Properties of substances

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Physical vs. Chemical Changes

Physical changes do not change the chemical properties of a substance; examples include cutting, boiling, melting, dissolving, and whipping.
Chemical changes (chemical reactions) transform one or more substances into new substances with different properties.
Examples of chemical changes: burning gas, milk turning sour, iron rusting, frying eggs.
Physical changes are often reversible, while chemical changes are usually not (e.g., you can't unbake a cake).

Melting and freezing of water

Signs of a Chemical Reaction

Color change occurs (not just mixing colors).
Gas formation – often seen as bubbles (not boiling).
Formation of a solid – a precipitate or crystals appear in a liquid.
Odor change – a new smell is produced.
Energy change – heat, light, sound, or cold is produced or absorbed.
Extreme property changes – e.g., changes in density, flammability, or state.
The only definitive sign is the formation of a new substance.

Everyday chemical reactions show new substances with different properties

Reactants and Products

Reactants are the starting substances in a chemical reaction.
Products are the new substances formed by the reaction.
Comparing the properties of the reactants and products (colour, state, odor, and so on) is how we tell that a reaction has taken place.

Properties of Materials

Properties are distinctive characteristics that describe a material.
Important properties include: strength, durability, flexibility, malleability, ductility, electrical conductivity, heat conductivity, hardness, solubility, density, color, odor, state, melting point, boiling point, and flammability.
Materials are chosen for specific uses based on their properties.
Advantages are desirable properties; disadvantages are unfavorable features (e.g., plastic bags are strong but cause pollution).
Strength can be measured by testing how much force is needed to break a material (e.g., tearing paper with marbles).

Testing paper strength with marbles in a yoghurt tub

Heat and Temperature

Heat is the transfer of energy between objects due to a temperature difference.
Temperature measures how hot or cold something is; it is measured with a thermometer.
Adding heat usually raises temperature, but during a phase change, temperature stays constant.
Heat and temperature are related but not the same.

Melting and Boiling Points

Melting point is the temperature at which a solid changes to a liquid.
Boiling point is the temperature at which a liquid changes to a gas (bubbles form).
For pure water, melting point is 0°C and boiling point is 100°C at sea level.
Boiling point depends on atmospheric pressure (lower at high altitudes) and purity (impurities raise it).
Different substances have different melting and boiling points (e.g., nitrogen boils at -200°C, ethanol at 78°C).

Apparatus for determining the boiling point of water

Matter and Classification

Matter is anything that has mass and volume.
Matter can be classified as pure substances (elements or compounds) or mixtures.
Elements consist of one kind of atom; compounds consist of two or more kinds of atoms chemically bonded in a fixed ratio.
Mixtures contain more than one kind of particle and can be separated by physical methods.
Physical separation methods (e.g., filtering, evaporation) cannot break chemical bonds.

Diagrams to show the difference between elements, compounds and mixtures

Chemical Reactions in Everyday Life

Cooking involves chemical reactions (e.g., baking bread changes ingredients into a new substance).
Burning (combustion) is a chemical reaction (e.g., burning gas, logs).
Rusting is a chemical reaction between iron and oxygen.
Digestion and photosynthesis are examples of chemical reactions in living organisms.
Indigenous practices often use chemical reactions, such as making dyes or preserving food.

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1.Which of the following is a physical property of a material?
Easy
- AFlammability
- BReactivity with acid
- CMalleability
- DAbility to rust
2.Which of the following is a chemical property of a substance?
Easy
- ADensity
- BMelting point
- CFlammability
- DElectrical conductivity
3.A pure substance is best defined as:
Easy
- AA material that is composed of only one type of matter throughout
- BA material that is natural and not man-made
- CA material that is a solid at room temperature
- DA material that cannot be separated by physical means
4.Which of the following are signs that a chemical reaction may have taken place? (Select all that apply)
Medium
- AA color change occurs
- BThe substance changes state from solid to liquid
- CBubbles of gas are produced
- DA solid precipitate forms from a solution
- EThe substance dissolves in water
5.Arrange the following steps in the correct order to determine the boiling point of water experimentally.
Medium
- Heat the water with a Bunsen burner
- Record the temperature when it becomes constant
- Set up the apparatus with a thermometer in the beaker
- Measure the initial temperature of the water
6.Match each property of a material with its correct description.
Medium
- Malleability
- Ductility
- Flexibility
- Solubility
- Ability to be hammered into sheets
- Ability to be drawn into wires
- Ability to bend without breaking
- Ability to dissolve in a solvent
7.The boiling point of water is always exactly 100°C.
Easy
True or false?
8.A student mixes baking soda and vinegar in a beaker and observes bubbles forming. The beaker feels colder. What is the most likely conclusion?
Medium
- AA physical change occurred because bubbles are always a sign of a physical change.
- BA chemical reaction occurred, producing a new gas and absorbing energy.
- CThe substances simply mixed without any new substance forming.
- DThe beaker became colder because the vinegar was cold.

Thêm câu hỏi

9.Which of the following are physical properties? (Select all that apply)
Medium
- AMelting point
- BReactivity with acid
- CDensity
- DAbility to rust
- EOdor
10.Match each substance with the correct classification (element, compound, or mixture).
Medium
- Oxygen gas (O2)
- Water (H2O)
- Air
- Salt (NaCl)
- Element
- Compound
- Mixture
11.In the investigation to determine the boiling point of water, the temperature becomes constant even though heating continues. What does this constant temperature represent?
Medium
- AThe boiling point of water
- BThe melting point of water
- CThe temperature at which water evaporates
- DThe temperature of the Bunsen burner flame
12.In the naked egg experiment, what observation on the eggshell after a few minutes indicates that a chemical reaction is taking place?
Easy
- ABubbles forming on the surface of the eggshell
- BThe eggshell turning brown
- CThe egg sinking to the bottom
- DThe vinegar turning clear
13.In the paper investigation, the crumpled piece of paper had a different odor compared to the solid piece of paper.
Easy
True or false?
14.A student heats a mixture of ethanol (boiling point 78°C) and water (boiling point 100°C) at room temperature. What will happen first?
Hard
- AThe ethanol will begin to boil at 78°C.
- BThe water will begin to boil at 100°C.
- CBoth will boil simultaneously at 78°C.
- DThe mixture will boil at 89°C.
15.In the paper strength investigation, why is it important to punch the holes at the same distance from the end of each paper strip?
Medium
- ATo ensure the paper strips are all the same length
- BTo make the test fair by keeping the distance from the hole to the edge the same for each strip
- CTo make the paper strips easier to hold
- DTo allow the paper clips to fit through the holes
16.A student measures the boiling point of tap water and gets 101.5°C. Which of the following is the most likely reason for this value being higher than 100°C?
Medium
- AThe thermometer is broken
- BThe water contains impurities such as dissolved salts
- CThe altitude is very high
- DThe Bunsen burner flame was too large
17.Which of the following is the definition of a chemical reaction?
Easy
- AA process in which one or more substances are changed into new substances
- BA process in which a substance changes state without forming new substances
- CA process in which substances are mixed together without any change
- DA process in which a substance is separated into its components
18.Which of the following is a physical change?
Easy
- ABurning paper
- BRusting iron
- CMelting ice
- DMilk turning sour
19.Which of the following is a chemical change?
Easy
- ACutting paper
- BBoiling water
- CFrying an egg
- DDissolving sugar in water
20.Which of the following is a mixture?
Easy
- APure water
- BOxygen gas
- CSalt water
- DCarbon dioxide
21.In the paper investigation, which piece of paper showed evidence of a chemical change?
Medium
- AThe torn piece
- BThe crumpled piece
- CThe burned piece
- DThe solid piece
22.Which of the following is NOT a sign that a chemical reaction may have occurred?
Medium
- AA color change
- BFormation of a gas
- CA change in state from solid to liquid
- DFormation of a precipitate
23.Water boils at a lower temperature at higher altitudes because the air pressure is lower.
Medium
True or false?
24.A chemical reaction can be undone by a physical change.
Easy
True or false?
25.Evaporation can occur at any temperature, but boiling only occurs at the boiling point.
Easy
True or false?
26.Which property of a material is important when choosing a material for making electrical wires?
Medium
- AMalleability
- BElectrical conductivity
- CMelting point
- DFlexibility
27.Which property of a material is important when choosing a material for making cookware?
Medium
- AElectrical conductivity
- BHeat conductivity
- CMalleability
- DFlexibility
28.Complete the sentence.
Easy
A material that can be hammered or rolled into thin sheets without breaking is said to be ____.
29.Complete the sentence about the signs of a chemical reaction.
Easy
When a solid forms from a solution during a chemical reaction, it is called a ____.
30.What is the term for the temperature at which a solid changes into a liquid?
Easy
31.What is the term for the temperature at which a liquid boils?
Easy
32.In the paper strength investigation, a strip of paper tore when an average of 8 marbles was used. Each marble has a mass of 5 grams. What mass (in grams) was needed to tear the paper?
Easy
33.Fill in the blanks with the correct terms.
Easy
The temperature at which a solid changes into a liquid is called the ____ point, and the temperature at which a liquid changes into a gas is called the ____ point.
34.Explain why burning paper is a chemical change, while tearing paper is a physical change. Use properties in your explanation.
Medium
35.In the paper investigation, explain why the burned piece of paper is considered to have undergone a chemical change while the torn and crumpled pieces have not. Use evidence from the data.
Hard
36.In the investigation to determine the boiling point of water, the temperature becomes constant even though heating continues. What does this constant temperature indicate, and why does it stay constant?
Medium
37.A camping stove burns propane gas to cook food. State ONE piece of evidence a person could observe that shows a chemical reaction is taking place during this combustion.
Medium
38.A student makes pancakes and records observations at each step. | Step | Ingredients added | Observations | |---|---|---| | 1. Combine dry ingredients | Flour, salt, sugar, baking powder | White powder in bowl | | 2. Add liquid, mix to batter | Egg, milk, oil, vanilla | Powder becomes a liquid batter with small bubbles | | 3. Heat batter in a pan | None | Top stays white; more bubbles appear | | 4. Flip and heat other side | None | Flipped side turns brown | | 5. Remove from heat | None | Both sides brown, middle white and solid | Which step gives the best evidence that a chemical reaction took place?
Medium
- ACombining the dry ingredients in a bowl
- BAdding the liquid ingredients and mixing
- CHeating the batter in the pan
- DRemoving the pancake from the heat
39.Rust is produced when iron reacts with oxygen and water. The reaction is shown below. Which statement correctly identifies a property of the substances that is different before and after this reaction has taken place?
Medium
- ABefore the reaction, oxygen is a gas; after the reaction, oxygen is part of a solid (rust).
- BBefore the reaction, iron is a solid; after the reaction, rust is a solid.
- CBefore the reaction, water is a vapor; after the reaction, water is a liquid.
- DBefore the reaction, the substances are a solid, a liquid, and a gas; after the reaction, the substances are a solid and a gas.
40.A student tests whether water and oxygen are both needed for iron to rust. Three steel nails are sealed in test tubes, shown below. - Test tube 1: nail partly in water, with air (containing oxygen) above the water. - Test tube 2: nail in boiled (oxygen-free) water, sealed under a layer of oil so no more oxygen can get in. - Test tube 3: nail in air, with a chemical that removes water vapor from the air. After three weeks: | Test tube | Rust formed | Rust did not form | |---|---|---| | 1 | Yes | | | 2 | | Yes | | 3 | | Yes | Use the results to explain why rust did or did not form in ONE of the test tubes.
Medium
41.A student compares an uncooked egg with a hard-boiled egg. | Object | Observations | |---|---| | Uncooked egg | clear, thick, cool liquid; round, cool, yellow liquid; broken, cool eggshell | | Hard-boiled egg | warm, white solid; warm, yellow solid; broken, warm eggshell | The student claims a chemical change occurred while the eggs were boiled. Which observation best supports this claim?
Medium
- AThe eggshell went from cool to warm.
- BThe clear liquid turned into a white solid that cannot be changed back into a liquid by cooling it.
- CThe egg white and egg yolk are still two different colors.
- DThe egg was broken both before and after boiling.
42.In which of the following situations is a sugar cube undergoing a chemical change?
Easy
- AWhen it is burned
- BWhen it is crushed
- CWhen it is mixed with salt
- DWhen it is dissolved in water
43.A scientist heats an unknown liquid and measures its temperature every 3 minutes. The graph below shows her results. At what temperature (in °C) does the unknown liquid boil?
Medium
44.Use the boiling point you read from the graph and the table below to identify the unknown liquid. | Substance | Boiling point (°C) | |---|---| | Acetone | 56 | | Methanol | 65 | | Ethanol | 78 | | Isopropanol | 83 | | Water | 100 | Which substance is the unknown liquid?
Medium
- AAcetone
- BMethanol
- CEthanol
- DWater

Ghi chú ôn tập

## Properties of Substances A **substance** is matter with constant chemical composition and characteristic properties. Substances can be elements (e.g., diamond, carbon) or compounds (e.g., water H₂O, table salt NaCl). Pure substances have fixed composition; mixtures combine substances without chemical reaction. ### Physical vs. Chemical Properties - **Physical properties**: observed without changing composition (e.g., melting point, boiling point, density, state of matter). - **Chemical properties**: describe ability to react or transform into new substances (e.g., flammability, reactivity). ### Identifying Pure Substances - Pure substances have **constant composition** (law of constant composition). - Examples: pure water (H₂O) always boils near 100°C; diamond is pure carbon. - Mixtures (e.g., alloys, rocks) are not pure substances. ### Phase Changes Substances can change state (solid, liquid, gas) without altering chemical identity. Changes occur with temperature/pressure. ### Chemical Reactions - Reactants → Products; new substances form. - Evidence of reaction: color change, gas production, temperature change, precipitate formation. ### Key Points - **Inert substances** do not react easily. - **Isomers** have same composition but different atomic arrangement (e.g., tartaric acid isomers). - Polymers (e.g., polyethylene) are mixtures of chains with varying lengths. Remember: Characteristic properties (like boiling point) help identify substances and detect chemical changes.

Substance: A unique form of matter with constant chemical composition and characteristic properties.
Pure substance: A substance that is chemically uniform and has a fixed composition (element or compound).
Chemical property: A property that describes a substance's ability to undergo a chemical change (e.g., reactivity, flammability).
Physical property: A property that can be observed without changing the substance's chemical identity (e.g., melting point, density).
Law of constant composition: All samples of a compound have the same proportions by mass of the elements present.
Mixture: A combination of two or more substances that are not chemically bonded.
Chemical reaction: A process that transforms one or more substances into new substances with different properties.
Isomer: One of two or more compounds with the same molecular formula but different arrangement of atoms.

Thẻ ghi nhớ

What is a chemical substance?

A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. It can be a single element or a chemical compound.

What is the law of constant composition?

The law of constant composition states that all samples of a compound have the same proportions, by mass, of the elements present in the compound.

Give an example of a pure chemical substance.

Pure water (H2O) is an example of a chemical substance with constant composition of two hydrogen atoms bonded to one oxygen atom.

What are characteristic properties of a substance?

Characteristic properties are unique physical or chemical properties that define a substance, such as boiling point, melting point, density, or reactivity.

What is the boiling point of pure water?

Pure water boils near 100 °C (212 °F) at standard atmospheric pressure.

What is a chemical mixture?

A chemical mixture is formed when two or more chemical substances are combined without reacting. The substances retain their individual properties.

What does it mean for a substance to be chemically pure?

A chemically pure substance is isolated from a mixture to a desired degree, containing only one type of chemical substance with no contaminants.

List three examples of chemical substances mentioned in the source.

Diamond (carbon), table salt (NaCl), and refined sugar (C12H22O11).

What is the difference between a pure substance and a mixture?

A pure substance has constant composition and characteristic properties, while a mixture consists of two or more substances physically combined without fixed composition.

Can a chemical substance exist in different physical states?

Yes, chemical substances can exist as solids, liquids, gases, or plasma without changing their chemical composition, in response to temperature or pressure changes.

What is an inert chemical?

An inert chemical does not readily undergo chemical reactions; it lacks the ability to be combined or converted into new substances under normal conditions.

What is an isomer?

An isomer is a compound with the same molecular formula but different arrangement of atoms, leading to different properties.

What is stereoisomerism?

Stereoisomerism is a type of isomerism where atoms have the same connectivity but differ in their three-dimensional arrangement in space.

What is a mineral in geology?

A mineral is an inorganic solid substance of uniform composition found in nature.

What is a rock in geology?

A rock is a mixture or aggregate of two or more minerals.

What are characteristic physical properties?

Characteristic physical properties include melting point, boiling point, density, solubility, and color, which can help identify a substance.

What are characteristic chemical properties?

Characteristic chemical properties describe how a substance reacts with other substances, such as flammability, acidity, or reactivity with water.

How can you determine if a chemical reaction has occurred?

A chemical reaction is indicated by changes in characteristic properties, such as color change, gas production, temperature change, or formation of a precipitate.

What is the atomic ratio of hydrogen to oxygen in water?

In every molecule of water, the atomic ratio of hydrogen to oxygen is always 2:1.

What is the chemical formula of table salt?

Table salt is sodium chloride with the chemical formula NaCl.

What is the chemical formula of refined sugar?

Refined sugar is sucrose with the chemical formula C12H22O11.

What is a non-stoichiometric compound?

A non-stoichiometric compound is a substance that does not have a fixed ratio of elements, violating the law of constant composition.

What is an alloy?

An alloy is a mixture of metals, often with uncertain composition, but sometimes referenced as a chemical substance for indexing purposes.

What is a polymer?

A polymer is a large molecule made of repeating subunits, often existing as a mixture of molecules with different chain lengths.

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