Question

[PLEASE HELP] There is a 30% concentration of cobalt chloride in 90 g of a water and cobalt chloride solution. What mass, in grams, of water has to evaporate to have a 40% concentration of cobalt chloride?

Answer 1

Where do water come here?

Cobalt chloride or CoCl_2 doesn't stay in dry state it contains crystals of water in hydrated form

• The formula is CoCl_2.2H_2O

Now coming to question

Amount of Cobalt chloride

• 30% of 90g
• 0.3(90)
• 27g

Amount ofw water

• 90-27
• 63g

For 40% concentration of CoCl_2 concentration left =100-40=60%

Let new mass of water be m

• 27/40=m/60
• 27/4=m/6
• 4m=162
• m=162/4
• m=40.5g

Water has to be evaporated

• 63-40.5
• 22.5g

Answer 2

22.5 g

Explanation:

If there is a 30% concentration of cobalt chloride in 90g of a water and cobalt chloride solution then:

• 30% = cobalt chloride
• 70% = water

Mass of Cobalt Chloride

30% of 90 g

= 0.3 × 90

= 27 g

Mass of Water

70% of 90 g

= 0.7 × 90

= 63 g

If a certain amount of water evaporates (note, the mass of cobalt chloride doesn't change), the ratio of cobalt chloride to water changes to 40% : 60%.

Let x be the new mass the water (in grams).

Therefore:

`\implies \sf 27 :x = 40\% : 60\%`

`\implies \sf27 : x = 0.4 : 0.6`

`\implies \sf (27)/(x)=(0.4)/(0.6)`

`\implies \sf (27)/(x)=(4)/(6)`

`\implies \sf (27)/(x)=(2)/(3)`

`\implies \sf 27 \cdot 3= 2x`

`\implies \sf 81= 2x`

`\implies \sf x = 81 / 2`

`\implies \sf x=40.5`

Therefore, the new mass of water is 40.5 g.

To find the mass of water that has evaporated, simply subtract the new mass from the original mass:

`\implies \sf 63 - 40.5 = 22.5\: g`

Therefore, the mass, in grams, of water that has to evaporate to have a 40% concentration of cobalt chloride is 22.5 g.