Question

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) Responses The model should show 32 protons and 59 neutrons. The model should show 32 protons and 59 neutrons. The model should show 59 protons and 27 neutrons. The model should show 59 protons and 27 neutrons. The model should show 27 protons and 27 neutrons. The model should show 27 protons and 27 neutrons. The model should show 27 protons and 32 neutrons.

Answer 1

To understand how to model a cobalt atom based on its mass number and atomic number, we need to clarify what these terms mean:

• The atomic number (27) of cobalt tells us the number of protons in the atom.
• The mass number (59) is the total number of protons and neutrons in the atom.

To find the number of neutrons, we subtract the atomic number from the mass number:

Number of neutrons = Mass number - Atomic number Number of neutrons = 59 - 27 = 32

Thus, a cobalt atom has:

• 27 protons (since the atomic number is 27)
• 32 neutrons (since we calculated it as 59 - 27)

With that understanding, the correct statement about the cobalt atom model 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 A molecular model of lithium sulfide would have two spheres. A molecular model of lithium sulfide would have two spheres. The atoms in lithium sulfide are held together by bonds. The atoms in lithium sulfide are held together by bonds. The chemical formula for lithium sulfide is LiS2 The chemical formula for lithium sulfide is cap l i cap s sub 2 Both lithium and sulfur form positive ions.

Answer 3

In a molecule of lithium sulfide (Li₂S), there are indeed two lithium atoms and one sulfur atom. Let's evaluate each statement given:

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

   • This statement is incorrect because a complete model of lithium sulfide would require at least three spheres (two for lithium and one for sulfur).

2. The atoms in lithium sulfide are held together by bonds.

   • This statement is correct. Atoms in lithium sulfide are held together by ionic bonds, as lithium donates its electrons to sulfur.

3. The chemical formula for lithium sulfide is LiS₂.

   • This statement is incorrect. The correct formula for lithium sulfide is Li₂S, not LiS₂.

4. Both lithium and sulfur form positive ions.

   • This statement is incorrect. Lithium forms a positive ion (Li⁺), but sulfur forms a negative ion (S²⁻).

Given these evaluations, the correct statement about lithium sulfide is:

The atoms in lithium sulfide are held together by bonds.

Answer 4

Use the periodic table to answer the question. Which element has the same number of valence electrons as bromine (Br)? (1 point) Responses chlorine (Cl) chlorine (Cl) selenium (Se) selenium (Se) potassium (K) potassium (K) krypton (Kr) krypton (Kr)

Answer 5

Bromine (Br) is located in Group 17 (or VIIA) of the periodic table, which means it has 7 valence electrons.

To find which element has the same number of valence electrons as bromine, we will look at the options provided:

1. Chlorine (Cl): Located in Group 17, chlorine also has 7 valence electrons.
2. Selenium (Se): Located in Group 16, selenium has 6 valence electrons.
3. Potassium (K): Located in Group 1, potassium has 1 valence electron.
4. Krypton (Kr): Located in Group 18, krypton has 8 valence electrons.

Among the given options, chlorine (Cl) has the same number of valence electrons (7) as bromine (Br).

Thus, the correct response is:

Chlorine (Cl).

Answer 6

Which of the following would be considered most acidic?(1 point) Responses Soap Soap Lime Water Lime Water Vinegar Vinegar Ammonia

Answer 7

To determine the most acidic substance from the list provided, we can consider the typical pH levels of each item:

1. Soap: Typically alkaline (basic), with a pH above 7.
2. Lime Water: A solution of calcium hydroxide, also basic, with a pH above 7.
3. Vinegar: Contains acetic acid, which is acidic, with a pH around 2-3.
4. Ammonia: A basic substance with a pH above 7.

Among these substances, vinegar is the only one that is acidic, with a significantly low pH compared to the others.

Therefore, the most acidic substance from the options given is:

Vinegar.

Answer 8

The chemical formula for carbonic acid is H2CO3 . How many compounds are represented by this formula?(1 point) Responses 6 6 1 1 3 3 2

Answer 9

The chemical formula for carbonic acid is H₂CO₃. This formula represents a single compound, specifically carbonic acid itself.

Here's the breakdown:

• H₂ indicates there are 2 hydrogen atoms.
• C indicates there is 1 carbon atom.
• O₃ indicates there are 3 oxygen atoms.

The formula H₂CO₃ represents only one specific compound. Therefore, the correct response is:

1.

Answer 10

How are chemical changes different from physical changes?(1 point) Responses They form new substances. They form new substances. They involve heat. They involve heat. They include shifts in the phase of matter. They include shifts in the phase of matter. They are reversible.

Answer 11

Chemical changes and physical changes are distinct in several ways. Here’s a breakdown of the differences based on the responses provided:

1. They form new substances.

   • This statement is true for chemical changes. When a chemical change occurs, new substances are formed (e.g., rusting of iron). In contrast, physical changes do not produce new substances; the material may change form but retains the same chemical composition (e.g., melting ice).

2. They involve heat.

   • Both chemical and physical changes can involve heat, so this is not a distinguishing feature. For instance, a physical change like melting ice absorbs heat, and many chemical reactions either absorb or release heat.

3. They include shifts in the phase of matter.

   • This refers mostly to physical changes (like freezing, melting, or boiling). While some chemical changes can involve phase changes, it's primarily a characteristic of physical changes.

4. They are reversible.

   • Many physical changes are reversible (e.g., melting and freezing), while chemical changes are often not reversible (e.g., burning wood).

Considering these points, the correct distinction between chemical changes and physical changes is:

They form new substances.