The accurate measurement of the relative density of a substance in its powdered form is done with a beam balance and?

Analyze the question: We want the relative density of a powder. A powder can't be measured by simply lowering it into a measuring cylinder or by direct displacement, because it has air gaps, dissolves, or clumps. So we need a method that works for solids in powder form.

Concept: Relative density = (mass of substance) / (mass of an equal volume of water).

The density bottle (specific gravity bottle) has a fixed, known volume and a stopper with a capillary hole, so it fills to exactly the same volume every time. That makes it the accurate tool for powders and liquids.

Solution (using a beam balance and a density bottle):

1. Weigh the empty, dry bottle: m₁
2. Fill the bottle partly with powder and weigh it: m₂
3. Add water (or a liquid in which the powder does not dissolve) to fill the bottle, stopper it, and weigh: m₃
4. Empty and clean the bottle, fill it with water only, and weigh: m₄

Then:

• Mass of powder = m₂ − m₁
• Mass of water displaced by the powder = (m₄ − m₁) − (m₃ − m₂)

Relative density = (m₂ − m₁) / [(m₄ − m₁) − (m₃ − m₂)]

Why the others are wrong:

• B. Eureka can: It is used for larger, solid objects that sink in water, not for powders.
• C. Pipette: It delivers fixed volumes of liquid and does not measure density.
• D. Burette: It measures variable volumes of liquid, mainly in titration.

Answer: A. a density bottle

Exam tip: Think "powder or liquid → density bottle", and "irregular solid → eureka can or measuring cylinder".