Laws of Chemical Combination and Valency

Question 1

Which law states that matter can neither be created nor destroyed during a chemical reaction, but can only be transformed from one form to another?

Accepted Answer

Law of Conservation of Matter

Question 2

Who formulated the Law of Conservation of Matter in 1789?

Accepted Answer

Antoine Lavoisier

Question 3

If $10.00\text{ g}$ of calcium carbonate ($CaCO_3$) is heated in a sealed container and decomposes to produce $5.60\text{ g}$ of calcium oxide ($CaO$) and carbon dioxide ($CO_2$), what is the mass of the carbon dioxide produced?

Accepted Answer

$4.40\text{ g}$

Question 4

Which law states that all pure samples of a particular chemical compound always contain the same elements combined together in the same proportion by mass?

Accepted Answer

Law of Constant Composition

Question 5

Who proposed the Law of Constant Composition (or Definite Proportions) in 1799?

Accepted Answer

Joseph Proust

Question 6

Pure water ($H_2O$) always contains hydrogen and oxygen combined in what approximate ratio by mass?

Accepted Answer

$1:8$

Question 7

A sample of copper(II) oxide contains $1.20\text{ g}$ of copper and $0.30\text{ g}$ of oxygen. Another sample contains $2.40\text{ g}$ of copper and $0.60\text{ g}$ of oxygen. What is the constant mass ratio of copper to oxygen in these samples?

Accepted Answer

$4:1$

Question 8

Which law states that if two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a simple ratio of whole numbers?

Accepted Answer

Law of Multiple Proportions

Question 9

Who formulated the Law of Multiple Proportions in 1803?

Accepted Answer

John Dalton

Question 10

In one iron chloride, $2.00\text{ g}$ of iron combines with $2.54\text{ g}$ of chlorine. In a second iron chloride, $2.00\text{ g}$ of iron combines with $3.81\text{ g}$ of chlorine. What is the simple whole-number ratio of the masses of chlorine combining with the fixed mass of iron?

Accepted Answer

$2:3$

Question 11

Which law states that the weights of two elements A and B which combine separately with a fixed weight of a third element C are either the same or in a simple ratio of the weights in which A and B combine with each other?

Accepted Answer

Law of Reciprocal Proportion

Question 12

Who proposed the Law of Reciprocal Proportion in 1792?

Accepted Answer

Jeremias Richter

Question 13

What is defined as the combining power of an element, representing the number of hydrogen atoms (or their equivalent) that one atom of the element can combine with or displace?

Accepted Answer

Valency

Question 14

According to the Bohr model, what is the maximum number of electrons that the K and L shells can hold respectively?

Accepted Answer

2 and 8

Question 15

If a non-metal atom has 6 valence electrons (such as oxygen), how is its valency calculated to complete its octet?

Accepted Answer

$8 - 6 = 2$

Question 16

Nitrogen has an atomic number of 7 and an electronic configuration of 2, 5. What is its valency?

Accepted Answer

3

Question 17

Why is sodium (valency 1) generally more reactive than magnesium (valency 2)?

Accepted Answer

Sodium readily loses its single valence electron more easily than magnesium loses two

Question 18

Using the valency cross-over method, what is the correct chemical formula for aluminium oxide, given that aluminium has a valency of 3 and oxygen has a valency of 2?

Accepted Answer

$Al_2O_3$

Question 19

When writing the formula for calcium oxide using the cross-over method, the initial crossed-over subscripts are $Ca_2O_2$. What is the final simplified formula?

Accepted Answer

$CaO$

Question 20

In the practical activity to verify the Law of Conservation of Matter, what is the color of the barium sulfate ($BaSO_4$) precipitate formed when sodium sulfate reacts with barium chloride?

Accepted Answer

White

Strong work.

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