Test your knowledge with the 10 questions below about substances and mixtures. Clear your doubts about the topic with the comments after the feedback.
Which of the following does NOT belong to a substance?
a) It has a defined composition
b) Has constant physical properties
c) Contains a single type of constituent
d) It is made up of molecules
A substance is a portion of matter that has a defined chemical composition, that is, it consists of only one type of component, which can be atoms, molecules or ionic species. It is also characterized by having constant physical properties.
All matter is formed by atoms which, in turn, are organized into chemical species, such as molecules and ionic compounds, which constitute the diversity of materials that we know.
One way to recognize a pure substance, that is, one that has a fixed composition, is through its constant physical properties, such as
a) Melting and boiling temperature
b) Mass and volume
c) Elasticity and discontinuity
d) Inertia and extension
Melting temperature (TF) is the temperature at which a substance changes from a solid state to a liquid state. The boiling temperature (TE) is the temperature required for the substance to change from the liquid state to the gaseous state.
Each substance has its own characteristics and pure substances have a constant melting temperature (TF) and boiling temperature (TE) at a given pressure.
For example, distilled water is a pure substance because it is made up of only water molecules. Under a pressure of 1 atm, the TF of water is 0°C and the TE is 100°C.
Mass, volume, elasticity, discontinuity, inertia and extension are general properties of matter, that is, they apply to any matter, regardless of its constitution.
mineral water is
a) a pure substance
b) a simple substance
c) a compound substance
d) a mixture
a) WRONG. Mineral water has other components besides water molecules in its constitution.
b) WRONG. Simple substances are made up of atoms of just one chemical element, such as oxygen gas (O2).
c) WRONG. Compound substances have at least two chemical elements in their composition, such as carbon dioxide (CO2).
d) CORRECT. Mineral water is a homogeneous mixture, that is, we only see a single phase, but it is composed of different substances. Different chemical species are found dissolved in mineral water, such as calcium, magnesium, potassium and bicarbonate.
Carbon dioxide (CO2), water (H2O), sodium chloride (NaCl) and methane (CH4) are examples of
a) Ionic compounds
b) Compound substances
c) Molecular compounds
d) Simple substances
Compound substances are made up of atoms or ions of different chemical elements.
Carbon dioxide (CO2): made up of carbon (C) and oxygen (O)
Water (H2O): made up of hydrogen (H) and oxygen (O)
Sodium chloride (NaCl): made up of sodium (Na) and chlorine (Cl)
Methane (CH4): made up of carbon (C) and hydrogen (H)
a) WRONG. Only sodium chloride (NaCl) is formed by ionic bonding.
c) WRONG. With the exception of sodium chloride, the other compounds are formed by covalent bonds.
d) WRONG. All substances contain more than one chemical element in the composition.
Nitrogen (N2), oxygen (O2), argon (Ar), helium (He), neon (Ne) and krypton (Kr) are simple substances and the main constituents of atmospheric air.
As for atomicity, which gases mentioned above are diatomic?
a) nitrogen and oxygen
b) argon and helium
c) neon and krypton
d) All alternatives are correct
Simple substances are formed by a single chemical element, but their composition can have more than one atom.
Atomicity is then the number of atoms in a simple substance.
Monatomic substances have only one atom, such as argon (Ar), helium (He), neon (Ne) and krypton (Kr).
Diatomic substances, such as nitrogen (N2) and oxygen (O2), are formed by two atoms of the chemical element.
1. water and ice
2. water and oil
3. homemade serum
4. hydrated alcohol
Analyze the statements about the systems above.
I. Systems 1 and 4 are made up of only one component.
II. 3 and 4 have the same number of phases.
III. 2 and 4 have the same number of components.
IV. All systems are heterogeneous
The statements are correct:
a) I and II
b) II and III
c) III and IV
d) None of the statements
I. WRONG. The saline solution (3) has three components: water, salt and sugar. Hydrated alcohol (4) has two components: alcohol and water.
II. CORRECT. Saline (3) and hydrated alcohol (4) have a single phase.
III. CORRECT. The water and oil system (2) has two components, as well as hydrated alcohol (4), which is formed by alcohol and water.
IV. WRONG. 2 is an example of a heterogeneous mixture; 3 and 4 are homogeneous mixtures and 1 is formed by only one component in different physical states.
The alternative that does NOT present a mixture is
Metallic iron is a material with atoms joined by metallic bonds. It can be obtained from ores and isolated through chemical reactions.
a) WRONG. Blood is a colloidal solution, as seen with the naked eye it appears homogeneous, but microscopically it is possible to see its components.
b) WRONG. Air is a mixture of gases such as nitrogen, oxygen and carbon dioxide.
c) WRONG. Rainwater has dissolved substances and is therefore a mixture.
Which of the following systems forms an azeotropic mixture?
a) Ethyl alcohol + water
b) Sodium chloride + water
c) Soybean oil + olive oil
d) sugar + water
Azeotropic mixtures behave similarly to pure substances, but are formed by more than one component.
An azeotrope, such as ethyl alcohol + water, is characterized by keeping the boiling point constant and fixed in the change of physical state, even being formed by different compounds.
b) WRONG. Water and salt (sodium chloride) form a homogeneous mixture.
c) WRONG. Soybean oil and olive oil form a homogeneous mixture.
d) WRONG. Water and sugar form a homogeneous mixture.
(PUC-MG) Consider the following propositions:
I. There is no polyphase system formed from several gases or vapors.
II. Water is a mixture of hydrogen and oxygen.
III. Every homogeneous system is a homogeneous mixture.
IV. There is a single-phase system formed by several solids.
v. Every polyphase system is a heterogeneous mixture.
The following statements are true:
a) I, II and III
b) I and II only
c) I and IV only
d) III, IV and V
I. CORRECT. A mixture of gases forms a single-phase system.
II. WRONG. Water (H2O) is a substance made up of hydrogen (H) and oxygen (O).
III. WRONG. A homogeneous system can be a homogeneous mixture or a pure substance.
IV. CORRECT. Bronze, for example, is formed by a mixture of copper and tin metals.
v. WRONG. A glass of ice water has more than one phase, but the component is the same.
(UEL-PR) A boy asked his girlfriend to marry him, presenting her with an 18 carat gold ring.
To celebrate, knowing that alcohol is harmful to health, they toasted with ice carbonated water, outdoors. The systems: 18 carat gold, carbonated water with ice and atmospheric air are, respectively:
a) heterogeneous substance, heterogeneous mixture and homogeneous mixture.
b) heterogeneous mixture, homogeneous mixture and homogeneous substance.
c) homogeneous substance, heterogeneous mixture and homogeneous mixture.
d) homogeneous mixture, heterogeneous mixture and homogeneous mixture.
e) heterogeneous mixture, homogeneous substance and heterogeneous substance.
18 carat gold: a homogeneous mixture of gold, silver and copper.
Carbonated water with ice: heterogeneous mixture, as you can see the carbon dioxide bubbles in the water.
Atmospheric air: homogeneous mixture of gases and vapours.