Question

К 300 г. раствора натрий гидроксида с массовой долей щелочи 20 % добавили 200 мл воды. Определите массовую долю щелочи в новом растворе.

Answer 1

1) 20% = m(в-ва) : 300г × 100%
m(в-ва) = 60г
2) 200мл(Н2О) = 200г(Н2О)
3) m(р-ра после добавления воды) = 300г + 200г = 500г
4) W = 60г : 500г × 100% = 12%

Answer 2

Calculating the Mass Fraction of Alkali in the New Solution

To calculate the mass fraction of alkali in the new solution, we can use the following formula:

Mass fraction = (mass of solute / total mass of solution) × 100%

Given: - Initial solution mass = 300 g - Initial alkali mass fraction = 20% - Water volume added = 200 ml

First, let's calculate the mass of the alkali in the initial solution: Mass of alkali in the initial solution = Initial solution mass × Initial alkali mass fraction Mass of alkali in the initial solution = 300 g × 20%

Now, we need to calculate the total mass of the new solution after adding water. Since the density of water is 1 g/ml, the mass of 200 ml of water is 200 g.

Total mass of the new solution = Initial solution mass + Mass of added water Total mass of the new solution = 300 g + 200 g

Now, we can calculate the mass fraction of the alkali in the new solution using the formula mentioned above.

Mass fraction of alkali in the new solution = (Mass of alkali in the initial solution / Total mass of the new solution) × 100%

Let's calculate the mass fraction of the alkali in the new solution using the given values.

Mass of alkali in the initial solution = 300 g × 20% = 60 g Total mass of the new solution = 300 g + 200 g = 500 g

Mass fraction of alkali in the new solution = (60 g / 500 g) × 100%

Mass fraction of alkali in the new solution = (60 / 500) × 100%

Mass fraction of alkali in the new solution = 12%

So, the mass fraction of the alkali in the new solution is 12%.