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Answers
2. Preparation of Hydrogen by electrolysis of water
Electrolysis of water is the decomposition reaction of water molecules in a container into Hydrogen gas and Oxygen gas by using electric current. Two long electrode rods made of platinum or iridium are inserted in a water container. The electrons are connected through copper wires to a DC battery with potential more than 1.25 V. Hydrogen gas will appear at the cathode. Oxygen gas will appear at the anode. The amounts of the gases are proportional to the total electrical charge (current X time duration) passed by the circuit.
Pure water is not ionic. So higher DC battery potential is needed for electrolysis. Addition of salt or an acid or a base into water improves electrolysis outputs a lot.
In water: 2 H2O (l) => 4 H⁺ (aq) + 2 O⁻² (aq)
Current
At the Cathode : 2 H⁺ (aq) + 2e⁻ => H₂ (g)
At the anode : 2 O⁻² (sq) => O₂ (g) + 2 e⁻²
An arrangement is made to collect the gases at the electrodes through tubes into containers.
20 - vol or 20 - volume Hydrogen peroxide indicates the concentration of it in water. H₂O₂ is sold in pharmacies in this way. 20-vol means about 6% by weight solution in water, or 1.7 Molar solution. Number 20 means that 1 ml of it gives rise to 20 ml of Oxygen gas when decomposed at STP (lab conditions). The reaction of decomposition is :
2 H₂ O₂ (l) => 2 H₂O (l) + O₂ (g) + Heat
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5. Laboratory method for production of Hydrogen.
H₂ is not produced by electrolysis in the lab. It is inefficient or inconvenient. It is produced by displacement reactions.
1. H₂ is produced by reactions of dilute acids (HCL, H2SO4) with commonly available reactive metals like Aluminum or Zinc.
Zn (s) + H₂ SO₄ (aq) => Zn SO₄ (s) + H₂ (g)
2. Aluminum & alkali metals can react with bases also and produce H2.
2 Al + 2 Na OH (aq) + 2 H₂O => 2 Na (AlO₂) (s) + 3 H₂ (g) + Heat
6. Zn (s) + H2 SO₄ (aq) => Zn SO₄ (s) + H₂ (g)
Zinc sulphate is a white crystalline/powder solid.
Fe (catalyst)
3 H₂ (g) + N₂ => 2 N H₃ (g)
200 dm 675 K
Ammonia gas is produced by combining H2 & N2 at high temperature and pressure in presence of catalyst Iron.
7. Reaction of H2 with
UV light
a) Cl2 : H₂ (g) + Cl₂ (g) => 2 H Cl (g) + Heat
This reaction takes place in a HCl burner. It needs heat or UV light to trigger.
b) Na : 2 Na (l) + H₂ (g) => 2 Na H (s)
Sodium Hydride is a gray solid powder insoluble in water.
c) Cu O : Cu O (s) + H₂ (g) => Cu (s) + H₂O (l)
Cupric Oxide is reduced to Copper by Hydrogen. Hydrogen is more reactive or positive compared to Copper.
9. Hardness of water is caused by presence of Magnesium and Calcium salts (ions) in water. They are impurities in water usually from ground sources. These ions and salts do not allow water to form lather with soap. So it is inconvenient for people to bathe with hard water. Hard water forms Calcium scales on tea kettles, utensils, water heaters etc. You have seen right ? It is caused by Calcium salts mainly.
Temporary hardness is removed by boiling water. For example if Calcium Hydrogen Carbonate is removable from water by boiling. By boiling precipitation occurs. So water becomes purer.
Permanent hardness cannot be removed by boiling water. For example Calcium Sulphate (PoP) is not removable that way. It remains in water. It is poorly soluble in water.
10. Permanent hardness of water can be removed by adding washing soda to water. It is used by laundry shops to reduce hardness before washing with soaps.
Na₂ CO₃ (aq) + Ca SO₄ (s) => Na SO₄ (aq) + Ca CO₃ (s)
Calcium carbonate can precipitate as a white solid powdery substance. So hardness is removed.
Answer:
can anyone help me to give answers for all these question if u didnot give correct answer then I will report it ,I need all the questions if one answer won't be there then I will report