Why is a spectrum for a given element unique for that element?


A. No element has more than two electrons in the first shell.
B. Each element has a unique arrangement of electrons.
C. Atoms of different elements have different masses.
D. Atomic nuclei contain no electrons.

The answer is: Henry Moseley.

Henry Gwyn Jeffreys Moseley (1887–1915) proposed that the number of positive nuclear charges (protons) in atom is equal to its atomic number in the periodic table.

Mendeleev did not know about isotopes and he arranged the elements in order of increasing relative atomic mass.

For example, positions of iodine and tellurium were reversed in Mendeleev's table, because of different isotopes, but Moseley solved anomalies like this one.

The molality of a solution prepared by dissolving 175 g of KNO₃ in 750 g of water is 2.3m.

Molaity is used to define the concentration of any material present in any substance and it will be calculated as:

Molality = Moles of solute / kilograms of solvent

According to the question,

Mass of solute KNO₃ = 175g

Mass of solvent = 750g = 0.75kg

Moles of solute KNO₃ will be calculated as:

n = W/M, where

W = given mass

M = molar mass = 101.1 g/mol

n = 175 / 101.1 = 1.73 moles

On putting values, we get

m = 1.73 / 0.75 = 2.3m

Hence molality of given sample is 2.3m.

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Answer:

[tex]8.75~g~CaO[/tex]

Explanation:

First we have to start with the reaction:

[tex]HgS~+~CaO~->~Hg~+~CaS~+~CaSO_4[/tex]

The next step is to balance the reaction, we can start with Oxygen, so:

[tex]HgS~+~4CaO~->~Hg~+~CaS~+~CaSO_4[/tex]

Then we can continue with Ca:

[tex]HgS~+~4CaO~->~Hg~+~3CaS~+~CaSO_4[/tex]

Then we can balance S:

[tex]4HgS~+~4CaO~->~Hg~+~3CaS~+~CaSO_4[/tex]

And finally with Hg:

[tex]4HgS~+~4CaO~->~4Hg~+~3CaS~+~CaSO_4[/tex]

With the balance reaction we know that the molar ratio between Hg nd CaO is 4:4. Therefore, the nex step is the conversion of 31.28 g Hg to moles of Hg using the atomic mass of Hg (200.59 g/mol).

[tex]31.28~g~Hg\frac{1~mol~Hg}{200.59~g~Hg}[/tex]

[tex]0.156~mol~Hg[/tex]

The next step, using the molar ratio (4:4) and the molar mass of CaO (56.1 g/mol) we can calculate the grams of CaO that we need:

[tex]0.156~mol~Hg\frac{4~mol~CaO}{4~mol~Hg}\frac{56.1~g~CaO}{1~mol~CaO}[/tex]

[tex]8.75~g~CaO[/tex]

Answer: B. [tex]KOH[/tex]

Explanation:

According to the Arrhenius concept, an acid is a substance that ionizes in the water to give hydronium ion or hydrogen ion [tex](H^+)[/tex] and a bases is a substance that ionizes in the water to give hydroxide ion [tex](OH^-)[/tex].

According to the Bronsted Lowry conjugate acid-base theory, an acid is defined as a substance which donates protons and a base is defined as a substance which accepts protons.

According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.

[tex]KOH\rightarrow K^++OH^-[/tex]: is a Arrhenius base.

[tex]NH_3+H^+\rightarrow NH_4^+[/tex] : is a lewis base as it donates the lone pair of electrons.

[tex]HCl\rightarrow H^++Cl^-[/tex] is a Arrhenius acid and bronsted lowry acid.

The answer option which accurately describes the behavior of water when subjected to temperature change is: B. The volume of water will increase if cooled from 3°C to 2°C.

Water refers to a liquid molecule that is typically made up of two (2) main chemical elements in the following proportion;

Generally, the volume of water is directly proportional to its temperature.

Hence, an increase in the temperature of water causes the volume of water to increase because its molecules gain energy and move more rapidly, which in turn makes the water molecules to be further apart.

When water is cooled, it contracts (decrease in volume) until a temperature of approximately four degree Celsius (4°C) is reached and then it begins to expand (increase in volume) at lower temperatures (3°C to 2°C), until it reaches its freezing point, which is typically at zero degree Celsius (0°C).

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Answer : The mass of chlorine gas produced are, 26.95 grams.

Explanation : Given,

Mass of HCl = 27.8 g

Molar mass of HCl = 36.46 g/mole

First we have to calculate the moles of hydrochloric acid.

[tex]\text{Moles of HCl}=\frac{\text{Mass of HCl}}{\text{Molar mass of HCl}}=\frac{27.8g}{36.46g/mole}=0.76mole[/tex]

Now we have to calculate the moles of chlorine gas.

The given balanced chemical reaction is,

[tex]4HCI(aq)+O_2\rightarrow 2CI_2(g)+2H_2O(I)[/tex]

From the given balanced chemical reaction, we conclude that

As, 4 moles of hydrochloric acid react to give 2 moles of chlorine gas

So, 0.76 moles of hydrochloric acid react to give [tex]\frac{2}{4}\times 0.76=0.38[/tex] moles of chlorine gas

Now we have to calculate the mass of chlorine gas.

[tex]\text{Mass of }Cl_2=\text{Moles of }Cl_2\times \text{Molar mass of }Cl_2[/tex]

Molar mass of [tex]Cl_2[/tex] = 70.91 g/mole

[tex]\text{Mass of }Cl_2=0.38mole\times 70.91g/mole=26.95g[/tex]

Therefore, the mass of chlorine gas produced are, 26.95 grams.

Number of moles equals of potassium iodide;

The molar mass of potassium iodide is 166 g/mole

Moles = 300/166

            = 1.8072moles

According to the equation;

2 moles of KI produces 1 mole of PbI2 9lead (ii) iodide

Therefore; the number of moles of lead (ii) iodide produced will be;

                = 1.8072/2

                = 0.9036moles

Thus the number of moles of lead (ii) iodide is 0.904 mole

Answer : The correct option is, (d) 0.904 mole

Explanation : Given,

Mass of potassium iodide = 300 g

Atomic mass of potassium iodide = 166 g /mole

First we have to calculate the moles of potassium iodide.

[tex]\text{Moles of KI}=\frac{\text{Mass of KI}}{\text{Molar mass of KI}}=\frac{300g}{166g/mole}=1.807mole[/tex]

Now we have to calculate the moles of lead(ii) iodide.

The given balanced chemical reaction is,

[tex]Pb(NO_3)_2+2KI\rightarrow PbI_2+2KNO_3[/tex]

From the given balanced chemical reaction, we conclude that

As, 2 moles of potassium iodide react to give 1 mole of  lead(ii) iodide

So, 1.807 moles of potassium iodide react to give [tex]\frac{1.807}{2}=0.904[/tex] mole of  lead(ii) iodide

Therefore, the number of moles of lead(ii) iodide produced are, 0.904 mole

is the aswer   H2S:SO2=2:2 and O2:H2O=3:2

Answer:

The correct answer is 2.60 moles.

Explanation:

The balanced equation is:  

4P + 5O₂ ⇒ 2P₂O₅

The number of moles of O₂, n = mass/molar mass

208 g / 32 g/mol = 6.5 mol

From the balanced equation,  

5 moles of O₂ reacts with 2 moles of P₂O₅

So, 6.5 moles of O₂ reacts with M moles of P₂O₅

M = 6.5 × 2/5

= 2.6 moles

Therefore, the required moles of P₂O₅ are 2.60 moles.  

Answer:

U-235 and U-238 are two radioactive isotopes of Uranium. The main difference between U-235 and U-238 is that the number of neutrons present in the U-235 nucleus is 143 whereas the number of protons present in the U-238 nucleus is 146.

Explanation:

Explanation:

Number of protons present in an atom are actually the atomic number of atom. Each element will have different atomic number.

Hence, each element is different in nature. On the other hand, atomic mass is the sum of number of protons and number of neutrons present in an element.

For example, Molybdenum is the element with 42 protons and 49 neutrons. Molybdenum is represented by the symbol Mo.

Therefore, we can conclude that Mo is the correct symbol for the atom with 42 protons and 49 neutrons.

The correct symbol for the atom with 42 protons and 49 neutrons is ^91Mo.

The correct symbol for the atom with 42 protons and 49 neutrons is ^91Mo.

In atomic notation, the image for an component consists of the nuclear number (number of protons) as a subscript and the mass number (entirety of protons and neutrons) as a superscript.

For the given atom with 42 protons and 49 neutrons, the overall mass number is 42 + 49 = 91. Hence, the image for this particle is ^91Mo, speaking to the component Molybdenum (Moment) with a mass number of 91.

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Adding a base to water triggers a base ionization reaction, resulting in the formation of hydroxide ions and a conjugate acid, which increases the solution's pH. Strong bases fully dissociate, while weak bases only partially ionize.

When a base is added to water, a base ionization reaction occurs. This reaction involves the transfer of protons from water molecules to the base molecules, producing hydroxide ions (OH-) and a conjugate acid of the base. For instance, if we take pyridine, C5NH5, as a base, adding it to water will result in the formation of hydroxide ions and pyridinium ions. This process increases the pH of the solution as it raises the concentration of hydroxide ions. Strong bases, like soluble ionic hydroxides (e.g., NaOH), dissociate completely in water, leading to a significant increase in OH- concentration, while weak bases yield a smaller proportion of hydroxide ions.

A general reaction for base ionization can be represented as B(aq) + H₂O(l) ⇒ HB*(aq) + OH⁻(aq), where B is the base and HB* is the conjugate acid formed. This reaction is essential for understanding acid-base chemistry, where bases are seen as proton acceptors and their strength can be gauged by how completely they ionize in water.

Changing lead into gold requires changing the number of protons in the lead atoms, a process known as nuclear transmutation. This process is highly complex, energy intensive and has many potential risks, making it unfeasible as a method of gold production.

The process of changing one element into another, such as changing lead into gold, would require the manipulation of its atomic structure. The atomic structure of an atom is primarily dictated by the number of protons it has, which determines its atomic number and essentially defines the kind of element it is. In the case of lead and gold, lead has 82 protons and gold has 79 protons.

To turn lead into gold, scientists would have to remove 3 protons from each atom, which is an incredibly difficult task. This process, known as nuclear transmutation, would require a significant amount of energy and highly advanced technology. Even then, the process is far from efficient and produces a number of problems including the release of harmful radiation and the production of unstable, radioactive isotopes.

Furthermore, changing the number of neutrons and electrons in a lead atom alone would not turn it into gold; the number of protons must be changed. So the correct statement from the options provided is that scientists would have to change the number of protons in lead atoms to transform it into gold. However, due to the immense difficulty and possible risks involved, this is not a viable option for gold production.

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Final answer:

To find the mass of 2.75 x 10²¹atoms of Lithium, we first calculate the number of moles of Li and then use its molar mass. The mass is found to be 0.0317 g, which is option (b).

Explanation:

The question asks for the mass in grams of 2.75 x 10²¹ atoms of Lithium (Li). First, we need to calculate the number of moles of Li this number of atoms represents. Knowing that one mole contains 6.02 x 10²³atoms, the number of moles is calculated as follows:

(2.75 x 10²¹ atoms) / (6.02 x 10²³atoms/mol) = 4.57 x 10⁻³ mol

Next, using the molar mass of Li, which is 6.94 g/mol, we can find the mass of Li:

(4.57 x 10⁻³ mol) x (6.94 g/mol) = 0.0317 g

Therefore, the mass of 2.75 x 10²¹ atoms of Li is 0.0317 g, which corresponds to option (b).

Answer: The minimum force by which player should hit the puck to move it is 0.102 N.

Explanation:

Weight of the puck = 1.70 N

This weight of the puck is the force acting normal to the surface that is:

N = 1.70 N

The coefficient of friction =[tex]\mu _f=0.0600[/tex]

Frictional force = [tex]F_f=\mu _f\times N=0.0600\times 1.70 N=0.102 N[/tex]

The minimum force by which player should hit the puck to move it is 0.102 N.