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 + 2H2O --- 2KOH + some amount of H2
There are 4 atoms of hydrogen shown on the reactant side. How many total atoms of hydrogen must be on the product side?

PART B: what does the law of conservation of mass tell the students?

PART 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?
1. the total mass of the products would be greater than 114 grams, because water is really heavy.
2. the total mass of the products 114 grams, because mass cannot be gained or lost in the process.
3. the total mass of the products would be something less than 114 grams, because some of the mass burned into nothing.
4. the total mass of the products would equal 78 grams, because the mass of water doesn't make a difference.

Answer 1

PART A

In the chemical equation provided: \[ 2K + 2H_2O \rightarrow 2KOH + \text{some amount of } H_2 \]

On the reactant side, there are 4 hydrogen atoms in the water (2 from each \( H_2O \)), and the product side must maintain the same number of hydrogen atoms due to the law of conservation of mass.

In the products, there are 2 hydrogen atoms in each molecule of potassium hydroxide (2 KOH giving us 4 hydrogen atoms) and we also produce some hydrogen gas (\( H_2 \)). Thus, to balance the number of hydrogen atoms, there must be a total of 6 hydrogen in the products (4 from KOH and 2 from \( H_2 \)). The total number of hydrogen atoms on the product side is 6.

PART B

The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction. This means that the total mass of the reactants must equal the total mass of the products. The number of each type of atom must also be conserved, hence the number of atoms of hydrogen before the reaction should equal the number after the reaction.

PART C

Connie and Dewayne combine 78 grams of potassium with 36 grams of water. The total mass of the reactants is: \[ 78 , \text{grams (K)} + 36 , \text{grams (H}_2\text{O)} = 114 , \text{grams} \]

According to the law of conservation of mass, the total mass of the products will be equal to the total mass of the reactants. Therefore, the total mass of the products would be:

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