Question

помогите! Смесь меди и цинка массой 40 г обработали концентрированным раствором щёлочи. При этом выделился газ объемом 8,96 дм3 (н.у.) Рассчитайте массовую долю меди в смеси.

Answer 1

Zn+2NaOH+2H2O=Na2[Zn(OH)4]+H2

1                                                  

n(H2)=8,96:22,4=0,4;n(Zn)=0,4;m(Zn)=0,4*65=26;w(Zn)=26:40=0,65(65%);

w(Cu)=35%

Answer 2

Calculation of the Mass Fraction of Copper in the Mixture

To calculate the mass fraction of copper in the mixture, we need to use the information provided. According to the problem statement, a mixture of copper and zinc with a mass of 40 g was treated with a concentrated alkaline solution, resulting in the release of gas with a volume of 8.96 dm³ at standard conditions (n.u.).

To solve this problem, we can use the concept of stoichiometry. The balanced chemical equation for the reaction between copper and zinc with an alkaline solution is not provided. However, we can assume that the reaction proceeds as follows:

Cu + 2NaOH → Cu(OH)₂ + Na₂ZnO₂

From this equation, we can see that 1 mole of copper reacts with 2 moles of sodium hydroxide (NaOH) to form 1 mole of copper hydroxide (Cu(OH)₂). Since the volume of the gas produced is given at standard conditions, we can assume that the gas is hydrogen (H₂) produced from the reaction of excess sodium hydroxide with zinc.

To calculate the mass fraction of copper, we need to determine the number of moles of copper in the mixture and divide it by the total number of moles of copper and zinc.

Calculation Steps:

1. Calculate the number of moles of hydrogen gas produced: - The volume of the gas is given as 8.96 dm³ at standard conditions. - At standard conditions, 1 mole of any ideal gas occupies 22.4 dm³. - Therefore, the number of moles of hydrogen gas produced is 8.96 dm³ / 22.4 dm³/mol = 0.4 mol.

2. Determine the number of moles of copper in the mixture: - Since the reaction between copper and sodium hydroxide is 1:2, the number of moles of copper is half the number of moles of hydrogen gas produced. - Therefore, the number of moles of copper is 0.4 mol / 2 = 0.2 mol.

3. Calculate the mass of copper in the mixture: - The molar mass of copper (Cu) is approximately 63.55 g/mol. - Therefore, the mass of copper in the mixture is 0.2 mol * 63.55 g/mol = 12.71 g.

4. Calculate the mass fraction of copper: - The mass fraction of copper is the mass of copper divided by the total mass of the mixture. - The total mass of the mixture is given as 40 g. - Therefore, the mass fraction of copper is 12.71 g / 40 g = 0.31775.

Answer:

The mass fraction of copper in the mixture is approximately 0.31775, or 31.775%.

Please note that the balanced chemical equation provided is an assumption based on the reaction between copper and sodium hydroxide. The actual balanced equation may differ depending on the specific reaction conditions.