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Chemistry is all around us
Copyright 2015
This project has been funded with
support from the European Commission

Educational Packages

Chemistry at Home

Chemical substances in foods


Nutrients in foods
Foods contain six types of nutrients. Carbohydrates, fats, proteins, vitamins, minerals and trace-elements, and water are considered nutrients. Sufficient quantities of these nutrients are obtained from foods, in order to cover the needs of a living organism. Many times during the treatment of foods we add several chemical substances. Food additives are natural or artificial substances added to food to preserve or enhance its color, flavour, taste and appearance.

Raising Agents
When you want to bake bread or a cake you have to add a material in order to make it rise. Baking soda and baking powder are such materials. The rising of bread or a cake occurs with the addition of baking powder or baking soda. These substances react with certain ingredients of dough and a gas (carbon dioxide: CO2) is released allowing the bread to rise. Therefore, they are called raising agents.

Baking soda is a chemical substance known as sodium bicarbonate (NaHCO3). When baking soda is mixed with an acid in liquid form (such as vinegar or lemon juice), a chemical reaction is carried out to form a salt, water, and the carbon dioxide gas (CO2) .

Baking powder (a white powder) is a dry material used as a raising agent. It consists of three basic components: baking soda (sodium bicarbonate), tartaric acid, and corn starch. When baking powder is exposed to water, the first two of the above components react to form carbon dioxide gas, producing bubbles and allowing the dough to rise. The label of the commercial product indicates that corn starch is the ingredient with the highest proportion. Why should corn starch exists in such a high proportion since it does not participate in any chemical reaction? There are three reasons why this occurs: 1) Corn starch helps the product remain dry and prevents clotting, 2) Corn starch retains sodium bicarbonate and tartaric acid dry preventing their reaction while stored and 3) Corn starch increases baking powder’s mass and therefore makes measurements easier. It is easier to have to add a spoonful of a powder to a recipe instead of a few grains.

Most baking powders are double-acting, which means that they contain one acid that dissolves when it comes in contact with water and another acid that does not dissolve until it reaches a higher temperature in a hot oven. This type of double action ensures that the finished product is light and fluffy.

Concentrations of Substances
The concentration of a dissolved substance (e.g, sugar) is the quantity of the substance that has been dissolved in a certain amount of solvent (e.g. water) or solution (e,g. sugar water). The solution of a substance is denser when the concentration is high, and conversely the solution is dilute when the concentration is low. The amount of the dissolved substance as well as the amount of the solvent and the solution can be expressed in various metric units e.g. units of mass (kg, g), units of volume (L, mL) etc. That is the reason why there are many ways to express the concentration.

Reaction Rate - Factors Influencing Reaction’s Rate
Every chemical reaction proceeds with a different rate. The rate of a chemical reaction depends on how quickly the molecules of the reactants react in order to form the molecules of the products. It is known that there are some chemical reactions that are performed with higher rate than others. For example, the reactions that take place in the explosion of a bomb are performed with a high rate, while the transformation of graphite into diamond or the oxidation of iron (rusting) are done very slowly and may take even years to happen.

There are many factors that can affect the rate of a chemical reaction. These factors are: 1) The temperature in which the chemical reaction is performed, the rate of which is generally increased when the temperature increases, 2) The concentration of the reactants. The reaction rate increases as long as the concentration increases. 3) The contact surface of the solids. If the contact surface of a solid is increased the rate of the reaction increases as well. 4) The presence of substances that act as catalysts. These substances always increase the rate of the reaction.

The Chemistry’s section which studies the rate of chemical reactions is called “Chemical Kinetics”.

Iodine and Thyroid Gland
Iodine is a non metal element and is characterized as a micronutrient. Micronutrients are nutrients required by humans throughout life in small quantities in order to orchestrate a whole range of physiological functions, which however cannot be produced by the human body itself.

Iodine is an essential element because it enables the thyroid gland to produce the thyroid hormones. Iodine is stored in the thyroid gland and is used in the hormones’ synthesis procedure. Three iodine molecules are combined to make T3 (triiodothyronine), and four for making T4 (thyroxine), the two key hormones produced by the thyroid gland.

As iodine is essential for the production of these two hormones of the master gland of metabolism, an iodine deficiency leads to low production of these hormones. Less severe iodine deficiency is linked to thyroid enlargement (goiter). A severe iodine deficiency can cause hypothyroidism, and even developmental brain disorders (cretinism). On the other hand, excessive iodine intake is also associated with hyperthyroidism and goiter.

Every human needs the proper amount of iodine for optimal thyroid function. The problem is that there are many areas around the world where soils are deficient in iodine. In order to provide the population with a sufficient dietary supply of iodine we add colorless iodine compounds to table salt, and not elemental iodine (I2) which has a brown color. In this way, we produce the commercial product that is known as iodized table salt. The iodine compounds which are added to table salt contain also iodide ions (I-). One difficulty with this, is that the iodide ion (I-), of the iodized salt, is easily oxidized to iodine (I2) by atmospheric oxygen (O2). An accumulation of iodine (I2) in a package of table salt would result in the salt becoming brown in color and acquiring a very bad taste. To avoid this problem, we add a substance, usually dextrose, which has the ability to reverse this reaction and transform any iodine (Ι2), that may be formed, back to the colorless iodide ion (I-).

Table Salt
Table salt’s main ingredient is sodium chloride (NaCl), which absorbs the atmosphere’s moisture and tends to clot when it is exposed to air with high humidity. In order to prevent table salt’s clotting we add chemical substances, like silicon dioxide (SiO2) and calcium phosphate (Ca3(PO4)2), which absorb moisture and retain table salt dry.

To determine iodine in table salt we use starch in combination with a chemical substance (e.g. hydrogen peroxide) which transforms the colorless iodine compounds into iodine (Ι2). Starch along with iodine acquires a blue color.