Charlene Sci 7.1

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Questions and Answers

What is the approximate percentage of carbon dioxide in the composition of air?

  • 0.1%
  • 0.3%
  • 0.04% (correct)
  • 0.01%

Which of the following gases is present in air in the highest proportion?

  • Oxygen
  • Noble Gases
  • Carbon Dioxide
  • Nitrogen (correct)

What is the approximate total percentage of noble gases in the air?

  • 0.9% (correct)
  • 0.5%
  • 0.2%
  • 1.2%

Which of the following statements regarding tests for gases is true?

<p>Gases are identified using their properties. (D)</p> Signup and view all the answers

Which gas in the composition of air varies significantly in concentration?

<p>Water Vapour (A)</p> Signup and view all the answers

What color does dry cobalt chloride paper turn in the presence of water?

<p>Pink (D)</p> Signup and view all the answers

What is the result of adding alcohol to dry cobalt chloride paper?

<p>No change (A)</p> Signup and view all the answers

What color change indicates the presence of carbon dioxide?

<p>From colorless to milky (B)</p> Signup and view all the answers

Which of the following substances acts as an indicator for water?

<p>Dry cobalt chloride paper (C)</p> Signup and view all the answers

What effect does water have on dry cobalt chloride paper?

<p>It turns it from blue to pink (D)</p> Signup and view all the answers

Which indicator turns from red to yellow in the presence of carbon dioxide?

<p>Hydrogencarbonate indicator (C)</p> Signup and view all the answers

Why should the dry cobalt chloride paper not be touched with bare hands?

<p>To avoid changing its color due to moisture from the hands (D)</p> Signup and view all the answers

What color change indicates the presence of water when using dry cobalt chloride paper?

<p>From blue to pink (D)</p> Signup and view all the answers

Which of the following materials is used in the experiment to keep the cobalt chloride dry?

<p>Desiccator (B)</p> Signup and view all the answers

What role does oxygen play in the burning process?

<p>Oxygen supports the burning of fuel. (B)</p> Signup and view all the answers

In which application is oxygen NOT used?

<p>Cooling machinery. (D)</p> Signup and view all the answers

How is oxygen utilized in welding?

<p>Oxygen is mixed with a fuel gas to create a hot flame. (C)</p> Signup and view all the answers

What is a critical function of oxygen for living organisms?

<p>Oxygen is required for cellular respiration. (B)</p> Signup and view all the answers

What is the result of burning a fuel-oxygen mixture?

<p>It generates a very hot flame. (D)</p> Signup and view all the answers

What is the primary reason helium-filled balloons float in air?

<p>Helium is lighter than air (B)</p> Signup and view all the answers

Which noble gases are mentioned as being used in neon signs?

<p>Argon and neon (B)</p> Signup and view all the answers

What percentage of air is made up of oxygen?

<p>21% (C)</p> Signup and view all the answers

What is the role of electricity in neon tubes filled with argon and neon?

<p>To ionize the gas and produce light (D)</p> Signup and view all the answers

Which gas constitutes the largest proportion of the atmosphere?

<p>Nitrogen (D)</p> Signup and view all the answers

Which of the following statements is NOT true about noble gases?

<p>They react readily with other elements (B)</p> Signup and view all the answers

What is the approximate percentage of carbon dioxide in the atmosphere?

<p>0.04% (A)</p> Signup and view all the answers

What is the significance of the density of gases in relation to balloon flight?

<p>Lighter gases allow balloons to ascend (C)</p> Signup and view all the answers

What characteristics differentiate gases such as oxygen, carbon dioxide, and nitrogen from other substances?

<p>They are colorless and odorless, each with unique properties. (B)</p> Signup and view all the answers

Which of the following tests is NOT conclusive for identifying carbon dioxide?

<p>Relighting a glowing splint (D)</p> Signup and view all the answers

What observation indicates the presence of water when using dry cobalt chloride paper?

<p>The paper turns pink from blue (A)</p> Signup and view all the answers

Which gas is identified in the experiment as having no simple conclusive test?

<p>Nitrogen (D)</p> Signup and view all the answers

In the presence of carbon dioxide, which of the following changes would NOT occur?

<p>Glowing splint remains lit (C)</p> Signup and view all the answers

Which of the following observations is associated specifically with the presence of alcohol and not with water?

<p>Turning dry cobalt chloride paper blue (D)</p> Signup and view all the answers

Flashcards

Composition of air

Air is made up of various gases, with nitrogen being the main component.

Carbon Dioxide

A gas present in air in small amounts (approximately 0.04%).

Noble Gases

Gases in air that are present in a small amount (around 0.9%).

Identifying gases

Scientists developed tests to identify gases based on their characteristics.

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Air Composition

The proportion of gases in air.

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Cobalt chloride paper

A type of paper used to test for the presence of water.

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Water test

An experiment to detect the presence of water using cobalt chloride paper.

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Dry cobalt chloride paper

Cobalt chloride paper that hasn't been exposed to water, usually a light blue/pink color.

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Desiccator

A sealed container used to keep substances dry by removing moisture from the air.

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Dropper

A tool used to add small amounts of liquid, like water.

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Apparatus

Equipment used in a scientific experiment.

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Distilled water

Purified water, free from impurities.

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Color change

A visible change in the color of the cobalt chloride paper when exposed to water.

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Cobalt chloride paper test for water

Dry cobalt chloride paper turns from blue to pink in the presence of water.

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Oxygen test

Oxygen relights a glowing splint.

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Carbon dioxide test

Carbon dioxide turns hydrogencarbonate indicator from red to yellow and lime water from colorless to milky.

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Water test using cobalt chloride paper

Dry cobalt chloride paper changes from blue to pink in the presence of water.

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Antoine Lavoisier

A 18th-century scientist who investigated the burning process and discovered oxygen.

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Dry cobalt chloride paper color

Its color is blue in a dry state

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Alcohol Flammability

Alcohol is flammable and should be handled with care.

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Well-ventilated room for alcohol use

Essential for safety when handling alcohol to avoid inhalation of fumes.

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Burning's Evolution

The understanding of burning changed over time, from theories like phlogiston to discovering oxygen's role in combustion.

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Oxygen's Role

Oxygen was discovered as the essential component for burning, replacing the old phlogiston theory.

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Collaboration in Science

Scientists sometimes collaborate to make discoveries, but there can also be competition for credit and recognition.

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Technology's Impact

Advanced technology and tools helped scientists understand burning better by enabling precise experiments.

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Oxygen's Properties

Oxygen is a colorless and odorless gas vital for breathing and combustion.

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Carbon Dioxide's Role

Carbon dioxide is another colorless and odorless gas found in the air, important for plants and the greenhouse effect.

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Nitrogen's Importance

Nitrogen makes up most of the air we breathe, though it's not used directly by humans for breathing.

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Gases in Air

Air is a mixture of gases, primarily nitrogen, oxygen, and a small amount of carbon dioxide and other gases.

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Oxygen's Role in Burning

Oxygen is needed to support burning. It combines with a fuel to create a flame, producing heat and light.

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Oxygen in Welding

Oxygen is mixed with a fuel gas in a welding torch. The mixture burns very hot, allowing for cutting and welding metals.

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Oxygen and Rocket Propulsion

Oxygen is used as an oxidizer to burn fuel in rockets, creating the thrust for liftoff.

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Oxygen's Importance for Humans

Oxygen is essential for humans to survive. We breathe it in to power our bodies and cells.

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Why is Oxygen Important?

Oxygen plays a vital role in supporting burning, powering rockets, and enabling human survival. It's a crucial element for various processes on Earth.

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What is air?

A mixture of different gases, primarily nitrogen (78%) and oxygen (21%), with smaller amounts of carbon dioxide, noble gases, water vapor, and other gases.

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Helium's Property

Helium is less dense than air, which is why helium-filled balloons float.

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Neon Signs

Neon signs contain gases like argon and neon that emit colored light when electricity is passed through them.

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What are noble gases used for?

Noble gases like argon and neon are used to fill neon signs, which emit colorful light when electricity is passed through them.

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How do neon signs work?

When electricity passes through the tubes filled with gases like argon and neon, these gases give off colored light.

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What is air made of?

Air is a mixture of gases, including nitrogen (78%), oxygen (21%), carbon dioxide (0.04%), noble gases (about 0.9%), water vapor, and other gases.

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What is the composition of air?

Air is composed of various gases, with nitrogen making up the largest proportion (78%), followed by oxygen (21%).

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Nitrogen Test

There is no simple test for nitrogen. It extinguishes a flame and doesn't cause any color changes in the indicators used.

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Study Notes

Air Composition

  • Air is a mixture of gases
  • Predominantly nitrogen (78%) and oxygen (21%)
  • Contains small amounts of carbon dioxide (0.04%), noble gases, water vapor, and other gases
  • These gases are not chemically bonded
  • Air is essential for survival on Earth

Tests for Gases in Air

  • Identifying gases can be difficult visually
  • Scientists use specific tests based on the properties of each gas
  • Practical tests are used to study oxygen, carbon dioxide, and nitrogen
  • Specific experiments are outlined for these tests

Testing for Water Vapor

  • Dry cobalt chloride paper changes color in the presence of water.
  • Blue paper turns pink when exposed to water
  • Blue paper turns blue again when exposed to alcohol

Properties and Uses of Gases

  • Oxygen supports burning, essential for human life, used in welding
  • Oxygen is used when climbing and high altitudes.
  • Carbon dioxide does not support burning, heavier than air, used in fire extinguishers to isolate the fire from oxygen.
  • Nitrogen is unreactive and used to preserve food in packaging, used in freezing systems
  • Nitrogen has a very low boiling point (-196°C).

Section Summary - Air

  • Air is a mixture of nitrogen, oxygen, carbon dioxide, noble gases, water vapor, and other gases.
  • Tests can determine specific gases in the air based on their unique characteristics
    • Oxygen supports burning, relights a glowing splint, supports burning
    • Carbon dioxide does not support burning, denser than air, turns hydrogencarbonate indicator red to yellow, turns limewater milky
    • Nitrogen is unreactive, has a very low boiling point (-196°C)
  • Water vapor causes cobalt chloride paper to turn from blue to pink

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