Question

1. Which of the following are pure substances?

Answer 1

1) Answer: compounds

For example H2O, CO2, KNO3, H2SO4, CH4 are all compounds. All the molecules have the same composition. The composition of a molecule of H2O is the same of all molecules of H2O.

It is not the same for solutions, mixtures or colloids.

2) Answer: both an element and made of one kind of atom.


Compounds can be broken into the elements that constitue them.

3) When a physical change in a sample occurs, a change in shape, temperature or volume can happen.

Examples:

Shape change: fold a paper
Temperature change: evaporation of water absorbs heat from the surroundings.
Volumen change: boiling liquid causes the volume to increase.

You'd likely miss one choice. Compoistion does not change when physical change occurs.

Answer 2

1. Compounds are pure substances.

2. If an unknown substance cannot be broken down into simpler substances, it is both an element and made of one kind of atom.

3. Composition does not change when a physical change in a sample occurs.

Further explanation:

Pure substances:

As is evident from the name, pure substances are supposed to be composed of only one type of atoms or molecules or if substances have constant composition.

Classification of pure substance:

1.Elements:

The simplest form of substance that cannot be disintegrated into further smaller components is termed as element. No chemical method is available that can break elements into further simpler entities.

2.Compounds:

Such type of pure substances result from chemical combination of elements but their ratios always have to be specific. Since these are made by combination of elements, these can be broken down into these entities.

Mixture:

It is formed by combination of two or more substances. It has variable composition with no fixed formula. In mixtures, retention of properties of constituents is observed. Mixtures can be homogenous (uniform composition) or heterogeneous (non-uniform composition). Solution is a homogeneous mixture comprising of two or more substances.

Colloids:

A heterogeneous mixture having size of its particles in the range of 1 nm to 1000 nm is known as colloid.Some examples of colloids are blood, milk and mist.

Physical change:

The effect of such changes can be reversed by using physical methods. In such changes, composition of substance does not change but changes in shape, texture, size, volume, temperature or color can be observed.

1. Compounds are pure substances.

2.Element cannot be broken down into simpler substances. Also, these are made up of one kind of atoms.

3. No change in composition occurs whenever a physical change takes place.

Learn more:

1. Which sample is a pure substance? brainly.com/question/2227438
2. Which is a characteristic of a mixture? brainly.com/question/1917079

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Elements, compounds, and mixtures

Keywords: mixture, pure substance, elements, compounds, colloids, physical change, solutions, homogeneous, heterogeneous, composition, volume, temperature, shape.