## Put zinc particles with a mass of 18 g into 40 ml with a density of 1.29 g / cm ³ After the reaction, take out the remaining zinc particles, wash and dry them, and weigh them to 4.9 G Q: A. how many liters of hydrogen are produced? (in this case, the density of hydrogen is 0.09 g / cm ³） b. What is the percentage concentration of dilute sulfuric acid? c. What is the percentage concentration of the resulting zinc sulfate solution?

Zn + H2SO4 = = ZnSO4 + H2 ↑ 65 2 18G X65 / 2 = 18G / XX = 0.55g0.55g/0.09g/cm3 = 6.11ml = 0.0611l a; About 0.0611l hydrogen is produced. Let the percentage concentration of dilute sulfuric acid be x 40ml * 1.29g/cm3 = 51.6gzn + H2SO4 = = ZnSO4 + H2 ↑ 65 9818g 51.6g * X65 / 98 = 18G / 51.6g

### Solute mass (increase) solvent mass (constant) solution mass (increase) how to understand the increase of solute mass fraction? How to judge that the mass fraction of solute also increases when the molecular denominator increases at the same time

Mathematically,

Let a, B, C be any three positive numbers, and a < B,

The mass fraction before increasing the solute mass can be expressed as a / b,

After addition, it can be expressed as (a + C) / (B + C),

Obviously, b * (a + C) - A * (B + C) = (B-A) * C > 0,

Therefore, (a + C) / (B + C) > A / B, that is, the mass fraction will increase

### What matter evaporates the solvent and the mass fraction of solute becomes larger

As long as it is an unsaturated solution, the mass fraction of solute will increase after evaporating the solvent. When evaporating the saturated solution (constant temperature), no matter how many solvents are evaporated, the solution will still be saturated. Therefore, the mass fraction of solute remains unchanged

### How to calculate the mass fraction of solute in the reaction solution after reaction

1、 The calculation idea of solute mass fraction in the solution obtained after reaction: 1. What is the solute m after reaction? How many grams? 2. Calculate the mass of gas, precipitation and impurities respectively; A: Observe whether there is gas or precipitation in the equation and calculate their mass? B: Calculate the solid drugs participating in the reaction

### There are 100 grams of table salt solution with solute mass fraction of 10%. If the solute mass fraction is twice the original, calculate the steps

When 50 g of water is evaporated, the mass of solute remains unchanged and the mass of solution is halved, the mass fraction of solute is twice the original

### Put a small amount of iron powder into 20 g of copper sulfate solution, fully react and filter to obtain 19.6 g of filtrate, then what is the mass of iron powder? Does ferrous sulfate dissolve in water? Answer in writing

The simplest way to solve this problem is to use the difference method

Let the mass of iron powder added be X

Fe + CuSO4 = = FeSO4 + Cu ~ m represents poor quality

The solution is x = 2.8g

Therefore, the mass of iron powder is 2.8g