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THINK ABOUT IT

The safety of artificial sweeteners has been the subject of debate for years. More recently, some schools have banned the sale of both diet and regular soft drinks. Regular soft drinks are sweetened with fructose, while diet soft drinks are usually sweetened with aspartame. If you want to make a healthy decision, you need to consider the toxicities of fructose and aspartame and the amount of each substance in a can of beverage.

How can you use moles to compare toxicity?

To answer this question, you will explore

EXPLORING THE TOPIC

Comparing Moles of Sweeteners

It is hard for many of us to imagine a day without sugar. From cereal to flavored drinks and candy, our intake of sugar adds up. So, when the first artificial sweeteners came onto the market in the 1950s, it seemed a good idea to use this low-calorie substitute for a favorite ingredient.

Two sweeteners, fructose, C₆H₁₂O₆, and aspartame, C₁₄H₁₈N₂O₅, are shown. Notice that they are both medium-sized molecules made up of carbon, hydrogen, and oxygen atoms. The artificial sweetener, aspartame, also has two nitrogen atoms in its molecules.

The molar masses of fructose and aspartame represent the mass per mole of molecules. Recall that you can obtain the molar mass of a molecule by adding the molar masses of each atom in the molecule.

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The molar mass of fructose is less than that of aspartame. A 1 g sample of fructose will contain more molecules than a 1 g sample of aspartame because each fructose molecule has a smaller mass than an aspartame molecule.

A can of regular soft drink has about 40.0 g of fructose as a sweetener. A can of diet soft drink has about 0.225 g of aspartame as a sweetener. You can determine the number of molecules of sweetener in each can using the molar mass of each substance.

A diet soft drink needs only 0.00076 mol of aspartame molecules to replace the sweetness of 0.22 mol of fructose molecules in a regular soft drink. So you need significantly less aspartame to obtain the same sweetness provided by fructose.

Toxicity of Sweeteners

Artificial sweeteners allow people with diabetes, and others who must avoid sugar, to enjoy foods that would otherwise be dangerous for them to eat. Artificial sweeteners do not cause cavities, and because they are not digested, artificial sweeteners do not provide extra calories to the body. However, the safety of artificial sweeteners continues to be a subject of debate.

To make an informed decision about whether you want to consume artificial sweeteners, it is useful to compare the toxicities of fructose and aspartame. Take a moment to review this information about each sweetener.

The LD₅₀ of fructose in grams is about three times larger than the LD₅₀ for aspartame (30 g per kg versus 10 g per kg). The LD₅₀ in moles is almost five times larger for fructose than for aspartame (0.158 mol per kg versus 0.034 mol per kg). So, the sweetner aspartame is more toxic than fructose if you consume similar amounts of each.

It would be difficult to drink enough regular soda or diet soda to reach the lethal dose in a short period of time. So it is highly unlikely that exposure to either fructose or aspartame would be lethal in the short term. However, it is important to note that the LD₅₀ is not a good measure of health effects from long-term exposure. It is probably best to limit intake of both sugar and aspartame.

LESSON SUMMARY

How can you use moles to compare toxicity?

Chemists often find it useful to compare moles of substances rather than masses of substances. Moles allow you to compare numbers of molecules or formula units in your sample. Substances with large molar masses contain fewer molecules per gram than substances with smaller molar masses. The health effect of exposure to a toxic substance depends on both the LD₅₀ and the amount of the substance.