Answer: The kilograms of water must evaporate from 8kg of a 25% salt solution to produce 40% salt solution is 3 kg.
Explanation:
According to the ratio and proportion:
[tex]C_1m_1=C_2m_2[/tex]
where,
[tex]C_1[/tex] = concentration of ist solution = 25%
[tex]m_1[/tex] = mass of ist solution = 8 kg
[tex]C_2[/tex] = concentration of second solution = 40%
[tex]m_2[/tex] = mass of second solution = ? kg
[tex]25\times 8=40\times m_2[/tex]
[tex]m_2=5kg[/tex]
Thus the final solution must have a mass of 5 kg , i.e (8-5)= 3 kg of mass must be evaporated.
Therefore, the mass that must be evaporated from 8kg of a 25% salt solution to produce 40% salt solution is 3 kg.