Soft drinks contain a variety of sugars - Scottish Highers Chemistry - Question 11 - 2016

To measure the mass of 10.0 cm³ of each sucrose solution accurately, the student could use a pipette to dispense the solution into a weighing boat or container. First, tare the balance with the empty container. Then, use the pipette to add 10.0 cm³ of the sucrose solution to the container. Finally, measure the mass of the container with the solution and subtract the mass of the empty container to find the mass of the sucrose solution.

On graph paper, plot the % concentration of sucrose solution on the x-axis and the density of sucrose solution on the y-axis. Use appropriate scales and ensure all data points from the table are plotted correctly. Draw a best fit line through the points to show the relationship. All points should be within tolerance, with axes labeled.

The soft drink needed to be flat to ensure that no carbon dioxide gas was dissolved in the liquid. If gas is present, it can affect the measurement of density by increasing the volume and thereby giving an inaccurate density reading.

Using the equation provided, rearrange it to find the % concentration of sugars in the soft drink:

ext{density} = (0.0204 \times \text{% concentration}) + 1.00

Substituting in the soft drink density (1.07 g cm⁻³):

1.07 = (0.0204 \times \text{% concentration}) + 1.00

Solving for % concentration:

0.07 = 0.0204 \times \text{% concentration}

\text{% concentration} = \frac{0.07}{0.0204} \approx 3.43 ext{%}

Given that the soft drink contains 10⁻⁶ grams of sugar in 100 cm³, calculate the total mass in a 330 cm³ can:

$\text{Total mass} = \left( \frac{10^{-6} \text{ g}}{100 \text{ cm}^3} \right) \times 330 \text{ cm}^3 = 3.30 \times 10^{-6} \text{ g}$

The aldehyde functional group is represented as -CHO, where there is a carbon atom double-bonded to an oxygen (carbonyl) and single-bonded to a hydrogen atom.

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

$2\text{Cu}^{2+} + \text{reducing sugar} \rightarrow 2\text{Cu}^+ + \text{oxidized form of reducing sugar}$

The reducing sugars would change the color of Fehling’s solution from blue to brick-red or orange when reacted.

Using the titration data:

• The volume of Fehling's solution used is 19.8 cm³, which is 0.0198 dm³.
• The concentration of Cu²⁺ in Fehling's solution is 0.0250 mol dm⁻³.

Using the stoichiometric relationship:

$\text{Moles of } Cu^{2+} = 0.0198 \text{ dm}^3 \times 0.0250 \text{ mol dm}^{-3} = 0.000495 ext{ mol}$

Given the stoichiometry (1:1) between Cu²⁺ and reducing sugar:

The concentration of reducing sugars in the original sample is:

$C_s = \frac{0.000495 \text{ mol}}{0.0250 \text{ dm}^3} = 0.0198 \text{ mol dm}^{-3}$