which category of amino acid contains r groups that are hydrophobic? which category of amino acid contains r groups that are hydrophobic? polar acidic basic non-polar basic and acidic

After 100 years, there will be 6.25 grams of the substance remaining.

Half-life is the time it takes for half of the radioactive atoms in a sample to decay or for the concentration of a substance to decrease by half.

Amount remaining = initial amount x (1/2)^(number of half-lives)

In this case,  half-life of the substance is 10 years, which means that after 10 years, half of the substance will have decayed. After another 10 years (20 years total), half of remaining substance will decay, leaving 1/4 of the original amount. After another 10 years (30 years total), half of that remaining amount will decay, leaving 1/8 of the original amount. This process continues every 10 years.

To find the amount of substance remaining after 100 years, we need to know how many half-lives have occurred in that time: 100 years / 10 years per half-life = 10 half-lives

Amount remaining = 400 g x (1/2)¹⁰= 6.25 g

Therefore, after 100 years, there will be 6.25 grams of the substance remaining.

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The standard enthalpy change for the decomposition of hydrogen peroxide per mole of hydrogen peroxide is -98.2 kJ/mol.

when 1 mole of hydrogen peroxide (H2O2) ( H 2 O 2 ) undergoes decomposition, the heat evolved (ΔH) is −98.2kJ. − 98.2 k J . The molar mass of H2O2 H 2 O 2 is 34.015 g/mol. This means that the mass of 1 mole of H2O2 H 2 O 2 is 34.015 g.

This value is obtained from the standard enthalpy of formation of the products (H2 and O2) and the standard enthalpy of formation of the reactant (H2O2). Enthalpy of formation is the energy change that occurs when a compound is formed from its elements, in their standard states.

The difference between the enthalpies of formation of the products and the reactant is the enthalpy change for the reaction. In this case, the enthalpy change for the decomposition of hydrogen peroxide is -98.2 kJ/mol. This indicates that the decomposition of hydrogen peroxide is an exothermic reaction and it releases 98.2 kJ/mole of energy.

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9 pennies contain approximately [tex]2.13 x 10^23[/tex] atoms of copper.

To solve this problem, we need to use the following steps:

Determine the molar mass of copper.

Convert the mass of 9 pennies from grams to moles.

Use Avogadro's number to calculate the number of atoms of copper.

Step 1: The molar mass of copper (Cu) is approximately 63.55 g/mol.

Step 2: The mass of 9 pennies is:

9 pennies x 2.5 g/penny = 22.5 g

Converting this mass to moles, we get:

22.5 g / 63.55 g/mol = 0.354 moles

Step 3: Using Avogadro's number ([tex]6.022 x 10^23 atoms/mol)[/tex], we can calculate the number of atoms of copper:

Therefore, 9 pennies contain approximately[tex]2.13 x 10^23 a[/tex]toms of copper.

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Mercury has the widest variation in surface temperatures between night and day of any planet in the solar system.

This statement is true. Mercury experiences the greatest temperature variation between night and day due to several factors. The main reasons are its proximity to the Sun, slow rotation, and lack of atmosphere.

During the daytime, temperatures on Mercury can reach up to 800°F (430°C) due to its close proximity to the Sun. This extreme temperature difference is due to the fact that Mercury's thin atmosphere is unable to regulate temperature and its slow rotation causes one side of the planet to be constantly facing the sun while the other is in perpetual darkness.

At night, temperatures can drop as low as -290°F (-180°C) because of its slow rotation and the lack of an atmosphere to retain heat. This results in the widest variation in surface temperatures between night and day of any planet in our solar system.

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Mercury indeed has the widest variation in surface temperatures between night and day of any planet in the solar system. This is primarily due to its thin atmosphere, which cannot effectively retain heat, leading to extreme temperature fluctuations.

Mercury, being the closest planet to the sun, experiences extreme variations in temperature between its day and night sides. During the day, when the sun is overhead, the surface temperature on Mercury can rise to a scorching 430°C (800°F), which is hot enough to melt lead. However, as Mercury rotates and the sun sets, the temperature drops drastically to as low as -180°C (-290°F) at night.

The main reason for this extreme temperature variation is that Mercury has no atmosphere to regulate its surface temperature. Unlike Earth, which has an atmosphere that helps to distribute heat around the planet, Mercury's surface is directly exposed to the sun's radiation. This means that when the sun is shining on Mercury's surface, it heats up quickly and intensely, causing the temperature to rise to extreme levels.

Overall, the lack of an atmosphere and Mercury's proximity to the sun are the main factors contributing to the extreme temperature variations on the planet.

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The moles of NaF that must be dissolved in 1.00 liter of a saturated solution of PbF₂ at 25˚C to reduce the [Pb²⁺] to 1 x 10⁻⁶ molar is 2.0 x 10⁻⁵.

The solubility product expression for PbF₂ is given by:

At equilibrium, the product of the ion concentrations must be equal to the solubility product constant. We are given that the [Pb²⁺] in the saturated solution is 1 x 10⁻⁶ M. Therefore, we can use the Ksp expression to calculate the concentration of F- in the solution:

Now, we can calculate the amount of NaF needed to reduce the [F⁻] concentration to 2.0 x 10⁻¹ M. Since NaF is a 1:1 electrolyte, the concentration of F- will be equal to the concentration of NaF added.

However, we need to dissolve this amount of NaF in a saturated solution of PbF₂. Therefore, we need to check that the amount of NaF we added will not exceed the maximum amount that can dissolve in the solution at 25˚C.

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The pressure of gas is 1.05 atm when a 1.25 g sample of CO₂ is contained in a 750ml flask at 22.5°C.

Molecular weight of CO₂ is 1.25g ,Volume of CO₂ is 750ml,Temperature of CO₂ is 22.5°C and the gas constant is 0.08206 L atm/mol K.

Using the ideal gas law equation the pressure is found to be 1.05 atm.

To calculate the pressure of the gas, we can use the ideal gas law equation: [tex]PV=nRT[/tex]
Where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature in Kelvin.
First, we need to convert the volume to liters by dividing by 1000: 750 ml = 0.75 L.
Next, we need to calculate the number of moles of CO₂ present in the flask. We can use the molecular weight of CO₂ to convert from grams to moles:

[tex]1.25 * (1 /44.01 ) = 0.0284 mol[/tex]
Now we can plug in the values into the ideal gas law equation:

[tex]PV=nRT[/tex]
[tex]P * 0.75 L = 0.0284 mol  * 0.08206 L*atm/mol*K * (22.5 + 273.15) K[/tex]
Simplifying and solving for P, we get:
[tex]P = (0.0284 * 0.08206 * 295.65) / 0.75 = 1.05 atm[/tex]
Therefore, the pressure of the gas in the flask is 1.05 atm.

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Answer:

0.9g/L.

Explanation:

To calculate the density of hydrogen sulfide (H2S) at 0.7 atm and 322 K, we can use the ideal gas law:

PV = nRT

where P is the pressure in atmospheres (atm), V is the volume in liters (L), n is the number of moles of gas, R is the universal gas constant (0.08206 L·atm/(mol·K)), and T is the temperature in Kelvin (K).

We can rearrange this equation to solve for the number of moles of gas:

n = PV / RT

Next, we can use the molar mass of H2S (34.08 g/mol) to convert the number of moles to mass:

mass = n × molar mass

Finally, we can divide the mass by the volume to obtain the density:

density = mass/volume

Let's assume a volume of 1 L (since the volume is not given in the question). Then we have:

P = 0.7 atm

T = 322 K

R = 0.08206 L·atm/(mol·K)

molar mass of H2S = 34.08 g/mol

First, we calculate the number of moles of H2S using the ideal gas law:

n = PV / RT

n = (0.7 atm) (1 L) / (0.08206 L·atm/(mol·K) × 322 K)

n = 0.0265 mol

Next, we calculate the mass of H2S using the number of moles and the molar mass:

mass = n × molar mass

mass = 0.0265 mol × 34.08 g/mol

mass = 0.9 g

Finally, we calculate the density of H2S:

density = mass/volume

density = 0.9g/1 L

density = 0.9 g/L

Therefore, the density of hydrogen sulfide (H2S) at 0.7 atm and 322 K is approximately 0.9g/L.

Answer:

data given

mass of NaCl 4.56

dissolved volume 20ml(0.02l)

density of solution 1.03g/ml

Required molality

Explanation:

molarity=m/mr×v

where

m is mass

mr molar mass

v is volume

now,

molarity=4.56/58.5×0.02

molarity =3.9

: .molarity is 3.9mol/dm^3

According to molal concentration, the concentration (in molality) of an aqueous solution of NaCl is 0.0047 mole/kg.

Molal concentration is defined as a measure by which concentration of chemical substances present in a solution are determined. It is defined in particular reference to solute concentration in a solution . Most commonly used unit for molal concentration is moles/kg.

The molal concentration depends on change in volume of the solution which is mainly due to thermal expansion. Molal concentration is calculated by the formula, molal concentration=mass/ molar mass ×1/mass of solvent in kg.

In terms of moles, it's formula is given as molal concentration= number of moles /mass of solvent in kg.

Substitution in formula gives the answer but first mass of solution is determined which  is density×volume= 1.03×20=20.6 g , mass of solvent= 20.6-4.56=16.05, thus molal concentration=4.56/58.5×1/16.05=0.0047 moles/kg.

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Answer:

condensation nuclei

Explanation:

The value of Ksp for PbI2 is 4.05 × 10^-8 if the molar solubility of PBI 2 is 1.5 × 10 −3 m.

The molar solubility of PBI 2 = 1.5 × 10 −3 m

The solubility product constant  = 2 .4.5 x 10 -6

The solubility product constant (Ksp) for PbI2 can be estimated using the molar solubility of PbI2, the stoichiometry of the equilibrium equation is:

[tex]PbI2(s) = Pb2+(aq) + 2I-(aq)[/tex]

The equation for Ksp is:

Ksp = [tex][Pb2+][I-]^2[/tex]

[Pb2+] = S = 1.5 × 10−3 M,

[I-] = 2S = 3 × 10−3 M

The stoichiometric coefficient of I- is 2. Substituting these values into the Ksp equation we get:

Ksp =[tex](1.5 × 10^-3) × (3 × 10^-3)^2[/tex]

Ksp = 4.05 × 10^-8

Therefore, we can conclude that the value of Ksp for PbI2 is 4.05 × 10^-8.

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The value of Ksp for PbI2 is 3.375 × 10^-9 or 4.5 x 10 -6. The expression for the solubility product constant (Ksp) of a sparingly soluble salt such as PbI2 is: Ksp = [Pb2+][I-]^2

where [Pb2+] and [I-] are the molar concentrations of the lead ion and iodide ion, respectively, in a saturated solution of PbI2.

Given that the molar solubility of PbI2 is 1.5 × 10^-3 M, we can assume that [Pb2+] and [I-] in the saturated solution are also equal to 1.5 × 10^-3 M. Therefore, we can substitute these values into the Ksp expression and solve for Ksp:

Ksp = (1.5 × 10^-3 M)(1.5 × 10^-3 M)^2
Ksp = 3.375 × 10^-9

So the value of Ksp for PbI2 is 3.375 × 10^-9 or 4.5 x 10 -6 (if that was a typo in the question).

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When conducting a crystallization process, it is important to cool the solution at a slow and controlled rate to encourage crystal formation.

An ice bath is preferable over cold water or ice alone because it can maintain a consistent low temperature without causing the solution to freeze solid. Ice alone is too cold and can cause the solution to freeze rapidly, preventing the formation of crystals. Cold water, on the other hand, is not able to maintain a consistent low temperature as the heat from the solution will quickly dissipate into the surrounding water, resulting in a slower cooling rate.

An ice bath, which is a mixture of ice and water, provides a more stable and uniform cooling environment for the solution, allowing for the crystals to form at a slower rate. Additionally, an ice bath can contact the entire portion of the container immersed in the mixture, ensuring that the solution is evenly cooled. Overall, an ice bath is the preferred method for cooling a solution during the process of crystallization.

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complete question is:-

one of the techniques used in this experiment was that of crystallization. when cooling a solution in the process of crystallization, why would an ice bath be preferable over cold water or ice alone? none of the answers shown are correct. ice is too cold and will freeze any solution. cold water would dilute the solution making it impossible for crystals to form. a mixture of ice and water will keep the temperature above freezing and will contact the entire portion of the container immersed in the ice/water mixture.  EXPLAIN.

A compound turns completely into a liquid this observation best describes the physical appearance of a compound when it reaches the end of its melting point range. Here option B is the correct answer.

When a solid compound is heated, it undergoes a process called melting in which it transforms into a liquid state. The melting point of a compound is the temperature at which it changes from a solid to a liquid state. The melting process is characterized by a range of temperatures over which the compound is observed to be partially or fully melted.

The observation that best describes the physical appearance of a compound when the end of its melting point range is reached is B - the compound completely converts to a liquid. At the end of the melting point range, the compound has absorbed enough heat energy to fully overcome the intermolecular forces that hold its constituent particles together in a solid state, resulting in the complete transformation of the compound into a liquid.

This state is characterized by the loss of a crystalline structure, where the particles are free to move about and slide past each other, leading to an increased fluidity and mobility of the compound. At this stage, the compound is fully melted and can be poured or transferred into a new container in its liquid form.

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Complete question:

Which observation best describes the physical appearance of a compound when the end of its melting point range is reached?

A - the compound begins to convert to a liquid.

B - the compound completely converts to a liquid.

C - the compound begins to evaporate.

23 grams of water at 95°C can lose a maximum of 8883.64 Joules of heat before freezing completely.

To answer your question, we need to calculate the heat loss required to lower the temperature of 23 grams of water from 95 degrees Celsius to 0 degrees Celsius, which is the freezing point of water. The specific heat capacity of water is 4.184 Joules per gram per degree Celsius.

So, the initial energy of the water is:

E1 = m x c x ΔT
E1 = 23 g x 4.184 J/g°C x (95°C - 0°C)
E1 = 8883.64 J

Where E1 is the initial energy of the water, m is the mass of water, c is the specific heat capacity of water, and ΔT is the change in temperature.

The final energy of the water at 0°C is:

E2 = m x c x ΔT
E2 = 23 g x 4.184 J/g°C x (0°C - 0°C)
E2 = 0 J

So, the maximum amount of heat in joules that 23 grams of water at 95°C can lose before freezing completely is:

ΔE = E1 - E2
ΔE = 8883.64 J - 0 J
ΔE = 8883.64 J

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1) 5.1167 x 10²⁴atoms of chlorine. 2) 248.00 g. 3) 4.8825 x 10⁷ moles of helium. 4) 2.7757 x 10²⁴ atoms of sulfur.  5) Molar mass of Co (cobalt) is 58.93 g/mol.  6) Formula mass =  310.18 g/mol.

Sum of the atomic masses of all the atoms in chemical formula is called formula mass

1.)  Number of atoms = 8.500 moles x 6.022 x 10²³ atoms/mole = 5.1167 x 10²⁴ atoms of chlorine.

2.) Molar mass of oxygen is 16.00 g/mol. Therefore:

Mass of 15.50 moles of oxygen = 15.50 moles x 16.00 g/mol = 248.00 g.

3.) Molar mass of helium is 4.00 g/mol. Therefore, the number of moles of helium in 1.953 x 10⁸ g is:

Number of moles = 1.953 x 10⁸ g / 4.00 g/mol = 4.8825 x 10⁷ moles of helium.

4.) Molar mass of sulfur is 32.06 g/mol. Therefore, the number of moles of sulfur in 147.82 g is:

Number of moles = 147.82 g / 32.06 g/mol = 4.6084 moles of sulfur.

To find the number of atoms, we can use Avogadro's number again:

Number of atoms = 4.6084 moles x 6.022 x 10²³ atoms/mole = 2.7757 x 10²⁴ atoms of sulfur.

5.) Molar mass of Co (cobalt) is 58.93 g/mol.

6.) Ca₃(PO₄)₂ contains 3 calcium atoms, 2 phosphorus atoms, and 8 oxygen atoms.

Atomic masses of these elements are:

Calcium (Ca) = 40.08 g/mol

Phosphorus (P) = 30.97 g/mol

Oxygen (O) = 16.00 g/mol

Therefore, formula mass of Ca₃(PO₄)₂ is:

Formula mass = (3 x 40.08 g/mol) + (2 x 30.97 g/mol) + (8 x 16.00 g/mol)

= 120.24 g/mol + 61.94 g/mol + 128.00 g/mol

= 310.18 g/mol.

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At equilibrium, the concentrations of NO, Br2, and NOBr in the flask will remain constant. However, without specific values for the initial concentration of NOBr or the equilibrium constant (Kc), it's not possible to determine.

.Based on the provided information, it seems that a sample of NOBr was placed in a 1.00 L flask at equilibrium, which means that the NOBr has decomposed into NO and Br2.

At equilibrium, the concentrations of NO, Br2, and NOBr in the flask will remain constant. However, without specific values for the initial concentration of NOBr or the equilibrium constant (Kc), it's not possible to determine the exact concentrations of these substances in the flask.

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A sample of NOBr being placed in a 1.00 L flask containing no NO or Br2 at equilibrium, I'll first provide the balanced chemical equation for the reaction:

[tex]2 NOBr (g) ⇌ 2 NO (g) + Br2 (g)[/tex]

At equilibrium, the concentrations of the reactants and products remain constant. To determine the concentrations of NOBr, NO, and Br2 at equilibrium, we need to follow these steps:

1. Write the expression for the equilibrium constant (Kc) based on the balanced chemical equation:
[tex]Kc = [NO]^2 [Br2] / [NOBr]^2[/tex]

2. Set up an ICE (Initial, Change, Equilibrium) table to determine the equilibrium concentrations of the species involved in the reaction. The initial concentrations of NO and Br2 are 0 since they are not initially present in the flask.

      NOBr      NO      Br2
I      C0        0        0
C     -2x        +2x      +x
E     C0-2x     2x       x

3. Substitute the equilibrium concentrations from the ICE table into the Kc expression:
[tex]Kc = (2x)^2 * x / (C0-2x)^2[/tex]

4. To solve for x, you need the value of Kc for the reaction. Look up the Kc value for this reaction in a reference or use provided information. Once you have Kc, substitute it into the equation and solve for x.

5. Calculate the equilibrium concentrations of NOBr, NO, and Br2 by substituting the value of x back into the ICE table:

[NOBr] = C0-2x
[NO] = 2x
[Br2] = x

By following these steps, you can determine the concentrations of NOBr, NO, and Br2 in the 1.00 L flask at equilibrium.

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The rate of the reaction is directly proportional to the stability of the carbocation intermediate, and any changes in the solvent will affect the rate of the reaction.

In an SN1 reaction, the rate-determining step is the formation of a carbocation intermediate. The stability of the carbocation intermediate affects the rate of the reaction.

In this case, if 2-propanol (isopropanol) was used instead of 2-methyl-2-propanol (t-butanol), the rate of the reaction would decrease. This is because the carbocation intermediate formed in 2-propanol is less stable compared to the one formed in t-butanol.

The carbocation intermediate formed in t-butanol is tertiary, which is more stable than the one formed in isopropanol, which is secondary. This means that the reaction will be slower in isopropanol due to the less stable carbocation intermediate.

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