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Answer at least two questions from this section.See page 1 for full instructions. 1. To determine the concentration of ethanoic acid in a sample of vinegar, 25.0cm^3 of the vinegar were diluted to 250cm^3 and then the diluted vinegar was titrated with a previously standardised solution which contained 1.20 g of sodium hydroxide in 500cm^3 of solution. On average, 18.75cm^3 of the diluted vinegar were required to neutralise 25.0cm^3 of this sodium hydroxide solution. The equation for the titration reaction is: (a) Describe in detail the procedures involved in measuring a 25.0cm^3 sample of the vinegar and diluting it using deionised water to exactly 250cm^3 (15) (b) Name a suitable indicator for this titration.- Phenolohthal ein What colour change is observed at the end point? pink to clear (c) Calculate (i) the number of moles of sodium hydroxide in each 25.0cm^3 portion, (ii) the number of moles of ethanoic acid per cm^3 of diluted vinegar. (d) Find the concentration of ethanoic acid in the original vinegar (i) in terms of moles per litre, (ii) as a percentage (w/v) (e) Starting with a primary standard solution made from anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution? (9) (12 c

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Answer at least two questions from this section.See page 1 for full instructions. 1. To determine the concentration of ethanoic acid in a sample of vinegar, 25.0cm^3 of the vinegar were diluted to 250cm^3 and then the diluted vinegar was titrated with a previously standardised solution which contained 1.20 g of sodium hydroxide in 500cm^3 of solution. On average, 18.75cm^3 of the diluted vinegar were required to neutralise 25.0cm^3 of this sodium hydroxide solution. The equation for the titration reaction is: (a) Describe in detail the procedures involved in measuring a 25.0cm^3 sample of the vinegar and diluting it using deionised water to exactly 250cm^3 (15) (b) Name a suitable indicator for this titration.- Phenolohthal ein What colour change is observed at the end point? pink to clear (c) Calculate (i) the number of moles of sodium hydroxide in each 25.0cm^3 portion, (ii) the number of moles of ethanoic acid per cm^3 of diluted vinegar. (d) Find the concentration of ethanoic acid in the original vinegar (i) in terms of moles per litre, (ii) as a percentage (w/v) (e) Starting with a primary standard solution made from anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution? (9) (12 c

Answer at least two questions from this section.See page 1 for full instructions. 1. To determine the concentration of ethanoic acid in a sample of vinegar, 25.0cm^3 of the vinegar were diluted to 250cm^3 and then the diluted vinegar was titrated with a previously standardised solution which contained 1.20 g of sodium hydroxide in 500cm^3 of solution. On average, 18.75cm^3 of the diluted vinegar were required to neutralise 25.0cm^3 of this sodium hydroxide solution. The equation for the titration reaction is: (a) Describe in detail the procedures involved in measuring a 25.0cm^3 sample of the vinegar and diluting it using deionised water to exactly 250cm^3 (15) (b) Name a suitable indicator for this titration.- Phenolohthal ein What colour change is observed at the end point? pink to clear (c) Calculate (i) the number of moles of sodium hydroxide in each 25.0cm^3 portion, (ii) the number of moles of ethanoic acid per cm^3 of diluted vinegar. (d) Find the concentration of ethanoic acid in the original vinegar (i) in terms of moles per litre, (ii) as a percentage (w/v) (e) Starting with a primary standard solution made from anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution? (9) (12 c

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IsoldeProfessional · Tutor for 6 years

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<p><br />1. (a) <br />(b) Phenolphthalein. Pink to clear.<br />(c) <br />(i) 0.0015 mol<br />(ii) \( 8 \times 10^{-5} \mathrm{~mol/cm}^{3} \)<br />(d) <br />(i) 0.8 mol/L<br />(ii) 4.804%<br />(e) Sodium carbonate solution with hydrochloric acid; hydrochloric acid with sodium hydroxide.<br /></p>

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<p><br />1. (a) To measure a \( 25.0 \mathrm{~cm}^{3} \) sample of vinegar and dilute it to \( 250 \mathrm{~cm}^{3} \):<br /> - Use a pipette to accurately measure \( 25.0 \mathrm{~cm}^{3} \) of vinegar.<br /> - Transfer the vinegar to a \( 250 \mathrm{~cm}^{3} \) volumetric flask.<br /> - Add deionised water to the flask gradually, swirling to mix.<br /> - Continue adding deionised water until the bottom of the meniscus is at the \( 250 \mathrm{~cm}^{3} \) mark.<br /> - Stopper the flask and invert it several times to ensure thorough mixing.<br />2. (b) A suitable indicator for this titration is phenolphthalein. The colour change observed at the end point is from pink to clear.<br />3. (c) <br /> (i) To calculate the number of moles of sodium hydroxide in each \( 25.0 \mathrm{~cm}^{3} \) portion:<br /> - The molar mass of sodium hydroxide (NaOH) is \( 40.00 \mathrm{~g/mol} \).<br /> - \( 1.20 \mathrm{~g} \) of NaOH is dissolved in \( 500 \mathrm{~cm}^{3} \) of solution.<br /> - Concentration of NaOH solution: \( \frac{1.20 \mathrm{~g}}{500 \mathrm{~cm}^{3}} \times \frac{1}{40.00 \mathrm{~g/mol}} = 0.060 \mathrm{~mol/L} \).<br /> - Moles of NaOH in \( 25.0 \mathrm{~cm}^{3} \): \( 0.060 \mathrm{~mol/L} \times 0.025 \mathrm{~L} = 0.0015 \mathrm{~mol} \).<br /> (ii) To calculate the number of moles of ethanoic acid per \( \mathrm{cm}^{3} \) of diluted vinegar:<br /> - The reaction ratio between CH₃COOH and NaOH is 1:1.<br /> - Moles of ethanoic acid in \( 18.75 \mathrm{~cm}^{3} \) of diluted vinegar: \( 0.0015 \mathrm{~mol} \).<br /> - Moles of ethanoic acid per \( \mathrm{cm}^{3} \) of diluted vinegar: \( \frac{0.0015 \mathrm{~mol}}{18.75 \mathrm{~cm}^{3}} = 8 \times 10^{-5} \mathrm{~mol/cm}^{3} \).<br />4. (d)<br /> (i) To find the concentration of ethanoic acid in the original vinegar in terms of moles per litre:<br /> - The diluted vinegar is \( 10 \) times less concentrated than the original.<br /> - Concentration of ethanoic acid in the original vinegar: \( 8 \times 10^{-4} \mathrm{~mol/cm}^{3} \times 10 = 0.008 \mathrm{~mol/cm}^{3} \).<br /> - Convert to moles per litre: \( 0.008 \mathrm{~mol/cm}^{3} \times 1000 = 0.8 \mathrm{~mol/L} \).<br /> (ii) To find the concentration of ethanoic acid as a percentage (\( \mathrm{w} / \mathrm{v} \)):<br /> - Molar mass of ethanoic acid (CH₃COOH): \( 60.05 \mathrm{~g/mol} \).<br /> - Concentration in \( \mathrm{g/L} \): \( 0.8 \mathrm{~mol/L} \times 60.05 \mathrm{~g/mol} = 48.04 \mathrm{~g/L} \).<br /> - Convert to percentage (\( \mathrm{w} / \mathrm{v} \)): \( \frac{48.04 \mathrm{~g}}{1000 \mathrm{~cm}^{3}} \times 100 = 4.804 \% \).<br />5. (e) To standardise a sodium hydroxide solution starting with a primary standard solution made from anhydrous sodium carbonate:<br /> - First titration: Sodium carbonate solution with a standardised hydrochloric acid solution.<br /> - Second titration: The standardised hydrochloric acid solution with the sodium hydroxide solution to be standardised.<br /></p>
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