what is the difference between a pure substance and a mixture

ATI TEAS 7

TEAS 7 science study guide free

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

A. Pure substances have a fixed composition, mixtures don't.
B. Mixtures have a fixed composition, pure substances don't.
C. Pure substances can be in any state, mixtures are not always solids.
D. Pure substances are always elements, mixtures are always compounds.

Correct answer: A

Rationale: Pure substances have a definite and constant composition, meaning they are made up of only one type of atom or molecule with fixed proportions. This composition does not vary. On the other hand, mixtures are composed of two or more substances physically combined. The components of a mixture can be present in varying proportions, leading to a variable composition. Choice A is correct as it accurately distinguishes between pure substances and mixtures based on the fixed composition of pure substances and the variable composition of mixtures. Choice B is incorrect because mixtures, not pure substances, have variable compositions. Choice C is incorrect as both pure substances and mixtures can exist in different states. Choice D is incorrect because pure substances can be compounds as well, not exclusively elements, and mixtures can contain elements and compounds.

2. Which of the following is NOT a function of the lymphatic system?

A. Removing substances from the blood.
B. Releasing hormones.
C. Combating disease.
D. Maintaining tissue fluid balance.

Correct answer: B

Rationale: The correct answer is B. Releasing hormones is not a function of the lymphatic system. The lymphatic system plays crucial roles in removing substances from the blood, combating disease through the production of immune cells, and maintaining tissue fluid balance by circulating lymph. Releasing hormones is primarily the function of endocrine glands, not the lymphatic system.

3. Which term describes a substance's ability to undergo a change that transforms it into a different substance?

A. Density
B. Mass
C. Reactivity
D. Volume

Correct answer: C

Rationale: Reactivity refers to a substance's ability to undergo a change that transforms it into a different substance through a chemical reaction. In this context, reactivity specifically refers to the chemical behavior of a substance. Density, mass, and volume are physical properties of a substance and do not describe its ability to undergo a chemical change. Density is the mass per unit volume, mass is the amount of matter in an object, and volume is the amount of space occupied by an object. Therefore, reactivity is the most appropriate term to describe a substance's ability to undergo a transformation into a different substance.

4. Which statement most accurately compares and contrasts the structures of DNA and RNA?

A. Both DNA and RNA have 4 nucleotide bases. Three of the bases are the same, but the fourth base is thymine in DNA and uracil in RNA.
B. Both DNA and RNA have the same 4 nucleotide bases. However, the nucleotides bond differently in DNA compared to RNA.
C. Both DNA and RNA have different numbers of nucleotide bases. DNA is a double helix while RNA is a single strand.
D. Both DNA and RNA have a double helix structure. However, DNA contains 6 nucleotide bases and RNA contains 4 nucleotide bases.

Correct answer: A

Rationale: The correct answer is A because DNA and RNA both consist of 4 nucleotide bases, namely adenine, cytosine, and guanine, which are common in both. The key difference lies in the fourth base, which is thymine in DNA and uracil in RNA. This distinction is fundamental in understanding the structural variances between DNA and RNA. Choice B is incorrect as it incorrectly states that the nucleotides bond differently in DNA compared to RNA without specifying the crucial base differences. Choice C is inaccurate as it misrepresents the numbers of nucleotide bases in DNA and RNA, and incorrectly describes DNA as a double helix and RNA as a single strand, which is not related to the difference in bases. Choice D is incorrect as it inaccurately portrays DNA with 6 nucleotide bases and RNA with 4, which is not true; both DNA and RNA have 4 nucleotide bases, but with differences in one of the bases.

5. What is the law of conservation of energy?

A. Energy cannot be created, only destroyed
B. Energy can be created but not destroyed
C. Energy can neither be created nor destroyed, only transformed from one form to another
D. Energy is always created in any process

Correct answer: C

Rationale: The correct answer is C: 'Energy can neither be created nor destroyed, only transformed from one form to another.' The law of conservation of energy is a fundamental principle in physics. It states that the total energy in a closed system remains constant over time. Energy can change from one form to another (e.g., potential energy to kinetic energy), but the total amount of energy remains the same. Choices A, B, and D are incorrect because they do not accurately represent the law of conservation of energy. Energy is not created or destroyed according to this law, but rather transformed.