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Titration can be used to determine the exact amount of hydrochloric acid that reacts with a given amount of sodium hydroxide solution - Edexcel - GCSE Chemistry - Question 5 - 2013 - Paper 1
Question 5
Titration can be used to determine the exact amount of hydrochloric acid that reacts with a given amount of sodium hydroxide solution. HCl + NaOH → NaCl + H2O (a) ... show full transcript
Worked Solution & Example Answer:Titration can be used to determine the exact amount of hydrochloric acid that reacts with a given amount of sodium hydroxide solution - Edexcel - GCSE Chemistry - Question 5 - 2013 - Paper 1
Step 1
What type of reaction takes place when hydrochloric acid reacts with sodium hydroxide solution?
Answer
The reaction between hydrochloric acid and sodium hydroxide is a neutralisation reaction. This is because an acid reacts with a base (NaOH) to produce salt (NaCl) and water (H₂O). Therefore, the correct answer is A neutralisation.
Step 2
Suggest why universal indicator must not be used in titration experiments.
Answer
Universal indicator is not suitable for titration experiments because it changes color over a wide pH range. This means it can give a gradual change instead of a sharp endpoint, which makes it difficult to accurately determine when the reaction has reached completion.
Step 3
Describe a titration experiment to find the exact volume of hydrochloric acid needed to neutralise 25.0 cm³ of sodium hydroxide solution
Answer
- Rinse a pipette with sodium hydroxide solution, then use it to measure 25.0 cm³ of the solution into a clean, dry flask.
- Add 2-3 drops of a suitable indicator such as phenolphthalein to the sodium hydroxide solution in the flask.
- Rinse a burette with dilute hydrochloric acid and fill it.
- Place the flask on a white tile to better observe the color change.
- Slowly add hydrochloric acid from the burette to the sodium hydroxide solution while swirling the flask continuously until a stable color change indicates that all the alkali has been neutralised.
- Note the volume of hydrochloric acid used from the burette for accurate measurement and repeat the experiment until concordant results are obtained.
- To prepare pure crystals of sodium chloride, pour the resulting solution into an evaporating basin and leave it to evaporate until dry crystals are left.
Step 4
State the volume of hydrochloric acid that must be used to calculate the concentration of sodium hydroxide solution.
Answer
The volume of hydrochloric acid used to calculate the concentration of sodium hydroxide solution must be the average of the recorded titrations. Therefore, it is
rac{22.6 + 22.8}{2} = 22.7 ext{ cm}^3.
Step 5
Calculate the concentration of this sodium hydroxide solution, NaOH, in mol dm⁻³.
Answer
To calculate the concentration of sodium hydroxide (NaOH), we can use the equation from the titration:
Number of moles of HCl:
ext{moles HCl} = ext{concentration} imes ext{volume} = 0.1 imes 0.0232 = 0.00232 ext{ mol}
According to the equation, 1 mole of NaOH reacts with 1 mole of HCl. Therefore, moles of NaOH = 0.00232 mol.
To find the concentration of NaOH:
ext{concentration of NaOH} = rac{ ext{moles of NaOH}}{ ext{volume in dm}^3} = rac{0.00232}{0.0250} = 0.0928 ext{ mol dm}^-3.