![]() The negative terminal of the battery is also called the cathode (cathodes attract cations). At the negative electrode, electrons from a battery are added to the water molecules. Water can be decomposed by passing an electric current through it. You will track the changes in the pH values over time. In this chemistry science fair project, you will use a 9-volt (V) battery to cause the electrolysis of water. In addition to adding an acid or a base to water, the pH can be changed by electrolysis. For example, pH 9.0 is 10 times more alkaline than pH 8.0 and 100 times (10 times 10) more alkaline than pH 7.0. The same holds true for pH values above 7, each of which is 10 times more alkaline (another way to say basic) than the next lower whole value. A solution with a pH of 3.0 is 1,000 times more acidic than a solution with a pH of 6.0. For example, a solution with a pH of 4.0 is 10 times more acidic than a solution with a pH of 5.0. Each whole number value of pH below 7 is 10 times more acidic than the next higher value. The most acidic item on the scale is battery acid with a pH value of -0.1 and the most basic item is household lye with a pH of 13.5. The scale is red at the top (0 pH) and slowly changes to blue at the bottom of the scale (14 pH). A pH greater than 7 is basic.ĭiagram of the pH scale lists common items along the scale as examples for basic and acidic items. The pH scale measures how acidic or basic a substance is. ![]() For example, when sodium hydroxide is added to water, it gives rise to hydroxide ions: There are more hydrogen ions in the hydrochloric acid solution than there are hydroxide ions, so the solution is acidic.īases are solutions that have a higher concentration of hydroxide ions than hydrogen ions. The hydrochloric acid molecule dissociates into a hydrogen ion and a chloride ion. For example, when hydrochloric acid is added to water, it gives rise to hydrogen ions: As you will see later, this corresponds to a pH of 7.0.Īcids are solutions that have a higher concentration of hydrogen ions than hydroxide ions. One in 10 million is represented in scientific notation as 1.0 X10 -7. One water molecule in 10 million is split into hydrogen and hydroxide ions. In pure water at room temperature, the rate of dissociation is low. Also note that the net charge is also conserved-the neutral water molecule gives rise to one positive and one negative charge, which add up to zero charge. Note that the number of atoms is conserved-there are two hydrogens and one oxygen on both sides of the equation. The following equation represents a water molecule dissociating, into a hydrogen ion and a hydroxide ion. You will measure the change in pH of two salt solutions, connected by a salt bridge, as a current is passed through them. When this happens, it creates two ions, or charged particles, which can cause a change in the pH of the solution. But the hydrogen atoms are not so tightly attached that they can't occasionally drift apart from the oxygen atom. ![]() The hydrogen atoms are covalently bound to the oxygen atom. Water molecules are made up of two hydrogen atoms and one oxygen atom, H 2O. One of the goals of the clean energy movement is to find ways split water molecules more efficiently, so that the hydrogen gas produced can be used as a fuel. In the process, water molecules are split, creating hydrogen and oxygen gas. Electrochemistry deals with situations where oxidation and reduction reactions are separated, so that the electrons flow between the redox reactions as a current. Reactions that are caused by the flow of electrons from a battery are called electrochemical reactions. In this science fair project, the chemical reactions are driven by an external applied voltage: a battery is connected to a salt solution, and the voltage from the battery causes chemical reactions in the salt water. ![]() When the electrons move from one molecule to another, the processes involved are called oxidation/reduction (redox) reactions. The processes involved in the making of a breaking of chemical bonds all come down to the movement of electrons. ![]()
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