The correct statement about the model is:
• The model should show 27 protons and 32 neutrons.
Explanation:
The atomic number of cobalt (27) tells us the number of protons in the nucleus of the cobalt atom. The mass number (59) is the sum of protons and neutrons in the atom's nucleus. To find the number of neutrons, you subtract the atomic number from the mass number:
Number of neutrons = Mass number - Atomic number
Number of neutrons = 59 - 27
Number of neutrons = 32
So the correct model of a cobalt atom with a mass number of 59 would have 27 protons and 32 neutrons.
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)
• The model should show 32 protons and 59 neutrons.
• The model should show 27 protons and 32 neutrons.
• The model should show 59 protons and 27 neutrons.
• The model should show 27 protons and 27 neutrons.
29 answers
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)
• A molecular model of lithium sulfide would have two spheres.
• Both lithium and sulfur form positive ions.
• The atoms in lithium sulfide are held together by bonds.
• The chemical formula for lithium sulfide is LiSz.
• A molecular model of lithium sulfide would have two spheres.
• Both lithium and sulfur form positive ions.
• The atoms in lithium sulfide are held together by bonds.
• The chemical formula for lithium sulfide is LiSz.
The correct statement about lithium sulfide is:
• The atoms in lithium sulfide are held together by bonds.
Explanation:
Lithium sulfide is a compound formed by ions, specifically one sulfur ion and two lithium ions. The chemical formula is Li2S, where the lithium acts as a cation (Li+) and sulfur acts as an anion (S^2−). The compound results from the transfer of electrons from lithium to sulfur, forming ionic bonds that hold the atoms together in the molecule.
As for the other statements:
• A molecular model of lithium sulfide would not have just two spheres; it should represent three ions: two for lithium and one for sulfur.
• Both lithium and sulfur do not form positive ions; lithium forms a positive ion (Li+), but sulfur forms a negative ion (S^2−).
• The chemical formula for lithium sulfide is Li2S, not LiSz. The subscript '2' refers to the two lithium atoms needed to balance the charge of one sulfur ion with a charge of 2−.
• The atoms in lithium sulfide are held together by bonds.
Explanation:
Lithium sulfide is a compound formed by ions, specifically one sulfur ion and two lithium ions. The chemical formula is Li2S, where the lithium acts as a cation (Li+) and sulfur acts as an anion (S^2−). The compound results from the transfer of electrons from lithium to sulfur, forming ionic bonds that hold the atoms together in the molecule.
As for the other statements:
• A molecular model of lithium sulfide would not have just two spheres; it should represent three ions: two for lithium and one for sulfur.
• Both lithium and sulfur do not form positive ions; lithium forms a positive ion (Li+), but sulfur forms a negative ion (S^2−).
• The chemical formula for lithium sulfide is Li2S, not LiSz. The subscript '2' refers to the two lithium atoms needed to balance the charge of one sulfur ion with a charge of 2−.
Use the periodic table to answer the question.
- PERIODIC TABLE OF THE ELEMENTS
E CHALCOGENS ELEMENT
Li Be
B
B
N
F
STANDARD STATE (25 Ci 101 kPa
• Na Mg
K Ca Sc TI V Cr Mn Fe Co Ni Cu En Ga Ge As Se Br Kr Rb Sr Y Ze Nb Mo Te Ru Rh Pd Ag Cd in 5n Sb Te I Xe
Cs Ba
HE Ta W Re Os Ir Pt Au Hg TI Pb Bi Do At Rn
Er Ra - Bf Db 5g Bh Hs ME Jun üma Üub Üug
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Li
"Ac Th Pa U Np Du ÄmEm Bk Cf Es Fm Md No Lr
Which element has the same number of valence electrons as bromine (Br)?
(1 point)
O chlorine (CI)
• krypton (Kr)
• selenium (Se)
• potassium (K)
- PERIODIC TABLE OF THE ELEMENTS
E CHALCOGENS ELEMENT
Li Be
B
B
N
F
STANDARD STATE (25 Ci 101 kPa
• Na Mg
K Ca Sc TI V Cr Mn Fe Co Ni Cu En Ga Ge As Se Br Kr Rb Sr Y Ze Nb Mo Te Ru Rh Pd Ag Cd in 5n Sb Te I Xe
Cs Ba
HE Ta W Re Os Ir Pt Au Hg TI Pb Bi Do At Rn
Er Ra - Bf Db 5g Bh Hs ME Jun üma Üub Üug
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Li
"Ac Th Pa U Np Du ÄmEm Bk Cf Es Fm Md No Lr
Which element has the same number of valence electrons as bromine (Br)?
(1 point)
O chlorine (CI)
• krypton (Kr)
• selenium (Se)
• potassium (K)
Bromine (Br) is located in Group 17 (also known as Group 7A) of the periodic table. Elements in the same group have the same number of valence electrons. Thus, to find an element with the same number of valence electrons as bromine, you need to look for another element in the same group.
• Chlorine (Cl) is also in Group 17 of the periodic table, so it has the same number of valence electrons as bromine.
• Krypton (Kr) is in Group 18 (noble gases), so it doesn't have the same number of valence electrons as bromine.
• Selenium (Se) is in Group 16 (the chalcogens), so it has one fewer valence electron than bromine.
• Potassium (K) is in Group 1, and it has a very different number of valence electrons compared to bromine.
The correct answer is:
• chlorine (Cl)
• Chlorine (Cl) is also in Group 17 of the periodic table, so it has the same number of valence electrons as bromine.
• Krypton (Kr) is in Group 18 (noble gases), so it doesn't have the same number of valence electrons as bromine.
• Selenium (Se) is in Group 16 (the chalcogens), so it has one fewer valence electron than bromine.
• Potassium (K) is in Group 1, and it has a very different number of valence electrons compared to bromine.
The correct answer is:
• chlorine (Cl)
Why are sodium (Na) and potassium (K) in the same group on the periodic table? (1 point)
• They have similar atomic weights.
• They are both hard and brittle.
• They are both colorless.
• They have similar reactivity.
• They have similar atomic weights.
• They are both hard and brittle.
• They are both colorless.
• They have similar reactivity.
• They have similar reactivity.
Explanation:
Sodium (Na) and potassium (K) are in the same group on the periodic table, Group 1, which is also known as the alkali metals. Elements in the same group generally have similar chemical properties because they have the same number of valence electrons. For sodium and potassium, that number is one valence electron each. This single valence electron can be easily lost to form a +1 cation, which is why these elements are so reactive. Their reactivity, particularly with water and oxygen, is a notable property of the alkali metals.
Other choices, such as similar atomic weights, being hard and brittle, or being colorless, do not define the reasons for elements being in the same group on the periodic table. Atomic weights vary across a group, alkali metals are soft and easily cut, and color is not a group-defining trait.
Explanation:
Sodium (Na) and potassium (K) are in the same group on the periodic table, Group 1, which is also known as the alkali metals. Elements in the same group generally have similar chemical properties because they have the same number of valence electrons. For sodium and potassium, that number is one valence electron each. This single valence electron can be easily lost to form a +1 cation, which is why these elements are so reactive. Their reactivity, particularly with water and oxygen, is a notable property of the alkali metals.
Other choices, such as similar atomic weights, being hard and brittle, or being colorless, do not define the reasons for elements being in the same group on the periodic table. Atomic weights vary across a group, alkali metals are soft and easily cut, and color is not a group-defining trait.
Which of the following is considered acidic? (1 point)
• Soap
• Vinegar
• Ammonia
• Lime Water
• Soap
• Vinegar
• Ammonia
• Lime Water
• Vinegar
Explanation:
Vinegar is considered acidic because it contains acetic acid (CH3COOH). The presence of acetic acid gives vinegar its characteristic sour taste and acidic properties. Acids typically have a pH less than 7 and can donate protons (H+ ions) when dissolved in water.
The other substances listed have different properties:
• Soap is typically basic or alkaline, not acidic.
• Ammonia is a base; it accepts protons and has a pH greater than 7.
• Lime water (calcium hydroxide solution) is also basic, not acidic.
Explanation:
Vinegar is considered acidic because it contains acetic acid (CH3COOH). The presence of acetic acid gives vinegar its characteristic sour taste and acidic properties. Acids typically have a pH less than 7 and can donate protons (H+ ions) when dissolved in water.
The other substances listed have different properties:
• Soap is typically basic or alkaline, not acidic.
• Ammonia is a base; it accepts protons and has a pH greater than 7.
• Lime water (calcium hydroxide solution) is also basic, not acidic.
The chemical formula for carbonic acid is H2CO3. How many compounds are represented by this formula? (1 point)
1
6
2
or
3
1
6
2
or
3
The chemical formula H2CO3 represents a single compound, carbonic acid. So the correct answer is:
1
1
A student cuts some fabric into two pieces. Is this change physical or chemical? (1 point)
• It is a chemical change because the size changes.
• It is a physical change because there is no reaction.
• It is a chemical change because there is no phase change.
• It is a physical change because the process is reversible.
• It is a chemical change because the size changes.
• It is a physical change because there is no reaction.
• It is a chemical change because there is no phase change.
• It is a physical change because the process is reversible.
• It is a physical change because there is no reaction.
Explanation:
When a student cuts fabric into two pieces, the fabric's chemical composition remains unchanged. A physical change involves changes in the physical properties of a substance, such as shape, size, or phase, without altering the chemical identity of the substance. Cutting the fabric only alters its size and shape, not the chemical structure or composition.
Explanation:
When a student cuts fabric into two pieces, the fabric's chemical composition remains unchanged. A physical change involves changes in the physical properties of a substance, such as shape, size, or phase, without altering the chemical identity of the substance. Cutting the fabric only alters its size and shape, not the chemical structure or composition.
How are chemical changes different from physical changes? (1 point)
• They are reversible.
• They form new substances.
• They include shifts in the phase of matter.
• They involve heat.
• They are reversible.
• They form new substances.
• They include shifts in the phase of matter.
• They involve heat.
• They form new substances.
Explanation:
Chemical changes result in the formation of one or more new substances with different chemical properties than the original substance(s). During a chemical change, the bonds between atoms are broken and new bonds are formed, creating new compounds. Chemical changes are usually not easily reversible by simple physical means.
Physical changes, on the other hand, involve changes in the physical properties of a substance, like phase shifts, shape, or size, without altering the substance's chemical identity. Physical changes are often reversible.
While heat can be involved in both physical and chemical changes, it is not a defining characteristic that distinguishes the two. Similarly, reversibility is not a reliable distinguishing factor, as some chemical changes can be reversible under certain conditions (e.g., chemical equilibrium), but they generally require another chemical change to occur.
Explanation:
Chemical changes result in the formation of one or more new substances with different chemical properties than the original substance(s). During a chemical change, the bonds between atoms are broken and new bonds are formed, creating new compounds. Chemical changes are usually not easily reversible by simple physical means.
Physical changes, on the other hand, involve changes in the physical properties of a substance, like phase shifts, shape, or size, without altering the substance's chemical identity. Physical changes are often reversible.
While heat can be involved in both physical and chemical changes, it is not a defining characteristic that distinguishes the two. Similarly, reversibility is not a reliable distinguishing factor, as some chemical changes can be reversible under certain conditions (e.g., chemical equilibrium), but they generally require another chemical change to occur.
How does a balanced chemical equation demonstrate the Law of Conservation of Mass? (1 point)
• it shows that only physical changes follow the Law of Conservation of Mass
• it shows that all compounds remain bonded after the reaction
• it shows that no atoms have been gained or lost during the reaction
• it shows that the properties of the elements stay the same after the reaction
• it shows that only physical changes follow the Law of Conservation of Mass
• it shows that all compounds remain bonded after the reaction
• it shows that no atoms have been gained or lost during the reaction
• it shows that the properties of the elements stay the same after the reaction
• it shows that no atoms have been gained or lost during the reaction
Explanation:
A balanced chemical equation demonstrates the Law of Conservation of Mass by indicating that the number of atoms for each element is the same on both the reactant side and the product side of the reaction. This means that no atoms are created or destroyed during the chemical reaction, which is consistent with the Law of Conservation of Mass. According to this law, mass is neither created nor destroyed in an isolated system; the mass of the reactants must equal the mass of the products.
In a balanced chemical equation, the coefficients are used to ensure that for each element, the quantity of atoms is equal before and after the reaction. This balancing underscores that the total mass remains constant throughout the reaction.
Explanation:
A balanced chemical equation demonstrates the Law of Conservation of Mass by indicating that the number of atoms for each element is the same on both the reactant side and the product side of the reaction. This means that no atoms are created or destroyed during the chemical reaction, which is consistent with the Law of Conservation of Mass. According to this law, mass is neither created nor destroyed in an isolated system; the mass of the reactants must equal the mass of the products.
In a balanced chemical equation, the coefficients are used to ensure that for each element, the quantity of atoms is equal before and after the reaction. This balancing underscores that the total mass remains constant throughout the reaction.
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 - 2NaCI
If the total mass of the reactants is 58.44 amu, what will be the total mass of the products?
(1 point)
• 116.88 amu
• 60 amu
• 29.22 amu
• 58.44 amu
2Na + Cl2 - 2NaCI
If the total mass of the reactants is 58.44 amu, what will be the total mass of the products?
(1 point)
• 116.88 amu
• 60 amu
• 29.22 amu
• 58.44 amu
• 58.44 amu
Explanation:
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants in a chemical reaction must be equal to the total mass of the products.
In the given chemical equation, if the total mass of the reactants (2Na + Cl2) is 58.44 atomic mass units (amu), then according to the Law of Conservation of Mass, the total mass of the products (2NaCl) will also be 58.44 amu.
Explanation:
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants in a chemical reaction must be equal to the total mass of the products.
In the given chemical equation, if the total mass of the reactants (2Na + Cl2) is 58.44 atomic mass units (amu), then according to the Law of Conservation of Mass, the total mass of the products (2NaCl) will also be 58.44 amu.
Which procedure could be used to demonstrate that matter is conserved during a physical change? (1 point)
• Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
• Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
• Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
• Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
• Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
• Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
• Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
• Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
• Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
Explanation:
This procedure demonstrates that matter is conserved during a physical change. When ice, which is solid water, melts, it undergoes a physical change to become liquid water. Throughout this process, no matter is lost or gained; only the state of the water has changed from solid to liquid. By showing that the mass of the ice before melting is equal to the mass of the liquid water after melting, this procedure directly demonstrates the conservation of matter during the physical change.
Explanation:
This procedure demonstrates that matter is conserved during a physical change. When ice, which is solid water, melts, it undergoes a physical change to become liquid water. Throughout this process, no matter is lost or gained; only the state of the water has changed from solid to liquid. By showing that the mass of the ice before melting is equal to the mass of the liquid water after melting, this procedure directly demonstrates the conservation of matter during the physical change.
One molecule of bromine (Br) and two molecules of potassium chloride (KCI) combine in a reaction. How many atoms are in the products?
(1 point)
O six
O two
• four
• three
(1 point)
O six
O two
• four
• three
The correct answer is:
• six
Explanation:
A molecule of bromine (Br2) consists of two bromine atoms because bromine exists as a diatomic molecule. Each molecule of potassium chloride (KCl) contains one potassium atom and one chlorine atom. Since we have two molecules of KCl, we have a total of two potassium atoms and two chlorine atoms.
Therefore, the total number of atoms in the products is the sum of the two bromine atoms plus the two potassium atoms plus the two chlorine atoms, which equals 6 atoms.
• six
Explanation:
A molecule of bromine (Br2) consists of two bromine atoms because bromine exists as a diatomic molecule. Each molecule of potassium chloride (KCl) contains one potassium atom and one chlorine atom. Since we have two molecules of KCl, we have a total of two potassium atoms and two chlorine atoms.
Therefore, the total number of atoms in the products is the sum of the two bromine atoms plus the two potassium atoms plus the two chlorine atoms, which equals 6 atoms.
Use the unbalanced chemical equation to answer the question.
2NaHCO3 ---> Na2CO3 + CO2
Which of the following can be added to the products to balance the equation?
(1 point)
О СН2OH
O O2
O H2
O H2O
2NaHCO3 ---> Na2CO3 + CO2
Which of the following can be added to the products to balance the equation?
(1 point)
О СН2OH
O O2
O H2
O H2O
The correct answer is:
• H2O
Explanation:
To balance the chemical equation for the decomposition of sodium bicarbonate (baking soda), we need to ensure that the number of each type of atom on the reactants side is equal to the number on the products side. Let's look at the unbalanced equation:
2NaHCO3 —> Na2CO3 + CO2
Starting with this equation, we can see that there are:
- 2 sodium (Na) atoms on both sides
- 2 carbon (C) atoms on both sides (1 in Na2CO3 and 1 in CO2)
Now let's check hydrogen (H) and oxygen (O):
On the reactants side (2NaHCO3), there are:
- 2 × 1 = 2 sodium atoms (balanced with the product side)
- 2 × 1 = 2 carbon atoms (balanced with the product side)
- 2 × 3 = 6 oxygen atoms
- 2 × 1 = 2 hydrogen atoms
On the products side (Na2CO3 + CO2), there are:
- 1 sodium atom, which needs to be doubled to Na2CO3 to have 2 sodium atoms (already counted)
- 1 carbon atom in Na2CO3 and 1 carbon atom in CO2, which makes it 2 carbon atoms in total on the product side (balanced)
- 3 oxygen atoms in Na2CO3 and 2 oxygen atoms in CO2, which makes it 5 oxygen atoms in total on the products side (unbalanced with the reactants)
To balance the equation, notice that there's a deficit of one oxygen atom on the products side and that there are two hydrogen atoms on the reactants side that have not been accounted for. Water (H2O) contains both hydrogen and oxygen, and adding it to the product side can help balance the equation. Adding one molecule of water (H2O) will provide the two hydrogen atoms and an extra oxygen atom we need to balance the equation:
2NaHCO3 —> Na2CO3 + CO2 + H2O
Now we have:
- 6 oxygen atoms on both sides (3 in Na2CO3, 2 in CO2, 1 in H2O)
- 2 hydrogen atoms on both sides (2 in H2O)
The equation is now balanced.
• H2O
Explanation:
To balance the chemical equation for the decomposition of sodium bicarbonate (baking soda), we need to ensure that the number of each type of atom on the reactants side is equal to the number on the products side. Let's look at the unbalanced equation:
2NaHCO3 —> Na2CO3 + CO2
Starting with this equation, we can see that there are:
- 2 sodium (Na) atoms on both sides
- 2 carbon (C) atoms on both sides (1 in Na2CO3 and 1 in CO2)
Now let's check hydrogen (H) and oxygen (O):
On the reactants side (2NaHCO3), there are:
- 2 × 1 = 2 sodium atoms (balanced with the product side)
- 2 × 1 = 2 carbon atoms (balanced with the product side)
- 2 × 3 = 6 oxygen atoms
- 2 × 1 = 2 hydrogen atoms
On the products side (Na2CO3 + CO2), there are:
- 1 sodium atom, which needs to be doubled to Na2CO3 to have 2 sodium atoms (already counted)
- 1 carbon atom in Na2CO3 and 1 carbon atom in CO2, which makes it 2 carbon atoms in total on the product side (balanced)
- 3 oxygen atoms in Na2CO3 and 2 oxygen atoms in CO2, which makes it 5 oxygen atoms in total on the products side (unbalanced with the reactants)
To balance the equation, notice that there's a deficit of one oxygen atom on the products side and that there are two hydrogen atoms on the reactants side that have not been accounted for. Water (H2O) contains both hydrogen and oxygen, and adding it to the product side can help balance the equation. Adding one molecule of water (H2O) will provide the two hydrogen atoms and an extra oxygen atom we need to balance the equation:
2NaHCO3 —> Na2CO3 + CO2 + H2O
Now we have:
- 6 oxygen atoms on both sides (3 in Na2CO3, 2 in CO2, 1 in H2O)
- 2 hydrogen atoms on both sides (2 in H2O)
The equation is now balanced.
The image is a model of sulfuric acid that has a chemical formula of H,SO. In 1-2 sentences, explain why creating models, like the one shown in the image above, is important in understanding substances. In simple terms
Creating models of chemical substances, like sulfuric acid (H2SO4), is important because they provide a visual representation of the molecule's structure, including how the atoms are bonded and arranged. This helps in understanding the physical properties and reactivity of the substance, making complex chemical concepts more accessible and easier to comprehend.
Use the chemical equation to complete the activity.
2Cu + S -> Cu2s
Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (CuS). In 1-2 sentences, explain the law that the scientist used to predict that the product of the reaction would be 15.9 grams of copper sulfide.
2Cu + S -> Cu2s
Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (CuS). In 1-2 sentences, explain the law that the scientist used to predict that the product of the reaction would be 15.9 grams of copper sulfide.
The scientist used the Law of Conservation of Mass to predict that the product of the reaction would be 15.9 grams of copper sulfide. This law states that mass is neither created nor destroyed in chemical reactions, so the total mass of the reactants (12.7 grams of Cu + 3.2 grams of S) will equal the total mass of the products.