Study of the First Element - Hydrogen
ICSE · Class 9 · Chemistry
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See them allWhy is hydrogen placed at the top of the periodic table and why is its position controversial?
Answer
Hydrogen has atomic number 1, one electron in its valence shell, and valency 1. It is placed in the 1st Period and Group 1A. Its position is controversial because it resembles alkali metals in some wa…
What is the electronic configuration, symbol, molecular formula, and valency of hydrogen?
Answer
Symbol: H. Molecular formula: H2. Electronic configuration: 1 in the K shell. Valency: 1. Hydrogen is the first element of the periodic table and has atomic number 1.
State the balanced equation for potassium reacting with cold water.
Answer
Balanced equation: 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g). The reaction is highly exothermic and vigorous. Potassium floats, melts, and burns with a lilac flame.
State the balanced equation for sodium reacting with cold water.
Answer
Balanced equation: 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g). Sodium floats on water, melts into a silvery globule, and the reaction is less vigorous than potassium.
State the balanced equation for calcium reacting with cold water and give the observation.
Answer
Balanced equation: Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g). Calcium sinks in water and forms a milky, turbid alkaline solution because calcium hydroxide is formed.
State the balanced equation for magnesium reacting with boiling water.
Answer
Balanced equation: Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g). Magnesium reacts slowly with boiling water and liberates hydrogen.
State the balanced equation for magnesium reacting with steam.
Answer
Balanced equation: Mg(s) + H2O(g) → MgO(s) + H2(g). Magnesium burns in steam with intense white light and forms magnesium oxide.
State the balanced equation for aluminium reacting with steam at high temperature.
Answer
Balanced equation: 2Al(s) + 3H2O(g) →(800°C) Al2O3(s) + 3H2(g). Aluminium forms a protective oxide coating, but at high temperature the coating breaks and the reaction continues.
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