Law of conservation of mass (Lavoisier)

Complete the sentence with the missing words: "In any chemical reaction, the total mass of the $\dots$ is equal to the total mass of the $\dots$: mass is neither created nor $\dots$, it is only transformed."

Lucía weighs two solutions in a sealed beaker: before mixing them, the balance reads $185\ \text{g}$. When mixed, a white precipitate appears. The figure shows the sealed beaker on the balance, before and after mixing.

What will the balance read after the reaction? Justify your answer using Lavoisier's law.

We leave a burning candle on a balance, in the open air, and see that the reading gradually decreases, as shown in the figure.

Does this mean that matter is being destroyed? Where does the mass go that the balance no longer detects?

When cooking with butane gas, the cylinder gradually loses mass. Does this mean that matter disappears? Explain where the mass lost by the cylinder goes.

We dissolve an effervescent tablet of $4\ \text{g}$ in an open glass with $150\ \text{g}$ of water. When the bubbling stops, the glass with its contents weighs $152\ \text{g}$. The figure shows the open glass on the balance.

1. a) What mass of gas has escaped into the air?
2. b) How much would the whole assembly weigh if the experiment had been carried out in a sealed container?

In a reaction, $12\ \text{g}$ of carbon combine exactly with $32\ \text{g}$ of oxygen, with nothing left over, as shown in the diagram.

What mass of carbon dioxide is formed?

When heating $10\ \text{g}$ of copper in the presence of air, $12,5\ \text{g}$ of copper oxide are formed, as shown in the diagram.

Why does the oxide weigh more than the copper it comes from? What mass of oxygen has combined?

A magnesium ribbon of $6\ \text{g}$ burns in air, and $10\ \text{g}$ of powdered magnesium oxide are collected.

1. a) What mass of oxygen from the air has combined with the magnesium?
2. b) If we burned $12\ \text{g}$ of magnesium with excess oxygen, what mass of oxide would we obtain?

Inside an airtight glass bell jar, there are $250\ \text{g}$ of air and a candle of $20\ \text{g}$. We light it, and after a while, the candle weighs $14\ \text{g}$. The figure shows the sealed bell jar.

1. a) What is the total mass of the contents of the bell jar at that moment?
2. b) By how much has the mass of the air mixed with the gases produced increased?

An open container contains $200\ \text{g}$ of hydrogen peroxide, which decomposes slowly, releasing oxygen gas. When the decomposition finishes, $184\ \text{g}$ of water remains.

1. a) What mass of oxygen has escaped from the container?
2. b) Explain why this result does not contradict the law of conservation of mass.

Design an experiment using a bottle, a balloon, vinegar and bicarbonate of soda to demonstrate the law of conservation of mass even when a gas is given off in the reaction. Describe the setup step by step, predict what the balance will read before and after the reaction, and point out two experimental errors that could ruin the verification.

In a lime kiln, $100\ \text{kg}$ of limestone are heated to produce $56\ \text{kg}$ of quicklime.

1. a) A worker claims: "Mass has been lost, so Lavoisier was wrong." Explain to him why this is not the case.
2. b) Calculate the mass of carbon dioxide that has escaped through the chimney.
3. c) How would you repeat the experiment to test the law of conservation of mass directly?

Lavoisier heated mercury for twelve days in a retort (a sealed glass vessel) containing air. The mercury became covered with a red powder and its mass increased, while the air inside lost part of its volume. The figure shows the sealed retort.

1. a) Why did the mass of the mercury increase?
2. b) Where did the gained mass come from?
3. c) Explain why the total mass of the sealed retort did not change during the experiment.

A group of students checks the conservation of mass in a precipitation reaction and notes down: mass before mixing, $164,8\ \text{g}$; mass after, $164,6\ \text{g}$.

1. a) Do these data refute Lavoisier's law?
2. b) Calculate the difference between both measurements and express it in milligrams.
3. c) Give two possible experimental causes for this slight discrepancy.