Which is an example of a current research focus in chemistry?

A. applying gene therapy to treat certain diseases

B. using hook-and-loop tape in the clothing industry

C. developing smoke detectors for common use

D. studying coal combustion as an energy source

Answer:

[tex]\%sand=25\%[/tex]

Explanation:

Hello.

In this case, given the mass of the mixture, we can define it in terms of the mass of sand and table salt as shown below:

[tex]m_{sand}+m_{salt}=20.00g[/tex]

Moreover, as after filtering, the mass of dry sand turns out 5.00 g, we can compute the % sand in the original mixture by dividing this value over the mass of the mixture as shown below:

[tex]\%sand=\frac{m_{sand}}{m_{mixture}}*100\%\\ \\\%sand=\frac{5.00g}{20.00g}* 100\%\\\\\%sand=25\%[/tex]

Best regards!

matter is anything that has mass and volume...it has three state thus solid, liquid and gas.. It possess chemical and physical changes.

Answer:

[tex]m_{Cd(OH)_2}=36.6 gCd(OH)_2[/tex]

Explanation:

Hello.

In this case, for the given chemical reaction, in order to compute the grams of cadmium hydroxide that would be yielded, we must first identify the limiting reactant by computing the yielded moles of that same product, by 20.0 grams of NaOH (molar mass = 40 g/mol) and by 0.750 L of the 1.00-M solution of cadmium nitrate as shown below considering the 1:2:1 mole ratios respectively:

[tex]n_{Cd(OH)_2}^{by\ NaOH}=20.0gNaOH*\frac{1molNaOH}{40gNaOH} *\frac{1molCd(OH)_2}{2molNaOH} =0.25molCd(OH)_2\\\\n_{Cd(OH)_2}^{by\ Cd(NO_3)_2}=0.750L*1.00\frac{molCd(NO_3)_2}{L}*\frac{1molCd(OH)_2}{1molCd(NO_3)_2} =0.75molCd(OH)_2[/tex]

Thus, since 20.0 grams of NaOH yielded less of moles of cadmium hydroxide, NaOH is the limiting reactant, therefore the mass of cadmium hydroxide (molar mass = 146.4 g/mol) is:

[tex]m_{Cd(OH)_2}=0.25molCd(OH)_2*\frac{146.4gCd(OH)_2}{1molCd(OH)_2} \\\\m_{Cd(OH)_2}=36.6 gCd(OH)_2[/tex]

Best regards.

The mass of  Cd(OH)₂ that would be formed is 36.6 g

From the question,

We are to determine the mass of Cd(OH)₂ that would be formed

The given balanced chemical equation for the reaction is  

2NaOH(aq) + Cd(NO₃)₂(aq) → Cd(OH)₂ (s) + 2NaNO₃(aq)

This means

2 moles of NaOH reacts with 1 mole of Cd(NO₃)₂ to produce 1 mole of Cd(OH)₂ and 2 moles of NaNO₃

Now, we will determine the number of moles of each reactant present

Mass = 20.0 g

Molar mass = 39.997 g/mol

From the formula

[tex]Number\ of\ moles = \frac{Mass}{Molar\ mass}[/tex]

Number of moles of NaOH present = [tex]\frac{20.0}{39.997 }[/tex]

Number of moles of NaOH present = 0.50 mole

Volume = 0.750 L

Concentration = 1.00 M

From the formula

Number of moles = Concentration × Volume

∴ Number of moles of Cd(NO₃)₂ present = 1.00 × 0.750

Number of moles of Cd(NO₃)₂ present = 0.750 mole

Since,

2 moles of NaOH reacts with 1 mole of Cd(NO₃)₂

Then,

0.5 mole of NaOH will react with 0.25 mole of Cd(NO₃)₂

∴ The number of moles of Cd(NO₃)₂ that reacted is 0.25 mole

Now,

From the balanced chemical reaction

2 moles of NaOH reacts with 1 mole of Cd(NO₃)₂ to produce 1 mole of Cd(OH)₂

Then,

0.5 mole of NaOH will react with 0.25 mole of Cd(NO₃)₂ to produce 0.25 mole of Cd(OH)₂

∴ Number of moles of Cd(OH)₂ formed is 0.25 mole

Now, for the mass of Cd(OH)₂ that would be formed

From the formula

Mass = Number of moles × Molar mass

Molar mass of Cd(OH)₂ = 146.43 g/mol

∴Mass of Cd(OH)₂ formed = 0.25 × 146.43

Mass of Cd(OH)₂ formed = 36.6075 g

Mass of Cd(OH)₂ formed≅ 36.6 g

Hence, the mass of  Cd(OH)₂ that would be formed is 36.6 g

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Answer:

Radioactive decay

Explanation:

Answer:

D. Radioactive decay

Explanation:

Answer:

See explanation

Explanation:

A popular experiment that describes the effect of heat on the position of equilibrum is the change of colour when copper II chloride is heated.

As the solution is heated, it's colour changes from blue to green, this implies the the colour change (blue to green) is an endothermic process (equilibrum position shifts to the right with increase in temperature)

The equilibrum is represented by the equation;

[Cu(H2O)6]^2+(aq) + 4Cl^-(aq)<------>[CuCl4]^2-(aq) + 6H2O(l) ∆H=positive

The equilibrium mixture undergoing cooling or heating have colour changes. The temperature affects the colour of the products formed and the forward reaction is endothermic.

In the reaction copper (II) chloride or [tex]\rm CuCl_{4}[/tex] is the main species. The heat or the temperature affects the colour formation of copper (II) chloride as the equilibrium change affects the colouration of the product.

The heating of the solution affects the colour change from blue to the green of the reactant to products and the forward reaction shifts the equilibrium towards the right when the temperature is increased and is an endothermic reaction.

The reaction at the equilibrium can be shown as,

[tex]\rm [Cu(H_{2}O)_{6}]^{2+} (aq) + 4Cl^{-} (aq) \Leftrightarrow [CuCl_{4}]^{2-}(aq) + 6H_{2}O(l), \Delta H=positive[/tex]

Therefore, temperature changes the colouration and the forward reaction is an endothermic reaction.

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Answer:

valence electrons

Explanation:

other guy was close enough

Atoms of elements in the same group have the equal number of valence electrons. That is why they have similar chemical properties.

The chemical properties of elements depend on the number of valence electrons in their outermost shell. Those elements which are placed in the same group in the periodic table have the same number of valence electrons.

Therefore, elements present in the same group of the modern periodic table have similar chemical behavior.

The elements having a similar valence shell electronic configuration in their atoms are arranged in the same group of the periodic table. These valence electrons decide the chemical properties and reactivities of the chemical elements.

For example, all the elements in group 1 of the periodic table have one electron in their valence shell and all the elements present in group 17 have seven electrons in their valence shell.

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Answer:

Heat needed to increase the temperature by 50°C is 94 j.

Explanation:

Given data:

Specific heat of silver = 0.235 j/g.°C

Heat needed to increase temperature = ?

Mass of silver = 8 g

Temperature difference = ΔT= 50°C

Solution:

Formula:

q = mcΔT

c = specific heat capacity of substance

Now we will put the values i formula.

q = 8 g× 0.235 J/g.°C× 50°C

q = 94 J

Heat needed to increase the temperature by 50°C is 94 j.

Answer:

Amount of salt dissolved in each liter of seawater = 40 g

Explanation:

According to Archimedes principle, a body will float in a fluid if the upthrust experienced by a body is equal to the to the weight of the body.

Also, the volume of seawater displaced equals the volume of freshwater in the cup.

From the above principle, since the freshwater and cup floats in the seawater, their combined weight equals the upthrust.

Therefore, mass of equal volume of displaced seawater = mass of freshwater + mass of cup

Mass of freshwater = density of freshwater * volume

density of freshwater = 1 g/mL; volume = 375 mL

mass of freshwater = 375 mL * 1 g/mL = 375 g

mass of seawater = 375 + 15 = 390 g

mass of salt in 375 mL seawater = mass of seawater - mass of freshwater

mass of salt = (390 - 375) g = 15 g

Since 15 g of salt are dissolved in 375 mL seawater, mass of salt in 1 L of seawater =(1000 mL/ 375) * 15g = 40 g

Therefore, amount of salt dissolved in each liter of seawater = 40 g

Answer:

= .7567105263

Explanation:

1 atm = 760 mmHg

575.1 mmHg (1 atm/760mmHg) = .7567105263 atm

Answer:

3.48 x 1013 N2 molecules

step-by-step explanation:

Lets set up our equation first

P = 1.00 x 10-6 mm Hg T = 0.0° C + 273 = 273 K

We are given the V = 985 mL ,

R = 0.0821 L·atm/mol·K

Now use the ldeal gas law, but we are solving n, amount of substanvce

PV = nRT, we will change this equation to ;

n = PV/RT

n = 1.00 x 10-6 mm x 1 atm/760 mm x 985 mL x 1 L/103

mL/

(0.0821 L·atm/mol·K x 273 K) = 5.78 x 10-11 moles N2

nmolecules = 5.78 x 10-11 moles N2 x 6.02 x 1023 N2 molecules/1 mol N2

Answer:

A=element

B=compond

C=solution

Answer:

What Is The Molecular Shape Of A Silicon Disulfide Molecule, SiS2 Trigonal Planar None Of Above Tetrahedral Linear Bent Trigonal Pyramidal 13.

Explanation:

The Lewis structure of SiS₂ shows the 4 valence electrons of Si, which are shared with each sulphur atoms and sulphur in turn shares two valence electrons with Si atom.

The Lewis dot structure of a compound shows all the valence electrons as dots around its atom. From the dot structure  we can identify, which electron pairs are bonded , which are non-bonded and which are unpaired electrons.

SiS₂ is a covalent compound formed through the electrons sharing between two  sulphur and one silicon atoms. The silicon atom contains 4 valence electrons and one sulphur atom contains 6 valence electrons.

Si needs to gain 4 electrons and one S atom needs to gain 2 more electrons into their valence shell to achieve octet. Hence, One Si shares two electron to each S and S in turn shares its two electron with Si as shown in the image below.

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Explanation:

heat

the presence of hot, plastic like material

Answer:

C. molten rock below Earth’s surface

Explanation:

Answer:

∠

O

−

C

−

C

l

≅

120

∘

The central carbon is  

s

p

2

−

hybridized........

Explanation:

And thus  

∠

C

l

−

C

−

C

l

and  

∠

O

−

C

−

C

l

≅

are  

120

∘

to a first approximation.

Why this value? We look to  

VSEPR theory

. There are 3 regions of electron density around the central carbon, and the most stable geometry is a trigonal plane. While there is a  

carbonyl

group, i.e. a  

C

=

O

bond, the  

π

bond is conceived to lie above and below this trigonal plane.

The  

carbonyl oxygen

is likewise conceived to be  

s

p

2

-hybridized

, however, here, there are 2 lone pairs on the oxygen centre.

The approximate chlorine-carbon-chlorine bond angle in C2Cl4 is 120°.

The bond angle is defined as the angle between ant two bonds emanating from a common atom.

The compound C2Cl4 is tetrachloroethene. The carbon atoms are sp2 hybridized in this molecule.

Recall that the bond angle of an sp2 hybridized carbon atom is 120°. Therefore the chlorine-carbon-chlorine bond angle in C2Cl4 is 120°.

From the perspective of the VSEPR theory, the geometry of each carbon atom in C2Cl4 is trigonal planar which implies a bond angle of 120°.

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Answer:

5

Explanation:

According to this question, the chemical reaction is between Cobalt chloride (CoCl2) and sodium carbonate (Na2CO3) to produce Cobalt carbonate (CoCO3) and sodium chloride (NaCl).

The chemical equation is as follows:

CoCl2 + Na2CO3 ---> CoCO3 + NaCl

However, this equation is not balanced and needs to be with the use of coefficients. The balanced equation is:

CoCl2 + Na2CO3 ---> CoCO3 + 2NaCl

The sum of coefficients on the reactants side is 2 while the sum of coefficients on the product side is 3, hence, the total sum of all products and reactants is 5

In the balanced equation of the reaction of cobalt chloride and sodium carbonate reacting to form cobalt carbonate and sodium chloride, the sum of the coefficients for all the products and reactants is equal to 5.

A balanced equation is an equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products.

We will balance it using the trial and error method.

CoCl₂ + Na₂CO₃ ⇒ CoCO₃ + NaCl

We have 2 Cl atoms on the left and 1 Cl atom on the right. The same happens for Na. Thus, we can get the balanced equation by multiplying NaCl by 2.

CoCl₂ + Na₂CO₃ ⇒ CoCO₃ + 2 NaCl

The sum of the coefficients for all the products and reactants is:

1 + 1 + 1 + 2 = 5

In the balanced equation of the reaction of cobalt chloride and sodium carbonate reacting to form cobalt carbonate and sodium chloride, the sum of the coefficients for all the products and reactants is equal to 5.

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Answer:

F - O - S - Mg - Ba

Explanation:

as you move left to right on the periodic table the number of electrons increase.

The correct lists of the five atoms in order of increasing size smallest to

largest is :

D) F - O - S - Mg - Ba

The correct lists of the five atoms in order of increasing size smallest to

largest is F - O - S - Mg - Ba.

The atomic radius of a chemical element may be a degree of the measure of its molecule, as a rule the mean or commonplace remove from the center of the core to the furthest isolated electron.

The arrange will be:

As you move cleared out to right on the periodic table the number of electrons increment.

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Answer:

the answer to this question is c 140

Answer:

second energy level

Explanation:

Valence electrons are those electrons which are present in outer most orbital of the atom.

This can be easily found through the electronic configuration of atom.

Electronic configuration of F:

F₉ = 1s² 2s² 2p⁵

We can see that the valence electrons are present in second energy level of F atom.

There are seven valence electrons of fluorine.

It is called halogens.

Halogens are very reactive these elements can not be found free in nature. Their boiling points also increases down the group which changes their physical states. i.e fluorine is gas while iodine is solid.

Fluorine:

1. it is yellow in color.

2. it is flammable gas.

3. it is highly corrosive.

4. fluorine has pungent smell.

5. its reactions with all other elements are very vigorous except neon, oxygen, krypton and helium.  

Answer:

A. the wave is a mechanical wave

C. the wave moves energy through matter

F: the wave transfers energy perpendicular to the motion of the wave.

Answer:

Explanation:

Here you go!! Hope this helps.

Answer:

Nucleus

Explanation:

The nucleus because it is basically the control system for the cell.

Answer:

Explanation:

Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

https://medlineplus.gov/genetics/understanding/basics/dna/

Answer:

Explanation:

Caffeine is a weak base with pKb = 10.4

Kb = 10⁻¹⁰°⁴ = 3.98 x 10⁻¹¹

molecular weight of caffeine = 194.2

455 x 10⁻³ g / L = 455 x 10⁻³ / 194.2 moles / L

concentration of given solution a = 2.343 x 10⁻³ M

Let the caffeine be represented by B .

B    +   H₂O =  BH + OH⁻

a - x                   x        x  

x² / ( a - x ) = Kb

x² / ( a - x ) = 3.98 x 10⁻¹¹

x is far less than a so a -x is almost equal to a

x² = 3.98 x 10⁻¹¹ x 2.343 x 10⁻³ = 9.32  x 10⁻¹⁴

x = 3.05 x 10⁻⁷

[ OH⁻ ] = 3.05 x 10⁻⁷

pOH = - log ( 3.05 x 10⁻⁷ )

= 7 - log 3.05

= 7 - 0.484 = 6.5

pH = 14 - 6.5 = 7.5  

The pH of 455 mg/L of caffeine is 7.5

Using the formula;

Mass concentration = molar concentration × molar mass

Molar mass of caffeine = 194 g/mol

Mass concentration of caffeine = 455 mg/L

Molar concentration = Mass concentration/molar mass

Molar concentration = 455 × 10^-3g/L/194 g/mol

= 0.00235 M

Let Caffeine by depicted by the general formula BH

We can now set up the ICE table as follows;

           :B + H2O   ⇄ BH       +       OH^-

I      0.00235              0                      0

C           - x                  +x                    +x

E    0.00235  - x           x                      x

Note that water is present in large excess

Again; pKb of caffeine =10.4

Kb = Antilog[-pKb]

Kb = Antilog [-10.4]

Kb = 3.98 × 10^-11

Kb = [BH] [OH^-]/[:B]

3.98 × 10^-11 = [x] [x]/[ 0.00235  - x  ]

3.98 × 10^-11 [ 0.00235  - x  ] = [x] [x]

9.4 × 10^-14 - 3.98 × 10^-11x = x^2

x^2 + 3.98 × 10^-11x  - 9.4 × 10^-14 = 0

x = 3.1 × 10^-7 M

Recall  [BH] = [OH^-] = 3.1 × 10^-7 M

Now;

pOH = - log [OH^-]

pOH = log [3.1 × 10^-7 M]

pOH = 6.5

But;

pH + pOH = 14

pH = 14 - pOH

pH = 14 - 6.5

pH = 7.5

The pH of 455 mg/L of caffeine is 7.5

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Missing parts

Caffeine (C8H10N4O2) is a weak base with a pKb of 10.4.  Calculate the pH of a solution containing a caffeine concentration  of 455 mg/L.

Answer:

C

Explanation:

Answer:

10 moles of water are produced,

Explanation:

Given data:

Moles of H = 10 mol

Moles of O = 6 mol

Water obtained = ?

Solution:

Balance chemical equation:

2H₂ + O₂    →    2H₂O

Now we will compare the moles of H₂ and O₂ with water from balance chemical equation.

                            H₂             :          H₂O

                             2              :            2

                             10             :           10

                            O₂             :          H₂O

                             1              :            2

                             6             :           2×6 = 12

Number of moles of water produced by hydrogen are less so hydrogen will be limiting reactant and it will limit the yield of water thus, 10 moles of water are produced.