q1 chemistry: u1l7 unit 1 review
teacher: ____________
date: ____________
3. ** which statement correctly describes a mixture?
a. a mixture can consist of a single element
b. a mixture must have a uniform composition.
c. a mixture can be separated by physical means.
d. a mixture is always homogeneous.
4. one similarity between all mixtures and compounds is that both:
a. are heterogeneous
b. are homogeneous
c. combine in a uniform fashion
d. consist of two or more substance
5. **name two processes that can be used to separate two clear, miscible liquids. when would a scientist choose to use one of these methods over the other?
6. **which property of a substance is used to separate the liquids in question #3?
(a) melting point
(b) density
(c) boiling point
(d) solubility
7. what method would a scientist use to separate sand from water? justify your response.
8. *a scientist wants to separate oil from water. which separation method should they choose?
(a) evaporation
(b) chromatography
(c) filtration
(d) layer separation/decanting
9. justify your response to question #6.

Question

q1 chemistry: u1l7 unit 1 review
teacher: ____________
date: ____________
3. ** which statement correctly describes a mixture?
   a. a mixture can consist of a single element
   b. a mixture must have a uniform composition.
   c. a mixture can be separated by physical means.
   d. a mixture is always homogeneous.
4. one similarity between all mixtures and compounds is that both:
   a. are heterogeneous
   b. are homogeneous
   c. combine in a uniform fashion
   d. consist of two or more substance
5. **name two processes that can be used to separate two clear, miscible liquids. when would a scientist choose to use one of these methods over the other?
6. **which property of a substance is used to separate the liquids in question #3?
   (a) melting point
   (b) density
   (c) boiling point
   (d) solubility
7. what method would a scientist use to separate sand from water? justify your response.
8. *a scientist wants to separate oil from water. which separation method should they choose?
   (a) evaporation
   (b) chromatography
   (c) filtration
   (d) layer separation/decanting
9. justify your response to question #6.

Accepted Answer

### Question 3
# Brief Explanations:
- Option a: A mixture is a combination of two or more substances, so it can't consist of a single element. Eliminate a.
- Option b: Mixtures can be heterogeneous (like a salad) or homogeneous (like salt water), so they don't have to have a uniform composition. Eliminate b.
- Option c: Mixtures are physically combined, so they can be separated by physical means (e.g., filtering sand from water, distilling alcohol from water). This is correct.
- Option d: Mixtures can be heterogeneous (non - uniform) or homogeneous (uniform), so they aren't always homogeneous. Eliminate d.
# Answer:
c. A mixture can be separated by physical means.

### Question 4
# Brief Explanations:
- Option a: Compounds are homogeneous (have a uniform composition), and mixtures can be heterogeneous or homogeneous. So not all mixtures and compounds are heterogeneous. Eliminate a.
- Option b: Mixtures can be heterogeneous (e.g., a mixture of sand and gravel), so not all mixtures and compounds are homogeneous. Eliminate b.
- Option c: Compounds combine in a fixed ratio (chemical combination), while mixtures combine in any ratio (physical combination). So they don't combine in a uniform fashion in the same way. Eliminate c.
- Option d: A mixture is made of two or more substances (physically combined), and a compound is made of two or more elements (chemically combined). So both consist of two or more substances (or elements in the case of compounds, which are also substances). This is correct.
# Answer:
d. Consist of two or more substance

### Question 5
# Brief Explanations:
Two common processes to separate two clear, miscible liquids are distillation and fractional distillation.
- Distillation: It is used when the boiling points of the two liquids have a relatively large difference (usually more than 25 - 30 °C). For example, separating water and ethanol (if the difference in boiling points is large enough) can be done by simple distillation.
- Fractional distillation: It is used when the boiling points of the two miscible liquids are close to each other (less than 25 - 30 °C difference). For example, separating different components of crude oil, where the boiling points of the hydrocarbon fractions are relatively close, requires fractional distillation. A scientist would choose distillation over fractional distillation when the boiling point difference is large, as it is a simpler and less energy - intensive process. They would choose fractional distillation when the boiling points are close, as simple distillation would not separate them effectively.
# Answer:
Two processes are distillation and fractional distillation. A scientist uses distillation when the boiling point difference of the two miscible liquids is large (e.g., > 25 - 30 °C), and fractional distillation when the boiling point difference is small (e.g., < 25 - 30 °C) as simple distillation can't separate liquids with close boiling points effectively.

### Question 6
# Brief Explanations:
- Option A: Melting point is related to the temperature at which a solid turns into a liquid. It is not used to separate liquids. Eliminate A.
- Option B: Density is the mass per unit volume. While density differences can be used to separate some mixtures (like oil and water based on their density difference for layer separation), for separating miscible liquids, density is not the property used. Eliminate B.
- Option C: When separating miscible liquids (like in distillation), the difference in boiling points is used. The liquid with the lower boiling point will vaporize first, and then can be condensed and collected. This is the property used to separate the liquids in question 5 (separating miscible liquids). This is correct.
- Option D: Solubility is the ability of a substance to dissolve in a solvent. It is not used to separate two miscible liquids from each other. Eliminate D.
# Answer:
C. Boiling point

### Question 7
# Brief Explanations:
A scientist would use filtration to separate sand from water. Sand is an insoluble solid in water, and filtration works by passing the mixture through a filter medium (like filter paper) that allows the liquid (water) to pass through but retains the solid (sand) particles. The sand particles are too large to pass through the pores of the filter paper, while the water molecules can pass through, thus separating the sand from the water.
# Answer:
A scientist would use filtration. Justification: Sand is insoluble in water and is a solid, while water is a liquid. Filtration uses a filter (e.g., filter paper) that allows the liquid (water) to pass through but traps the solid (sand) particles, thus separating them.

### Question 8
# Brief Explanations:
- Option A: Evaporation is used to separate a dissolved solid from a liquid (e.g., salt from water by evaporating the water). It is not suitable for separating oil and water. Eliminate A.
- Option B: Chromatography is used to separate components of a mixture based on their different affinities for a stationary and mobile phase (e.g., separating different pigments in ink). It is not used for separating oil and water. Eliminate B.
- Option C: Filtration is used to separate an insoluble solid from a liquid. Oil and water are both liquids (with oil being immiscible), so filtration won't work. Eliminate C.
- Option D: Oil and water are immiscible liquids, and they form separate layers (oil is less dense and floats on water). Layer separation/decanting involves carefully pouring off the top layer (oil) from the bottom layer (water) or using a separatory funnel to separate the two layers. This is the correct method.
# Answer:
D. Layer separation/decanting

### Question 9
# Brief Explanations:
In question 6, the correct answer is boiling point (option C). When separating two miscible liquids (like in distillation, which is relevant to question 5), the difference in their boiling points is utilized. The liquid with the lower boiling point will vaporize when the mixture is heated to a temperature between the two boiling points. The vapor can then be condensed and collected, thus separating the two liquids. Melting point is for solids, density is not the key property for separating miscible liquids, and solubility is about dissolving in a solvent, not separating two miscible liquids from each other. So boiling point is the property used to separate the miscible liquids in question 5.
# Answer:
To separate miscible liquids (as in question 5), we use the difference in their boiling points. The liquid with the lower boiling point vaporizes first when heated, and then the vapor is condensed to separate it from the other liquid. Melting point (for solids), density (not for miscible liquid separation), and solubility (not for separating two miscible liquids) are not relevant here, so boiling point (option C) is the correct property.

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