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Physical Chemistry in Industrial Processes

Titration calculations and molarity

  • 3 things to know
  • AS 3

Overview

Molarity and converting cm³ to dm³, mean titres, concentration from mass, dilution, neutralisation calculations with sulfuric acid and sodium carbonate, and working back through a dilution factor.

What you need to know

Answer each one before you reveal it.

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Key term

What does the term molarity mean?

Numbers

How is a volume in cm³ converted to dm³ in a concentration calculation?

Key term

Titres of 23.85 cm³ (rough), 23.40 cm³, 23.10 cm³ and 23.20 cm³ are recorded. Which should be used, and what is the mean titre?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does the term molarity mean?

    Model answer

    Molarity is the concentration of a solution in moles of solute per cubic decimetre of solution. A 1 M solution contains 1 mol in each dm³.

  2. 2

    How is a volume in cm³ converted to dm³ in a concentration calculation?

    Model answer

    A volume in cm³ is divided by 1000 to give dm³. One cubic decimetre equals 1000 cm³.

  3. 3

    Titres of 23.85 cm³ (rough), 23.40 cm³, 23.10 cm³ and 23.20 cm³ are recorded. Which should be used, and what is the mean titre?

    Model answer

    The concordant titres 23.10 cm³ and 23.20 cm³ should be used, giving a mean of 23.15 cm³. The rough titre overshoots the end point, and 23.40 cm³ is anomalous.

  4. 4

    What is the concentration of a solution made by dissolving 4.00 g of sodium hydroxide (Mr = 40.0) in water to make 500 cm³?

    Model answer

    The concentration is 0.200 mol dm⁻³. The working is 4.00 ÷ 40.0 = 0.100 mol, and 0.100 ÷ 0.500 = 0.200 mol dm⁻³.

  5. 5

    Convert a sulfuric acid concentration of 9.81 g dm⁻³ into mol dm⁻³ (Mr = 98.1).

    Model answer

    The concentration is 0.100 mol dm⁻³. The working is 9.81 ÷ 98.1 = 0.100 mol dm⁻³.

  6. 6

    What volume of 2.00 mol dm⁻³ hydrochloric acid is needed to make 250 cm³ of 0.100 mol dm⁻³ acid?

    Model answer

    The volume of stock acid needed is 12.5 cm³. The working is 0.100 × 250 ÷ 2.00 = 12.5 cm³, made up to 250 cm³ with distilled water.

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