Unit 8: Solutions
What actually happens when one substance dissolves into another, and how chemists measure and control exactly how concentrated a solution is.
9 topics · 35 questions
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8.1 Solutions, Solutes, and Solvents
- How it worksHow do solvent particles surround and separate solute particles to form a solution?
- How it worksHow does a solute's particles end up spread evenly throughout every part of the solvent once it's fully dissolved?
- Common mistakeWhy isn't a solution the same thing as a mixture you can still see two parts of?
- Going furtherWhat happens to a solution once you've added so much solute that no more will dissolve?
- Ties togetherHow does this particle picture of dissolving explain why some substances dissolve easily in water while others barely dissolve at all?
Your turn1 of 2
Stirring a spoonful of sugar into a cup of hot tea makes the visible sugar crystals disappear completely, leaving the tea looking perfectly clear rather than cloudy or settled at the bottom. Why does stirring sugar into tea make it disappear instead of settling to the bottom?8.2 Like Dissolves Like
- How it worksHow do polar water molecules surround and pull apart a polar or ionic solute?
- How it worksHow does a nonpolar substance like oil end up surrounded by other nonpolar molecules instead of by water?
- Common mistakeWhy isn't dissolving the same process as melting a solid?
- Going furtherWhat happens when you try to dissolve a nonpolar substance like oil into a polar solvent like water?
- Ties togetherHow does this polar-versus-nonpolar matching rely on the same intermolecular forces covered back in the bonding unit?
Your turn1 of 2
Pouring oil into a bottle of water and shaking it vigorously produces a temporary cloudy mixture that quickly separates back into two distinct layers once the shaking stops. Why does oil refuse to mix into water no matter how hard you shake the bottle?8.3 Factors That Speed Up Dissolving
- How it worksHow does stirring, crushing, or heating a solute increase how fast it dissolves?
- How it worksHow does breaking a solid into smaller pieces expose more surface area to the surrounding solvent?
- Common mistakeWhy doesn't stirring a solution change how much solute can eventually dissolve, only how fast it does?
- Going furtherWhat happens to the dissolving rate when you crush a solid into a fine powder before adding it to water?
- Ties togetherHow do these same speed-of-dissolving factors reappear as the factors that affect reaction rate later in the course?
Your turn1 of 2
A spoonful of sugar dissolves within seconds when stirred into a hot cup of tea, but the same amount of sugar takes much longer to dissolve when dropped into a glass of iced tea. Why does sugar dissolve faster in hot tea than in iced tea?8.4 Saturated, Unsaturated, and Supersaturated Solutions
- How it worksHow does a solution hold more dissolved solute than normal in a supersaturated state?
- How it worksHow does a saturated solution keep dissolving and recrystallizing solute at equal rates even though it looks perfectly still?
- Worked exampleFind whether a solution holding 30 grams of salt in 100 grams of water at room temperature counts as saturated, given a solubility of 36 grams per 100 grams of water.
- Common mistakeWhy isn't a saturated solution the same as one that's simply full of any liquid at all?
- Going furtherWhat happens when you drop one seed crystal into a supersaturated solution?
Your turn1 of 2
A solute has a solubility of 75 grams per 100 grams of water at room temperature. A solution already has 24 grams of that solute dissolved in 100 grams of water. How many more grams of solute could still dissolve before the solution becomes saturated?8.5 Solubility and Temperature
- How it worksHow does raising the temperature of water usually increase how much solid solute it can dissolve?
- Worked exampleFind the maximum grams of potassium nitrate that dissolve in 100 grams of water at 60 degrees C using a solubility curve.
- Common mistakeWhy doesn't raising the temperature increase the solubility of every solute, including most gases?
Your turn1 of 2
A solute's solubility is 45 grams per 100 grams of water at a starting temperature, and its solubility on this solubility curve rises by about 10 grams per 100 grams of water for each 10 degree C increase in temperature. What is the solubility after 6 such 10-degree increases?8.6 Molarity as a Concentration Unit
- How it worksHow does dividing moles of solute by liters of solution define a solution's molarity?
- Worked exampleFind the molarity of a solution made by dissolving 2 moles of NaCl in enough water to make 4 liters of solution.
- Common mistakeWhy isn't molarity the same as the number of grams of solute dissolved?
Your turn1 of 2
Find the molarity of a solution made by dissolving 6.99 moles of a solute in enough water to make 5.23 liters of total solution.8.7 Preparing a Solution of Known Molarity
- How it worksHow does dissolving a measured mass of solute and adding solvent up to a fixed final volume set molarity?
- Worked exampleFind the mass of NaOH needed to prepare 500 mL of a 2 molar NaOH solution.
- Common mistakeWhy doesn't adding solute to a fixed volume of water give you the exact molarity you want?
Your turn1 of 2
Find the mass of solute, with a molar mass of 177 grams per mole, needed to prepare 1316 mL of a 5.6 molar solution.8.8 Dilution Calculations
- How it worksHow does the equation M1V1 equals M2V2 let you predict a solution's new concentration after dilution?
- Worked exampleFind the final concentration when 50 mL of a 6 molar solution is diluted to a total volume of 300 mL.
- Common mistakeWhy doesn't diluting a solution change the total number of moles of solute present?
Your turn1 of 2
Find the final concentration when 141 mL of a 7.96 molar solution is diluted to a total volume of 939 mL.8.9 Electrolytes and Nonelectrolytes
- How it worksHow do dissolved ions carry electric current through an electrolyte solution?
- Common mistakeWhy doesn't dissolving a molecular compound like sugar produce any ions in solution?
- Going furtherWhat happens to a solution's ability to conduct electricity when a strong electrolyte fully dissociates into ions?
Your turn1 of 2
Dipping two electrodes connected to a light bulb into a beaker of salt water lights the bulb brightly, but dipping the same electrodes into a beaker of sugar water leaves the bulb completely dark. Why does a solution of salt water conduct electricity while a solution of sugar water does not?