Which element has the same number of valence electrons as bromine (Br)?
(1 point)
Responses
krypton (Kr)
krypton (Kr)
selenium (Se)
selenium (Se)
chlorine (Cl)
chlorine (Cl)
potassium (K)
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 are both colorless.
They are both colorless.
They have similar reactivity.
They have similar reactivity.
They have similar atomic weights.
A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
Responses
It is a physical change because the process is reversible.
It is a physical change because the process is reversible.
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.
How are chemical changes different from physical changes?(1 point)
Responses
They involve heat.
They involve heat.
They are reversible.
They are reversible.
They include shifts in the phase of matter.
They include shifts in the phase of matter.
They form new substances.
How does a balanced chemical equation demonstrate the Law of Conservation of Mass?(1 point)
Responses
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
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 the properties of the elements stay the same after the reaction
Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)
Responses
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.
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 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 cup of water. Boil the water. Find the mass of the water that remains.
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
four
four
six
six
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
H2
H 2
H2O
H 2 O
O2
O 2
CH2OH
H2O
what is the answer to all the questions
Here are the correct answers to the questions:
1. Which element has the same number of valence electrons as bromine (Br)?
The answer is chlorine (Cl).
2. Why are sodium (Na) and potassium (K) in the same group on the periodic table?
The answer is they have similar reactivity.
3. Is cutting fabric into two pieces a physical or chemical change?
The answer is it is a physical change because there is no reaction.
4. How are chemical changes different from physical changes?
The answer is they form new substances.
5. How does a balanced chemical equation demonstrate the Law of Conservation of Mass?
The answer is it shows that no atoms have been gained or lost during the reaction.
6. Which procedure could be used to demonstrate that matter is conserved during a physical change?
The answer is Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
7. In the reaction: 2NaHCO3 → Na2CO3 + CO2, how many atoms are in the products?
The answer is four.
8. Which of the following can be added to the products to balance the equation?
The answer is H2O.
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.
(2 points)