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3 years ago

What contribution did these scientists make to atomic models of the atom?

Chemistry

1 answer:

SashulF [63]3 years ago

7 0

Answer:

Explanation:

Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.

In 1897, J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas.

Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure.

The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

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How many grams of water are contained in a 0.127 l sample at 20°c?

kvasek [131]

The density of water at 20 °C is 0.9982 g/cm^{3} or 998.2 g/L. The volume of water is 0.127 L thus, its mass can be calculated from the following formula:

d=\frac{m}{V}

Here, d is density, m is mass and V is volume of water.

On rearranging,

m=d×V=(998.2 g/L)(0.127 L)=126.7 g

Thus, mass of water is 126.7 g.

3 0

3 years ago

Which of the following involves a chemical reaction?

Andrews [41]

A combustion involves a chemical reaction.

6 0

3 years ago

Which of the followings is true about G0'? A. G0' can be determined using Keq' B. G0' indicates if a reaction can occur under no

nekit [7.7K]

Answer:

A and D are true , while B and F statements are false.

Explanation:

A) True. Since the standard gibbs free energy is

ΔG = ΔG⁰ + RT*ln Q

where Q= [P1]ᵃ.../([R1]ᵇ...) , representing the ratio of the product of concentration of chemical reaction products P and the product of concentration of chemical reaction reactants R

when the system reaches equilibrium ΔG=0 and Q=Keq

0 = ΔG⁰ + RT*ln Q → ΔG⁰ = (-RT*ln Keq)

therefore the first equation also can be expressed as

ΔG = RT*ln (Q/Keq)

thus the standard gibbs free energy can be determined using Keq

B) False. ΔG⁰ represents the change of free energy under standard conditions . Nevertheless , it will give us a clue about the ΔG around the standard conditions .For example if ΔG⁰>>0 then is likely that ΔG>0 ( from the first equation) if the temperature or concentration changes are not very distant from the standard conditions

C) False. From the equation presented

ΔG⁰ = (-RT*ln Keq)

ΔG⁰>0 if Keq<1 and ΔG⁰<0 if Keq>1

for example, for a reversible reaction ΔG⁰ will be <0 for forward or reverse reaction and the ΔG⁰ will be >0 for the other one ( reverse or forward reaction)

D) True. Standard conditions refer to

T= 298 K

pH= 7

P= 1 atm

C= 1 M for all reactants

Water = 55.6 M

5 0

3 years ago

Just as carbon dating is used to measure the age of organic material, Argon-40 can be used to measure the age of rocks. A volcan

arsen [322]

Answer:

3.77 mg of K-40 decayed into Ar-40.

Data:

1) K-40, Ca-40, Ar-40: all three have the same atomic mass

2) 90% of the potassium-40 will decay into calcium-40

3) 10% of the potassium-40 will decay into argon-40.

4) K-40 inside the rock = 0.81 mg

5) Ar-40 trapped = 0.377 mg

Soltuion:

1) 0.377 mg of Ar-40 is the 10% of the mass of the K-40 that decayed

=> x * 10% = 0.377 mg => x * 0.1 = 0.377mg

=> x = 0.377 mg / 0.1 = 3.77 mg

That means that 3.77 mg of K-40 decayed into Ar-40. And this is the answer to the question.

Additionaly, you can analyze the content of all K-40 and Ca-40, to understand better the case.

2) The mass of the K-40 that decayed into Ca-40 is 9 times (ratio 9:1) the amount that decayed into Ar-40 =>

mass of K-40 that decayed into Ca-40 = 9 * 0.377 = 3.393 mg

3) Total amount of K-40 that decayed = amount that decayed into Ar-40 + amount that decayed into Ca-40 = 0.377mg + 3.393mg = 3.77 mg

4) Original amount of K-40 = amount of K-40 that decayed + amount of K-40 present in the rock = 3.77mg + 0.81 mg = 4.58 mg

5) amount of K-40 that decayed into Ar-40 as percent

% = [3.77 mg / 4.58mg] * 100 = 82.31 %.

8 0

4 years ago

A flask is filled with 50.0 ml of 0.15 M HCl acid. Exactly 0.054 grams of CaCo3 are placed in the acid,

ira [324]

Answer:

See explanation

Explanation:

2HCl(aq) + CaCO3(aq) ------->CaCl2(aq) + CO2(g) + H2O(l)

Number of moles of acid present = 50/1000 * 0.15 = 0.0075 moles

Number of moles of calcium carbonate = 0.054g/100 g/mol = 0.00054 moles

2 moles of HCl reacts with 1 mole of calcium carbonate

x moles of HCl reacts with 0.00054 moles of calcium carbonate

x = 2 * 0.00054/1

x = 0.00108 moles of HCl

Amount of acid left = 0.0075 moles - 0.0075 moles = 0.00642 moles

Reaction of HCl and NaOH

HCl(aq) + NaOH(aq) ------> NaCl(aq) + H2O(l)

Since the reaction is in the mole ratio of 1:1

0.00642 moles of HCl is neutralized by 0.00642 moles of NaOH

8 0

3 years ago