Soft drinks contain a variety of sugars - Scottish Highers Chemistry - Question 11 - 2023

To accurately measure the mass of 10.0 cm³ of each sucrose solution, the student should first zero the balance with a clean, dry container or beaker placed on it. Then, using a pipette or a burette, draw exactly 10.0 cm³ of the sucrose solution and transfer it to the pre-weighed container. Finally, place the container with the solution back on the balance and record the mass displayed, ensuring to subtract the mass of the container for accurate results.

Using the data in the table, plot the % concentration of sucrose solution along the x-axis and the corresponding density on the y-axis. Each point should be plotted accurately within the tolerance of ½ a box. Connect all points with a best-fit line.

The soft drink needed to be flat because the carbon dioxide gas dissolved in it could affect the measured density. Bubbles of gas could decrease the mass of the liquid in the measurement, leading to an inaccurate density value.

Using the equation density

= (0.0204 × % concentration) + 1.00, substituting the density of the soft drink, which is 1.07 g cm⁻³, results in:

1.07 = (0.0204 × % concentration) + 1.00.

Rearranging gives:

0.07 = 0.0204 × % concentration.

Thus,

% concentration = \frac{0.07}{0.0204} \approx 3.43%.

To find the total mass of sugar in a 330 cm³ can, use the known concentration of 10.6 grams in 100 cm³. To calculate the total mass:

Total mass = concentration × volume

= (10.6 g/100 cm³) × 330 cm³ = 34.98 g.

The aldehyde functional group can be represented as -CHO, consisting of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom.

The ion-electron equation for the oxidation of a reducing sugar with Fehling's solution is:

C₁₂H₂₂O₁₁ + 2Cu²⁺ → 2Cu⁺ + C₁₂H₂₄O₁₁ + 2H⁺.

The observed colour change when a reducing sugar reacts with Fehling's solution is from blue to orange or brick red, indicating the presence of Cu⁺ ions.

The concentration of reducing sugars can be calculated using the titration results. First, calculate the moles of Cu²⁺:

Moles of Cu²⁺ = concentration × volume = 0.0250 mol dm⁻³ × 0.0198 dm³ = 0.000495 moles. Since the reaction with reducing sugar is 1:1, moles of reducing sugars = 0.000495 moles. For 25 cm³ of diluted soft drink, concentration = \frac{0.000495}{0.025} = 0.0198 mol dm⁻³.