Module III -CEGR 338

Water with a hardness value of 100 mg/L as CaCO₃ is classified as:

• Soft

• Moderately hard

• Hard

• Very hard

According to the classification of water hardness, which of the following ranges correctly defines hard water in terms of mg/L as CaCO₃?

• 0–60 mg/L

• 61–120 mg/L

• 121–180 mg/L

• >180 mg/L

carbonate hardness is ___________

• equal to the total hardness, regardless of alkalinity

• the amount of hardness equal to the lesser of total hardness or total alkalinity

• always higher than non-carbonate hardness

• determined by the concentration of sodium and chloride ions

Balance the following chemical equation:

C₄H₁₀ + O₂ → CO₂ + H₂O

• C₄H₁₀ + 9 O₂ → 4 CO₂ + 4 H₂O

• 3C₄H₁₀ + 8 O₂ → 4 CO₂ + 5 H₂O

• 2C₄H₁₀ + 10 O₂ → 4 CO₂ + 6 H₂O

• 2C₄H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O

What is alkalinity in water?

• The ability of water to neutralize acids

• The amount of calcium and magnesium in the water

• The presence of dissolved oxygen

• The total hardness of the water

Total alkalinity in water is primarily calculated based on the concentration of which ions?

• Ca²⁺ and Mg²⁺

• HCO₃⁻, CO₃²⁻, and OH⁻

• Na⁺ and K⁺

• Fe³⁺ and SO₄²⁻

A water sample contains the following ion concentrations:

• HCO₃⁻ (Bicarbonate) = 150 mg/L

• CO₃²⁻ (Carbonate) = 30 mg/L

• OH⁻ (Hydroxide) = 5 mg/L

Which formula should be used to calculate the total alkalinity in mg/L as CaCO₃, knowing that the equivalent weight of CaCO₃ is 50?

• Alkalinity (as CaCO₃) = [HCO₃⁻] / 61 × 50

• Alkalinity (as CaCO₃) = ([HCO₃⁻] / 61 + [CO₃²⁻] / 30 + [OH⁻] / 17) × 50

• Alkalinity (as CaCO₃) = [CO₃²⁻] / 30 × 50

• Alkalinity (as CaCO₃) = [OH⁻] × 50

What is molarity, and how is it calculated?

• Molarity is the concentration of a solution.

  M = Moles of solute × Volume of solution

• Molarity is the concentration of a solution.

  M = Moles of solute / Volume of solution (L)

• Molarity is the amount of solute in a solution.

  M = Mass of solute × Volume of solution

• Molarity is the amount of solute in a solution.

  M = Moles of solute / Mass of solvent

What is the molarity of a solution that contains 6 moles of sodium chloride (NaCl) dissolved in 3 liters of water?

• 2 M

• 3 M

• 6 M

• 9 M

How do you calculate the non-carbonate hardness as CaCO₃ in mg/L?

• (Total hardness - Carbonate hardness) × 50

• (Ca²⁺ + Mg²⁺) × 50

• (Total hardness - Alkalinity) × 50

• (Total hardness - Non-carbonate ions) × 50