Key Formulas and Concepts

Concentration in g/L:

$$ \text{Concentration (g/L)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (L)}} $$

Percentage by Mass (% w/w):

$$ \text{% w/w} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100 $$

Percentage by Volume (% v/v):

$$ \text{% v/v} = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100 $$

Concentration in g/mL:

$$ \text{Concentration (g/mL)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} $$

Types of Mixtures:

  • Pure substances: Single component with fixed composition
  • Homogeneous mixtures: Uniform composition throughout (solutions)
  • Heterogeneous mixtures: Visible different phases
  • Colloids: Particles between solutions and suspensions (show Tyndall effect)

1. Classify the following substances according to their type Pure Substance (P), Homogeneous Mixture (O), Heterogeneous Mixture (E), or Colloid (C): (2 points)

a ) distilled water

b ) salad

c ) mayonnaise

d ) cloud

e ) lemonade

f ) bronze

g ) gold

h ) granite

i ) wine

j ) gravel and sand

2. Separation of contaminated soil mixture (2 points)

3. Calculate the concentration of disolving 250 g of ethanol in 200 mL of water; density of ethanol = 0.73 kg/L, density of water 1 kg/L, final volume ≈ sum of individual volumes) (8 points)

a ) In g/L.

b ) In mass percent (% w/w).

c ) In volume percent (% v/v).

4. Solubility graph interpretation (4 points)

a ) What is the solubility of potassium chloride (KCl) at 40°C in g/L?

b ) What is the solubility of sodium chloride (NaCl) at 90°C in g/L?

c ) How much calcium chloride (CaCl₂) could be dissolved in 40 mL of water at 20°C? Answer in grams.

d ) How much volume of water would be needed to prepare a saturated solution of 500 g of potassium nitrate (KNO₃) at 30°C? Answer in liters.

5. Lemonade preparation - concentration calculations (6 points)

a ) To prepare 600 mL of lemonade with a sugar concentration of 20 g/L, how many grams of sugar are required? Answer in grams.

b ) A mixture contains 80 g of sugar in 2 L of solution. What is the concentration in g/mL? Answer with 2 decimal places.

c ) With 7 kg of sugar available and a required concentration of 30 g/L, how many liters of lemonade can be prepared? Answer in liters.

6. Alcohol extraction from wine (2 points)

a ) How much pure alcohol (ethanol) can be obtained by distilling a 70 cL bottle of wine with an alcohol concentration of 14% (v/v)? Answer in mL.