Answer:
After the solution is heated, but before additional solute is added
Explanation:
An unsaturated solution is a solution that contains less solute than it can normally hold at a given temperature. Hence an unsaturated solution can still dissolve more solute.
When the solution is heated, the saturated cold solution becomes an unsaturated hot solution which is capable of dissolving more solute at this point.
Once more solute is dissolved, the solution becomes saturated again just before it begins to cool since no more solute dissolves in the solution at some point before cooling and addition of seed crystals.
Answer & Explanation:
(a)
reducing agent = Fe²⁺
Oxidizing agent = NO₃⁻
oxidation
Fe²⁺ ⇒ Fe(OH)₃
reduction
NO₃⁻ ⇒ N₂
Oxidation Half Reaction
(<em>redox reactions are balanced by adding appropriate H⁺ and H₂O atoms)</em>
Fe²⁺ ⇒ Fe(OH)₃
Balance O atoms
Fe²⁺ + 3H₂O ⇒ Fe(OH)₃
Balance H atoms
Fe² + 3H₂0 ⇒ Fe(OH)₃ + 3H⁺
balance Charge
Fe² + 3H₂0 ⇒ Fe(OH)₃ + 3H⁺ + e⁻..............(1)
reduction Half Reaction
NO₃⁻ ⇒ N₂
Balance N atoms
2NO₃⁻ ⇒N₂
Balance O atoms by adding appropriate H₂O
2NO₃⁻ ⇒ N₂ + 6H₂O
Balance H atoms
2NO₃⁻ + 12H⁺ ⇒ N₂ + 6H₂O
Balance Charge
2NO₃⁻ + 12H⁺ + 10e⁻⇒ N₂ + 6H₂O.................(2)
Combine Equation (1) and (2)
(1) × 10: 10Fe² + 30H₂0 ⇒ 10Fe(OH)₃ + 30H⁺ + 10e⁻
(2) × 1: 2NO₃⁻ + 12H⁺ + 10e⁻⇒ N₂ + 6H₂O
(1) + (2): 10Fe² + <u><em>30H₂0</em></u> + 2NO₃⁻ + <u><em>12H⁺</em></u> + <u><em>10e⁻</em></u> ⇒10Fe(OH)₃ + <u><em>30H⁺</em></u><u><em> </em></u>+ <em><u>10e⁻</u></em> +
N₂ + <u><em>6H₂O</em></u>
10Fe² + 24H₂0 + 2NO₃⁻ ⇒ 10Fe(OH)₃ + 18H⁺ + N₂
this is the balanced reaction
REDUCTION POTENTIAL
10Fe²⁺(aq) + 10e⁻ ⇒ 10Fe(OH)₃(aq) E°ox = 10(-0.44) = -4.4V
2NO₃⁻(aq) - 2e⁻ ⇌ N₂(g) + 18H⁺ E°red = 2(+0.80) = +1.6
10Fe² + 24H₂0 + 2NO₃⁻ ⇒ 10Fe(OH)₃ + 18H⁺ + N₂ E°cell = -2.8V
E°cell = E°red + E°ox
Answer:
Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tyres skidding on the road. When you walk, friction is caused between the tread on shoes and the ground. This friction acts to grip the ground and prevent sliding. Sometimes we want to reduce friction.
Explanation:
On the periodic table, hydrogen and helium are the only two elements in the first row, or period, which reflects that they only have electrons in their first shell. Hydrogen and helium are the only two elements that have electrons exclusively in the 1 s 1s 1s orbital in their neutral, non-charged, state.