Question

Рассчитайте массовую долю гидроксида калия в растворе, полученном при растворении 10 г металлического калия в 80 мл воды.

Answer 1

2К+2H2O=2KOH+H2
78---------------112--------------2
10----------------х=14,36 гр-----0,26
       
      14,36
__________% = 16% 
10+80-0,26

Answer 2

Calculation of Mass Fraction of Potassium Hydroxide in Solution

To calculate the mass fraction of potassium hydroxide (KOH) in the solution obtained by dissolving 10 g of metallic potassium in 80 ml of water, we need to consider the balanced chemical equation for the reaction between potassium and water:

2K + 2H2O -> 2KOH + H2

From the equation, we can see that 2 moles of potassium react with 2 moles of water to produce 2 moles of potassium hydroxide and 1 mole of hydrogen gas.

To determine the mass fraction of KOH, we need to find the molar mass of KOH and the total mass of the solution.

The molar mass of KOH is calculated as follows: - Molar mass of K = 39.10 g/mol - Molar mass of O = 16.00 g/mol - Molar mass of H = 1.01 g/mol

Therefore, the molar mass of KOH = (39.10 + 16.00 + 1.01) g/mol = 56.11 g/mol.

Next, we need to calculate the total mass of the solution. Since the density of water is approximately 1 g/ml, we can assume that 80 ml of water has a mass of 80 g.

Now we can calculate the mass of KOH produced in the reaction. Since the molar ratio between K and KOH is 1:1, the number of moles of KOH produced is equal to the number of moles of K used.

The number of moles of K can be calculated using its molar mass: - Molar mass of K = 39.10 g/mol - Mass of K used = 10 g

Therefore, the number of moles of K = 10 g / 39.10 g/mol = 0.255 moles.

Since the molar ratio between K and KOH is 1:1, the number of moles of KOH produced is also 0.255 moles.

Finally, we can calculate the mass fraction of KOH in the solution: - Mass of KOH = number of moles of KOH * molar mass of KOH = 0.255 moles * 56.11 g/mol = 14.33 g

The total mass of the solution is 80 g (from the water) + 14.33 g (from KOH) = 94.33 g.

Therefore, the mass fraction of KOH in the solution is: - Mass fraction of KOH = (mass of KOH / total mass of solution) * 100% = (14.33 g / 94.33 g) * 100% ≈ 15.19%.

So, the mass fraction of potassium hydroxide in the solution obtained by dissolving 10 g of metallic potassium in 80 ml of water is approximately 15.19%.