Question

Помогитеее, очень прошуу!К 300 г раствора с массовой долей HBr 16,2% прибавили 200 г раствора с массовой долей КОН x%. Полученный раствор разделили на две порции. Одну из них выпарили, причем образовалось 23,8 г КВr. Какой была массовая доля х? Какое из двух веществ- гидроксид натрия или серную кислоту- и какой массы следует добавить ко второй порции раствора для полной нейтрализации?

Answer 1

В исх. р-ре HBr n HBr = (300*0.162)/81 = 0.6 моль;

n KBr = 23.8/119 = 0.2 моль, n Br- = n KBr = 0.2 моль;

если бы в изб. оказался KOH, то независимо от масс. соотн-я порций р-ра, после выпаривания была бы пол-а смесь KBr+KOH;

след-но, в изб. - HBr, кот-я при нагр. улет-я;

презюмируя, что р-р разделен на 2 одинаковые порции, пол-м, что
в каждой части р-ра по 0.2 моль KBr и (0.6/2)-0.2 = 0.1 моль HBr;

тогда 0.2*2 = 0.4 моль ионов K+ и соотв-о 0.4 моль KOH было в исх-м р-ре KOH с м.д. x% = ((56*0.4)/200)*100 = 11.2%;

т.к. в изб. HBr, то надо доб-ь NaOH массой 40*0.1 = 4 г ко 2 порции.

Answer 2

Problem Analysis

To solve this problem, we need to determine the mass fraction of KOH (x%) in the solution and identify which substance, sodium hydroxide (NaOH) or sulfuric acid (H2SO4), should be added to the second portion of the solution for complete neutralization.

Solution

Let's break down the problem step by step:

1. We have a 300 g solution with a mass fraction of HBr of 16.2%. This means that in 300 g of the solution, there are 16.2 g of HBr. 2. We add 200 g of a solution with a mass fraction of KOH of x% to the original solution. 3. The resulting solution is divided into two portions. 4. One portion is evaporated, and 23.8 g of KBr is formed. 5. We need to find the mass fraction of KOH (x%) and determine which substance, NaOH or H2SO4, should be added to the second portion of the solution for complete neutralization.

Let's solve the problem step by step:

Step 1: Calculate the mass of HBr in the original solution: - Mass of HBr = Mass of solution * Mass fraction of HBr - Mass of HBr = 300 g * 16.2% = 48.6 g

Step 2: Calculate the mass of KOH in the added solution: - Mass of KOH = Mass of solution * Mass fraction of KOH - Mass of KOH = 200 g * (x/100)

Step 3: Calculate the total mass of KBr formed after evaporation: - Total mass of KBr = Mass of KBr formed + Mass of KBr from HBr - Total mass of KBr = 23.8 g + 48.6 g = 72.4 g

Step 4: Calculate the mass of KOH in the added solution using the total mass of KBr: - Mass of KOH = Total mass of KBr - Mass of KBr from HBr - (200 g * (x/100)) = 72.4 g - 48.6 g - 200 g * (x/100) = 23.8 g - x = (23.8 g / 200 g) * 100 - x = 11.9%

Therefore, the mass fraction of KOH (x%) in the added solution is 11.9%.

Step 5: Determine which substance, NaOH or H2SO4, should be added to the second portion of the solution for complete neutralization: - Since KOH is a base and HBr is an acid, we need to add an acid to the second portion of the solution for complete neutralization. - The acid that can be added is H2SO4.

Step 6: Calculate the mass of H2SO4 needed for complete neutralization: - The molar ratio between KOH and H2SO4 is 1:1. - The molar mass of KOH is 56.11 g/mol. - The molar mass of H2SO4 is 98.09 g/mol. - Therefore, the mass of H2SO4 needed = Mass of KOH added * (Molar mass of H2SO4 / Molar mass of KOH) - Mass of H2SO4 needed = 200 g * (98.09 g/mol / 56.11 g/mol) - Mass of H2SO4 needed = 349.82 g

Therefore, to the second portion of the solution, 349.82 g of sulfuric acid (H2SO4) should be added for complete neutralization.

Summary

In summary, the mass fraction of KOH (x%) in the added solution is 11.9%. To the second portion of the solution, 349.82 g of sulfuric acid (H2SO4) should be added for complete neutralization.