}$ is formed: $$\ce{CH3NH2 + HBr -> CH3NH3Br} $$ In water this dissociates completely into $\ce{CH3NH3+}$ and $\ce{Br-}$ In my chemistry book, it ...
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1answer
2k views

When an expansion of a system does work on its surroundings, is the sign for work negative?

This question comes to me from trying to explain the answer $1.67\ \mathrm{L}$ of this question: A cylinder with a moving piston expands from an initial volume of $0.250\ \mathrm{L}$ against an ...
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2answers
736 views

Common ion effect math problem

The question was: If you are given a $1$ Litre solution of $\ce{CaF_2}$where there is $2.0 \times 10^{-5}$ M $\ce{Ca^{2+}}$. How many mililitres of $0.1$ M $\ce{NaF}$ would you need to precipitate $...
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2answers
115 views

If PQ, T2U2, RS2 and VW4 have the same Ksp, which has the lowest solubility in moles of solute per litre?

If the solubility products of the following ionic compounds all have the same numerical value, and all solubilities have values between zero and one, which one would have the lowest solubility in ...
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1answer
466 views

Does lowering temperature of a gas make it easier to compress?

My teacher said that for ideal gases, the lower the temperature, the lower the kinetic energy of a gas will be, and it will be easier to compress the gas. Using the ideal gas equation $PV=nRT$, if ...
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4answers
435 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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1answer
473 views

Change in internal energy of a gas upon expansion against a constant external pressure

I have a question about the following problem which I got wrong: During expansion of its volume from $\mathrm{1.00\,L}$ to $\mathrm{10.00\,L}$ against a constant external pressure of $\mathrm{2.00\,...
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1answer
894 views

Bond lengths: 1-D particle-in-a-box for 1,3-butadiene

When estimating the length for a one-dimensional particle-in-a-box model for a hydrocarbon (such as 1,3-butadiene), do we include the bond lengths between the (terminal) carbon and hydrogen atoms at ...
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1answer
1k views

How to extract thymol from oregano leaves?

This is my second graders in highschool project of science report. I try to a make natural hand sanitizer using thymol from oregano leaves as the antiseptic ingredient instead of alcohol. I want ...

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