Titration: Finding an Unknown Concentration · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Titrations that tell the truth

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Which routine gives reliable titration results?

    • Rinse all glassware with water only and take one reading
    • Guess the endpoint colour and add indicator at the end
    • Rinse with the solution it will hold, swirl, repeat until titres agree

  2. The rough titre is left out when calculating the mean.

    Circle one:   True   False

  3. Titres are 25.4 (rough), 24.8, 24.6 and 24.7 cm3. What is the mean titre?

    Answer: ______________

  4. Which routine gives reliable titration results?

    • Rinse with the solution it will hold, swirl to mix, repeat until titres agree
    • Rinse everything with water only, never swirl, accept the first titre
    • Add indicator at the end, guess the endpoint colour
    • Use the rough titre in the mean for safety

  5. A student overshoots the endpoint so the titre is too big. What happens to the calculated concentration?

    • It comes out lower than the truth
    • It stays exactly right
    • It comes out higher than the truth

  6. Titres are 25.4 (rough), 24.8, 24.6, and 24.7 cm3. What is the mean titre?

    Answer: ______________

  7. 25.0 cm3 of 0.100 mol/dm3 NaOH is used. How many moles is that?

    Answer: ______________

  8. 0.00224 mol of acid reacts 1 to 1 with the alkali. How many moles of alkali reacted?

    • 0.00224
    • 0.0224
    • 0.224

  9. Two titres read 24.8 and 26.5 cm3. What should the student do next?

    • Repeat again, since the pair disagrees by more than 0.1
    • Average both and report the result
    • Drop the lower one and keep the higher

  10. 25.0 cm3 of alkali needs 22.4 cm3 of 0.100 mol/dm3 acid in a 1 to 1 reaction. What is the alkali concentration in mol/dm3?

    Answer: ______________

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Titrations that tell the truth W1-mt_7WLN35XxYx-s1

  1. Rinse with the solution it will hold, swirl, repeat until titres agree · Correct rinsing, mixing and repetition give concordant titres.
  2. True · Only concordant titres join the mean, and the rough run is only a scout.
  3. 24.7 · Drop the rough 25.4, then average 24.8, 24.6 and 24.7 to get 24.7.
  4. Rinse with the solution it will hold, swirl to mix, repeat until titres agree · Correct rinsing, mixing, and repetition give concordant titres.
  5. It comes out higher than the truth · A bigger titre counts more moles, which inflates the concentration.
  6. 24.7 · Discard the rough 25.4, then average 24.8, 24.6, and 24.7 to get 24.7.
  7. 0.0025 · Moles equal 0.1 x 0.025 = 0.0025 mol.
  8. 0.00224 · A 1 to 1 ratio means equal moles on both sides.
  9. Repeat again, since the pair disagrees by more than 0.1 · The pair differs by far more than 0.1, so neither is confirmed yet.
  10. 0.0896 · 0.00224 mol of alkali in 0.025 dm3 gives 0.0896 mol/dm3.
Worksheet · LightMySky