Mechanical Mixture Chemistry Example 4

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Example 4

hard
A prospector has a pan of sand mixed with small gold flakes. Describe two physical methods to separate the gold from the sand, and explain which physical property each method exploits.

Solution

  1. 1
    Method 1 — Panning (density separation): Gold (ρ=19.3 g/cm3\rho = 19.3\,\text{g/cm}^3) is much denser than sand (ρ≈2.6 g/cm3\rho \approx 2.6\,\text{g/cm}^3). Swirling with water washes away lighter sand while gold settles to the bottom.
  2. 2
    Method 2 — Magnetism/manual picking: Gold's distinctive color and luster (physical properties) allow visual identification and manual separation. Alternatively, some sand minerals are weakly magnetic while gold is not.
  3. 3
    Both methods rely on differences in physical properties and do not change the chemical identity of either component.

Answer

Panning (density) and visual sorting (color/luster)\text{Panning (density) and visual sorting (color/luster)}
Separating mechanical mixtures relies on exploiting differences in physical properties between the components. The large density difference between gold and sand makes panning an effective and ancient separation technique.

About Mechanical Mixture

A mixture in which the individual components are visibly distinguishable and not uniformly distributed throughout the sample, meaning different regions of the mixture have different.

Learn more about Mechanical Mixture →

More Mechanical Mixture Examples

Example 1 easy

Define a mechanical mixture and give three examples.

Example 2 medium

A student examines a rock sample and sees distinct bands of black and white minerals. Is this a pure

Example 3 medium

Explain why soil is considered a mechanical mixture rather than a pure substance or a solution.

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