Question 9
The early Greeks thought that earth, fire, water and air were the four basic elements that made up the world. An early scientist, Georg Ernst Stahl, first proposed that combustible substances contained a fire-like element called phlogiston, released when substances burned (combustion), as in Figure 9.
In 1774, Antoine Lavoisier challenged the Phlogiston Theory when he carried out combustion of mercury with air in a sealed container. He recorded the mass of mercury used and the product after combustion.
| Mass of substance (g) | Before combustion | After combustion |
|---|---|---|
| |1.00|1.08|
(a) Explain how Lavoisier's experimental results had disproved the Phlogiston Theory. [1 mark]
(b) Lavoisier also showed water was not an element. He reacted oxygen with an “inflammable air” to obtain water and concluded water was a compound of oxygen and “inflammable air”. What is this “inflammable air”? [0.5 mark]
(c) Complete the word equation by naming the substances needed and formed during complete combustion. [1.5 marks]
Combustible substance + ______ → (combustion) ______ + ______
(d) To cook soup noodles, a mountain climber heated pieces of ice (frozen at −15°C) in a pot until the water boiled for a few minutes. At atmospheric pressure 0.5 atm at his base camp, ice melts at 0°C and water boils at 81°C. Sketch a graph showing how the temperature of water in the pot changed over time. Clearly label the various temperatures. [2 marks]
In 1774, Antoine Lavoisier challenged the Phlogiston Theory when he carried out combustion of mercury with air in a sealed container. He recorded the mass of mercury used and the product after combustion.
| Mass of substance (g) | Before combustion | After combustion |
|---|---|---|
| |1.00|1.08|
(a) Explain how Lavoisier's experimental results had disproved the Phlogiston Theory. [1 mark]
(b) Lavoisier also showed water was not an element. He reacted oxygen with an “inflammable air” to obtain water and concluded water was a compound of oxygen and “inflammable air”. What is this “inflammable air”? [0.5 mark]
(c) Complete the word equation by naming the substances needed and formed during complete combustion. [1.5 marks]
Combustible substance + ______ → (combustion) ______ + ______
(d) To cook soup noodles, a mountain climber heated pieces of ice (frozen at −15°C) in a pot until the water boiled for a few minutes. At atmospheric pressure 0.5 atm at his base camp, ice melts at 0°C and water boils at 81°C. Sketch a graph showing how the temperature of water in the pot changed over time. Clearly label the various temperatures. [2 marks]