CHEMISTRY HIGH SCHOOL

Which scientist first attempted to construct a periodic table based on an element's atomic mass? A. Mendeleev B. Newton C. Dalton D. Moseley

Answers

Answer 1
Answer: A. The Russian chemist Dmitri Mendeleev 
Answer 2
Answer:

Answer:

The correct answer is A.

Explanation:

The periodic table published by Mendeleev in 1869 was the first periodic table to group the elements. Based on the hypothesis that the properties of the elements are a periodic function of their atomic weights, he placed in the table all the elements known up to that moment, which became 63 elements, ordering them in such a way that the elements belonging to the same family appear in the same vertical line. The elements were arranged in the increasing order of their atomic masses.

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Related Questions

Which law states that the volume of a gas is proportional to the moles of the gas when pressure and temperature are kept constant?
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Calculate the number of atoms of each type in C12H22O11 and record
Can someone help me find the 5 digits numbers in here?

What mass of solute is needed to prepare each of the following solutions? a. 3.00 L of 0.125 M K2SO4 b. 550 mL of 0.015 M NaF c. 700 mL of 0.350 M C6H12O6

Answers

a.
M = 0.125 M
V = 3.0 L
M=n/V(L) ⇒ n = 0.125 mol/L *3.0L = 0.375 mol

MM of K2SO4

K2 = 2* 39 = 78 g/mol
S= 32 g/mol
O4 = 4*16 = 64 g/mol

MM = 78g/mol + 32g/mol + 64g/mol =174 g/mol

mass = n*MM = 0.375 mol*174 g/mol = 65.25 g

b.
M= 0.015 M
V = 0.55L

n = 0.015 mol/L * 0.55L = 0.00825 mol

MM NaF

Na: 23g/mol
F: 19 g/mol

MM = 23g/mol + 19g/mol = 42g/mol

mass = n * MM = 0.00825 mol * 42g/mol = 0.3465 g

c.

n = M*V(L) = 0.350 mol/L * 0,700L = 0.245 mol
MM = 6*12 g/mol + 12*1g/mol + 6*16g/mol = 180 g/mol

mass = n*MM = 0.245 mol * 180g/mol = 44.1 g
 

How many atoms are in 11.9 moles of chromium?

Answers

Answer:

7,16.10^(24)

Explanation:

We know that in 1 mole of any substances there are 6,02. 10^(23) atoms

This number (6,02. 10^(23)) is a constant that is known as the avogadros number

if we know how many atoms are in a mole of chromium to calculate how many there are in 11.9 moles we apply a simple rule of three

1 mol Cr\longrightarrow 6,02.10^(23) atoms\n 11.9 moles Cr\longrightarrow x\nx=((11.9)(6,02.10^(23)))/(1)\n x= 7,16.10^(24) atoms

In 11.9 moles of chrome there are 7,16.10^(24) atoms
Use the following equation:
Given # of moles *  molar mass (g) per mol = Mass (g)
This gives us 11.9 x  51.9962 (g) per mol.

618.75 moles

Which of the following is a measure of randomness in a system?A) entropy.
B) kinetic energy.
C) potential energy.
D) chemical energy.

Answers

Answer:

A) entropy

Explanation:

Why it is that evaporation causes cooling,but boiling causes heating?

Answers

in evaporation due to internal heat, kinetic energy of molecules increases and they come to the top and take out that heat with them when they evaporate thus causes cooling 
in boiling as heat is given to the molecules so their kinetic energy increases and they start vibrating with great energy and thus causes heating
During evaporation, particles which have a high kinetic energy come out of the body by gaining heat due to which there is a cooling effect on the particle of the body itself. that is why, evaporation causes cooling. For example: sweating 

Which of the following can only be separated into two or more pure substances by a chemical change?a. an element
b. a compound
c. a homogeneous mixture
d. a heterogeneous mixture

Answers

The best answer to the question that is being presented above would be letter b. A compound can only be separated into two or more pure substances by a chemical change. Mixtures can be separated without chemical change. 

Compounds that do not conduct an electric current in either aqueous solution or when molten are referred to as _____.a. electrolyte
b. nonelectrolyte
c. not listed
d. ionic

Answers

The answer is B. Nonelectrolyte. Nonelectrolytes are substances that do not dissociate into ions when dissolved in a solution. In some cases, they dissociate into molecules rather than ions. They are usually polar covalent substances such as sucrose (C12H22O11). Nonelectrolytes are considered to be poor conductors of electricity.
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