One crystalline form of silica (SiO2) has a cubic unit cell, and from X-ray diffraction data it is known that the cell edge length is 0.700 nm. If the measured density is 2.32 g/cm3, how many (a) Si4 and (b) O2- ions are there per unit cell

Answer:

attached below

Explanation:

The Four Claisen condensation are grouped into :

Self Claisen condensation is when R = R'

Cross Claisen condensation is when R ≠ R'

attached below are the four Claisen condensation

Answer: The question wants you to determine the energy that the incoming photon must have in order to allow the electron that absorbs it to jump from  

n

i

=

2

to  

n

f

=

6

.

A good starting point here will be to calculate the energy of the photon emitted when the electron falls from  

n

i

=

6

to  

n

f

=

2

by using the Rydberg equation.

1

λ

=

R

⋅

(

1

n

2

f

−

1

n

2

i

)

Here

λ

si the wavelength of the emittted photon

R

is the Rydberg constant, equal to  

1.097

⋅

10

7

m

−

1

Plug in your values to find

1

λ

=

1.097

⋅

10

7

.

m

−

1

⋅

(

1

2

2

−

1

6

2

)

1

λ

=

2.4378

⋅

10

6

.

m

−

1

This means that you have

λ

=

4.10

⋅

10

−

7

.

m

So, you know that when an electron falls from  

n

i

=

6

to  

n

f

=

2

, a photon of wavelength  

410 nm

is emitted. This implies that in order for the electron to jump from  

n

i

=

2

to  

n

f

=

6

, it must absorb a photon of the same wavelength.

To find the energy of this photon, you can use the Planck - Einstein relation, which looks like this

E

=

h

⋅

c

λ

Here

E

is the energy of the photon

h

is Planck's constant, equal to  

6.626

⋅

10

−

34

.

J s

c

is the speed of light in a vacuum, usually given as  

3

⋅

10

8

.

m s

−

1

As you can see, this equation shows you that the energy of the photon is inversely proportional to its wavelength, which, of course, implies that it is directly proportional to its frequency.

Plug in the wavelength of the photon in meters to find its energy

E

=

6.626

⋅

10

−

34

.

J

s

⋅

3

⋅

10

8

m

s

−

1

4.10

⋅

10

−

7

m

E

=

4.85

⋅

10

−

19

.

J

−−−−−−−−−−−−−−−−−  

I'll leave the answer rounded to three sig figs.

So, you can say that in a hydrogen atom, an electron located on  

n

i

=

2

that absorbs a photon of energy  

4.85

⋅

10

−

19

J

can make the jump to  

n

f

=

6

.

Explanation:

Answer:

Attached below

Explanation:

The starting agents : attached below

There is no Solvent required to carry out this electrophilic alkene addition reaction

The products are :  attached below ( Cl )

The TLC values can only be determined by carrying out the experiment in the laboratory ( i.e. it is an experimental observation )

Attached below is the Mechanism showing the starting agents and products

Answer:

The right answer is "6 gm".

Explanation:

Given:

Amount of Li,

= 0.3 gm

Battery rated,

= 5 Ah per cell

Total number of cells,

= 4

The total power limit will be:

= [tex]5\times 4[/tex]

= [tex]20 \ Ah[/tex]

hence,

The amount of Li in battery will be:

= [tex](0.3)\times 20[/tex]

= [tex]6 \ gm[/tex]

(Allowed for transportation).

 9 is the element Florine

Florine has 9 electrons as well as the 9 protons that determine its atomic number.

The ground state configuration is the lowest energy configuration.

Answer:

37.0. gsgggsgsghddhhdd

Answer:

the answer is C

Explanation:

Answer:

See explanation

Explanation:

The average speed of the molecules of a gas depends on the temperature of the gas and its molar mass and not on the volume of the gas.

The average velocity of a gas is given by; vrms=√3RTM

R= gas constant

T= Absolute temperature

M= molar mass of the gas

Where the temperature of the gas is held constant, the average velocity of gas molecules depends on the molar mass of the gas. Hence, if a sample of gas is slowly compressed to one-half of its original volume with no change in temperature, the average speed of the molecules in the sample of gas remains the same.

Answer:

[tex]m_{isoborneol }=0.39g\\\\m_{Camphor}=0.38g\\[/tex]

Explanation:

Hello there!

In this case, according to the given information, it turns out possible for us to infer that the reaction whereby isoborneol goes to camphor occurs in a 1:1 mole ratio, that is why the theoretical yield of the latter is also 2.5 mmol (0.0025 mol) but the masses can be calculated as follows:

[tex]m_{isoborneol }=0.0025mol*\frac{154.25g}{1mol} =0.39g\\\\m_{Camphor}=0.0025mol*\frac{152.23 g}{1mol} =0.38g\\[/tex]

Because of the fact this is a rearrangement reaction whereas the number of atoms is not significantly modified.

Regards!

Answer:

Explanation:

The best way to explain this is to use an example

[tex]I\frac{125}{53} + e \frac{0}{-1} ====> Te\frac{125}{52}[/tex]

You have to understand what happened. A electron was shot into the nucleus of the Iodine. That electron change the entire composition of the nucleus resulting in 52 protons. The mass remained the same (125) but the nucleus was altered. The chemical became 125 52 Tellurium.  But what is important is that it takes a tremendous amount of energy to disrupt a nucleus, and a new chemical is born from that disruption.

Answer:

B.Lone pair in pyrrolidine ring is localized and, therefore, is expected to be more reactive.

Explanation:

There are two nitrogen atoms bearing lone pairs of electrons in the structure of nicotine as shown in the image attached.

One nitrogen atom is found in the pyrrolidine ring. The lone pair on this nitrogen atom is localized hence it is more reactive than the lone pair of electrons found on the nitrogen atom in the pyridine ring which is delocalized a shown in the image attached to this answer.

Answer:

1.12 mol/L.

Explanation:

From the question given above, the following data were obtained:

Mole of LiCl = 3.75 moles

Volume = 3.36 L

Molarity =?

Molarity is simply defined as the mole of solute per unit litre of the solution. Mathematically, it is expressed as:

Molarity = mole / Volume

With the above formula, we can obtain the molarity of the solution as follow:

Mole of LiCl = 3.75 moles

Volume = 3.36 L

Molarity =?

Molarity = mole /Volume

Molarity = 3.75 / 3.36

Molarity = 1.12 mol/L

Thus, the molarity of the solution is 1.12 mol/L

Answer:

[tex]\boxed {\boxed {\sf 0.078 \ L }}[/tex]

Explanation:

We are asked to find the volume of a solution given the moles of solute and molarity.

Molarity is a measure of concentration in moles per liter. It is calculated using the following formula:

[tex]molarity= \frac{moles \ of \ solute}{liters \ of \ solution}[/tex]

We know there are 0.14 moles of potassium chloride (KCl), which is the solute. The molarity of the solution is 1.8 molar or 1.8 moles of potassium chloride per liter.

Substitute these values/variables into the formula.

[tex]1.8 \ mol \ KCl/ L = \frac { 0.14 \ mol \ KCl}{x}[/tex]

We are solving for x, so we must isolate the variable. First, cross multiply. Multiply the first numerator and second denominator, then the first denominator and second numerator.

[tex]\frac {1.8 \ mol \ KCl/L}{1} = \frac{0.14 \ mol \ KCl}{x}[/tex]

[tex]1.8 \ mol \ KCl/ L *x = 1*0.14 \ mol \ KCl[/tex]

[tex]1.8 \ mol \ KCl/ L *x = 0.14 \ mol \ KCl[/tex]

Now x is being multiplied by 1.8 moles of potassium chloride per liter. The inverse operation of multiplication is division, so we divide both sides by 1.8 mol KCl/L.

[tex]\frac {1.8 \ mol \ KCl/ L *x}{1.8 \ mol \ KCl/L} = \frac{0.14 \ mol \ KCl}{1.8 \ mol \ KCl/L}[/tex]

[tex]x= \frac{0.14 \ mol \ KCl}{1.8 \ mol \ KCl/L}[/tex]

The units of moles of potassium chloride cancel.

[tex]x= \frac{0.14 }{1.8 L}[/tex]

[tex]x=0.07777777778 \ L[/tex]

The original measurements of moles and molarity have 2 significant figures, so our answer must have the same. For the number we found, that is the thousandth place. The 7 in the ten-thousandth place tells us to round the 7 up to a 8.

[tex]x \approx 0.078 \ L[/tex]

There are approximately 0.078 liters of solution.

Answer:

Both have solutions in the  graduated cylinder.

Explanation:

Recording the amount of alcohol used as the difference between two masses is the wrong method used for measuring tert-butyl alcohol for the experiment.  For measuring tert-butyl alcohol for this experiment, the student has to measure the two masses when both the graduated cylinders has solution of tert-butyl alcohol not when one of it is empty (having no tert-butyl alcohol ).

The wrong aspect is that the liquid didn't need to be weighed. Instead the volume should have been recorded with the aid of the graduated cylinder.

This is a cylinder with marked readings and is used to measure the volume of liquids in the laboratory.

The graduated cylinder will accurately measure the amount of  alcohol used due to it being volatile and the mass fluctuating during the measurement.

Read  more about Graduated cylinder here https://brainly.com/question/24869562

Answer:

False

Explanation:

Electrophilic addition reactions may be under kinetic or thermodynamic control. Whether the reaction is under kinetic or thermodynamic control is easily deducible from the reaction time.

Shorter reaction time often reflect kinetic control while longer reaction reaction times favour thermodynamic control.

Hence, electrophilic addition reaction of conjugated dienes that occur at high temperature and/or long reaction times (reversible conditions) are said to be under thermodynamic and not kinetic control.

Answer:

1. Pyruvate reacts with TPP and is decarboxylated forming hydroxyethyl-TPP.

2. The lipoamide arm of E2 moves to the active site of E1, enabling the transfer of the acetyl group to the lipoamide.

3. The acetyl lipoamide arm of E2 moves to the active site of E2, where the acetyl group is transferred to CoA, forming acetyl-CoA and the reduced form of lipoamide.

4. The lipoamide arm moves to the active site of E3 where the reduced lipoamide is oxidized by FAD forming the active lipoamide and FADH2.

5. FADH2 is reoxidized to FAD reducing NAD+ to NADH.

Explanation:

The oxidation of pyruvate to AcetylCoA is catalyzed by the pyruvate dehydrogenase complex. The reaction is an irreversible oxidative decarboxylation process in which the carboxyl group of pyruvate is removed as a molecule of carbon dioxide, CO₂, while the remaining two carbons are attached to a CoASH molecule to form acetylCoA.

The pyruvate dehydrogenase complex contains three enzymes - Pyruvate dehydrogenase known as E₁, dihydrolipoyl transacetylase known as E₂, and dihydrolipoyl dehydrogenase known as E₃. It also requires five coenzymes namely: thiamine pyrophosphate (TPP), flavine adenine dinucleotide (NAD), coenzyme A (CoA-SH), nicotinamide adenine dinucleotide (NAD) and lipoate.

Oxidative decorbyxylation of pyruvate takes place in the pyruvate dehydrogenase complex in five steps:

1. Pyruvate reacts with TPP and is decarboxylated forming hydroxyethyl-TPP.

2. The lipoamide arm of E2 moves to the active site of E1, enabling the transfer of the acetyl group to the lipoamide.

3. The acetyl lipoamide arm of E2 moves to the active site of E2, where the acetyl group is transferred to CoA, forming acetyl-CoA and the reduced form of lipoamide.

4. The lipoamide arm moves to the active site of E3 where the reduced lipoamide is oxidized by FAD forming the active lipoamide and FADH2.

5. FADH2 is reoxidized to FAD reducing NAD+ to NADH.

Answer:

Aerate solution

Explanation:

aerate solution is the best way to remove CO2 from water (Carbon dioxide in the water that does not form bicarbonates is “uncombined” and can be removed by aeration).

A beaker with 120mL of an acetic acid buffer with a pH of 5.00 is sitting on a benchtop. The total molarity of acid and conjugate base in this buffer is 0.1M. A student adds 6.60mL of a 0.300M HCl solution to the beaker. How much will the pH change?

The pKa of acetic acid is 4.76.

Chemistry Buffer Calculations

1 Answer

Stefan V.

May 8, 2016

Δ

pH

=

0.29

Explanation:

!! LONG ANSWER !!

The idea here is that you need to use the Henderson-Hasselbalch equation to determine the ratio that exists between the concentration of the weak acid and of its conjugate base in the buffer solution.

Once you know that, you can use the total molarity of the acid and of the conjugate base to find the number of moles of these two chemical species present in the buffer.

So, the Henderson-Hasselbalch equation looks like this

∣

∣

∣

∣

∣

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

pH

=

p

K

a

+

log

(

[

conjugate base

]

[

weak acid

]

)

a

a

∣

∣

∣

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

In your case, you have acetic acid,

CH

3

COOH

, as the weak acid and the acetate anion,

CH

3

COO

−

, as its conjugate base. The

p

K

a

of the acid is said to be equal to

4.76

, which means that you have

pH

=

4.76

+

log

(

[

CH

3

COO

−

]

[

CH

3

COOH

]

)

The pH is equal to

5

, and so

5.00

=

4.76

+

log

(

[

CH

3

COO

−

]

[

CH

3

COOH

]

)

log

(

[

CH

3

COO

−

]

[

CH

3

COOH

]

)

=

0.24

This will be equivalent to

10

log

(

[

CH

3

COO

−

]

[

CH

3

COOH

]

)

=

10

0.24

which will give you

[

CH

3

COO

−

]

[

CH

3

COOH

]

=

1.74

This means that your buffer contains

1.74

times more conjugate base than weak acid

[

CH

3

COO

−

]

=

1.74

×

[

CH

3

COOH

]

Now, because both chemical species share the same volume,

120 mL

, this can be rewritten as

n

C

H

3

C

O

O

−

120

⋅

10

−

3

L

=

1.74

×

n

C

H

3

C

O

O

H

120

⋅

10

−

3

L

which is

∣

∣

∣

∣

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

n

C

H

3

C

O

O

−

=

1.74

×

n

C

H

3

C

O

O

H

a

a

∣

∣

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

(

1

)

So, the buffer contains

1.74

times more moles of acetate anions that of acetic acid.

Now, the total molarity of the buffer is said to be equal to

0.1 M

. You thus have

[

CH

3

COOH

]

+

[

CH

3

COO

−

]

=

0.10 M

Once again, use the volume of the buffer to write

n

C

H

3

C

O

O

H

120

⋅

10

−

3

L

+

n

C

H

3

C

O

O

−

120

⋅

10

−

3

L

=

0.1

moles

L

This will be equivalent to

∣

∣

∣

∣

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

n

C

H

3

C

O

O

−

+

n

C

H

3

C

O

O

H

=

0.012

a

a

∣

∣

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

(

2

)

Use equations

(

1

)

and

(

2

)

to find how many moles of acetate ions you have in the buffer

1.74

⋅

n

C

H

3

C

O

O

H

+

n

C

H

3

C

O

O

H

=

0.012

n

C

H

3

C

O

O

H

=

0.012

1.74

+

1

=

0.004380 moles CH

3

COOH

This means that you have

n

C

H

3

C

O

O

−

=

1.74

⋅

0.004380 moles

n

C

H

3

C

O

O

−

=

0.007621 moles CH

3

COO

−

Now, hydrochloric acid,

HCl

, will react with the acetate anions to form acetic acid and chloride anions,

Cl

−

H

Cl

(

a

q

)

+

CH

3

COO

−

(

a

q

)

→

CH

3

COO

H

(

a

q

)

+

Cl

−

(

a

q

)

Notice that the reaction consumes hydrochloric acid and acetate ions in a

1

:

1

mole ratio, and produces acetic acid in a

1

:

1

mole ratio.

Use the molarity and volume of the hydrochloric acid solution to determine how many moles of strong acid you have

∣

∣

∣

∣

∣

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

c

=

n

solute

V

solution

⇒

n

solute

=

c

⋅

V

solution

a

a

∣

∣

∣

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

In your case, this gets you

n

H

C

l

=

0.300 mol

L

−

1

⋅

volume in liters

6.60

⋅

10

−

3

L

n

H

C

l

=

0.001980 moles HCl

The hydrochloric acid will be completely consumed by the reaction, and the resulting solution will contain

n

H

C

l

=

0 moles

→

completely consumed

n

C

H

3

C

O

O

−

=

0.007621 moles

−

0.001980 moles

=

0.005641 moles CH

3

COO

−

n

C

H

3

C

O

O

H

=

0.004380 moles

+

0.001980 moles

=

0.006360 moles CH

3

COOH

The total volume of the solution will now be

V

total

=

120 mL

+

6.60 mL

=

126.6 mL

The concentrations of acetic acid and acetate ions will be

[

CH

3

COOH

]

=

0.006360 moles

126.6

⋅

10

−

3

L

=

0.05024 M

[

CH

3

COO

−

]

=

0.005641 moles

126.6

⋅

10

−

3

L

=

0.04456 M

Use the Henderson-Hasselbalch equation to find the new pH of the solution

pH

=

4.76

+

log

(

0.04456

M

0.05024

M

)

pH

=

4.71

Therefore, the pH of the solution decreased by

Δ

pH

=

|

4.71

−

5.00

|

=

∣

∣

∣

∣

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

0.29 units

a

a

∣

∣

−−−−−−−−−−−−−

Answer link

Related topic

Buffer Calculations

Questions

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Answer:

radical-initiated

Explanation:

Radical-initiated polymerization is unpredictable and difficult to control. The reaction proceeds indiscriminately and produces shortened chains, loops, and branches that create holes in the polymer. This reduces its mass to volume ratio.

Answer:

Nitrobenzene < Bromobenzene < Benzene < Phenol

Explanation:

Aromatic compounds undergo electrophilic aromatic substitution reaction in the presence of relevant electrophiles. Certain substituents tend to increase or decrease the tendency of an aromatic compound towards electrophilic aromatic substitution reaction.

Substituents that increase the electron density around the ring such as in phenol tends to make the ring more reactive towards electrophilic substitution. Halogens such as bromine has a -I inductive effect as well as a +M mesomeric effect.

However the -I(electron withdrawing effect) of the halogens supersedes the +M electron donation due to mesomeric effect.

Putting all these together, the order of increasing reactivity of the compounds towards electrophilic aromatic substitution is;

Nitrobenzene < Bromobenzene < Benzene < Phenol

Answer:

Option D. 17.5

Explanation:

Equiibrium is: CO + 2H₂  ⇄  CH₃OH

1 mol of CO is in equibrium with 2 moles of hydrogen in order to make, methanol.

Initially we have 0.42 moles of CO and 0.42 moles of H₂

If 0.29 moles of CO remained, (0.42 - 0.29) = 0.13 moles have reacted.

So in the equilibrium we may have:

0.29 moles of CO, and (0.42 - 0.13 . 2) = 0.16 moles of H₂

Ratio is 1:2, if 0.13 moles of CO haved reacted, (0.13 . 2) moles have reacted of hydrogen

Finally 0.13 moles of methanol, are found after the equilibrium reach the end.

Let's make expression for KC: [Methanol] / [CO] . [Hydrogen]²

0.13 / (0.29 . 0.16²)

Kc = 17.5

Follow the rules of Bronsted Lowry theory

So

#a

NH_2-

Add a H

#b

HnO_3

Take a H

#1

Conjugate acid means one H+ is added

sw

#2

Conjugate base means donate a H+

Answer:

a mixture that doesn't really show the ingredients or things put into the material or food.

Answer:

a. Endothermic.

b. [tex]Q_{rxn}=5493.6J[/tex]

c. [tex]\Delta H_{rxn}=35.0kJ/mol[/tex]

Explanation:

Hello there!

In this case, according to the given information for this calorimetry problem, it turns out possible for us to proceed as follows:

a. Due to the fact that the temperature of water goes from 23.0 °C to 18.0 °C, we infer this reaction is endothermic as the ammonium nitrate absorbed heat from the water.

b. Here, we consider the following heat equation:

[tex]Q_{rxn}=-Q_{water}[/tex]

Whereas we solve for the heat of reaction by means of the mass of the solution (both water and ammonium nitrate), the specific heat of the solution (we assume it is equal to that of water) and the temperature change:

[tex]Q_{rxn}=-m_{solution}C_{solution}(T_f-T_i)\\\\Q_{rxn}=-(12.6g+250.g)(4.184\frac{J}{g\°C} )(18.0\°C-23.0\°C)\\\\Q_{rxn}=5493.6J[/tex]

c. Here, we divide the previously calculated heat by the moles of ammonium nitrate (molar mass = 80.043 g/mol) to obtain the enthalpy of reaction per mole of this compound:

[tex]n_{NH_4NO_3}=12.6g*\frac{1mol}{80.043 g}=0.157mol\\\\\Delta H_{rxn}=\frac{5493.6J}{0.157mol} =34898.7J/mol\\\\\Delta H_{rxn}=35.0kJ/mol[/tex]

Regards!

Answer:

The right answer is "105.17 ppb".

Explanation:

According to the question,

The amount of [tex]Pb^{2+}[/tex] in ppb will be:

= [tex]0.5076\times 10^{-6}\times 207.2\times 106[/tex]

= [tex]105.17 \ ppb[/tex]

Thus, the amount of [tex]Pb^{2+}[/tex] is above action limit.

Answer:

the % yield is 82%

Explanation:

Given the data in the question,

we know that;

Molar mass of benzil is 210.23 g·mol−1

Molar mass of dibenzyl ketone is 210.27 g·mol−1

Molar mass of tetraphenylcyclopentadienone is 384.5 g·mol−1

Now,

2.0 g benzil = 2 g / 210.23 g·mol−1 = 0.0095 mole

2.2 g dibenzyl ketone = 2.2 / 210.27 = 0.0105 mole

3.0 g of tetraphenylcyclopentadienone = 3 / 384.5  = 0.0078 mole

Now, the limiting reagent is benzil. 0.0095 mole can reacts wiyh 0.0095 mole of dibenzyl ketone

percentage yield = ( 0.0078 mole / 0.0095 mole ) × 100%

= 0.82 × 100%

= 82%

Therefore, the % yield is 82%

Answer:

b. Additive manufacturing

Explanation:

Additive manufacturing is defined as that manufacturing process where light parts and components are being developed or manufactured in 3D form by adding materials to it.

It is a process of adding materials to produce the final product. It is also known as 3D printing.

In the context, Oregon Technologies Inc. uses computer-aided design model in order to manufacture a spare part required by Sofia for her custom made bike by using a process called additive manufacturing.

Thus the correct option is (b).