Under certain conditions, water can be separated into oxygen and hydrogen gases according to the equation 2H2O → 2H2 + O2.

Question

In a lab, 112g of hydrogen gas and 888g of oxygen gas were collected. Student A says that the amount of water to start cannot be determined, but Student B says that the water must have been 1000g. Who is correct?

(1 point)
Responses

Student B, because of the law of conservation of matter.
Student B, because of the law of conservation of matter.

Student A, because the water was not measured to start with.
Student A, because the water was not measured to start with.

Neither are correct. It would have been 1112g, because there are 2 H2 to 1 O2.
Neither are correct. It would have been 1112g, because there are 2 H 2 to 1 O 2 .

Neither are correct. It was 2000g because the equation shows 2H2O.
Neither are correct. It was 2000g because the equation shows 2H 2 O.

Answer 1

To determine who is correct, we need to apply the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction.

According to the provided equation, the reaction of water (H2O) produces hydrogen gas (H2) and oxygen gas (O2) in a specific ratio: \[ 2H_2O \rightarrow 2H_2 + O_2 \]

From the problem, we know:

• Mass of hydrogen gas collected = 112 g
• Mass of oxygen gas collected = 888 g

To find the total mass of gas collected, we can add the two masses together: \[ 112 , \text{g} , (H_2) + 888 , \text{g} , (O_2) = 1000 , \text{g} \]

Because of the law of conservation of mass, the mass of the water that was used originally must equal the total mass of the products formed (hydrogen and oxygen): Thus, the mass of the water should equal the total mass of hydrogen and oxygen obtained, which is 1000 g.

Therefore, Student B is correct: the water must have been 1000g.