Find the answer to the third grade chemistry calculation question (the best analysis)

Special exercises of chemical calculation in grade three.

Calculation is the compulsory content of the senior high school entrance examination, and it is also the last question of the examination paper. It will also be interspersed with experimental questions and inquiry questions, accounting for about 4 ~ 7 points. Typical problems in the senior high school entrance examination: the calculation of chemical reaction equation and equation in solution, the calculation of hydrogen generated by the reaction between metal and acid, and the calculation of graphic image analysis. It is mainly divided into three categories: calculation according to chemical formula, calculation according to chemical equation and calculation of related solutions.

First, according to the chemical formula.

Basic knowledge:

① Relative molecular mass = sum of atomic mass of each atom in the molecule (number of atoms × relative atomic mass);

② Element mass ratio = element mass fraction ratio = atomic number ratio × relative atomic mass ratio;

③ Mass fraction of elements = relative atomic mass of elements × atomic number ÷ relative molecular mass.

Examination questions:

① Calculate the atomic number ratio of each element in the molecule.

② Calculate the relative molecular mass of molecules.

③ Calculate the mass ratio of each element in the molecule.

④ Calculate the mass fraction of an element in the molecule.

⑤ Give the mass of a substance and calculate the mass of an element.

example

1.(07 Jilin Province) The following is the solving process of Xiaogang's calculation of nitrogen content in ammonium nitrate (NH4NO3).

Solution: the mass fraction of nitrogen in NH4NO3 =×100% =× l00% =17.5%.

A: The mass fraction of nitrogen in NH4NO3 is 17.5%.

Xiao Gang's calculation error is:

A: The number of nitrogen atoms in the formula is not multiplied by 2.

practise

1.(08 Fuzhou, Fujian) (4 points) "Opposing the use of illegal drugs by athletes" is an important embodiment of the "People's Olympics" in Beijing in 2008. Ethylestrol (C20H32O) is a banned drug, which is composed of three elements, and the number ratio of carbon, hydrogen and oxygen atoms in the molecule.

2.(08 Guangdong) (7 points) At the beginning of 2008, snow melting agent played a certain role in the fight against snowstorms in the south. The main component of a snow melting agent is potassium acetate (CH3COOK). The snow melting agent has good snow melting effect and no pollution. Please answer:

(1) mass ratio of carbon, hydrogen and oxygen in potassium acetate

(2) The relative molecular mass of potassium acetate is, and the mass fraction of potassium element is (keep one decimal place).

3.(08 Jieyang, Guangdong) (4 points) Recently, the national anti-drug exhibition with the theme of "Cherish life and refuse drugs" was held in major cities across the country. A drug extracted from cannabis leaves is called cannabinol, and its chemical formula is C2 1H26O2, which is burned in the air to produce carbon dioxide and water.

(1), and the relative molecular mass of this substance is.

(2) The mass ratio of carbon, hydrogen and oxygen in a substance.

4.(08 Heilongjiang) (2 points) The glue used in leather shoes production contains n-hexane (C6H 14). Please answer the following questions: ① The mass ratio of carbon to hydrogen in n-hexane is _ _ _ _ _ _ _ _; ② The mass fraction of carbon in n-hexane is (expressed by fraction)

5.(08 Yichang, Hubei) (2 points) The chemical formula of chemical fertilizer ammonium nitrate is (NH4NO3). Try asking:

(1) The mass ratio of N, H and O in ammonium nitrate;

(2) In order to ensure that a certain crop can obtain 3.5㎏ nitrogen, ammonium nitrate is needed.

6.(08 Tai 'an, Shandong) (2 points) Shikimic acid is an important component of Chinese traditional spice Illicium verum, and it is also the raw material of Tamiflu, an international anti-avian influenza medicine. Please calculate according to the chemical formula of shikimic acid (C7H 10O5):

(1) mass ratio of hydrogen to oxygen in shikimic acid;

(2) 174 g shikimic acid contains g carbon.

7.(08 Leshan, Sichuan) (4 points) The right picture shows some information of "△△" brand potash fertilizer: according to this information, it is calculated that:

(1) mass ratio of each element in potassium sulfate;

(2) What is the highest content of potassium in this potash fertilizer?

8.(08 Yantai, Shandong Province) (5 points) In recent years, our city has actively explored the service system of building a new socialist countryside, and many farmers have obtained the service of "testing soil and formulating fertilization", which effectively solved the problem of unreasonable fertilization ratio, increased production and reduced environmental pollution. Xiaoming's family planted a piece of wheat. According to the determination of agricultural personnel, this soil needs to be supplemented with 39 kilograms of potassium and 42 kilograms of nitrogen. Please help Xiaoming figure out how many kilograms of potassium nitrate and ammonium nitrate should be bought at least?

Second, according to the chemical equation calculation

Examination questions:

① Calculation of reactants and products: describe a chemical reaction, give the mass of reactants or products, or give charts or images related to the chemical reaction (usually the relationship between a reactant and the generated gas or precipitate), and find the mass of other reactants or products;

(2) Calculation of impurities: Calculate the mass fraction of impurities in reactants through the known information in the questions;

③ Overcalculation

(4) Given the actual situation in life, use chemical reaction to judge whether the product is qualified.

example

1. (Changchun, 08) CaCO3 is decomposed at high temperature to generate CaO and CO2, and the mass of CaO generated by 200g CaCO3 is calculated.

Solution: CaCO3, high temperature CaO+ CO2↑ =

100 56

200 grams x

X/56 = 200g/ 100 gives x = 1 12g.

A: The mass of CaO produced by pyrolysis of 200gCaCO3 is 1 12g.

practise

1. (Changchun 09) If a certain mass of coal contains 16g of sulfur, calculate the mass of sulfur dioxide produced when these coals are completely burned.

2.(07 Jilin Province) In industry, calcium oxide (CaO) and carbon dioxide can be produced by calcining limestone (CaCO3) at high temperature. If limestone containing 80% calcium carbonate is calcined at high temperature for 25 t (impurities do not react), how many tons of carbon dioxide can be produced at most?

3.(08 Anhui) (6 points) Xiaoming learned through consulting the data that increasing the CO2 concentration in the air in the vegetable greenhouse can effectively increase the yield of vegetables. He intends to use dilute hydrochloric acid and limestone (CaCO3 is the main component, impurities do not participate in the reaction) to supplement CO2 to his vegetable greenhouse. It is estimated that Xiaoming will input 88gCO2 into the greenhouse. How many grams of dilute hydrochloric acid does he need at least 10%?

4.(08, Dazhou, Sichuan) The ninth grade comprehensive practice activity group of a school uses a certain amount of hydrogen peroxide solution and manganese dioxide with solute mass fraction of 10% to generate oxygen, and the relationship between gas quality and time is shown in the right figure.

Please calculate: What is the mass of the hydrogen peroxide solution used? (Write the problem-solving process)

5.(08 Fuzhou, Fujian) On a certain day in September 2007, a tanker full of concentrated sulfuric acid capsized in Qingliu County, our province, causing 26 tons of concentrated sulfuric acid with 98% solute mass fraction to leak and flow into a nearby stream. Armed police officers and soldiers who heard the news immediately built a dam and neutralized diluted sulfuric acid with lime slurry (mainly calcium hydroxide). Calculation: How many tons of calcium hydroxide is needed theoretically to neutralize the leaked sulfuric acid? (accurate to 0. 1)

6.(08 Jinjiang, Fujian) The National Water Cube used 1 1200 tons of steel. If these steels are obtained by reducing iron oxide with carbon monoxide, what is the minimum mass of iron oxide? (The chemical equation of the reaction is 3CO+Fe2O3, high temperature, 2Fe+3CO2).

7.(08 Sanming, Fujian) In the laboratory of Sanming Minxin Cement Factory, in order to determine the mass fraction of calcium carbonate in limestone of a mine, limestone samples were taken and reacted with enough dilute hydrochloric acid in a beaker (assuming that impurities in limestone samples did not react with dilute hydrochloric acid and were insoluble in water). ) The experimental data are as follows:

Before and after reaction

Experimental data: mass of beaker and dilute hydrochloric acid: mass of limestone sample: mass of beaker and its mixture.

150g12g157.6g.

Relative atomic mass: C 12 O 16 Ca 40.

(1) According to the law of conservation of mass, the mass of carbon dioxide produced in the reaction is g.

(2) Calculate the mass fraction of calcium carbonate in limestone. (The chemical equation of this reaction is CaCO3+2 HCl CaCl2+H2O+CO2 =).

8.(08, Jieyang, Guangdong) (5 points) There is a layer of scale at the bottom of the thermos bottle that has been used for a long time, and the main components are CaCO3 and Mg(OH)2. The students of a chemical research group in a school measured the content of CaCO3 in the scale through experiments: taking 200g scale, adding excessive dilute hydrochloric acid, and measuring the quality of gas generated within 5 minutes. The results are as follows:

Time/minute 1 2 3 4 5

Quality /g 30 50 60 66 66

Try to answer the following questions:

(1) After 4 minutes, the generated CO2 no longer increased, indicating that CaCO3 (filled or unfilled) in the scale completely reacted.

(2) What is the mass fraction of CaCO3 in the scale?

9.(08 Shantou, Guangdong) After deliquescence, NaOH can easily react with CO2 in the air to generate Na2CO3 and deteriorate. In order to determine the NaOH content in a bottle of caustic soda that has been kept in the laboratory for a long time, a classmate took a proper amount of caustic soda sample and dissolved it in a certain amount of water to get 200g solution. Then add 200 grams of dilute sulfuric acid (enough) and fully stir until bubbles are no longer released. The solution is 395.6 grams. Please calculate:

The mass of CO2 produced by (1) reaction is g.

(2) If the sample of caustic soda is 50.0g, what is the mass fraction of NaOH in the sample?

(3) The sulfuric acid with the same concentration is used to react with a bottle of caustic soda sample that has not deteriorated, partially deteriorated and completely deteriorated (the impurity is Na2CO3), and the required sulfuric acid quality is equal. The reason is: (explained from the perspective of sodium mass conservation).

10.(08 Heilongjiang) There is a layer of scale at the bottom of the long-used hot water kettle, and the main components are CaC03 and Mg(OH)2. The students in the school chemistry research study group want to determine the content of CaC03 in the scale through experiments. They took a 200g balance, added excessive dilute hydrochloric acid, and measured the quality of CO2 produced within 5 minutes (min). The measurement data are as follows:

Time/minute 1 2 3 4 5

Mass of carbon dioxide produced/g 30 50 60 66 66

Calculation: ① After 4 min, does CaCO3 in the scale react completely? ② What is the mass fraction of CaCO3 in the scale?

1 1.(08 Xuzhou, Jiangsu) The main component of eggshells is calcium carbonate. In order to determine the mass fraction of calcium carbonate in an egg shell, a group of students carried out the following experiments: after washing, drying and mashing the egg shell, weighing 10g into a beaker, then adding enough dilute hydrochloric acid 90g into the beaker, and after full reaction, weighing the reaction residue as 97. 14g. (Assuming that other substances do not react with hydrochloric acid)

(1) produces carbon dioxide gas g.

(2) Calculate the mass fraction of calcium carbonate in eggshells.

12.(08 Shandong) The environmental protection department analyzed the wastewater from a factory, and the results showed that:

The waste water contains a small amount of sulfuric acid. Take a certain amount of wastewater and neutralize it with 2% sodium hydroxide solution (other components in wastewater are known not to react with sodium hydroxide). When pH = 7, the mass of sodium hydroxide solution consumed is 40g, and the mass of solution measured after the reaction is 138g. Please calculate the mass fraction of sulfuric acid in the wastewater discharged from this factory.

13.(08 Taian, Shandong) (4 points) On Sunday, Xiao Qiang's mother wanted to bake bread and asked Xiao Qiang to buy a pack of soda from the store. Xiao Qiang carefully read the packaging instructions (as shown below) and had questions:

When he got back to school, he took out a small bag of soda samples brought from home for an experiment: accurately weigh 5.5 g of the sample, put it into a beaker, and then add hydrochloric acid dropwise until the reaction is just complete (ignoring that CO2 is dissolved in water), and * * use 25 g of dilute hydrochloric acid to get a solution with a mass of 28.3 g (impurities are dissolved in water and do not react with hydrochloric acid). It is found that the mass of CO2 produced by (1) is:

(2) Whether the mass fraction of sodium carbonate in the soda ash sample is consistent with the packaging instructions is judged by calculation. (The calculation result is accurate to 0. 1%)

14. (Yantai 08, Shandong Province) After completing the experiment of "Preparation and Properties of Carbon Dioxide", there are a lot of mixed solutions of hydrochloric acid and calcium chloride in the waste bucket (regardless of other impurities). In order to avoid environmental pollution and recycle waste liquid, the chemistry interest group did the following experiments: take the supernatant of waste liquid barrel *** 1 1.88kg, and add sodium carbonate solution with solute mass fraction of 2 1.2% to it. The relationship between the pH value of the obtained solution and the quality of the added sodium carbonate solution is shown in the right figure:

(1) As can be seen from the figure on the right, when the mass of sodium carbonate solution is increased to kg, the waste liquid is just treated (the mixed solution of hydrochloric acid and calcium chloride is completely converted into sodium chloride solution).

(2) Can the solution obtained at this time be used for wheat seed selection in the biology interest group of our school (the seed selection solution requires the solute mass fraction of sodium chloride to be between 10%-20%)? Please answer by calculation.

15.(08 Taiyuan, Shanxi) The quality inspector detected the content of NaHCO3 in a brand of baking powder. Take 20.0g of baking powder and add enough hydrochloric acid to get 3.30g of carbon dioxide (other components in baking powder do not react with hydrochloric acid). Find the mass fraction of sodium bicarbonate in this brand of baking powder.

16.(08 Meishan, Sichuan) Soda soda products produced by chemical plant often contain a small amount of sodium chloride, and each batch of products must be tested and labeled by chemists in the factory before they can be put on the market. A chemist in a factory takes 44g sample and dissolves it in a beaker, then drops 20% dilute hydrochloric acid several times, and keeps stirring and weighing, and records the relevant data as follows (Note: The first reaction when adding hydrochloric acid is:

Na2CO3+HCl = NaHCO3+NaCl, and then NaHCO3+HCl = NaCl+CO2↑+ H2O).

Mass of dilute hydrochloric acid added /g 0 73 74 146 147.

Mass of solution in beaker/g 200 273 273.76 328.4 329.4

Please answer the following questions according to the information given and the data in the table:

(1) Adding g dilute hydrochloric acid began to produce carbon dioxide, and at most carbon dioxide g was produced.

(2) Mark the curve between the quality of carbon dioxide produced and the quality of hydrochloric acid added dropwise in the figure below. (The quality of carbon dioxide and hydrochloric acid should be indicated on the drawings. )

(3) Calculate the mass of each component in 44g sample.

Third, the calculation of the solution

Basic knowledge:

① mass fraction of solute = solute mass/solution mass × 100%

② Solute mass = solution mass × solute mass fraction

(3) Solution mass = total mass of reactants-generated gas mass-generated precipitate mass or solution mass = solute mass/solute mass fraction.

Examination questions:

Calculation of solubility of 1.

(1) Calculate the solubility of a substance according to the amount of solute and solvent in its saturated solution at a certain temperature.

(2) According to the solubility of the substance at a certain temperature, the mass of solute and solvent in the quantitative saturated solution at this temperature is calculated.

(3) According to the solubility of the substance at a certain temperature, the quality of the crystals that can be precipitated from the saturated solution when the solvent quality is reduced (evaporating the solvent) is obtained.

(4) According to the solubility of a substance at a certain temperature, the quality of crystals that can be precipitated or added from a saturated solution during cooling or heating is obtained.

2. Calculation of solute mass fraction in solution

(1) Knowing the mass of solute and solvent, find the mass fraction of solution.

(2) Knowing the mass and mass fraction of the solution, find the mass of solute and solvent contained in the solution.

(3) Dilute the solution with known concentration with a certain amount of water, or add solid solute, and find the mass fraction of the solution after dilution or after adding solid.

(4) Combining with the chemical equation, the mass fraction of solute after the reaction is obtained.

(5) Give the solubility curve or table, and find the mass fraction of solute;

3. Conversion between solubility and solute mass fraction

4. Solution preparation: solid dissolution, concentrated solution dilution, etc. Find the solid mass, concentrated solution mass or volume, and added water mass or volume required to prepare a solution with a certain volume or mass fraction;

example

1. (Changchun, 08) prepares 50g sodium oxide solution with solute mass fraction of 16%, and the required sodium chloride mass is g.

Answer: 50g× 16% = 32g.

2. In ethanol C2H5OH solution, the total number of hydrogen atoms in ethanol molecules is equal to the total number of hydrogen atoms in water molecules, so the mass fraction of solute in this ethanol solution is ().

A.B. 7 1% C. 46% D. 33%

Solution: According to the equal number of hydrogen atoms, find out the relationship between ethanol molecules and water molecules, and then determine the mass relationship.

C2H5OH~6H~3H2O

46 54

The mass fraction of solute in this ethanol solution is 46/(46+54) × 100% = 46%.

3. Dilute 400g NaCl solution with 20% solute mass fraction into a solution with 16% solute mass fraction, and add water ().

A. 100 g 200 g 400 g 800 g

Analysis: it can be solved according to the mass conservation of solute before and after dilution: let the mass of water to be added be X.

400g× 20% = (400g+x )×16% x =100g.

4.(08 Guigang, Guangxi) Soda produced by "Hou Shi combined soda production method" often contains a small amount of sodium chloride. In order to determine the content of sodium carbonate in a soda ash sample, Xiaoming said that 3.3g soda ash sample should be fully dissolved in water, and then calcium chloride solution should be added dropwise. The relationship between the precipitation quality and the added calcium chloride solution quality is shown in the right figure. Q:

(1) Mass fraction of sodium carbonate in soda ash sample. (accurate to 0. 1%)

(2) Adding solute mass fraction of calcium chloride solution.

Solution: Let the mass of sodium carbonate and calcium chloride participating in the reaction be X and Y, respectively.

As can be seen from the figure, the amount of precipitate generated is 3.0g, and the mass of CaCl2 solution consumed is 22.2g.

Na2CO3+CaCl2 NaCl+CaCO3↓

106 1 1 1 100

X y 3.0g g

X/106 = y/11= 3.0g/100.

Solution: x = 3. 18g, y = 3.33g

The mass fraction of sodium carbonate in soda ash is 3.18g/3.3g×100% = 96.3%.

The mass fraction of solute in calcium chloride solution is: 3.33g/22.2g×100% =15.0%.

practise

Soilless culture 1. (08 Jinjiang, Fujian) can significantly improve the output and quality of products. The nutrient solution of eggplant soilless culture contains 7.08% potassium nitrate.

(1)KNO3 belongs to (fill in "compound fertilizer", "nitrogen fertilizer", "potassium fertilizer" or "phosphate fertilizer"). Wherein the mass ratio of nitrogen to oxygen is.

(2) In order to prepare this nutrient solution of 150kg, the mass of KNO3 is required.

2.(08 Sanming, Fujian) During the earthquake relief in Wenchuan, Sichuan, in order to prevent the occurrence of post-disaster epidemic, a large amount of disinfectant needs to be sprayed every day.

(1) In 800 kg of 0.5% peracetic acid disinfectant, the mass of peracetic acid is kg.

(2) Prepare 800kg of 0.5% peracetic acid disinfectant. What is the mass of 16% peracetic acid solution?

3.(08) A chemical interest group in Guangdong took 100g wastewater and added 10% sodium hydroxide solution to determine the content of sulfuric acid in wastewater from a factory, and the reaction was just complete (there was no soluble substance in the wastewater, and other components did not react with sodium hydroxide). Please calculate:

(1) mass fraction of sulfuric acid in wastewater;

(2) The factory uses 75% hydrated lime containing calcium hydroxide to treat 150t wastewater every day. How many tons of hydrated lime do you need?

4.(08 Shantou, Guangdong) In order to prevent the spread of germs in Wenchuan earthquake-stricken areas, epidemic prevention personnel used a lot of "bleaching powder" for sterilization and disinfection. The effective component of "bleaching powder" is calcium hypochlorite [chemical formula: Ca(ClO)2]. Please answer:

(1) The metal element in calcium hypochlorite is (write element symbol); Mass ratio of calcium, chlorine and oxygen.

(2) The mass fraction of chlorine in calcium hypochlorite is (accurate to 0. 1%).

(3) If at least 250g bleaching powder is needed for every 50kg of drinking water in the disaster area, at least 20g bleaching powder should be added to disinfect a bucket of water (about 20kg).

5.(08 Hainan) 100 g dilute hydrochloric acid just reacts with 100 g 16% sodium hydroxide solution, so:

(1) mass of sodium chloride: (2) mass fraction of solute in dilute hydrochloric acid.

6.(08 Hebei) Hydrogen peroxide solution will naturally decompose after long-term storage, which will reduce the solute mass fraction. Xiaojun brought a bottle of medical hydrogen peroxide from home and measured the solute mass fraction with his classmates. They took out 5 1g solution and added appropriate amount of manganese dioxide. The relationship between the generated gas quality and the reaction time is shown in the figure.

(1) The mass of oxygen produced after complete reaction is.

(2) Calculate the mass fraction of solute in the solution.

7.(08 Harbin) A classmate wants to prepare 3% hydrogen peroxide as disinfectant. There is a bottle of hydrogen peroxide with broken label. In order to determine the mass fraction of solute in the solution in the bottle, 34g of solution was put into a beaker and a certain amount of manganese dioxide was added. After the complete reaction, after filtration, washing and drying, the total mass of the remaining substances in the beaker was 33.8 g, and 3 g of filter residue was obtained. Please answer the following questions as required:

(1) The chemical equation of the reaction after adding manganese dioxide is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

(2) The quality of oxygen produced is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

(3) According to the mass of oxygen, the proportional formula for solving the mass (x) of hydrogen peroxide is _ _ _ _ _ _ _ _ _

(4) The mass fraction of solute in the hydrogen peroxide solution in the bottle is _ _ _ _ _ _ _ _ _ _ _.

(5) If a certain amount of solution in the bottle is prepared into a 100g hydrogen peroxide solution with a solute mass fraction of 3%, the added water mass is _ _ _ _ _ _.

8.(08 Enshi, Hubei) It is known that Na2CO3 aqueous solution is alkaline, and there is a solid mixture of Na2CO3 and NaCl in the beaker. Dilute hydrochloric acid with solute mass fraction of 65438 00% was gradually dropped into it. The relationship curve between the total mass of released gas and the mass of diluted hydrochloric acid added dropwise is shown in the figure. Please answer the question according to its meaning:

(1) When dilute hydrochloric acid drops to point B in the figure, the pH value of the solution in the beaker is 7 (fill in >, =,

(2) When dilute hydrochloric acid drops to point A in the figure, the beaker is an unsaturated solution (normal temperature), and the mass fraction of solute in it is calculated. (One decimal place is reserved for the calculation result)

9.(08 Huanggang, Hubei) A student used 36.5g hydrochloric acid to react with a certain amount of scale (mainly composed of calcium carbonate) to produce 4.4g CO2 gas. What is the solute mass fraction of this hydrochloric acid?

10.(08 Yichang, Hubei) After 50 grams of Ca (NO3) 2 solution and 50 grams of K2CO3 solution were mixed, the reaction was complete. After filtration, drying and weighing, 5g of precipitate was obtained. The chemical equation of the reaction is: K2CO3+Ca(NO3)2==CaCO3↓+2KNO3. Please calculate:

(1) The mass of K2CO3 participating in the reaction.

(2) Solute mass fraction of the solution obtained after filtration.

1 1.(08 Nantong, Jiangsu) After the Wenchuan earthquake in Sichuan on May 12, 2008, epidemic prevention personnel used various disinfectants to disinfect the environment in order to prevent the epidemic. Sodium chlorite is an important disinfectant. Trial calculation:

(1) The mass ratio of Na, Cl and O in sodium chlorite is _ _ _ _ _ _ _ _ _.

(2) Now it takes _ _ _ _ _ _ _ kg of sodium chlorite to prepare sodium chlorite disinfectant 1500 kg with mass fraction of 16%.

12. (Leshan, Sichuan, 08) 29. 1g solid mixture composed of NaCl and BaCl2 was dissolved in 94.2mL water (p water = 1g/cm3), and Na2SO4 solution with mass fraction of 14.2% was added dropwise to the obtained solution. The figure on the right shows the relationship between the quality of added Na2SO4 solution and the quality of generated precipitate, which is calculated as follows:

(1) What is the sediment mass?

(2) What is the mass fraction of solute in the obtained solution?

13.(08 Nanchong, Sichuan) The students in the chemistry extracurricular activity group of a middle school measured the mass fraction of NaCl in a batch of physiological saline in the laboratory. Take130g of this physiological saline, add enough AgN03 solution, and after complete reaction, 2.87g of silver chloride precipitate is generated. Calculate the mass fraction of NaCl in physiological saline.