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 59 protons and
27 neutrons.
The model should show 27 protons and
32 neutrons.
The model should show 27 protons and
27 neutrons.
The correct statement about the model is: The model should show 27 protons and 32 neutrons.
The model should show 27 protons and 32 neutrons.
To determine which statement about the model of a cobalt atom is correct, we need to understand the relationship between the atomic number and mass number.
The atomic number of an atom represents the number of protons in its nucleus. In this case, cobalt has an atomic number of 27, so it has 27 protons.
The mass number of an atom represents the total number of protons and neutrons in its nucleus. In this case, cobalt has a mass number of 59.
Since the atomic number (protons) represents 27 and the mass number (protons + neutrons) represents 59, we can subtract the atomic number from the mass number to determine the number of neutrons.
Number of neutrons = mass number - atomic number
Number of neutrons in cobalt = 59 - 27 = 32
Therefore, the correct statement about the model of a cobalt atom is:
The model should show 27 protons and 32 neutrons.
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)
The atoms in lithium sulfide are held
together by bonds.
A molecular model of lithium sulfide
would have two spheres.
The chemical formula for lithium sulfide
is LiS . 2
Both lithium and sulfur form positive ions.
The correct statement about lithium sulfide is: Both lithium and sulfur form positive ions.
Which element has the same number of valence
electrons as bromine (Br)?
(1 point)
selenium (Se)
potassium (K)
krypton (Kr)
chlorine (Cl)
The element that has the same number of valence electrons as bromine (Br) 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
Sodium (Na) and potassium (K) are in the same group on the periodic table because they have similar reactivity. The elements in the same group of the periodic table have similar chemical properties and tend to react in similar ways. Sodium and potassium both belong to Group 1 or the alkali metals, which are highly reactive and have similar properties such as low melting points and the ability to easily lose their outermost electron to form a positive ion.
Which of the following is considered acidic? (1 point)
Lime Water
Vinegar
Soap
Ammonia
Vinegar is considered acidic.
The chemical formula for carbonic acid is h2co3 How many compounds are represented by this formula? (1 point)
6
2
1
3
The chemical formula for carbonic acid, H2CO3, represents one compound.
A student cuts some fabric into two pieces. Is this
change physical or chemical? (1 point)
It is a chemical change because there is
no phase change.
It is a physical change because there is
no reaction.
It is a chemical change because the size
changes.
It is a physical change because the
process is reversible.
The student cutting the fabric into two pieces is a physical change because there is no reaction or change in the chemical composition of the fabric. The process is reversible as the pieces of fabric can be reassembled or repaired.
How are chemical changes different from physical
changes? (1 point)
They include shifts in the phase of
matter.
They are reversible.
They form new substances.
They involve heat.
Chemical changes are different from physical changes in that they form new substances. Physical changes, on the other hand, do not involve the formation of new substances. Both types of changes can involve shifts in the phase of matter, be reversible, or involve heat, but the key distinction is that chemical changes result in the formation of new substances with different properties.
How are chemical changes different from physical changes? (1 point)
They include shifts in the phase of
matter.
They are reversible.
They form new substances.
They involve heat.
Chemical changes are different from physical changes because they form new substances. Physical changes, on the other hand, do not result in the formation of new substances. While both types of changes can involve shifts in the phase of matter, be reversible, or involve heat, the key distinction is that chemical changes lead to the creation of different substances with new properties.
How are chemical changes different from physical changes? (1 point)
a. They include shifts in the phase of
matter.
b. They are reversible.
c. They form new substances.
d. They involve heat.
The correct answer is c. They form new substances.
How does a balanced chemical equation demonstrate the Law of Conservation of Mass? (1 point)
a. it shows that only physical changes follow the Law of Conservation of Mass
b. it shows that no atoms have been gained or lost during the reaction
c. it shows that all compounds remain bonded after the reaction
d. it shows that the properties of the elements stay the same after the reaction
The correct answer is b. it shows that no atoms have been gained or lost during the reaction. A balanced chemical equation ensures that the number of atoms of each element is the same on both sides of the equation, demonstrating the Law of Conservation of Mass which states that matter cannot be created or destroyed in a chemical reaction.
Use the chemical reaction to answer the question.
Which number will balance the equation?
(1 point)
2H2 + O2 → □ H2O
8
4
6
2
To balance the chemical equation 2H2 + O2 → □ H2O, we need to determine the coefficient that will balance the number of atoms on both sides of the equation.
The equation currently has a total of 4 hydrogen atoms on the left side (2 from H2) and 2 hydrogen atoms on the right side (from H2O).
To balance the hydrogen atoms, we need to have the same number on both sides. Therefore, the coefficient in front of H2O should be 2.
Now, let's check the oxygen atoms. There are 2 oxygen atoms on the left side (from O2) and 2 oxygen atoms on the right side (from H2O). The oxygen atoms are already balanced.
Therefore, the number that will balance the equation is 2: 2H2 + O2 → 2H2O.
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 + Cl → 2NaCl
If the total mass of the reactants is 58.44 amu, what will be the total mass of the products? (1 point)
a. 116.88 amu
b. 29.22 amu
c. 58.44 amu
d. 60 amu
To determine the total mass of the products, we need to understand the concept of the Law of Conservation of Mass. According to this law, the total mass of the reactants must be equal to the total mass of the products in a chemical reaction.
In the given reaction, 2Na + Cl → 2NaCl, we have a 2:1 ratio between sodium (Na) and sodium chloride (NaCl). This means that for every two moles of sodium reacting, we will obtain two moles of sodium chloride.
Since the total mass of the reactants is given as 58.44 amu, we can divide this mass equally between sodium and chlorine, as their molar masses are approximately 23 amu and 35.5 amu, respectively.
Therefore, the total mass of the products will also be 58.44 amu.
The correct answer is c. 58.44 amu.
Which procedure could be used to demonstrate that
matter is conserved during a physical change? (1 point)
a. Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
b. Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
c. Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
d. Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
The correct answer is a. Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
By finding the mass of the raw egg and then the mass of the cooked egg, we can determine if the mass has remained the same during a physical change (cooking the egg). If the mass of the cooked egg is the same as the mass of the raw egg, it demonstrates that matter is conserved during a physical change, as no matter has been lost or gained. This is in accordance with the Law of Conservation of Mass.
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)
a. two
b. three
c. four
d. six
To determine the number of atoms in the products, we need to examine the chemical equation and count the number of atoms of each element.
The chemical equation is:
Br2 + 2KCl → 2KBr + Cl2
For bromine (Br2), we have 2 atoms.
For potassium chloride (KCl), we have 2 atoms of potassium (K) and 2 atoms of chlorine (Cl).
After the reaction, we have 2 molecules of potassium bromide (KBr) and 1 molecule of chlorine (Cl2).
For potassium bromide (KBr), we have 2 atoms of potassium (K) and 2 atoms of bromine (Br).
For chlorine (Cl2), we have 2 atoms of chlorine (Cl).
Adding up the number of atoms in the products, we have:
2 atoms of potassium (K) + 2 atoms of bromine (Br) + 2 atoms of chlorine (Cl)
This gives us a total of 6 atoms.
Therefore, the correct answer is d. six.
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?
a. O2
b. H2
c. CH2OH
c. H2O
To balance the chemical equation 2NaHCO3 → Na2CO3 + CO2, we need to determine what can be added to the products to balance the equation.
On the left side of the equation, we have 2 sodium atoms (Na), 2 hydrogen atoms (H), 2 carbon atoms (C), and 6 oxygen atoms (O).
On the right side of the equation, we have 2 sodium atoms (Na) and 3 oxygen atoms (O) in Na2CO3 and 1 carbon atom (C) and 2 oxygen atoms (O) in CO2.
To balance the sodium (Na) atoms, we already have 2 on both sides.
To balance the hydrogen (H) atoms, we have 2 on the left side but none on the right side. Therefore, we can add 2H2O to the products to provide the necessary hydrogen atoms.
Adding 2H2O to the products gives us:
2NaHCO3 → Na2CO3 + CO2 + 2H2O
Now, let's check the carbon (C) atoms. We have 2 on the left side from NaHCO3 and 1 on the right side from Na2CO3. Therefore, we can add 1 more NaHCO3 to the reactants to account for the missing carbon atom.
Adding NaHCO3 to the reactants gives us:
3NaHCO3 → Na2CO3 + CO2 + 2H2O
Finally, let's check the oxygen (O) atoms. On the left side, we have 3 oxygen atoms from NaHCO3. On the right side, we have 3 oxygen atoms from Na2CO3 and 4 oxygen atoms from 2H2O. This gives us a total of 7 oxygen atoms, which is not balanced. To balance the oxygen atoms, we can add 3O2 to the reactants.
Adding 3O2 to the reactants gives us:
3O2 + 3NaHCO3 → Na2CO3 + CO2 + 2H2O
Now, the equation is balanced, and the correct answer is a. 3O2.