Respuesta :
Answer:
The boiling point of the water by adding 2.5 moles of aluminium nitrate will be changed by 4° C.
Explanation:
Step 1: define the formula for an elevation of the boiling point
Δ T b = i *K b *bB
⇒with Δ T b = the elevation of the boiling point ( in °C or Kelvin)
⇒with i = van't Hoff i -factor for the solute. The factor i shows the number of individual particles (typically ions) that are formed by a compound in the solution.
⇒ with Kb = ebullioscopic constant, which depends on the properties of the solvent. (Eventually can be calculated).
⇒ with bB= the molal concentration (molality) of the solute.
Since we have 2 different solutions ( component 1 = sugar and component 2 = aluminium nitrate) of the same molality in the same solvent ( water). We can express this as followed:
Δ T b,2 / Δ T b,1 = (i2 * Kb * bB ) / (i1 * Kb *bB)
⇒after he was simplifying this becomes:
Δ T b,2 / Δ T b,1 = i2 / i1
⇒ Now we can isolate either Δ T b,2 or Δ T b,1:
Δ T b,2 =(i2/i1) x Δ T b,1
Sugar
⇒ is a covalent compound, so it doesn't dissociate in water ⇔ i1=1
Aluminium nitrate
⇒ it's a soluble ionic compound and in solution it will dissociate as the following equation:
Al(NO3)3 (aq) → Al3+(aq) + 3NO3- (aq)
⇒thus here are 4 particels formed : 1 Al3+ + 3NO3-
i2=4
As given, we also know that the temperature was raised by 1°C after adding sugar ⇒ Δ T b,1 = 1°C
Step 2: insert all the numbers in the formula for boiling point elevation
(i2/i1) x Δ T b,1
(4/1 ) x 1°C = 4°C
⇒ The boiling point of the water by adding 2.5 moles of aluminium nitrate will be changed by 4°C
