Tutor profile: Yanna C.
What is the difference between molecular and empirical formula?
The molecular formula, or true formula, tells us the kinds of atoms in the compound and the actual number of each atom. For example, the molecular formula H2O, tells us that there are two atoms of Hydrogen bonded with one atom of oxygen in the molecule of water. The small number that follows the symbol of an element is called a subscript and indicates the number of atoms of the specific elements that are present in a molecule. When there is only one atom of an element in the molecule, then there is no need to include a subscript (as for Oxygen in the example of the water molecule). An empirical formula indicates the unique kinds of elements in a compound and the lowest whole-number ratio of each type of atom in the molecule. The molecular formula of Vitamin C (L-ascorbic acid) is C6H8O6, meaning there are 6 Carbon, 8 Hydrogen and 6 Oxygen atoms present in the molecule (6:8:6). If we simplify this ratio, we will find its simplest whole number form to be 3:4:3, making the empirical formula of the molecule to be C3H4O3. Sometimes, the empirical formula happens also to be the molecular formula. In the previous example of H2O, the simplest whole-number ratio of Hydrogen to Oxygen atoms is 2:1, which makes the molecular formula also the empirical formula of water.
Subject: Basic Chemistry
What is a “chemically pure substance”?
A pure substance in Chemistry is a substance made from a single type of atom of compound throughout; this can be either an element or a compound. It is important to remember that the composition of a pure substance does not vary. An element, for example iron (Fe), is composed of a single type of atom. An atom is the tiniest particle of an element that still possesses all the properties of the element. The atoms of an element all have the same number of protons. In our example, all the atoms in iron have 26 protons in their nucleus. A compound is made of two or more elements in a specific ratio. Water (H2O) is an example of a compound that is composed of two elements, hydrogen (H) and oxygen (O). These elements are combined in a precise way — in a ratio of two hydrogen atoms to one oxygen atom (hence, H2O). Various compounds contain hydrogen and oxygen, but only one has that unique 2-to-1 ratio called water. A compound has physical and chemical properties different from the elements that make it up. In order to separate the components of a compound, we need to resort to chemical reactions.
What is human accelerated eutrophication?
Eutrophication (from Greek εύτροφος, meaning "well-nourished") is the process on which the excessive increase in photosynthetic nutrients in bodies of water (lakes, rivers and ponds) act as a source of fertilisers, stimulating an abnormal proliferation of aquatic algae. Human accelerated eutrophication impacts severely water quality and biodiversity. The two most common nutrients that amplify eutrophication are nitrogen and phosphorous and are usually introduced to the body of water through to the direct depositing of non-treated sewage or fertiliser run-off. As the alga population grows uncontrollably and covers the surface of the water, a significantly reduced amount of light accesses the photic zone. Reduced light means that the aquatic autotrophs decrease their photosynthetic rate, producing lower amounts of oxygen. The decreased levels of dissolved oxygen can result in the death of any number of larger communities. The rise in the death of organisms also increases the number of aerobic bacteria that decompose organic matter. The abundance of these bacteria diminishes the oxygen dissolved in the water, killing fish and other animals. Moreover, the shortage of oxygen causes the decomposition to be carried out by anaerobic bacteria. These multiply and release hydrogen sulfide, which makes water unfit for other living organisms and creates a putrid smell. The main human activities that led to widespread eutrophication in water bodies around the world are: a. Direct sewage and industrial waste discharge into water bodies b. Agricultural practices with excessive use of fertilisers (nitrates and phosphates) c. Concentrated animal feeding operations (CAFOs) d. Aquiculture (a technique of growing fish, shellfish, and aquatic plants directly into the water that contains dissolved nutrients)
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