Science - Chapter 8: Elements, Compounds and Mixtures

What is the scientific definition of matter?

Matter is anything that has mass and takes up space.

What is a mixture?

A mixture is when two or more substances are mixed, where each substance retains its own properties and does not react chemically.

The individual substances that make up a mixture are called its _____.

components

What defines a non-uniform mixture?

A mixture where the different components are generally visible with the naked eye and are not evenly distributed.

Provide an example of a non-uniform mixture from the source material.

Sprout salad (containing green gram, chickpeas, onion, and tomato).

What defines a uniform mixture?

A mixture where the components are evenly distributed and cannot be distinguished from each other, even with a microscope.

Provide an example of a uniform mixture from the source material.

Sugar dissolved in water, or lemonade.

What is an alloy?

An alloy is a uniform mixture of two or more metals, or a metal and a small amount of non-metal, where the components are so uniformly mixed they appear as one substance.

What elements is stainless steel composed of?

It is an alloy containing iron, nickel, chromium, and a small amount of carbon.

Brass is an alloy made from a mixture of which two metals?

Copper and zinc.

Bronze is an alloy made from a mixture of which two metals?

Copper and tin.

In ancient Indian texts, what was the term for a mixture of two or more metals?

Mishraloha.

The ancient text *Charaka Samhita* mentions an alloy called Kamsya, also known as Bronze, which was used for medicinal purposes. What is its composition?

It is composed of Copper (Tamra, 4 parts) and Tin (Vanga, 1 part).

What type of mixture is air?

Air is a uniform mixture of gases.

What are the main components of air mentioned in the text?

Nitrogen, oxygen, argon, carbon dioxide, and water vapour.

What happens when lime water is exposed to air for a few hours?

It turns milky, demonstrating the presence of carbon dioxide in the air.

What chemical reaction causes lime water to turn milky?

Calcium hydroxide reacts with carbon dioxide to form calcium carbonate (insoluble white particles) and water.

What are the major air pollutants mentioned in the source material?

Particulate matter (dust, soot) and gases like carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide.

What tool is used to describe air quality?

The air quality index (AQI).

In scientific terms, what must the components of a mixture be?

The components of a mixture must be pure substances only.

Classify the mixture of oil and water.

It is a non-uniform mixture of two liquids.

Classify seawater as a mixture type.

Seawater is a uniform mixture of a solid (salt) and a liquid (water).

In common usage, what does the word 'pure' mean when seen on food packs?

It means the product is unadulterated.

What is the scientific definition of a pure substance?

A pure substance is a kind of matter that cannot be separated into other kinds of matter by any physical process and consists of the same type of particles.

When electricity is passed through water (electrolysis), what two gases are produced?

Hydrogen gas and oxygen gas.

How can you test for the presence of hydrogen gas?

Bringing a burning candle near the mouth of the test tube will produce a 'pop' sound.

How can you test for the presence of oxygen gas?

The flame of a burning candle brought near the mouth of the test tube will glow brighter.

What is an element?

An element is a pure substance that cannot be further broken down into simpler substances and is made up of identical particles called atoms.

What is a molecule?

A molecule is a stable particle formed when two or more atoms combine.

How many elements are known at present?

There are 118 known elements.

Which two elements are liquid at room temperature?

Mercury (a metal) and bromine (a non-metal).

Which elements, although solid, become liquid around $30 ^\circ C$?

Gallium and caesium.

Elements like silicon and boron, which have intermediate properties between metals and non-metals, are called _____.

metalloids

What is a compound?

A compound is a pure substance formed when different elements combine chemically in a fixed ratio, creating something new with different properties.

What is the ratio of the number of atoms of hydrogen to oxygen in a water molecule?

The ratio is 2:1.

What is the chemical name for common salt, and what is the ratio of its constituent atoms?

Sodium chloride, made of sodium and chlorine atoms in a 1:1 ratio.

When sugar is heated, it decomposes. What are the products of this decomposition?

It decomposes into carbon (charcoal) and water.

Sugar is a compound consisting of which three elements?

Carbon, hydrogen, and oxygen.

In the experiment with iron and sulfur, what is Sample A?

Sample A is a non-uniform mixture of iron filings and sulfur powder.

How can the components of the iron-sulfur mixture (Sample A) be separated?

They can be separated using a magnet, which attracts the iron filings.

When the iron-sulfur mixture (Sample A) is heated, it forms a new substance (Sample B). What is this new substance?

A compound called iron sulfide.

How do the properties of iron sulfide (Sample B) differ from the original mixture (Sample A) regarding magnetism?

Iron sulfide is not attracted by a magnet, unlike the iron in the original mixture.

When dilute hydrochloric acid is added to the iron-sulfur mixture (Sample A), what gas is produced?

Hydrogen gas, which is colourless, odourless, and burns with a 'pop' sound.

When dilute hydrochloric acid is added to iron sulfide (Sample B), what gas is produced?

Hydrogen sulfide gas, which is colourless and has a rotten egg-like odour.

What is graphene aerogel, and what is its most notable physical property?

It is a material made from carbon that is said to be the lightest material on earth.

Due to its high porosity and absorbing capacity, what is a potential environmental use for graphene aerogel?

It can be used to clean up oil spills in seas and on land.

What are minerals?

Minerals are natural, solid substances found on the Earth that have a fixed chemical composition.

What are native minerals?

Native minerals are minerals that are pure elements and not compounds, such as gold, silver, or carbon.

Talcum powder is made from which mineral?

The mineral talc.

Name two examples of things that are not made of matter.

Light, heat, electricity, thoughts, and emotions.

What is Dhokra art?

It is an old craft from Bihar and Odisha that uses the lost-wax casting technique to create figures from molten brass or bronze.

A _____ substance consists of only one type of particle.

pure

What is the key difference between how a compound and a mixture are formed?

A compound is formed by a chemical combination of elements in a fixed ratio, while a mixture is a physical blending of substances in any ratio.

Can the constituent elements of a compound be separated by physical methods?

No, they can only be separated by chemical reactions.

Classify carbon dioxide.

Compound.

Classify sand.

Mixture (primarily silicon dioxide, but with impurities).

Classify magnesium oxide.

Compound.

Classify aluminium.

Element.

Classify gold.

Element.

Classify oxygen.

Element.

Classify rust.

Compound (hydrated iron oxide).

Classify iron sulfide.

Compound.

Classify glucose.

Compound.

Classify fruit juice.

Mixture.

Classify nitrogen.

Element.

Classify sulfur.

Element.

Classify hydrogen.

Element.

Classify baking soda.

Compound (sodium bicarbonate).

Classify muddy water.

Non-uniform mixture.

How can gold be classified as both a mineral and a metal?

Gold is a metal because of its physical and chemical properties, and it is also a native mineral because it is found in nature as a pure element.

In the reaction: Iron + Dilute Hydrochloric acid $\rightarrow$ Iron chloride + Hydrogen gas, classify each substance.

Iron: Element; Dilute Hydrochloric acid: Mixture; Iron chloride: Compound; Hydrogen gas: Element.

What defines adulteration?

It is the illegal process of adding cheaper or poor-quality substances to a product, usually to increase quantity or reduce manufacturing costs.