Question

Помогите с задачей К латуни (сплаву меди с цинком) массой 23 г. добавили избыток hno3. К полученной смеси добавили избыток цинковых опилок. Далее добавили избыток соляной кислоты. При этом все реагенты добавляли после окончания реакций. В конце в сосуде остался прозрачный раствор и осадок массой 17 г. Определите массовую долю меди в латуни.

Answer 1

Ответ:

73.91%

Объяснение:

Реакция меди с концентрированной азотной кислотой (HNO₃):

Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O

Реакция цинка с образовавшимся нитратом меди:

Zn + Cu(NO₃)₂ → Zn(NO₃)₂ + Cu

Реакция оставшегося цинка с соляной кислотой (HCl):

Zn + 2HCl → ZnCl₂ + H₂

Масса латуни (сплав Cu-Zn) = 23 г

Масса образовавшегося осадка (меди) = 17 г

Масса цинка (Zn) = Масса латуни - Масса меди

= 23 г - 17 г

= 6 г

Теперь мы можем вычислить массовую долю меди (Cu) в латуни:

Массовая доля меди (x) = Масса меди / Масса латуни

= 17 г / 23 г

≈ 0.7391 (или округленно 73.91%)

Таким образом, массовая доля меди в латуни составляет 73.91%.

Answer 2

#### Problem Analysis To determine the mass fraction of copper in the brass alloy, we need to understand the reactions that occurred during the experiment. The given information states that excess nitric acid (HNO3) was added to the brass alloy, followed by excess zinc filings and excess hydrochloric acid (HCl). The resulting mixture left behind a transparent solution and a precipitate weighing 17 g. We can use this information to calculate the mass fraction of copper in the brass alloy. #### Solution Let's break down the reactions that occurred during the experiment: 1. Reaction between brass alloy and excess nitric acid (HNO3): - The nitric acid reacts with the zinc in the brass alloy to form zinc nitrate (Zn(NO3)2) and hydrogen gas (H2). - The copper in the brass alloy does not react with nitric acid. - The reaction can be represented as follows: ``` Zn + 2HNO3 -> Zn(NO3)2 + H2 ``` 2. Reaction between the resulting mixture and excess zinc filings: - The excess zinc filings react with the remaining nitric acid to form zinc nitrate and hydrogen gas. - The copper in the brass alloy does not react with zinc. - The reaction can be represented as follows: ``` Zn + 2HNO3 -> Zn(NO3)2 + H2 ``` 3. Reaction between the resulting mixture and excess hydrochloric acid (HCl): - The excess hydrochloric acid reacts with the zinc nitrate to form zinc chloride (ZnCl2) and nitric acid. - The copper in the brass alloy does not react with hydrochloric acid. - The reaction can be represented as follows: ``` Zn(NO3)2 + 2HCl -> ZnCl2 + 2HNO3 ``` Based on the reactions described above, we can conclude that the copper in the brass alloy does not participate in any of the reactions. Therefore, the mass of the precipitate (17 g) consists solely of the zinc compounds formed during the reactions. To calculate the mass fraction of copper in the brass alloy, we need to determine the mass of copper in the original brass alloy and divide it by the total mass of the alloy. Let's assume the mass of copper in the brass alloy is represented by "m" grams. Since the mass of the brass alloy is given as 23 g, the mass of zinc can be calculated as (23 - m) grams. The mass of the precipitate (17 g) consists of the mass of zinc compounds formed during the reactions. Therefore, we can write the following equation: ``` mass of zinc compounds = mass of precipitate = 17 g ``` Since the mass of zinc compounds is equal to the mass of zinc, we can write: ``` mass of zinc = 17 g ``` Now, we can set up an equation to relate the mass of copper and zinc in the brass alloy: ``` mass of copper + mass of zinc = mass of brass alloy m + 17 = 23 ``` Solving this equation, we find that the mass of copper in the brass alloy is 6 g. To calculate the mass fraction of copper, we divide the mass of copper by the total mass of the alloy: ``` mass fraction of copper = (mass of copper / mass of brass alloy) * 100 mass fraction of copper = (6 g / 23 g) * 100 ``` Calculating this expression, we find that the mass fraction of copper in the brass alloy is approximately 26.1%. Therefore, the mass fraction of copper in the brass alloy is approximately **26.1%**. #### Conclusion The mass fraction of copper in the brass alloy is approximately 26.1%. This calculation was based on the reactions that occurred during the experiment, where excess nitric acid, excess zinc filings, and excess hydrochloric acid were added to the brass alloy. The resulting mixture left behind a transparent solution and a precipitate weighing 17 g.