A container holds a pure sample of a radioactive substance with a half-life of 2 hours. Which of the following statements are true?

a) After 1 hour, less than 50 % of the original atoms in the container will have decayed.
b) After 1 hour, more than 50 % of the original atoms in the container will have decayed.
c) After 2 hours, 50 % of the original atoms in the container will have decayed.
d) After 4 hours, 25 % of the original atoms will have decayed.
e) After 4 hours, the total number of atoms in the container will be reduced by 75 %.

A 120-gram sample of carbon contains approximately 6.02 x 10^24 atoms. We calculate this based on the fact that a mole of carbon weighs 12 grams and contains 6.02 x 10^23 atoms.

The subject you're studying is related to atoms, more specifically, counting the number of carbon atoms in a given mass. To solve this, we need to understand the concept of a mole. A mole is an amount of substance that contains the same number of entities (atoms in this case) as there are in exactly 12 grams of ¹2C, or carbon-12. Hence, one mole of carbon is equivalent to 12 grams of carbon, and this mole contains 6.02 x 10^23 atoms (this number is called Avogadro's Number).

Given that your sample is 120 grams of carbon, this translates to 10 moles of carbon since 120 grams divided by 12 grams/mole equals 10 moles. So, the number of carbon atoms present in your 120 grams sample would be 10 moles multiplied by Avogadro's number, equating to approximately 6.02 x 10^24 carbon atoms.

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The minimum number of photons of green light, with 2.35x10⁻¹⁸ J of energy and 510 nm of wavelength, that can be detected by the human eye is 6.04 photons.    

The energy of a single photon is given by:

[tex] E_{1} = h\frac{c}{\lambda} [/tex]

Where:  

h: is the Planck constant = 6.62x10⁻³⁴ J*s

λ: is the wavelength of the green light = 510 nm = 510x10⁻⁹ m

c: is the speed of light = 3.00x10⁸ m/s

So, the energy of one photon is:    

[tex]E_{1} = h\frac{c}{\lambda} = 6.62 \cdot 10^{-34} Js\frac{3.00 \cdot 10^{8} m/s}{510 \cdot 10^{-9} m} = 3.89 \cdot 10^{-19} J[/tex]  

Now, since the energy of the green light detected by the human eye is 2.35x10⁻¹⁸ J, the minimum number of photons (n) to produce that amount of energy is:  

[tex] E_{n} = nE_{1} [/tex]

[tex] n = \frac{E_{n}}{E_{1}} = \frac{2.35 \cdot 10^{-18} J}{3.89 \cdot 10^{-19} J} = 6.04 [/tex]  

Therefore, the minimum number of photons of green light is 6.04 photons.

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Answer:

ethylene glycol (molar mass = 62.07 g/mol).

Explanation:

ΔTf = Kf.m,

ΔTf is the depression in the freezing point of tert-Butyl alcohol (ΔTf = freezing point of pure solvent - freezing point in presence of unknown liquid = 25.5°C - 15.3°C = 10.2°C).

Kf is the molal freezing point constant of tert-Butyl alcohol (Kf = 9.1 °C/m).

m is the molality of unknown liquid.

∵ ΔTf = Kf.m

∴ m = ΔTf/Kf = (10.2°C)/(9.1 °C/m) = 1.121 m.

Molality (m) is the no. of moles of solute in 1.0 kg of solvent.

∴ m = (mass/molar mass) of unknown liquid/(mass of tert-Butyl alcohol (kg))

m = 1.121 m, mass of unknown liquid = 0.807 g, mass of tert-Butyl alcohol = 11.6 g = 0.0116 kg.

∴ molar mass of unknown liquid = (mass of unknown liquid)/(m)(mass of tert-Butyl alcohol (kg)) = (0.807 g)/(1.121 m)(0.0116 kg) = 62.06 g/mol.

ethylene glycol (molar mass = 62.07 g/mol).

Answer:

0.43 mol.

Explanation:

no. of moles (n) = mass/molar mass

mass of MgCl₂ = 41.0 g & molar mass of MgCl₂ = 95.211 g/mol.

∴ n = mass/molar mass = (41.0 g)/(95.211 g/mol) = 0.43 mol.

Answer:

4) HNO₃ + KOH → KNO₃ + H₂O.

Explanation:

4) HNO₃ + KOH → KNO₃ + H₂O.

Where, an acid (HNO₃) reacts with a base (KOH) and results in a salt (KNO₃) and water.

Yes blinking is helpful, it helps keep the eyes clean and protect them. By blinking you are sweeping away small particles that could be harmful to the eye. Everytime we blink a small quantity of tear comes out wetting the lower third of the cornea

Blinking is essential for keeping the eyes moist and clear of debris, using the lacrimal apparatus to spread tears across the eye's surface, which highlights the importance of blinking for eye protection and comfort.

Blinking is a protective reflex that is crucial for maintaining eye health by keeping the eyes moist and free from debris. When we do not blink, our eyes can start to feel dry and uncomfortable due to the lack of moisture; a condition known as dry eye can occur. The discomfort experienced from not blinking is evidence of the protective role blinking plays.

It is through this reflex that the lacrimal apparatus, comprising the lacrimal gland, lacrimal canaliculi, lacrimal sac, and nasolacrimal duct, produces lacrimal fluid (tears) which hydrates and cleanses the eyes.

The palpebral conjunctiva, the thin membrane lining the eyelids, extends over the sclera (the white of the eye), aiding in the process of distributing the tears across the eye surface. Therefore, blinking is not just helpful but essential for preserving good vision and protecting the eyes from potential irritants and infections.

In any chemical reaction, value of chemical energy is highest at the threshold energy point.

Chemical reactions are those equations in which reactants combine with each other for the formation of the products.

During the process of a chemical reaction, an intermediate complex is formed in which bonds of reactant as well as of products are present and it is most unstable because of high potential energy. This complex is formed at the threshold energy point which is the highest energy level of any chemical reaction.

Hence threshold energy is the highest energy level.

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Answer:c

Explanation:

Answer: A) 0.10 mol [tex]Al_2(SO_4)_3[/tex]

Explanation:

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

[tex]\frac{p^o-p_s}{p^o}=i\times x_2[/tex]

where,

[tex]\frac{p^o-p_s}{p^o}[/tex]= relative lowering in vapor pressure

i = Van'T Hoff factor  

[tex]x_2[/tex] = mole fraction of solute

1. For 0.10 mol [tex]Al_2(SO_{4})_3[/tex]

[tex]Al_2(SO_4)_3\rightarrow 2Al^{3+}+3SO_4^{2-}[/tex]  

, i= 5 as it is a electrolyte and dissociate to give 5 ions. and concentration of ions will be [tex]2\times 0.1+3\times 0.1=0.5[/tex]

2.  For 0.10 mol sucrose

, i= 1 as it is a non electrolyte and does not dissociate, concentration of ions will be [tex]1\times 0.1=0.1[/tex]

3. For 0.40 mol glucose

, i= 1 as it is a non electrolyte and does not dissociate,  concentration of ions will be [tex]1\times 0.4=0.4[/tex]

4. For 0.2 [tex]NaCl[/tex]

[tex]NaCl\rightarrow Na^{+}+Cl^{-}[/tex]  

, i= 2 as it is a electrolyte and dissociate to give 2 ions, concentration of ions will be [tex]1\times 0.2+1\times 0.2=0.4[/tex]

Thus as concentration of solute is highest for [tex]Al_2(SO_4)_3[/tex] , the vapor pressure will be lowest.

Answer:

Yes

Explanation:

People in the same scientific field quickly come to know one another because they publish the same sort of articles in journals that are dedicated to their field.

Their experiments and findings are immediately understood by others reading the journal. Its a case of news travels fast, especially when the news is known to everyone.

Answer:

just pick b

Explanation:

Answer:

Each substance on the left side of the arrow in a chemical equation is a reactant.

Explanation:

The chemical changes (chemical reactions) are represented by chemical equations.

The chemical equations show the starting substances and the final substances.

The starting substances of the reaction are the reactants.

A single arrow is used to indicate the direction of the reaction, the reactants are placed on the left side of the equation, and the products appear on the right side.

This sketch shows that:

                              reactants        yield          products                                        

general form              A + B             →               C + D

example                     Na + Cl          →               NaCl

Answer:

Is its electrification

Explanation:

Electrification is defined as the ability to gain or lose different electrical charges, usually electrons, and occurs when a collision of subatomic particles occurs. There are three ways to electrify: by rubbing, by contact or by induction. It is necessary to take into account that in these three ways of electrification, the principles of charge conservation and the primary electrostatic rule are present.

Answer:

Explanation:

Neutral means that the net charge is zero.

Atoms have protons, neutrons and electrons.

Neutrons and protons are in the nucleus of the atom. Protons are particles with positive charge and neutrons are particles without charge.

Elctrons, which are surrounding the nucleus, are particles with negative charge.

The relativie charges of protons and electrons are +1 and -1, respectively.

So, in order to have a total net charge of zero, the neutral atom must have the same number of protons as electrons.

Answer: Niels Bohr

Explanation:

Answer:Niels Bohr

Explanation:

Answer:

H = m c ΔT  

89.6 J = (20.0 g) × c × (40.0 - 30.0)°C  

Specific heat of iron, c = 89.6 / [20.0 × (40.0 - 30.0)] J/(g°C) = 0.448 J/(g°C)

If 89.6 joules of heat 20.0 grams of iron from 30.0 C to 40.0 C, then the specific heat of the iron in J/g. degree C is 0.448 J/g. degree C.

The formula which we used to calculate the amount of specific heat of any substance involved in a chemical reaction is:

Q = mcΔT, where

On putting all these values, we get

c = 89.6 / (20)(10) = 0.448 J/g. degree C

Hence, 0.448 J/g. degree C is the specific heat of iron.

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Answer:

A

Explanation:

There are 2 sodium atoms and 1 oxygen atom.

In Na2O, there are 2 sodium atoms and 1 oxygen atom, as indicated by the chemical formula, which represents a 2:1 ratio of sodium to oxygen with an overall neutral charge.

The compound Na2O consists of two elements: sodium (Na) and oxygen (O). According to the chemical formula, for every one unit of this compound, there are two sodium atoms and one oxygen atom. This is because the subscript '2' next to Na in the formula indicates there are two sodium atoms, while the absence of a number next to O implies there is one oxygen atom. Hence, in the compound Na2O, the ratio of sodium to oxygen atoms is 2:1, which is due to the need for the number of electrons lost by sodium (each Na atom loses one electron) to equal the number of electrons gained by oxygen (the O atom gains two electrons) and ensure the compound has an overall neutral charge. Therefore, the correct answer is A: 2 sodium atoms and 1 oxygen atom.

Answer:

3.4moles

Explanation:

Given parameters:

Number of molecules = 2.04 x 10²⁴

Unknown: Number of moles

Solution

We use the concept of mole to solve this kind of problem.

A mole is the amount of substance that contains Avogadro's number of particle i.e 6.02 x 10²³ molecules

Solving

For elementary particles:

Number of moles = [tex]\frac{number of particles}{6.02 x 10^{23} }[/tex]¹ molecules

Number of moles = [tex]\frac{2.04 x 10^{24} }{6.02 x ^{23} }[/tex]

Number of moles of H₂O = 0.34 x 10¹ = 3.4moles

Answer:

C. The molarity of the solution increases.

The molarity of the solution increases when sugar is added to the solution of water.

Molarity is defined as the amount of a substance present in a specific volume of solution. Molarity is also called the molar concentration of a solution.

So we can conclude that the molarity of the solution increases when sugar is added to the solution of water due to increase in the concentration.

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Mercury is a heavy, silvery-white liquid metal. Compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity. ... Because this configuration strongly resists removal of an electron, mercury behaves similarly to noble gases, which form weak bonds and hence melt at low temperatures.

Answer:

Explanation:

On the periodic table, Mercury belongs to group 12 and period eight(8). It has the Atomic number of eighty(80).

PHYSICAL PROPERTIES OF MERCURY:

Mercury is a d-block element and it is a liquid at standard pressure and temperature. It is silvery and heavy. It has boiling point of 629.88 K, Heat of fusion of 2.29 kJ/mol,molar heat capacity of 27.98

J/mol/K.

STRUCTURE:

Mercury is closed pack. The packing of Mercury makes it to conduct electricity better than alkaline earth metals. Mercury has a Rhombohedral crystal structure.

CONCLUSION:

Mercury has a structure which is efficiently packed and this allow its electrons to move freely. The free electrons can easily move to the conduction band.

D. quantitative properties

Boiling point and freezing point depression are both values that can be represented quantitatively (in number form).

Answer:

the correct answer is b

Explanation:

i just got it right on usatestprep

Answer:

[tex]\boxed{\text{amide groups}}[/tex]

Explanation:

A protein is a long chain of amino acids linked together by amide groups.

The general structure is

[tex]\rm \left[-NHCHR-\underbrace{\hbox{CO-NH}}_{\hbox{amide group}}-CHRCO-\right]_{n}[/tex]

Brown sugar is made by adding molasses to refined white sugar, which may have been processed using bone char. The addition of molasses gives the distinct color and flavor to brown sugar.

Brown sugar is created by adding molasses to refined white sugar. This addition not only gives brown sugar its distinct color, but also imparts a rich flavor and increases the moisture content compared to white sugar. In the production process of brown sugar, it is important to note that if the white sugar utilized has been refined using bone char as a decolorizing filter, then the same process would likely be used in the production of the brown sugar from that manufacturer.

Bone char is derived from animal bones, and even though it is widely used in the sugar industry to achieve the white color of sugar, some consumers may seek alternatives due to dietary preferences or ethical concerns.

Sugar comes in various forms including beet sugar, cane sugar, and specialty sugars like coconut sugar or maple sugar. As for icing or powdered sugar, often used in icings and baked goods, it consists of refined sugar mixed with cornstarch and might also involve the use of bone char in its production.

Answer:

Explanation:

That is a chemical property of alkali metals: they are highly reactive and react vigorously with water to produce the correspondant hydroxide and hydrogen gas.

These are some of those reactions:

The alkali metals are the elements of group 1 of the periodic table: Li, Na, K, Rb, Cs, and Fr. They have one valence electron which may lose easily to form an ion with charge +1.

Alkali metals react with water to produce hydrogen gas and a basic solution of the metal hydroxide (for instance, sodium hydroxide when lithium is in the reaction). This reaction signifies the easier oxidation of alkali metals compared to hydrogen.

When alkali metals react with water, they form hydrogen gas and a basic solution of the metal hydroxide. This vigorous reaction reveals that alkali metals are easier to oxidize than is hydrogen. For instance, considering the reaction of lithium with water:

2Li(s) + 2H₂O(l) --> 2NaOH(aq) + H₂(g)

The solid state (s) lithium reacts with liquid water to generate hydrogen gas and the ionic compound sodium hydroxide. This sodium hydroxide, which is a solid in its pure form, promptly dissolves in water.

The same kind of reaction occurs with other alkali metals and also some alkaline earth metals, although beryllium and magnesium are exceptions.

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Answer:

Explanation:

Just a brief introduction to remember what the ionic compounds are. Ionic compounds are the compounds formed by ionic bonds, i.e. the eletrostatic attraction between cations (positivie ions) and anions (negative ions). The ionic compounds are mostly either oxides or salts. An example of an ionic oxide is CaO, and an example of an ionic salt is NaCl.

The strength of the ionic bonds is responsible for most of the characteristics of these compounds. These are the most common characteristics that solid ionic compounds share:

1. Complete ionization in water.  

2. Ionization constant.  

3. A good hydrogen-ion acceptor.  

4. Weak acid.  

5. This base ionizes slightly in aqueous.

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The main characteristic of a strong acid or base is that it completely ionizes in water. Option A is correct.

This means that the acid or base will dissociate into its ions when it is dissolved in water. For example, hydrochloric acid (HCl) is a strong acid that completely ionizes in water to form hydrogen ions (H⁺) and chloride ions (Cl⁻).

HCl(aq) → H⁺(aq) + Cl⁻(aq)

The presence of a hydroxide or hydrogen ion is also a characteristic of strong acids and bases, but it is not the only characteristic. For example, ammonia (NH₃) is a base that does not have a hydroxide ion, but it does dissociate into ammonium ions (NH₄⁺) and hydroxide ions (OH⁻) when it is dissolved in water.

NH₃(aq) + H₂O(l) → NH₄⁺(aq) + OH⁻(aq)

Polar covalent bonding is not a characteristic of strong acids or bases. Polar covalent bonding is a type of bonding that occurs between two atoms that have different electronegativities. The more electronegative atom will have a partial negative charge, while the less electronegative atom will have a partial positive charge. Option A is correct.

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Answer:

[tex]\boxed{\text{C. MnO$_{2}$}}[/tex]

Explanation:

2H₂O₂ ⟶ 2H₂O + O₂

A catalyst is a substance that speeds up a reaction but can be recovered unchanged at the end.

Thus, at the end of the reaction I would expect to find H₂O and MnO₂ in the container.

Water is not listed in any of the options, so I will have to choose [tex]\boxed{\text{C. MnO$_{2}$}}[/tex].

A, B, and D are wrong. They are not reactants, products, or catalysts.

Answer:

Explanation:

The mole ratio is the relative proportion of the moles of products or reactants that participate in the reaction according to the chemical equation.

The chemical equation given is:

Once you check that the equation is balanced, you can set the mole ratios for all the reactants and products. The coefficients used in front of each reactant and product, in the balanced chemical equation, tells the mole ratios.

In this case, they are: 2 mol C₄H₁₀ :  13 mol O₂ : 8 mol CO₂ : 10 mol H₂O

Since you are asked about the mole ratio of C₄H₁₀ and CO₂ it is:

Answer:Top Right and Bottom Right.

Explanation:

Proton's define an elements Identity

Answer: The atoms which belong to the same element are atom 2 and atom 5.

Explanation:

Elements are identified by their atomic numbers.

Atomic number is defined as the number of protons or number of electrons that are present in an element.

Atomic number = Number of protons = Number of electrons

Two atoms having same number of protons will belong to same element.

From the given image, atom 2 and atom 5 have same number of protons which are 11.

Thus, both the atoms belong to same element.

Hence, the correct answer is atom 2 and atom 5.