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 always gained or lost in a chemical or physical process.
Matter is always gained or 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 might be lost in a chemical or physical process.
Matter might be lost in a chemical or physical process.

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

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

(1 point)
Responses

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

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 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.

Answer 1

Let's analyze each question one by one:

Question 1: a. In the chemical equation \( 2K + 2H_2O \rightarrow 2KOH + \text{some amount of } H_2 \), there are 4 hydrogen atoms on the reactant side (2 from \( H_2O \) and 2 from \( KOH \)) plus some amount of hydrogen gas \( H_2 \). Since we have 4 hydrogen atoms already accounted for in the products, the answer is:

• 4 (Total hydrogen atoms on product side)

Question 2: b. The law of conservation of matter (or mass) states that in a chemical reaction, matter is not created or destroyed. Therefore, the correct answer is:

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

Question 3: c. Connie and Dewayne are starting with 78 grams of potassium and 36 grams of water, giving us a total of: \[ 78 \text{ grams K} + 36 \text{ grams H}_2O = 114 \text{ grams}. \] According to the law of conservation of mass, the total mass of the products will equal the total mass of the reactants. Therefore, the total mass of the products would be:

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