Pure Substances
What is a pure substance?
A. Matter with a fixed chemical composition
B. Matter made of different substances physically combined
C. Matter that has no definite properties
D. Matter that changes its composition easily
A. Matter with a fixed chemical composition
What is an element?
A. A mixture of different substances
B. A pure substance made of one type of atom
C. A substance made of two or more compounds
D. A substance that always contains water
B. A pure substance made of one type of atom
What is the atomic number of an atom?
A. Number of protons
B. Number of neutrons
C. Number of electrons and neutrons
D. Total number of particles in the nucleus
A. Number of protons
What is a compound?
A. A substance made of only one type of atom
B. A substance formed when two or more different elements are chemically combined
C. A substance made of physically combined materials
D. A substance with no fixed composition
B. A substance formed when two or more different elements are chemically combined
Which statement best describes a mixture?
A. It contains two or more substances physically combined.
B. It contains only one type of atom.
C. It has a fixed chemical composition.
D. It is always made of chemically combined elements.
A. It contains two or more substances physically combined.
Which of the following is an example of a pure substance?
A. Soil
B. Air
C. Gold
D. Saltwater
C. Gold
Which of the following is an element?
A. Water
B. Carbon dioxide
C. Oxygen
D. Saltwater
C. Oxygen
What is the atomic number of hydrogen?
A. 2
B. 6
C. 1
D. 8
C. 1
Which is the chemical formula of water?
A. CO₂
B. O₂
C. H₂O
D. Na
C. H₂O
Which of the following is a mixture?
A. Gold
B. Oxygen
C. Pure water
D. Saltwater
D. Saltwater
Which two are examples of pure substances?
A. Air and soil
B. Elements and compounds
C. Saltwater and air
D. Soil and saltwater
B. Elements and compounds
Which symbol represents gold?
A. Gd
B. Go
C. Au
D. Ag
C. Au
An atom has 6 protons. What is its atomic number?
A. 8 B. 11 C. 17 D. 6
D. 6
What elements make up carbon dioxide (CO₂)?
A. Carbon and oxygen
B. Hydrogen and oxygen
C. Sodium and chlorine
D. Carbon and hydrogen
A. Carbon and oxygen
Which statement correctly compares an element and a compound?
A. Both are made of only one type of atom.
B. An element has one type of atom, while a compound contains different elements chemically combined.
C. An element is a mixture, while a compound is not.
D. Both have compositions that can vary.
B. An element has one type of atom, while a compound contains different elements chemically combined.
Which statement describes a pure substance?
A. Its composition can vary.
B. It contains substances physically combined.
C. It always has different properties in every sample.
D. It has a definite and constant composition.
D. It has a definite and constant composition.
What determines the identity of an element?
A. Number of electrons
B. Number of protons
C. Number of neutrons
D. Size of the atom
B. Number of protons
Which element has an atomic number of 17?
A. Oxygen B. Chlorine C. Sodium D. Carbon
B. Chlorine
Why is water considered a pure substance?
A. Its composition changes depending on its amount.
B. It contains different substances physically combined.
C. It is always made of hydrogen and oxygen in a fixed ratio.
D. It contains only one type of atom.
C. It is always made of hydrogen and oxygen in a fixed ratio.
A student adds different amounts of salt to water. Why is saltwater considered a mixture?
A. Salt and water are chemically combined in a fixed ratio.
B. Saltwater contains only one type of atom.
C. The amount of salt can vary.
D. Saltwater has the same composition in every sample.
C. The amount of salt can vary.
A student compares a drop of pure water with a bucket of pure water. What is true about their chemical composition?
A. The bucket contains different elements.
B. The drop has less oxygen than hydrogen.
C. Both have the same chemical composition.
D. Their chemical compositions are different because of their sizes.
C. Both have the same chemical composition
An atom has 8 protons. Which element is it?
A. Carbon
B. Hydrogen
C. Sodium
D. Oxygen
D. Oxygen
An atom has 11 protons. Which statement is correct?
A. Its atomic number is 11, and it is sodium.
B. Its atomic number is 8, and it is oxygen.
C. Its atomic number is 17, and it is chlorine.
D. Its atomic number is 6, and it is carbon.
A. Its atomic number is 11, and it is sodium.
A student examines water from two different samples of pure water. What should the student expect?
A. The samples have different elements because they came from different sources.
B. One sample contains only hydrogen.
C. The samples have the same fixed chemical composition.
D. The samples are mixtures because water contains two elements.
C. The samples have the same fixed chemical composition.
An atom loses an electron but keeps the same number of protons. What happens to its identity as an element?
A. It becomes a different element.
B. It remains the same element because its number of protons does not change.
C. It becomes a compound.
D. Its atomic number becomes zero.
B. It remains the same element because its number of protons does not change.