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Questions and Answers
Which of the following substances is a gas at room temperature (25°C)?
Which of the following substances is a gas at room temperature (25°C)?
- Ethanol
- Water
- Carbon dioxide (correct)
- Sulfur
What is the physical state of sulfur at room temperature (25°C)?
What is the physical state of sulfur at room temperature (25°C)?
- Plasma
- Solid (correct)
- Gas
- Liquid
Which substance has the highest boiling point listed in Table 1.2?
Which substance has the highest boiling point listed in Table 1.2?
- Ethanol
- Common salt (Sodium chloride)
- Sulfur
- Copper (correct)
Which substance sublimes at atmospheric pressure?
Which substance sublimes at atmospheric pressure?
Which pair of substances are liquids at room temperature (25°C)?
Which pair of substances are liquids at room temperature (25°C)?
How do impurities affect the melting point of a substance?
How do impurities affect the melting point of a substance?
If seawater is impure, how will its boiling point compare to that of pure water?
If seawater is impure, how will its boiling point compare to that of pure water?
Which of the following is true for the determination of the physical state of a substance at room temperature?
Which of the following is true for the determination of the physical state of a substance at room temperature?
What happens to the freezing point of water when it contains impurities?
What happens to the freezing point of water when it contains impurities?
Which method can be used to measure the melting point of a solid?
Which method can be used to measure the melting point of a solid?
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Study Notes
Pure Substances
- A pure substance consists of only one substance without any contaminating impurities.
- Pure substances have definite melting and boiling points.
- A substance's melting and boiling points in relation to room temperature (25°C) determine whether it is usually seen as a solid, liquid, or gas.
Properties of Pure Substances
- Oxygen is a gas at room temperature with a melting point of -219°C and a boiling point of -183°C.
- Nitrogen is a gas at room temperature with a melting point of -210°C and a boiling point of -196°C.
- Ethanol is a liquid at room temperature with a melting point of -117°C and a boiling point of 78°C.
- Water is a liquid at room temperature with a melting point of 0°C and a boiling point of 100°C.
- Sulfur is a solid at room temperature with a melting point of 115°C and a boiling point of 444°C.
- Common salt (Sodium chloride) is a solid at room temperature with a melting point of 801°C and a boiling point of 1465°C.
- Copper is a solid at room temperature with a melting point of 1083°C and a boiling point of 2600°C.
- Carbon Dioxide is a gas that sublimes at atmospheric pressure.
Effect of Impurities
- Impurities can affect the value of the melting or boiling point of a substance.
- Impure substances often melt or boil over a range of temperatures, not at the precise point of the pure substance.
- Seawater, an impure substance, freezes at a temperature below 0°C and boils at a temperature above 100°C.
Physical Changes
- Liquid to solid: freezing
- Liquid to gas at a precise temperature: boiling
- Gas to liquid: condensation
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