science midterm exam study guide
matter part i:
pure substances and mixtures
1. identify each statement below as describing either a pure substance or a mixture
a. consists of elements and compounds
b. can contain 2 or more substances chemically bonded together
c. can be separated by physical means
d. cannot be separated using physical means
e. cannot be chemically combined
f. can be homogeneous or heterogeneous
2. label the following as an element, compound, homogeneous mixture, or heterogeneous mixture:
| | element, compound, het. mixture, or hom. mixture | can the particles be physically separated? | is this a pure substance? (all the same molecules) |
| kool - aid drink mixture in water | | | |
| pizza | | | |
| milk | | | |
| sugar ($c_{12}h_{22}o_{11}$) | | | |
| water ($h_2o$) | | | |
| salt (nacl) | | | |
| oxygen ($o_2$) | | | |
| air | | | |
3. label the following images as a pure substance or a mixture:
image i: a grid of similar - looking particles
image ii: particles that seem to be of two types bonded together
image iii: particles of multiple types

Question

science midterm exam study guide
matter part i:
pure substances and mixtures
1. identify each statement below as describing either a pure substance or a mixture
   a. consists of elements and compounds
   b. can contain 2 or more substances chemically bonded together
   c. can be separated by physical means
   d. cannot be separated using physical means
   e. cannot be chemically combined
   f. can be homogeneous or heterogeneous
2. label the following as an element, compound, homogeneous mixture, or heterogeneous mixture:
| | element, compound, het. mixture, or hom. mixture | can the particles be physically separated? | is this a pure substance? (all the same molecules) |
| kool - aid drink mixture in water |  |  |  |
| pizza |  |  |  |
| milk |  |  |  |
| sugar ($c_{12}h_{22}o_{11}$) |  |  |  |
| water ($h_2o$) |  |  |  |
| salt (nacl) |  |  |  |
| oxygen ($o_2$) |  |  |  |
| air |  |  |  |
3. label the following images as a pure substance or a mixture:
image i: a grid of similar - looking particles
image ii: particles that seem to be of two types bonded together
image iii: particles of multiple types

Accepted Answer

# Brief Explanations:
### Question 1:
- **a. Consists of elements and compounds**: Mixture (Mixtures can have elements and compounds combined physically)
- **b. Can contain 2 or more substances chemically bonded together**: Pure substance (Compounds have elements chemically bonded; elements are pure, but this refers to substances bonded, so pure substance - compound)
- **c. Can be separated by physical means**: Mixture (Mixtures are separated physically as components retain their properties)
- **d. Cannot be separated using physical means**: Pure substance (Pure substances (elements/compounds) need chemical methods for separation of components)
- **e. Cannot be chemically combined**: Pure substance (Elements in pure substances are not chemically combined in a mixture - this is a bit tricky, but pure substances (elements) are single types, so they don't combine chemically in the sense of a mixture; better: Mixture? Wait no - Pure substances: elements are single atoms, compounds are fixed ratios. Mixtures have substances that can be mixed without chemical bonding. Wait, the statement "Cannot be chemically combined" - maybe pure substance (elements can't be chemically combined in the sense of a mixture's components? Maybe I messed up. Let's re - think: Pure substances (elements and compounds) have fixed compositions. Mixtures have variable compositions. So "Cannot be chemically combined" - maybe pure substance (because in a pure substance, the components (in a compound) are chemically combined, but elements are not combined. Wait, the question is about the statement. Let's use definitions:
  - Pure substance: matter with definite composition (element or compound).
  - Mixture: matter with variable composition, components retain properties.
  So:
  - a. Mixture (mixtures can have elements and compounds)
  - b. Pure substance (compounds have 2 + substances (elements) chemically bonded)
  - c. Mixture (mixtures are separated physically)
  - d. Pure substance (pure substances can't be separated physically)
  - e. Mixture? No - wait, pure substances (elements) are not chemically combined (they are single atoms). Wait, the statement "Cannot be chemically combined" - maybe mixture? No, mixtures can have substances that are not chemically combined. Wait, I think I made a mistake. Let's check standard definitions:
    - Pure substance: element (one type of atom) or compound (two or more elements chemically bonded).
    - Mixture: two or more substances (elements or compounds) physically combined, not chemically bonded.
    So:
    - a. Mixture (has elements and compounds)
    - b. Pure substance (compounds have 2 + substances chemically bonded)
    - c. Mixture (separated physically)
    - d. Pure substance (not separated physically)
    - e. Mixture? No, pure substances (elements) are not chemically combined (they are single). Wait, the statement "Cannot be chemically combined" - maybe pure substance (elements can't be chemically combined in the way a mixture's components are not combined? This is confusing. Let's proceed to the next part.
  - f. Mixture (mixtures can be homogeneous (solution) or heterogeneous (suspension/colloid))

### Question 2:
- **Kool - aid drink mixture in water**: Homogeneous mixture (uniform composition), Can the particles be physically separated? Yes (e.g., evaporation to separate water and Kool - aid solids), Is this a pure substance? No (has water and Kool - aid components)
- **Pizza**: Heterogeneous mixture (non - uniform, different toppings etc.), Can the particles be physically separated? Yes (pick off toppings), Is this a pure substance? No
- **Milk**: Homogeneous mixture (colloid, uniform in appearance), Can the particles be physically separated? Yes (e.g., centrifugation to separate cream), Is this a pure substance? No
- **Sugar ($C_{12}H_{22}O_{11}$)**: Compound (pure substance), Can the particles be physically separated? No (needs chemical methods to break down), Is this a pure substance? Yes
- **Water ($H_2O$)**: Compound (pure substance), Can the particles be physically separated? No, Is this a pure substance? Yes
- **Salt (NaCl)**: Compound (pure substance), Can the particles be physically separated? No, Is this a pure substance? Yes
- **Oxygen ($O_2$)**: Element (pure substance), Can the particles be physically separated? No, Is this a pure substance? Yes
- **Air**: Homogeneous mixture (uniform composition of gases), Can the particles be physically separated? Yes (e.g., fractional distillation), Is this a pure substance? No

### Question 3:
- **Image I**: Pure substance (all particles are the same, so it's an element or compound - since all dots are same, pure substance)
- **Image II**: Pure substance (all molecules are the same, so compound or element - since it's a molecule with two different atoms? Wait, no - if all molecules are the same, it's a pure substance (compound). Wait, the image: if all the particles (molecules) are identical, it's a pure substance.
- **Image III**: Mixture (there are different types of molecules, so it's a mixture of different substances)

# Answers:
### Question 1:
a. Mixture
b. Pure substance
c. Mixture
d. Pure substance
e. Pure substance (or Mixture? Wait, re - checking: The statement "Cannot be chemically combined" - if we consider that in a pure substance (element), the atoms are not chemically combined in the sense of a mixture's components. But maybe the correct answer is Mixture? No, I think I was wrong earlier. Let's use the standard answer key logic:
  - a. Mixture
  - b. Pure substance (compound)
  - c. Mixture
  - d. Pure substance
  - e. Mixture? No, the correct answers are:
    a. Mixture
    b. Pure substance
    c. Mixture
    d. Pure substance
    e. Pure substance (element)
    f. Mixture

### Question 2:
| Substance | Element, Compound, Het. Mixture, or Hom. mixture | Can the particles be physically separated? | Is this a pure substance? (all the same molecules) |
| --- | --- | --- | --- |
| Kool - aid drink mixture in water | Homogeneous mixture | Yes | No |
| Pizza | Heterogeneous mixture | Yes | No |
| Milk | Homogeneous mixture | Yes | No |
| Sugar ($C_{12}H_{22}O_{11}$) | Compound | No | Yes |
| Water ($H_2O$) | Compound | No | Yes |
| Salt (NaCl) | Compound | No | Yes |
| Oxygen ($O_2$) | Element | No | Yes |
| Air | Homogeneous mixture | Yes | No |

### Question 3:
I: Pure substance
II: Pure substance
III: Mixture

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QUESTION IMAGE

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Explanation:

Question 1:

Question 2:

Answer:

Question 1:

Question 2:

Question 3:

	element, compound, het. mixture, or hom. mixture	can the particles be physically separated?	is this a pure substance? (all the same molecules)
kool - aid drink mixture in water
pizza
milk
sugar ($c_{12}h_{22}o_{11}$)
water ($h_2o$)
salt (nacl)
oxygen ($o_2$)
air

Substance	Element, Compound, Het. Mixture, or Hom. mixture	Can the particles be physically separated?	Is this a pure substance? (all the same molecules)
Pizza	Heterogeneous mixture	Yes	No
Milk	Homogeneous mixture	Yes	No
Sugar ($C_{12}H_{22}O_{11}$)	Compound	No	Yes
Water ($H_2O$)	Compound	No	Yes
Salt (NaCl)	Compound	No	Yes
Oxygen ($O_2$)	Element	No	Yes
Air	Homogeneous mixture	Yes	No