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

The student could use a balance to measure the mass of an empty volumetric flask first. Then, using a pipette, fill the flask with 10.0 cm³ of the sucrose solution. After that, weigh the filled flask again. The difference in mass gives the mass of the solution, thus allowing the calculation of its density.

On the x-axis, plot the % concentration of sucrose solution (0-20) and on the y-axis, plot the density of sucrose solution (1.00-1.50 g cm⁻³). Mark the points from the table and draw a best-fit line through the points.

The presence of dissolved carbon dioxide gas would affect the measurement of density as it would lead to a lower density reading due to the gas bubbles in the solution. This interference could result in an inaccurate estimation of the sugar concentration.

Using the formula provided: ext{Density in g cm}^{-3} = (0.0204 imes ext{% concentration}) + 1.00 Substituting the density of the soft drink (1.07 g cm⁻³) into the equation:

1.07 = 0.0204 imes ext{% concentration} + 1.00

Rearranging gives: 0.07 = 0.0204 imes ext{% concentration}

Thus: ext{% concentration} = rac{0.07}{0.0204} ext{ which equals approximately } 3.43 ext{%}

Using the concentration of the sugar found in 100 cm³:

Total mass = (Concentration in grams per 100 cm³) × (Volume in cm³) / 100

In this case, it would be: Total mass = (10.6 g / 100 cm³) × 330 cm³ = 34.98 g.

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

The ion-electron equation for the oxidation reaction can be represented as:

The color change observed would be from blue to orange/red/brown, indicating the reduction of Cu²⁺ ions to Cu⁺ ions.

To find the concentration in mol dm⁻³, use the formula:

$C_1V_1 = C_2V_2$

where

• $C_1$ is the concentration of Cu²⁺ = 0.0250 mol dm⁻³,
• $V_1$ is the volume of Fehling's solution used = 19.8 cm³,
• $V_2$ is the volume of the diluted soft drink sample = 25.0 cm³.

Calculating: ext{Moles of Cu}^{2+} = C_1 imes V_1 = 0.0250 imes rac{19.8}{1000} = 0.000495

Now, using stoichiometric ratios from the reaction, the moles of reducing sugar in the solution would be the same:

Calculating the concentration, in moles per dm³: ext{Concentration} = rac{0.000495 moles}{rac{25.0}{1000}} = 0.0198 ext{ mol dm}^{-3}