Notes
Solutions and solubility
- A solution is a homogeneous mixture of a solute dissolved in a solvent. Water is polar and dissolves many ionic and polar substances.
- Solubility is the maximum solute that dissolves at a given temperature. Solids usually dissolve better when warm; gases dissolve better when cold.
Concentration
- Mass percent $\displaystyle = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$.
- Molarity $\displaystyle M = \frac{\text{moles of solute}}{\text{liters of solution}}$.
Acids, bases and pH
- Acids release $\text{H}^+$, taste sour and have pH below 7. Bases release $\text{OH}^-$, feel slippery and have pH above 7. Each pH step is a factor of 10.
- Neutralization: acid + base $\rightarrow$ salt + water.
Topics in this unit
Each topic has its own short notes and practice.
Practice
The solvent is the substance that dissolves the solute.
Solution mass is $30 + 120 = 150$ g, and $\displaystyle \frac{30}{150} = 20\%$.
$\displaystyle \frac{4}{2} = 2$ M.
pH 3 is two steps lower, so $10^2 = 100$ times more acidic.
Warm liquids hold less dissolved gas.
Neutralization gives a salt and water.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student dissolves 25 g of sugar in 175 g of water to make a solution.
(a) Identify the solute and solvent.
Show the answer and scoring guide
Sugar is the solute; water is the solvent.
Check off the points you earned:
(b) Calculate the mass percent of sugar in the solution.
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Solution mass $= 25 + 175 = 200$ g. $\displaystyle \frac{25}{200} \times 100\% = 12.5\%$.
Check off the points you earned:
(c) The student adds more water to the solution. Describe the effect on the concentration, and explain what neutralization would do to a solution with pH 2.
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The solution becomes more dilute (lower concentration). Neutralization with a base would raise the pH toward 7 as the acid is used up.
Check off the points you earned: