Congratulations, hopefully conducting the same experiments as Priestley, Lavoiser, and others has helped you understand how John Dalton came up with his theory of matter. Dalton’s theory has four basic principles:
· Matter is composed of tiny particles called atoms;
· Atoms of a given element are the same, atoms of different elements differ;
· Atoms can combine or separate during a chemical reaction, they are not created or destroyed;
· When atoms react, they do so in defined, whole-number ratios.
If you would like to learn more about Dalton's theory of matter, please visit our module "Matter: Atoms from Democritus to Dalton."
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Well into the 17th century, all of the things around us were thought to be made of some mystical combination of earth, air, water, and fire. Robert Boyle first challenged this idea in the 1600s. Then, in the late 18th century, Joseph Priestly, Antoine Lavoisier, and others conducted key experiments that would help lay the foundation for an atomic theory of matter that was later proposed by John Dalton. Understanding these experiments – how different materials combine or break apart – provides clues to why scientists began thinking of matter as being made up of tiny atoms. To peer into their laboratories and try some of these experiments yourself, please hit next.
Each of the three experiments shown include a digital scale to show the weight, in grams, of material as it is produced or consumed during the reaction. As you navigate through the experiments, pay attention to how the weight of the initial starting materials (reactants) changes as well as how the weight of the final materials produced (the products) changes. Note whether anything is lost or gained during the reaction. In addition, for those experiments that involve gases, a digital meter showing volume in liters is provided. The volume of a gas is directly proportional to the amount of material present. Pay attention to how the gases are consumed or produced in the reactions. Please note that you will not be able to continue in this animation until you select the correct answers for each quiz.
Given the poor understanding of the nature of matter, the art of alchemy flourished well into the 18th century. Alchemists believed that inexpensive “base” metals like lead, could be magically transmuted into precious metals like gold. Supporting this idea was the way certain common materials, like the ore red calx appeared to magically transform into other materials. Red calx, a mineral commonly used in women’s cosmetics into the 1700s because of its red color, appeared to magically transform into the silver, liquid metal mercury upon heating. The English natural philosopher, Joseph Priestly, was one of the first scientists to carefully observe this transformation. Priestley observed that red calx did not magically transform when heated, rather it appeared to release a strange gas and in the process mercury was left behind. Try this experiment yourself and as you do, be careful to observe what happens. How much material do you start with? What is produced after the experiment? How do the starting and ending amounts compare?
The volume of gas changed randomly.
The mass of the gas did not change during heating.
The mass of the gas changed randomly.
Yes, it increased.
The volume of gas changed proportionally to its mass.
The mass of the gas decreased by the same amount that the flask increased.
3. How did the volume of the gas produced change in the experiment?
The mass of the gas increased by the same amount that the flask decreased.
Continue to next section
2. How did the mass of the gas compare to the mass of materials in the flask?
1. Did the mass of calx in the flask change upon heating?
Yes, it decreased.
The volume of gas did not change.
Priestley collected the gas but had no idea what it was. He observed that a candle burned brightly in it, and when he placed a mouse in a container with the gas it lived normally. Priestley did not fully understand the nature of the gas, he thought it was air absent of some poisonous substance (phlogiston) that would snuff the candle or kill the mouse. As a result, he named the gas dephlogisticated air (air without phlogiston). Others, including Antoine Lavoisier, would carry out additional experiments. Click “Next” to continue to Lavoisier’s lab.
The masses of reactants and products changed randomly.
1. Observe how the volumes of gas change in the reaction and compare the rate at which the starting gases were used up. How do they compare?
The total mass of all materials decreased after the reaction occurred.
The total mass of all the materials increased after the reaction occurred.
2 volumes to 1
1 volume to 2
They were consumed at equal rates.
2 volumes to 2
Oxygen was consumed faster than phlogiston.
3. How did the mass of the gases in all three vessels before burning compare to the total mass after burning?
There was no change in total mass of the materials after the
1 volume to 1
Phlogiston was consumed faster than oxygen.
2. With relation to the volumes of the gases, in what specific proportion did the phlogiston react with oxygen?
Lavoisier observed that the gas produced by his reaction condensed into a clear liquid, which he later realized was water. This observation prompted him to change the name of phlogiston to hydrogen, from the Greek words that mean water maker. Click “Next” to continue to another important 18th century experiment.
The diamond would grow in size as the sunlight were
absorbed by its surface.
The mass of gas formed equaled the total mass of reactants consumed.
The mass of gas formed was greater than the total mass of reactants
The diamond would not change as it could not undergo
1. If no oxygen were present, what do you think would happen to the diamond?
3. How did the mass of gas produced compare to the mass of the reactants
that were consumed?
The diamond would disintegrate just as it does in the
presence of oxygen.
The mass of gas formed was less than the total mass of reactants
2. Diamonds are made of carbon, which of the following might be the gas produced when the diamond is heated?
Lavoisier observed that the gas that was formed when diamond was burned could be mixed with water to form carbonic acid, which forms when carbon dioxide is mixed with matter. From this observation, he was the first to show that diamonds are made of primarily carbon, the same substance that makes up coal which was a common fuel during his time period. Now that you have completed all of the activities, click “Next” to test your understanding.
Diamond can form carbon dioxide when neither air nor oxygen is present.
Some substances are composed of precise amounts of two or more other substances.
1. Which of the core concepts below most logically follows from the experiments you conducted in Priestley’s lab?
2. Which of the core concepts below most logically follows from the experiments you conducted in Lavoisier’s lab?
Red calx turns into mercury when it is heated.
The total mass of the products of a chemical reaction is greater than the mass of
3. Which of the core concepts below most logically follows from the experiments you conducted with diamonds?
All substances can be broken down into simpler materials by heating them.
Elements combine in specific, defined rations in chemical reactions.
The total mass of the products of a chemical reaction is exactly equal to the mass
of the reactants.
The total mass of the products of a chemical reaction is less than the mass of
Carbon reacts to form different compounds depending on whether there is oxygen present or not.