Introduction to Chemistry

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Questions and Answers

What is chemistry?

Chemistry is the scientific study of the composition, characteristics, and interactions of matter.

How has chemistry contributed to the nation's development?

Weather patterns, brain function, computer operation, chemical industries, manufacturing, fertilizers, alkalis, acids, salts, dyes, polymers, medicines, soaps, detergents, metals, alloys, and other fields of chemistry have all contributed to the national economy.

Differentiate solids, liquids & gases in terms of volume & shapes. Solids have a volume and shape.

definite, fixed

Differentiate solids, liquids & gases in terms of volume & shapes. Liquids have a volume and shape.

definite, not fixed, take the shape of the container Signup and view all the answers

Differentiate solids, liquids & gases in terms of volume & shapes. Gases have a volume and shape.

not definite, takes the shape of the container Signup and view all the answers

Name the different methods that can be used for separation of components of a mixture.

Physical procedures such as handpicking, filtration, crystallization, distillation, and others can be used to separate the components of a mixture. Signup and view all the answers

Classify the following as pure substances and mixtures: Air, Glucose, Gold, Sodium, Milk. Which of these are pure substances?

Sodium Signup and view all the answers

What is the difference between molecules and compounds? Molecules are made up of ______.

either distinct atoms or the same atoms Signup and view all the answers

What is the difference between molecules and compounds? A compound is created when ______.

two or more distinct atoms join in a simple proportion Signup and view all the answers

How can we separate the components of a compound?

The constituents of a compound cannot be separated by physical methods. They can only be separated by chemical methods. Signup and view all the answers

How are physical properties different from chemical properties?

Physical properties can be measured or observed without changing the substance's identity, whereas chemical properties require a chemical change to be measured. Signup and view all the answers

What are the two different systems of measurement?

The different systems of measurement are the English system and the metric system. Signup and view all the answers

What is the SI unit of density?

Kg m-3 or Kg/m3 Signup and view all the answers

What are the reference points in a thermometer with Celsius scale?

The thermometers with Celsius scale are calibrated from 0°C to 100°C, where these two temperatures are the freezing and boiling of water. Signup and view all the answers

What is the SI unit of volume? What is the other common unit which is not an SI unit of volume?

L (liter) Signup and view all the answers

What is the difference between precision and accuracy? Precision refers to how near different measurements for the same amount are to each other, while accuracy informs us how close they are to the ______.

real value Signup and view all the answers

What do you understand about significant figures?

Significant figures are used to define those numbers which have some uncertainty in the form of digits. Signup and view all the answers

State the law of definite proportions.

The law of definite proportions states that a given element always contains exactly the same proportion of elements by weight. Signup and view all the answers

State Avogadro’s law.

Avogadro’s law states that at the same temperature and pressure, gases which have equal volume will contain equal number of molecules. Signup and view all the answers

Define one atomic mass unit (amu).

One atomic mass unit is defined as the mass that is exactly equivalent to 1/12th of the mass of a carbon atom. Signup and view all the answers

What is formula mass?

The formula mass is calculated by summing the atomic masses of all the individual atoms present in a material with a three-dimensional structure. Signup and view all the answers

Study Notes

What is Chemistry?

Chemistry is the study of matter and its properties, as well as how matter changes.

Contributions of Chemistry

Chemistry has played a crucial role in national development.
Examples include: advancement in weather patterns, brain function, computer operation, chemical industries, manufacturing, fertilizers, alkalis, acids, salts, dyes, polymers, medicines, soaps, detergents, metals, alloys.

States Of Matter

Solids have a definite volume and shape.
Liquids have a definite volume but take the shape of their container.
Gases have no definite volume or shape, they take the shape and volume of their container.

Separation of Mixtures

Physical methods can be used to separate components of a mixture.
These methods include: handpicking, filtration, crystallization, distillation.

Pure Substances and Mixtures

Pure Substances: glucose, gold, sodium
Mixtures: air, milk

Molecules and Compounds

Molecules: can be made up of the same or different atoms.
- Example: Hydrogen molecule (H₂)
Compounds: formed when two or more different atoms combine in a fixed ratio.
- Example: Water (H₂O)

Separation of Compounds

Components of a compound cannot be separated by physical methods, only by chemical methods.

Physical vs. Chemical Properties

Physical Properties: can be observed or measured without changing the substance's identity.
- Examples: color, odor, density, melting point, boiling point.
Chemical Properties: describe how a substance reacts with other substances.
- Examples: flammability, reactivity with acids, ability to rust.

Systems Of Measurement

The English system and the metric system are the two primary systems of measurement.

SI Unit of Density

kg/m³ (kilogram per cubic meter)

Celsius Scale

The Celsius scale has reference points of 0°C for the freezing point of water and 100°C for the boiling point of water.

SI Unit of Volume

m³ (cubic meter)
Liters (L) are commonly used but are not SI units.

Precision and Accuracy

Precision: how close repeated measurements are to each other.
Accuracy: how close a measurement is to the true value.

Significant Figures

Significant figures indicate the level of certainty in a measurement.
The number of significant figures reflects the precision of the measurement.

Law of Definite Proportions (Law of Constant Proportions)

A chemical compound always contains the same elements in the same proportion by mass, regardless of the source of the compound.

Avogadro's Law

At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.

Atomic Mass Unit (amu)

One atomic mass unit (amu) is defined as 1/12th of the mass of a carbon-12 atom.

Formula Mass

Formula mass is the sum of the atomic masses of all the atoms in a molecule or formula unit.
This concept is used for compounds that do not form discrete molecules but rather extend in a three-dimensional structure.

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Description

This quiz covers the fundamental concepts of chemistry, including the states of matter, the separation of mixtures, and the definitions of pure substances and mixtures. Explore how chemistry contributes to various industries and its role in national development through practical applications. Test your knowledge on molecules and compounds as well.