Connie and Dewayne know that solid potassium reacts very strongly with water, producing a chemical called potassium hydroxide along with hydrogen gas. They know the chemical equation looks like this.

Question

2K + 2H 2
O → 2KOH + some amount of H 2



a. There are 4 atoms of hydrogen shown on the reactant side. How many total atoms of hydrogen must be on the product side?

(1 point)
Responses

2
2

4
4

6
6

8
8
Question 2
b. What does the law of conservation of matter (or the law of conservation of mass) tell the students?(1 point)
Responses

Matter is never gained or lost in a chemical or physical process.
Matter is never gained or lost in a chemical or physical process.

Matter might be lost in a chemical or physical process.
Matter might be lost in a chemical or physical process.

Matter might be gained in a chemical or physical process.
Matter might be gained in a chemical or physical process.

Matter is always gained or lost in a chemical or physical process.
Matter is always gained or lost in a chemical or physical process.
Question 3
c. Connie and Dewayne combine 78 grams of potassium with 36 grams of water. What would they expect the total mass of the products to be? Why?

You can use the calculator (below the answers) if desired.

(1 point)
Responses

The total mass of the products would be greater than 114 grams, because water is really heavy.
The total mass of the products would be greater than 114 grams, because water is really heavy.

The total mass of the products would equal 78 grams, because the mass of water doesn't make a difference.
The total mass of the products would equal 78 grams, because the mass of water doesn't make a difference.

The total mass of the products would be 114 grams, because mass cannot be gained or lost in the process.
The total mass of the products would be 114 grams, because mass cannot be gained or lost in the process.

The total mass of the products would be something less than 114 grams, because some of the mass burned into nothing.

Answer 1

Let's address each question step by step.

Question 1

a. There are 4 atoms of hydrogen shown on the reactant side. How many total atoms of hydrogen must be on the product side?

To determine the number of hydrogen atoms on the product side, we first note that the reaction has 4 hydrogen atoms on the reactant side (2 from \(H_2O\) and 2 from the 2 potassium):

• Reactant side: \(4\) atoms of \(H\) (2 from \(2H_2O\) = 4 + 0 from potassium)
• Product side: Each \(KOH\) contributes 1 hydrogen atom, and since the reaction shows 2 \(KOH\), there are also \(2\) hydrogen atoms from \(H_2\) (resulting from the reaction).

Thus, the total on the product side is \(4\) hydrogen atoms.
Response: 4

Question 2

b. What does the law of conservation of matter (or the law of conservation of mass) tell the students?

The law of conservation of mass states that in a closed system, matter cannot be created or destroyed. Therefore, the total mass of the reactants must equal the total mass of the products.

Response: Matter is never gained or lost in a chemical or physical process.

Question 3

c. Connie and Dewayne combine 78 grams of potassium with 36 grams of water. What would they expect the total mass of the products to be? Why?

According to the law of conservation of mass, the total mass before the reaction (reactants) must equal the total mass after the reaction (products).

Calculating the total mass of the reactants:

• Mass of potassium = 78 grams
• Mass of water = 36 grams
• Total mass = 78 + 36 = 114 grams

Thus, the total mass of the products must be 114 grams as well, because mass is conserved during the reaction.

Response: The total mass of the products would be 114 grams, because mass cannot be gained or lost in the process.