Question

The particle size of the solute in true solution is:

• A. 1 Å – 10 Å
• B. 10 Å – 100 Å
• C. 100 Å – 1000 Å
• D. More than 1000 Å

Hint:

True solutions have very fine particles, typically in the range of 1 Å to 10 Å, which do not scatter light or settle out.

Answer 1

The Correct Option is A

Take a glass of clear salt water as the reference for a true solution. The dissolved sodium and chloride ions are far too small to see, and the water never turns cloudy or settles.

1. 1 Å - 10 Å: this matches the size of ions like sodium and chloride, or small molecules like sugar, once they are fully dissolved in water. That fits the salt-water reference exactly.
2. 10 Å - 100 Å: particles this size would make the water look faintly cloudy or scatter a light beam, unlike clear salt water.
3. 100 Å - 1000 Å: particles here are large enough to behave like a colloid, more like milk than clear salt water.
4. More than 1000 Å: particles this size would be visible and would settle, unlike anything happening in a glass of salt water.

Since dissolved ions and small molecules in salt water sit in the 1 Å - 10 Å range, that is the correct answer.

Answer 2

Rank the four ranges from smallest to largest and place a true solution's particles at the bottom of that scale, since dissolved ions and molecules are the smallest dispersed units possible.

1. 1 Å - 10 Å: this is the lowest band on the scale, matching single ions and small molecules, which is where a true solution's solute sits.
2. 10 Å - 100 Å: this is one step up the scale, into colloidal particle sizes.
3. 100 Å - 1000 Å: this is further up still, also within the colloidal range.
4. More than 1000 Å: this is the top of the scale, matching suspension-sized particles.

Since a true solution's solute occupies the lowest band on the size scale, the correct answer is 1 Å - 10 Å.