Which of the following is the best description of a gaseous substance?

Answer: Option (b) is the correct answer.

Explanation:

When there is no change in chemical composition of a substance  then this change is known as physical change.

Where as when there is change in chemical composition of a substance then it is known as chemical change.

When sugar is heated, it results in the formation of carbon dioxide and water. This means that composition of sugar has changed thus, it is a chemical change.

When solid ice is melted, it turns into liquid. This shows that only state of water has changed. There is no change in chemical composition because when we freeze water then again liquid water changes into solid ice. Thus, it is a physical change.

When sodium reacts with chlorine then the reaction is as follows.

         [tex]2Na + Cl_{2} \rightarrow 2NaCl[/tex]

It shows that chemical composition of sodium has changed due to the formation of sodium chloride. Thus, it is a chemical change.

Also, when aluminium is is heated in air then it results in the formation of aluminium oxide. This means that the chemical composition of aluminium has changed.

Hence, we can conclude that out of the given options, solid ice, when heated, turning into liquid water is an example of a physical change.

In this net ionic equation, we can see that the silver ion ([Ag(NH3)2]+) reacts with the chloride ion (Cl-) to form silver chloride (AgCl). Additionally, the two hydrogen ions (2H+) react with the two ammonia molecules (2NH3) to form two ammonium ions (2NH4+).


To write the net ionic equation for the reaction between diamminesilver(I) chloride and dilute nitric acid, let's break down the steps:

1. Start with the balanced molecular equation: [Ag(NH3)2]Cl(aq) + HNO3(aq) ->

2. Identify the ions present in the reactants and determine if any of them are spectator ions. In this case, we have [Ag(NH3)2]Cl and HNO3.

  The [Ag(NH3)2]Cl dissociates into two ions: [Ag(NH3)2]+ and Cl-. However, HNO3 is a strong acid and fully dissociates into H+ and NO3- ions.

  Therefore, the spectator ions in this reaction are Cl- and NO3-.

3. Write the net ionic equation by removing the spectator ions:

  [Ag(NH3)2]+ + 2H+ -> AgCl + 2NH4+

In this net ionic equation, we can see that the silver ion ([Ag(NH3)2]+) reacts with the chloride ion (Cl-) to form silver chloride (AgCl). Additionally, the two hydrogen ions (2H+) react with the two ammonia molecules (2NH3) to form two ammonium ions (2NH4+).

To determine the oxidation numbers, you are correct in assigning +1 to silver (Ag) and -1 to chloride (Cl). However, the oxidation number of ammonia (NH3) is 0 because hydrogen (H) has an oxidation number of +1 and there are no other elements to balance out the charge.

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The solubility product constant is the equilibrium constant of a substance in an aqueous solution. The solubility of iron (ii) hydroxide is [tex]2.07 \times 10^{-5}\;\rm g.[/tex]

Ksp is the solubility product constant, which is given as the product of the concentration of cation and anion dissociated in the aqueous solution.

Given,

Ksp =  [tex]4.87 \times 10^{-17}[/tex]

Thus,

[tex]\begin{aligned}&= \rm [Fe^{2+}][OH^{-}]^{2} \\\\&= \rm (X)(2X)^{2} \\\\&= \rm 4X^{3}\end{aligned}[/tex]

The molarity can be calculated as:

[tex]\begin{aligned}\rm 4X^{3} =4.87 \times 10^{-17}\\\\\rm X= 2.30 \times 10^{-6}\;\rm M\end{aligned}[/tex]

The mass of  iron (ii) hydroxide in 100 mL of water is calculated as:

[tex]\begin{aligned}2.30 \times 10^{-6} \;\rm mol/L &= 2.3 \times 10^{-5}\;\rm mole/100 mL\\\\&= 2.07 \times 10^{-5} \;\rm g\end{aligned}[/tex]

Therefore, the solubility of iron (ii) hydroxide is [tex]2.07 \times 10^{-5}\;\rm g.[/tex]

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Yes, the precipitate of silver carbonate will form.

To determine if a precipitate will form when 65.0 mL of 0.0200 M Ag2SO4 is mixed with 50.0 mL of 0.00500 M K2CO3, we need to compare the ion product (Qsp) with the solubility product constant (Ksp) for silver carbonate (Ag2CO3).

First, let's calculate the concentrations of ions after mixing the solutions:

For Ag2SO4:

- Initial moles of Ag2SO4 = 0.0200 M * 0.0650 L = 0.00130 moles

- Moles of Ag+ ions = 2 * 0.00130 moles = 0.00260 moles

- Concentration of Ag+ ions = 0.00260 moles / (0.0650 L + 0.0500 L) = 0.0200 M

For K2CO3:

- Initial moles of K2CO3 = 0.00500 M * 0.0500 L = 0.000250 moles

- Moles of CO3^2- ions = 0.000250 moles

- Concentration of CO3^2- ions = 0.000250 moles / (0.0650 L + 0.0500 L) = 0.00192 M

Now, to find out if a precipitate will form, we calculate the ion product, Qsp, for silver carbonate:

Qsp = [tex][Ag+]^2 * [CO3^2-][/tex]

Qsp = [tex](0.0200)^2 * (0.00192)[/tex]

Qsp = 7.68 x 10^-6

Compare Qsp with the Ksp of silver carbonate (Ag2CO3):

Ksp = 8.00 x 10^-12

Since Qsp (7.68 x 10^-6) is greater than Ksp (8.00 x 10^-12), the ion product exceeds the solubility product constant. According to the principles of solubility and precipitation, when Qsp > Ksp, a precipitate of silver carbonate (Ag2CO3) will form.

The precipitate of silver carbonate (Ag2CO3) will form when 65.0 mL of 0.0200 M Ag2SO4 is mixed with 50.0 mL of 0.00500 M K2CO3.

The words 'matter', 'accuracy', 'precision', 'meniscus', 'volume', and 'density' have been linked with their suitable definitions, clarifying their individual meanings.

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Answer : The heat absorbed by the water is 19.4 kJ

Explanation :

Formula used :

[tex]Q=m\times c\times \Delta T[/tex]

or,

[tex]Q=m\times c\times (T_2-T_1)[/tex]

where,

Q = heat absorbed = ?

m = mass of water = 15.5 g

c = specific heat of water = [tex]4.184J/g^oC[/tex]

[tex]T_1[/tex] = initial temperature  = [tex]20.0^oC[/tex]

[tex]T_2[/tex] = final temperature  = [tex]50.0^oC[/tex]

Now put all the given value in the above formula, we get:

[tex]Q=15.5g\times 4.184J/g^oC\times (50.0-20.0)^oC[/tex]

[tex]Q=1945.56J=1.94\times 10^3J=1.94kJ[/tex]

Therefore, the heat absorbed by the water is 19.4 kJ

The dissociation reaction of HCN in water is HCN(aq) ↔ H⁺(aq) + CN⁻(aq).

Here is the balanced dissociation reaction for hydrocyanic acid (HCN) in water:

HCN(aq) ↔ H⁺(aq) + CN⁻(aq)

The equilibrium expression for the acid dissociation constant (Ka) for this reaction is given by:

Ka = [H⁺][CN⁻] / [HCN]

This expression shows that the equilibrium constant (Ka) for HCN dissociation is determined by the concentrations of the hydrogen ions (H⁺), the cyanide ions (CN⁻), and the undissociated hydrocyanic acid (HCN) in the solution.

When solute concentration exceeds the solubility limit in a solution, a supersaturated solution is created, which subsequently initiates precipitation in order to achieve equilibrium. This results in the formation of a new solid phase that is distinct from the original solution.

The concept you're referring to involves solubility and the formation of new phases when the concentration of a solute in a solution exceeds its solubility limit. Solubility refers to the maximum amount of solute that can be dissolved in a solvent at a given temperature. When this limit is surpassed, a supersaturated solution is formed. This is not a stable state, and it often results in precipitation. This is the process where a solute becomes insoluble and forms a new, separate solid phase.

For instance, if we take a saturated solution of silver chloride (AgCl), and add more AgCl to it, the excess will precipitate out of solution. Here, the concentration of AgCl has exceeded its solubility, leading to the formation of a new solid phase that is distinct from the original solution.

The exact composition and form of the new solid phase can depend on a variety of factors, including the type of solvent and solute involved, temperature, and pressure.

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The amount of carbon that could be recovered from 769g of a substance that is 35.7% carbon by mass is approximately 275g.

The question involves a percentage by mass calculation, which falls under the subject of Chemistry. The substance in question is 35.7% carbon by mass. Therefore, to find the amount of carbon in a 769g sample, we multiply the total mass of the substance by the percentage of carbon.

Here's the calculation: 769g (total mass) x 0.357 (percentage of carbon as a decimal) = 274.653g. Therefore, we can recover approximately 275g (if we round to the nearest whole number) of carbon from the 769 g of the substance.

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To find how much carbon is in 769 g of a substance that is 35.7% carbon by mass, multiply 769 g by 0.357. This calculation shows that 274.833 g of carbon can be recovered.

To determine this, we can use the percentage by mass to find the amount of carbon in the total mass of the substance. Here's the step-by-step calculation:

First, convert the percentage into a decimal: 35.7% = 0.357

Amount of carbon = mass of the substance × percentage of carbon (in decimal form)

Amount of carbon = 769g × 0.357

Amount of carbon = 274.553g

Therefore, you could recover approximately 274.553 grams of carbon from 769 grams of the substance.

Answer: According to continental drift, the continents were once connected

Explanation:

According to continental drift, the continents were once connected this statement is true.

Pangaea split into fragments over the course of millions of years, and each piece migrated away from the other. These components gradually came together to form the continent that is known today.

Today's scientists believe that a number of supercontinents, including Pangaea, have developed and fragmented during the Earth's history.

The theory of continental drift holds that Earth's continents have shifted relative to one another during geologic time, giving the impression that they have "drifted" over the ocean floor.

During one or more geologic periods, continents moved horizontally at a huge scale in relation to one another and to the ocean basins. This idea served as a crucial building block for the theory of plate tectonics, which includes it.

Thus, option C is correct.

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Answer: 0.23 grams

Explanation:

According to avogadro's law, 1 mole of every substance weighs equal to its molecular mass and contains avogadro's number [tex]6.023\times 10^{23}[/tex] of particles.

To calculate the number of moles, we use the equation:

[tex]\text{Number of moles}=\frac{\text{Given molecules}}{\text{Avogadro's number}}=\frac{7.20\times 10^{20}}{6.023\times 10^{23}}=1.2\times 10^{-3}moles[/tex]

1 mole of caffeine [tex](C_8H_{10}N_4O_2)[/tex] weighs = 194 g

[tex]1.2\times 10^{-3}[/tex]  moles of  [tex](C_8H_{10}N_4O_2)[/tex] weigh = [tex]\frac{194}{1}\times 1.2\times 10^{-3}=0.23g[/tex]

Thus mass of caffeine [tex](C_8H_{10}N_4O_2)[/tex] is 0.23 grams.

Answer: "physical change" .

________________________________________________________

This would be a "physical change" . ________________________________________________________

Note: This would change from a "solid" to a "liquid" / mere rearrangement of molecules/ NOT a new chemical substance—hence, a "physical change".

________________________________________________________

Each element has a unique arrangement of electrons, so each element has different spectrum. Therefore, the correct option is option B.

The quantity of protons an element has defines it. An element's atoms all contain the same amount of protons, but its electron and neutron counts might vary. Ions are produced by altering the electron to proton ratio, whereas isotopes are produced by altering the neutron count.

A material that cannot be destroyed chemically is referred to as a chemical element. Although chemical processes cannot modify an atom, nuclear reactions can create new elements. Each element has a unique arrangement of electrons, so each element has different spectrum.

Therefore, the correct option is option B.

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