Question

Indicate whether each of the following increases, decreases, or has no effect on the rate at which \(10.0 \mathrm{~g}\) of sugar dissolves in a liter of water. (a) using water from the refrigerator (b) shaking the sugar and water (c) using powdered sugar rather than crystals (d) using tap water rather than distilled water

Short answer

(a) Decreases, (b) Increases, (c) Increases, (d) No effect.

Step-by-step solution

Analyze Temperature Effect

Cooling the water from the refrigerator decreases molecular motion, and thus reduces the rate of sugar dissolving. Therefore, using water from the refrigerator decreases the dissolution rate.

Consider Mechanical Agitation

Shaking the mixture provides mechanical energy, which increases molecular motion and helps sugar molecules disperse into the water faster. Therefore, shaking increases the dissolution rate.

Evaluate Surface Area Impact

Powdered sugar has a greater surface area compared to sugar crystals, allowing more sugar molecules to interact with water simultaneously. Thus, using powdered sugar increases the dissolution rate.

Water Impurity Assessment

Tap water contains impurities and dissolved ions which might slightly enhance or inhibit dissolution; however, the effect is usually negligible in comparison to distilled water. Generally, using tap water has minimal or no effect on the dissolution rate.

Key concepts

Dissolution Rate

The dissolution rate is the speed at which a solute dissolves in a solvent. Imagine mixing sugar in water; how quickly the sugar disappears is its dissolution rate. Several factors can influence this rate, such as the temperature, agitation, and the physical form of the solute. Understanding these factors helps us optimize and control the dissolution process in everyday applications like making sweetened drinks or in industries such as pharmaceuticals.

• Key Factors: Temperature, Mechanical Agitation, Surface Area, Solvent Purity.

By manipulating these conditions, we can increase or decrease how fast a substance dissolves, providing us with better control over chemical reactions and solutions.

Temperature Effect on Solubility

Temperature is a crucial factor affecting the solubility and dissolution rate of a substance. In general, increasing the temperature speeds up molecular movement, which facilitates a faster and more effective interaction between the solute and solvent molecules. For example, sugar dissolves more rapidly in hot water than in cold water.

• Increased Temperature: Enhances molecular motion, increases dissolution rate.
• Decreased Temperature: Slows molecular motion, reduces dissolution rate.

Using water from the refrigerator, as in the given exercise, would lower the dissolution rate because the molecules move less energetically.

Surface Area Impact

The surface area of a solute plays a significant role in how quickly it dissolves. When a substance like sugar is in powdered form, it has a higher surface area compared to larger crystals of the same mass. More surface area allows for more simultaneous contact with the solvent, leading to an increased dissolution rate.

• Powdered Form: Greater surface area, faster dissolution.
• Coarse Crystals: Smaller surface area, slower dissolution.

By utilizing a greater surface area, the diffusion of molecules occurs more rapidly, thereby enhancing the rate at which the substance dissolves.

Mechanical Agitation

Mechanical agitation, such as stirring or shaking, can significantly impact the dissolution rate of a substance. This agitation means manually moving the mixture, which helps distribute solute particles throughout the solvent more evenly and swiftly.

• Effectiveness: Increases dissolution rate by promoting uniform distribution.
• Energy Input: Adds energy into the system, enhancing particle interaction.

When you shake or stir the sugar-water mixture, you physically encourage the solute particles to intermingle with the solvent, thereby quickening the process of dissolution.