What is the color of potassium

Understanding chemistry 4, student book

54 4  Workbook page 27 Alkali metals and halogens 1. What are alkali metals? In 1807 the English chemist Humphry Davy noticed that some substances can be influenced by electric current. This is how he invented electrolysis. When he electrolyzed molten caustic potash (potassium hydroxide, KOH), small metal balls were formed on the negative pole. The globules exploded violently in the water. J. J. Berzelius later named the metal potassium because it is obtained from an alkali (= base). Davy discovered the elements sodium, strontium, calcium, magnesium and boron through melt flow electrolysis ( page 23). Dangerous in water! (Fig. 54.2) E1 Prepare a crystallizing dish with water (about 5 cm high), a drop of washing-up liquid and a little phenolphthalein solution. a) A piece of lithium approx. 5mm in size dissolves in water with the formation of hydrogen gas and lithium hydroxide (Li + OH -). The H 2 gas can be ignited. b) A piece of sodium about 5mm in size reacts more violently with water. It melts into a drop that hisses across the surface of the water. If you put the piece of sodium on a piece of filter paper on the surface of the water, the H 2 gas can ignite by itself. Sodium hydroxide solution (Na + OH -) is formed. Alkali metals only have a single, loosely bound outer electron, which they can give off very easily. The larger the atoms, the more loosely the outer electrons are bound to the atom. Alkali metals are therefore very reactive. In water they form hydrogen gas and a hydroxide, eg 2 Na + 2 H 2 O H 2 + 2 Na + OH -. Alkali metals, especially sodium and potassium, occur in many compounds: Sodium carbonate (Na + 2 CO 3 2–, washing soda), sodium hydrogen carbonate (Na + HCO 3–, cooking soda), potassium nitrate (K + NO 3 -, potassium nitrate)… Flame colors ( Fig. 54.3) E1 Dip a moistened magnesia stick into the chlorides of the alkali metals. Hold the sample in the flame and observe the color of the flame. 54.1 The yellow flame color of sodium creates strong contrasts. LV1 54.2 Dangerous in the water! Alkali metals react with water and form H 2 gas and a hydroxide. 3p + lithium sodium 11p + potassium 19p + V1 alkali metals are the metals of the first group of the PSE: lithium Li, sodium Na, potassium K, rubidium Rb and cesium Cs. They are soft and react violently with water to form hydrogen gas and its hydroxides. Alkali metals are very reactive because they can easily give up their only external electron. M 54.3 Flame colors: The alkali metals lithium Li, sodium Na, potassium K, rubidium Rb and cesium Cs are revealed by their characteristic flame color. Li Na K Rb Cs Film q73v9q Film 8q979c Film 2n8e82 For testing purposes only - property of publisher öbv

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