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 .
Both lithium and sulfur form positive ions.
Both lithium and sulfur form positive ions.
The atoms in lithium sulfide are held together by bonds.
The atoms in lithium sulfide are held together by bonds.
A molecular model of lithium sulfide would have two spheres.
A molecular model of lithium sulfide would have two spheres.
The correct response is "They have similar reactivity." Sodium (Na) and potassium (K) are both in Group 1 of the periodic table, also known as the alkali metals. Elements in the same group tend to have similar properties and reactivity, which is why sodium and potassium share this classification.
The statement "The atoms in lithium sulfide are held together by bonds" is correct.
Which element has the same number of valence electrons as bromine (Br)?
(1 point)
Responses
selenium (Se)
selenium (Se)
krypton (Kr)
krypton (Kr)
chlorine (Cl)
chlorine (Cl)
potassium (K)
The element that has the same number of valence electrons as bromine is chlorine (Cl).
Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
Responses
They are both hard and brittle.
They are both hard and brittle.
They have similar atomic weights.
They have similar atomic weights.
They have similar reactivity.
They have similar reactivity.
They are both colorless.
They are both colorless.
How are chemical changes different from physical changes?(1 point)
Responses
They include shifts in the phase of matter.
They include shifts in the phase of matter.
They form new substances.
They form new substances.
They are reversible.
They are reversible.
They involve heat.
The correct response is "They form new substances." Chemical changes involve the formation of new substances with different chemical properties. Physical changes, on the other hand, do not produce new substances but instead involve changes in the physical state or appearance of a substance, such as changes in size, shape, or phase of matter.
The correct response is "it shows that no atoms have been gained or lost during the reaction." The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. A balanced chemical equation ensures that the number of atoms of each element is the same on both sides of the equation, demonstrating that no atoms have been gained or lost during the reaction and thus confirming the Law of Conservation of Mass.
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
60 amu
60 amu
58.44 amu
58.44 amu
116.88 amu
116.88 amu
29.22 amu
To determine the total mass of the products, we need to calculate the molar mass of NaCl, which is the product formed in the reaction.
The molar mass of Na is 22.99 g/mol, and the molar mass of Cl is 35.45 g/mol.
Since the balanced equation tells us that 2 moles of Na react with 1 mole of Cl2 to form 2 moles of NaCl, we can calculate the molar mass of NaCl:
Molar mass of NaCl = 2 * (molar mass of Na) + 1 * (molar mass of Cl)
= 2 * 22.99 g/mol + 35.45 g/mol
= 45.98 g/mol + 35.45 g/mol
= 81.43 g/mol
Now, to find the total mass of the products, we need to convert the molar mass of NaCl to amu:
Total mass of products = (molar mass of NaCl) * (total number of moles of NaCl)
The balanced equation tells us that 2 moles of NaCl are formed for every 2 moles of Na and 1 mole of Cl2. This means that 2 moles of NaCl are formed for every 58.44 amu (total mass of reactants).
So, the total mass of the products will be:
Total mass of products = (81.43 g/mol) * (58.44 amu / 81.43 g/mol)
= 58.44 amu
Therefore, the correct response is "58.44 amu".
Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)
Responses
Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
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 cup of water. Boil the water. Find the mass of the water that remains.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
The correct response is "Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water."
This procedure demonstrates that matter is conserved during a physical change because the mass of the ice before melting should be equal to the mass of the liquid water after melting. The physical change from solid ice to liquid water does not result in the gain or loss of any atoms.
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
six
six
four
four
three
three
two
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)
Responses
H2O
H 2 O
CH2OH
CH 2 OH
H2
H 2
O2
To balance the given chemical equation, we need to ensure that the number of atoms of each type is the same on both sides of the equation.
The unbalanced equation is: 2NaHCO3 → Na2CO3 + CO2
To balance it, we need to add coefficients to the molecules or compounds involved. Let's try to determine what should be added to balance the equation:
Looking at the atoms involved, we have:
- Sodium (Na): There are 2 sodium atoms on the left side (2NaHCO3) and 2 sodium atoms on the right side (Na2CO3), so sodium is already balanced.
- Hydrogen (H): There are 2 hydrogen atoms on the left side (2NaHCO3) and no hydrogen atoms on the right side, so we need to balance hydrogen.
- Carbon (C): There is 1 carbon atom on each side, so carbon is already balanced.
- Oxygen (O): There are 8 oxygen atoms on the left side (2NaHCO3) and 3 oxygen atoms on the right side (Na2CO3 + CO2), so we need to balance oxygen.
To balance the equation, we can add H2O to the products. Adding water (H2O) will introduce two hydrogen atoms and one oxygen atom to the right side, helping balance the hydrogen and oxygen:
2NaHCO3 → Na2CO3 + CO2 + H2O
Now, let's check the atoms again:
- Sodium (Na): 2 sodium atoms on both sides, so sodium is balanced.
- Hydrogen (H): 2 hydrogen atoms on both sides, so hydrogen is balanced.
- Carbon (C): 1 carbon atom on both sides, so carbon is balanced.
- Oxygen (O): 8 oxygen atoms on both sides, so oxygen is balanced.
Therefore, the correct response is "H2O" as it can be added to the products to balance the equation.
Creating models is important in understanding substances because they provide visual representations that can help us visualize and conceptualize complex structures and interactions at the microscopic level, aiding in comprehension and furthering our understanding of substances.
where they all right?????
How does a balanced chemical equation demonstrate the Law of Conservation of Mass?(1 point)
Responses
it shows that the properties of the elements stay the same after 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
it shows that no atoms have been gained or lost during the reaction
it shows that only physical changes follow the Law of Conservation of Mass
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 all compounds remain bonded after the reaction
In 1-2 sentences, explain why creating models, like the one shown in the image above, is important in understanding substances.
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 (Cu2S). 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.
To find the number of atoms in the products, we need to calculate the total number of atoms in each product separately and then add them up.
Starting with the reactants, we have one molecule of bromine (Br2) and two molecules of potassium chloride (KCl).
In one molecule of bromine (Br2), there are two atoms of bromine (Br).
In two molecules of potassium chloride (KCl), there are two atoms of potassium (K) and two atoms of chlorine (Cl) in each molecule. Multiplying by two gives us a total of four atoms of potassium (K) and four atoms of chlorine (Cl) in the two molecules.
Summing up the total atoms in the products:
Total atoms = 2 bromine (Br) + 4 potassium (K) + 4 chlorine (Cl) = 2 + 4 + 4 = 10
Therefore, the correct response is "ten."