Cobalt has a mass number of 59 and an atomic number of 27. A student wants to create a model of a cobalt atom. Which statement about the model is correct?(1 point)

Question

Responses

The model should show 27 protons and 32 neutrons.
The model should show 27 protons and 32 neutrons.

The model should show 27 protons and 27 neutrons.
The model should show 27 protons and 27 neutrons.

The model should show 59 protons and 27 neutrons.
The model should show 59 protons and 27 neutrons.

The model should show 32 protons and 59 neutrons.

Answer 1

To understand which statement is correct about the model of a cobalt atom, we need to clarify a couple of key points regarding atomic structure:

1. Atomic Number: This is the number of protons in the nucleus of an atom. For cobalt, the atomic number is 27, which means it has 27 protons.

2. Mass Number: This is the total number of protons and neutrons in the nucleus. For cobalt, the mass number is 59.

Using these definitions:

• The number of neutrons can be calculated by subtracting the number of protons from the mass number: \[ \text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number} = 59 - 27 = 32. \]

Now, let's review the options given:

1. The model should show 27 protons and 32 neutrons. (Correct)
2. The model should show 27 protons and 27 neutrons. (Incorrect)
3. The model should show 59 protons and 27 neutrons. (Incorrect)
4. The model should show 32 protons and 59 neutrons. (Incorrect)

Thus, the correct statement about the model of a cobalt atom is:

The model should show 27 protons and 32 neutrons.

Answer 2

In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?(1 point)
Responses

The chemical formula for lithium sulfide is LiS2.
The chemical formula for lithium sulfide is LiS 2 .

A molecular model of lithium sulfide would have two spheres.
A molecular model of lithium sulfide would have two spheres.

Both lithium and sulfur form positive ions.
Both lithium and sulfur form positive ions.

The atoms in lithium sulfide are held together by bonds.

Answer 3

Let's evaluate the statements regarding lithium sulfide (Li₂S):

1. The chemical formula for lithium sulfide is LiS2. (Incorrect)

   • The correct formula for lithium sulfide is \( \text{Li}_2\text{S} \), which indicates there are two lithium atoms for every one sulfur atom.

2. A molecular model of lithium sulfide would have two spheres. (Incorrect)

   • A molecular model would actually have three spheres: two for lithium atoms and one for the sulfur atom.

3. Both lithium and sulfur form positive ions. (Incorrect)

   • Lithium forms a positive ion (Li⁺) because it loses one electron. However, sulfur typically forms a negative ion (S²⁻) by gaining electrons.

4. The atoms in lithium sulfide are held together by bonds. (Correct)

   • In lithium sulfide, the lithium ions and sulfur ions are held together by ionic bonds.

Therefore, the correct statement about lithium sulfide is:

The atoms in lithium sulfide are held together by bonds.

Answer 4

Question
Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
Responses

They are both colorless.
They are both colorless.

They have similar reactivity.
They have similar reactivity.

They are both hard and brittle.
They are both hard and brittle.

They have similar atomic weights.

Answer 5

Sodium (Na) and potassium (K) are in the same group on the periodic table because they share similar chemical properties, especially in terms of reactivity.

Here are the evaluations of the options:

1. They are both colorless. (Incorrect)

   • While sodium and potassium are colorless in their elemental forms (as gases); this is not a defining characteristic that places them in the same group.

2. They have similar reactivity. (Correct)

   • Sodium and potassium are both alkali metals (Group 1) and have similar reactivity, particularly with water and halogens. Their reactivity increases down the group.

3. They are both hard and brittle. (Incorrect)

   • In fact, sodium and potassium have different physical characteristics; sodium is more ductile and softer than potassium, which is also relatively soft but is considered more malleable. Both are classified as soft metals, but this is not why they are in the same group.

4. They have similar atomic weights. (Incorrect)

   • While they do have similar atomic weights (sodium is approximately 23 u, and potassium is approximately 39 u), atomic weight is not the reason they are in the same group.

Therefore, the correct answer is:

They have similar reactivity.

Answer 6

A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
Responses

It is a chemical change because the size changes.
It is a chemical change because the size changes.

It is a physical change because there is no reaction.
It is a physical change because there is no reaction.

It is a chemical change because there is no phase change.
It is a chemical change because there is no phase change.

It is a physical change because the process is reversible.

Answer 7

In this scenario, cutting fabric into two pieces is an example of a physical change. Let's evaluate the provided options:

1. It is a chemical change because the size changes. (Incorrect)

   • Size change alone does not indicate a chemical change.

2. It is a physical change because there is no reaction. (Correct)

   • Cutting the fabric does not involve a chemical reaction; it simply alters the size and shape of the material.

3. It is a chemical change because there is no phase change. (Incorrect)

   • A chemical change involves forming new substances, while a physical change can occur without changing the substance itself.

4. It is a physical change because the process is reversible. (Partially Correct)

   • While cutting fabric is a physical change, it is not necessarily reversible since you cannot "uncut" the fabric to return to its original state. This statement doesn't apply specifically to this context.

Thus, the most accurate answer is:

It is a physical change because there is no reaction.

Answer 8

Sodium reacts with chlorine to form the compound sodium chloride, or salt. The chemical formula below shows how the two elements combine into a compound.

2Na + Cl2 → 2NaCl

If the total mass of the reactants is 58.44 amu, what will be the total mass of the products?

(1 point)
Responses

29.22 amu
29.22 amu

116.88 amu
116.88 amu

58.44 amu
58.44 amu

60 amu

Answer 9

According to the law of conservation of mass, the total mass of the reactants in a chemical reaction is equal to the total mass of the products. Therefore, if the total mass of the reactants (sodium and chlorine) is 58.44 amu, then the total mass of the products (sodium chloride) will also be 58.44 amu.

Thus, the correct answer is:

58.44 amu

Answer 10

One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)
Responses

two
two

three
three

six
six

four

Answer 11

To determine how many atoms are in the products of the reaction between bromine (Br₂) and potassium chloride (KCl), we can analyze the molecules involved:

1. Bromine (Br₂) contains 2 bromine atoms.
2. Potassium Chloride (KCl): There are 2 molecules of KCl, and each molecule contains 1 potassium atom and 1 chlorine atom. Therefore, for 2 KCl molecules:
   • 2 potassium (K) atoms
   • 2 chlorine (Cl) atoms

Now, let's add up the total number of atoms in the products:

• From 1 molecule of Br₂: 2 Br atoms
• From 2 molecules of KCl: 2 K atoms + 2 Cl atoms = 4 atoms

Now we combine these:

• Total atoms = Br atoms (2) + K atoms (2) + Cl atoms (2) = 6 atoms

Therefore, the correct response is:

six