Question

separation of the components of a mixture | 3 pre-lab questions
before beginning this experiment in the laboratory, you should be able to answer the following questions.

1. classify each of the following as a pure substance or a mixture; if it is a mixture, state whether it is heterogeneous or homogeneous: (a) concrete, (b) tomato juice, (c) marble, (d) seawater, and (e) iron.

1. suggest a way to determine whether a colorless liquid is pure water or a salt solution without tasting it.

1. what distinguishes a mixture from an impure substance?

1. define the process of sublimation.

process in which a solid passes directly to the gaseous state and back to solid state without the appearance of the liquid state

1. how do decantation and filtration differ? which should be faster?

decantation separates liquid from a solid while filtration separates solid from a liquid.

1. why should you never place a hot object on the pan of a balance?

Explanation:

Question 1

Step 1: Recall definitions

A pure substance has a fixed composition (element or compound). A mixture has two or more substances; heterogeneous has distinct phases, homogeneous is uniform.

Step 2: Classify each

• (a) Concrete: Mixture (cement, sand, gravel), heterogeneous (distinct components).
• (b) Tomato juice: Mixture, heterogeneous (pulps, liquid phases).
• (c) Marble: Mixture (calcite, other minerals), heterogeneous.
• (d) Seawater: Mixture (water, salts), homogeneous (uniform composition).
• (e) Iron: Pure substance (element, Fe).

Step 1: Identify properties

Pure water and salt solution differ in boiling point, freezing point, or conductivity.

Step 2: Propose method

Boil a sample: Pure water boils at 100°C (1 atm), salt solution has higher boiling point. Or freeze: Pure water freezes at 0°C, salt solution at lower temp. Or test conductivity: Salt solution conducts (ions), pure water (very little) doesn’t.

Step 1: Define mixture and impure substance

Mixture: Two+ substances physically combined, can be separated by physical means, components retain properties. Impure substance: A pure substance with impurities (small amounts of other substances), impurities alter properties, separation of impurities from pure substance is purification.

Step 2: Distinguish

Mixture has multiple substances (components) in any proportion, separable physically. Impure substance is a mostly pure substance with small impurities (not a mixture of distinct substances in significant proportions).

Answer:

(a) Mixture, Heterogeneous; (b) Mixture, Heterogeneous; (c) Mixture, Heterogeneous; (d) Mixture, Homogeneous; (e) Pure Substance

Question 2