Xuzhou no.26 high school
Fill-in-the-blank is one of the required questions every year, accounting for about 20%. It mainly examines students' mastery and application of basic theories and concepts. The examination form mainly starts from the following aspects:
First, the writing and significance of chemical terms. This kind of topic requires students to express accurately on the basis of understanding and memorizing chemical terms, especially the examination of chemical equations, which is all-round and multi-angle. No matter how they change, as long as they master the writing principles and steps, they can write accurately.
1 (Wuxi, 2007), fill in the blanks with numbers and chemical symbols:
(1) chlorine atom; 2 sodium ion; (3) three carbon dioxide molecules;
(4)- divalent sulfur; 5] The smallest particle that keeps the chemical properties of water.
2 (Wuxi, 2007), fill in the blanks with appropriate substances in "quicklime, alum, calcium carbonate, stainless steel, polyethylene and soda ash".
(1) used for manufacturing medical instruments and cookers; (2) used as food desiccant is;
(3) Salt used in papermaking and textile industry is; (4) used as calcium salt;
5] belongs to the organic polymer compound is; [6] It can be used as flocculant when purifying water.
3 (Wuxi, 2007), please select one or more of the existing four elements of sodium, oxygen, carbon and hydrogen, and write a chemical formula that meets the following requirements:
(1) The most ideal fuel; (2) a gas with a second volume fraction in the air;
(3) Soda contains unstable acid; (4) Baking soda, the main component of baking powder.
4 (Wuxi, 2007), write the chemical equations of the following reactions, and indicate the basic types of reactions in brackets:
(1) mixing hydrogen peroxide and manganese dioxide to generate oxygen, (1) reacting;
(2) The iron wire burns in oxygen, resulting in () reaction;
(3) copper wire immersed in silver nitrate solution;
(4) Magnesium is burned in carbon dioxide to produce magnesium oxide and carbon black.
5 (Changzhou, 2007) and (1) Write the names, common names or chemical formulas of the following substances.
Calcium oxide and sodium carbonate
Commonly known as mercury quicklime
Chemical formula Hg Na2CO3
(2) Write the following chemical equations:
① Hydrogen production by electrolysis of water:
② Zeng Qing (CuSO4 _ 4) was transformed into copper.
6 (Changzhou, 2006) and (1) Write the chemical formulas of the following substances:
(1) ferrous ion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _; (2) aluminum sulfate _ _ _ _ _ _ _ _ _ _.
(2) Since ancient times, chemical reactions have played a very important role in production. Please write the chemical equation as required:
(1) The hydrometallurgy of ancient copper was _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _;
(2) Use hematite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ to make iron.
7 (Changzhou, 2005), write the following chemical equations as required:
(1) Add a small amount of manganese dioxide _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
(2) Zinc particles react with hydrochloric acid _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
(3) The reaction between sulfuric acid and sodium hydroxide _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
(4) Glucose (C6H 12O6) slowly oxidizes _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
Among the above reactions, _ _ _ _ _ _ belongs to decomposition reaction, and _ _ _ _ _ belongs to displacement reaction. (Fill in serial number)
8 (Nantong in 2006), four cities in northern Jiangsu began to promote the use of ethanol gasoline this year. Ethanol can be obtained by decomposing glucose (C6H 12O6) produced by crop fermentation. Glucose is an organic substance composed of three elements, of which the element with the highest mass fraction is _ _ _ _ _ _ _. Glucose is decomposed into ethanol and another common gas under the action of alcoholase, namely.
9 (Nantong, 2006) Nano-sized elemental iron is highly reactive, commonly known as "nano-iron".
(1) At high temperature, hydrogen reacts with FeCl2 _ 2, which can generate "nano-iron" and a strongly acidic gas dissolved in water. Write the chemical equation of the reaction.
(2) Nano-iron will burn when it is hit in air, and its reaction is the same as that of iron burning in pure oxygen. Write the chemical equation of this reaction.
⑶ Please predict other chemical properties of "nano-iron" and express them by chemical reaction equation.
10 (Suzhou, 2007). In order to convert NO in gasoline engine exhaust into N2, NH3 reacts with NO under the action of catalyst, and its chemical equation is: 4NH3+6NO = = = 5N2+6H2O; In general, according to the order of the left formula, the stoichiometric ratio of reactant to gas in the product = 1.
1 1 (Nantong, 2006) and "green chemistry" emphasize taking effective measures to prevent environmental damage and pollution.
(1) Before the experiment of sulfur burning in oxygen, add an appropriate amount of NaOH solution into the gas cylinder, and then carry out the experiment, because (expressed by chemical equation).
⑵ Installing a "catalytic converter" on the automobile exhaust pipe can make NO and CO in the automobile exhaust react to generate two kinds of non-toxic gases that can participate in the atmospheric ecological cycle. The chemical equation for the reaction of NO and CO is.
12 (Xuzhou City, 2005), we learned a lot about chemical reactions through chemistry study. Please use chemical equations to answer the following questions.
The reason why (1) iron drum does not contain copper sulfate solution.
(2) Brushing the wall with lime milk can form a hard wall.
(3) It is convenient, rapid and environmentally friendly to make oxygen with hydrogen peroxide in the laboratory.
13 (Zhenjiang City, 2007) and (4 points) are expressed in chemical terms:
① Nitrogen element ② Two hydrogen molecules ③ Three magnesium ions ④ Ferric sulfate
14 (Zhenjiang, 2007), (2 points) CH4, the main component of natural gas, is also a gas that causes greenhouse effect. In view of the same molecular number of CH4 and CO2, the greenhouse effect caused by CH4 is more obvious, and the greenhouse effect caused by the above two gases with the same mass is more obvious.
15 (Zhenjiang, 2007) and calcium oxalate (CaC2O4 _ 2 O _ 4) are sediments that cannot be absorbed by human body. Tofu contains more calcium salts [such as calcium sulfate (CaSO4)], and spinach, onion and bamboo shoots are rich in oxalic acid (H2C2O4), sodium oxalate (Na2C2O4) and tofu.
Mixed consumption of the above vegetables may induce "calculus" disease.
(1) According to the chemical formula of oxalic acid, the valence of carbon element is;
1.(2) The chemical equation of the reaction between oxalic acid and calcium sulfate is H2C2O4 = = CaC2O4 ↓ H2SO4. Please write the chemical equation of the reaction between sodium oxalate and calcium sulfate.
Second, the nature and use of common substances. This kind of topic is usually closely related to the practice of production and life, which requires students to understand and remember the nature and use of common substances, observe and think more in life and production, connect what they have learned with the practice of production and life, and learn to think and apply.
16 (Changzhou, 2007) and 1 (Changzhou, 2007) have the following factors: a. Different kinds of ions; B. the composition of molecules is different; C. different mass fractions of solutes, etc. , please select the factors that lead to the different properties of the following substances (fill in the serial number).
(1) carbon monoxide is flammable, but carbon dioxide is not flammable:
②FeSO4 is green and Fe2(SO4)3 is yellow;
(3) concentrated sulfuric acid has water absorption, and dilute sulfuric acid does not.
(2) Write down the chemical formula of the substance (or its main components) for the following purposes. Please choose from the following substances:
Methane, salt, hydrated lime, oxygen, ammonium bicarbonate and limestone.
① It can be used as fuel;
② It can be used as chemical fertilizer;
③ It can be used as seasoning;
④ It can be used as rocket combustion improver.
17 (Changzhou, 2006), (4 points) Some substances we learned in junior high school chemistry have important uses in real life. There are four substances: potassium nitrate, dilute sulfuric acid, copper sulfate and dry ice. Please fill in the blanks with their chemical formulas (or main components).
(1) can be used to prepare the bactericide bordeaux mixture _ _ _ _ _ _ _ _.
(2) Can be used for rust removal _ _ _ _ _ _ _ _ _ _ _ _
(3) can be used for artificial rainfall _ _ _ _ _ _ _ _ _
(4) can be used as compound fertilizer has _ _ _ _ _ _ _ _ _ _ _ _.
18 (Changzhou City, 2005) (5 points) Of the eight substances such as formaldehyde, ceramics, rubber, ammonium bicarbonate, ethanol, hydrated lime, marble and potassium nitrate, _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
19 (Xuzhou, 2005), chemistry is around us, and it can improve our lives. Please fill in the blanks with appropriate substances from "A, oxygen B, nitrogen C, quicklime D, hydrated lime E, vinegar F, urea G, stainless steel H, polyethylene" (fill in the letters).
(1) The commonly used substances for rescuing critically ill patients are: (2) The substances used as crop fertilizers are:
(3) commonly used as bagged food desiccant is; (4) The pH value of kitchen seasoning is less than 7;
(5) can be made into food packaging bags are; (6) The materials that can be used to manufacture cutting tools are:
20 (Nantong, 2006) Chemicals are widely used in industrial and agricultural production and daily life. Please fill in the blanks with the chemical formulas of the following substances: helium, nitrogen, calcium oxide, hydrochloric acid, nitric acid and ferrous sulfate.
(1) As a rare gas, hydrogen balloons can be used instead.
It can be used to produce explosives and dyes, and generally does not produce hydrogen when reacting with metals.
⑶ Drugs that can be used to treat iron deficiency anemia are.
(4) In order to prevent some foods from getting wet, put a small bag of desiccant in its packaging bag. This desiccant.
2 1 (Suzhou, 2007), chemistry is around us and closely related to our lives. Please fill in the blanks with appropriate alphanumeric characters from eight substances: A. slaked lime, B. soda ash, C. natural gas, D. potassium nitrate, E. cellulose, F. vitamins, G. hydrochloric acid and H. sulfuric acid.
(1) The acids contained in human gastric juice are:
(2) The materials transported by the "West-to-East Gas Transmission Project" implemented in China are:
(3) The "alkali" in Hou Shi's combined alkali production method is;
(4) The compound fertilizer applied in farmland is:
(5) The main components of natural plant fibers such as cotton and hemp are:
(6) It can be used to improve acid soil and prepare pesticide Bordeaux mixture.
22 (Changzhou City, 2007), (4 points) Fill in the following nouns in the corresponding spaces (only fill in the serial numbers).
① emulsification ② crystallization ③ deliquescence ④ volatilization
(1) When sodium hydroxide solid is exposed to air, its surface becomes wet.
(2) Open the cork of reagent bottle bottle filled with concentrated hydrochloric acid, and white fog appears at the bottle mouth.
(3) Wash the detergent to remove oil stains from the tableware.
(4) cooling the hot saturated solution of potassium nitrate to form crystals.
23 (Zhenjiang City, 2007), (4 points) Fill in the serial numbers of the following operation names on the back horizontal line (each serial number is only filled once): ① stirring ② evaporation filtration ④ heating.
Obtaining (1) salt crystals from saturated salt solution; (2) changing a saturated solution of potassium nitrate into an unsaturated solution;
(3) removing the precipitate in the salt, dissolving it first, and then; (4) Inject concentrated sulfuric acid into the water to make the heat dissipate quickly.
24 (Changzhou, 2005), please select one of the provided reagents to remove a small amount of impurities (impurities in brackets) in the following substances. Fill in the serial number of the reagent on the corresponding horizontal line (the reagent cannot be reused).
Substitute reagents: ① concentrated sulfuric acid ② water ③ dilute nitric acid ④ hydrochloric acid ⑤ sodium hydroxide solution.
(1) copper powder (Fe) _ _ _ _ _ _ _ (2) calcium carbonate powder (CaCl 2)_ _ _ _ _ _ _ _(3) carbon monoxide (CO2) _ _ _ _ _ _.
25 (Nantong, 2007) We should pay attention to reasonable intake of nutrients and essential elements in our daily life.
(1) protein is the basic substance of life and an important part of daily diet. The following foods:
Apples, raisins, milk, rice and soybeans
It is rich in protein (fill in the number).
(2) The starch ingested by human body reacts with water under the catalysis of enzyme, and finally becomes glucose, which is slowly oxidized under the catalysis of enzyme, and at the same time, it releases energy for the needs of body activity and keeping body temperature constant.
(3) At present, a health care product called calcium iodate has entered some supermarkets, which contains trace elements necessary for human body.
26 (Zhenjiang in 2007),
After learning about vitamins, Xiao Li made a small card about vitamin C, but it was incomplete. Please help him fill in the blanks in the form.
Vitamin c knowledge card
Molecular structure chemical formula
relative molecular mass
The nature of Vc is soluble in water, and it is easy to be destroyed by oxidation in heating or alkaline environment.
Vc exists in green vegetables (such as cucumber and lettuce) and fruits (such as citrus).
Matters needing attention in eating cucumber
Matters needing attention in saving Vc film
27 (Suzhou, 2007), try to use ">" or "
(1) acid rain pH distilled water ph;
(2) The number of protons in the nucleus and the number of electrons outside the nucleus of carbon atoms;
(3) metal activity of sodium metal activity of aluminum
(4) The volume fraction of nitrogen and the volume fraction of oxygen in air;
(5) Add 5g of sodium carbonate powder into 95g of hydrochloric acid with solute mass fraction of 10%, and the mass of the solution after full mixing is100g.
28 (Xuzhou, 2007) Chemistry is closely related to our food, clothing, housing and transportation. Please answer the following questions:
(1) The reason why oil stains on clothes can be decontaminated with washing powder is _ _ _
(2) add iodine water to rice soup, it will appear blue, indicating that rice soup contains _ _ _
(3) home decoration, install a solar shower in the bathroom, which converts solar energy into _ _.
(4) Complex, copper and its alloys can be seen everywhere in vehicles. Now, chromium (Cr) is inserted into the solution of Cu(NO3)2, and the red substance is precipitated on the chromium. Compared with copper, the metal activity of chromium is _ _ _
29 (Xuzhou City, 2007) According to the report of Urban Morning News, on May 28th this year, the water conservancy department of our city transferred 3 million cubic meters of water from Weishan Lake to the old Yellow River to improve the water quality.
(1) In order to check whether the water quality meets the ornamental water quality standards of scenic spots, _ _ _ _ _ can be used to detect the pH value of water quality.
In order to protect the excellent water quality of the old Yellow River, please put forward two reasonable suggestions.
①__________________②_____________________。
⑶ Aqueous solution is widely used in production and life. Adding a small amount of ethylene glycol to the water tank of a car in winter can make the freezing point of the water solution _ _ and prevent the water from freezing. The electrolyte in motor vehicle battery is sulfuric acid solution with solute mass fraction of 28%. If the solution is prepared in the laboratory, the glass instruments needed are rubber head dropper, _ _ _, _ _ and _ _.
(4) Water is an important solvent, which can dissolve many salt substances. The color of a salt solution is usually determined by the ions in the solution. It is known that NaCl solution contains Na+ and Cl-, and FeCl3 solution contains Fe3+ and Cl-. Based on this, it is inferred that the yellow color of FeCl3 _ 3 solution is related to _ _ (ion filling symbol) ions, and the reason is _ _ _ _ _ _ _.
30 (Changzhou, 2007), learning chemistry well can help us better understand various phenomena, solve practical problems more reasonably, and cope with unexpected events that may occur in our lives more easily.
(1) Detergent is often used to wash oil stains, because it is effective when mixed with oil and water; In winter, a small amount of ethylene glycol and other compounds are often added to the water tank of a car to prevent the water in the water tank from freezing, because ethylene glycol dissolves in water, which makes the solution freeze. (Fill in "increase" or "decrease")
(2) Different iron products adopt different iron protection methods. For example, the chain of bicycles often rusts, and the body of bicycles often rusts.
(3) Different fire extinguishing methods are also different. For example, when putting out fierce and rapidly spreading forest fires, the usual method is: when putting out fires caused by aging power lines, put out the fire first and then put out the fire.
Third, the inference of simple materials. This kind of topic highlights students' analytical reasoning ability, logical thinking ability and comprehensive application ability. Teachers can let students master the general problem-solving methods and strategies of inferring problems through practice: grasping the characteristics, choosing some breakthroughs, using forward deduction, reverse deduction, holistic method and so on.
3 1 (Changzhou, 2006), the following is a schematic diagram of mutual transformation between some common substances (some reaction conditions are not specified).
(1) Fully heat solid A until no gas is generated, and the substances contained in filtrate H are:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (Write the chemical formula)
(2) The chemical formula of solid B is _ _ _ _ _ _ _ _ _ _ _, which plays a role in the reaction with colorless liquid E.
(3) If gas Z is the simplest organic matter and burns in gas X, different substances will be generated due to the change of the amount of X and the different conditions. Try to write the chemical equations of solid simple substance M and colorless liquid F generated by the reaction of X and Z:
______________________________________________________________。
32 (Nantong in 2006), (5 points) Marble and hematite are the main raw materials in industry.
You can prepare B and G, and their transformation relationship is shown in the right figure.
It is known that the main components of D and G are simple substances.
Try to answer the following questions:
(1) Write the chemical formulas of two substances manufactured in industry:
B, G.
(2) Write the chemical equations of the following reactions:
Reaction ②:;
Reaction ③:;
Test gas c:.
33 (Suzhou, 2007) and A~D are common substances in junior high school chemistry, and there is a transformation relationship as shown in the figure (reaction conditions, other reactants and redundant products have been omitted).
Please write down the chemical formula of the following substances:
a； b； c； d .
34 (Zhenjiang, 2007), it is known that seven substances A to G are compounds that have appeared in junior high school chemistry textbooks, among which F is a commonly used building material.
Materials; H is a common simple substance. There is the following transformation relationship between substances (the reaction conditions are shown in the figure below).
(1) Please write down the chemical formula of substance A..
The solute in the blue solution is.
(2) Among the reactions from ① to ⑥, the compound reaction is (fill in serial number).
(3) In the above transformation process, there are changes that can reflect the great contribution made by ancient people in China to mankind in chemistry.
Please give an example and express it by chemical equation.
Fourth, it is related to the solubility curve of solid matter. This kind of topic requires students to use the information expressed by solubility curve flexibly. Relevant test sites include: comparing solubility, comparing or calculating the mass fraction of solute in solution, calculating the mass of solution, solving the transformation between saturated solution and unsaturated solution and many other problems.
35 (Nantong in 2006), (1 1) Our city faces the river and the sea, with a long coastline and rich marine resources.
(1) salt can be dried in seawater to obtain crude salt, and dissolved in laboratory to obtain refined salt.
(2) The brine obtained after salt drying contains magnesium chloride, KCl and magnesium sulfate, and their solubility curves are shown in the right figure.
① Let the solubility of magnesium chloride, KCl and magnesium sulfate at t 1℃ be A, B and C, respectively, then their size relationship is.
(2) The brine is heated above t2℃, and according to the solubility curve, the first crystal precipitated is.
36 (Xuzhou, 2005), solubility curve provides convenience for us to quantitatively describe the solubility of substances. Please answer the following questions according to the solubility curve on the right:
At (1)20℃, the solubility of substance A _ _ (fill in "greater than", "equal to" or "less than") the solubility of substance B.
(2) At _ _ _ _ _℃, the solubility of the two substances is equal.
(3) At 60℃, put 80 g of substance A into 100 g of water, and the solute mass fraction of the obtained solution is.
37 (Wuxi, 2007), according to the solubility curve of KNO3 and NaCl, answer the following questions:
(solubility of KNO3 at l0℃ (fill in ">", "
(2) at t℃, if magnesium nitrate and sodium chloride are dissolved in 20 ml of water and just saturated, then m _ _ n (fill in ">", "
(3) The following processes are used in industry to extract refined salt from seawater:
In the above process, I, II and III are ①, ② and ③ respectively.
Xiao Qiang designed an interesting experiment (as shown on the right). After a long time, he observed crystal precipitation in the small test tube.
(1) The following is Xiao Qiang's partial explanation of this phenomenon. Please help him complete the rest of the explanation: concentrated sulfuric acid is absorbent.
.
(2) If the temperature is unchanged before and after the experiment, the solute mass fraction of the potassium nitrate solution after the experiment (fill in "greater than", "equal to" or "less than") is the solute mass fraction of the original saturated potassium nitrate solution.
Calculation of solution (teaching plan and related exercises)
Learning objectives:
1, through the analysis of the formation of the solution, master the relevant calculation of the solution.
2. Cultivate the ability to analyze problems-meticulous and rigorous.
3. Form a rigorous and realistic scientific attitude through practice.
Important and difficult
Comprehensively apply the knowledge learned to improve the accuracy of analysis.
Teaching process:
1, Introduction: Introduce the content and significance of this section.
2, review the basic theoretical knowledge:
Solute mass fraction
saturated solution
Importance of solubility
3. (Guided Analysis) In the relevant calculation of solution, the calculation of solute mass fraction of solution is the most common. In this calculation, nothing more than two values are considered: the mass of solute and the mass of solution.
Problem analysis 1: solute quality analysis
Theoretical preparation:
Solute, that is, dissolved substance. The quality of solute should be: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
According to the composition or composition relationship between substances, can the quality relationship between substances be determined?
Students practice "Example 1" and exchange experiences.
Summary: consider and analyze the problem correctly and comprehensively.
It is caused by the misunderstanding that "the substance put into water is solute".
It is not comprehensive enough to consider the question of whether the solute is completely dissolved.
Practice consolidation
Students practice "Example 2" and exchange experiences.
Summary: the relationship between a substance and its composition and composition, and the conversion relationship between the mass of a substance and the number of particles.
Practice consolidation
Problem Analysis 2: Solution Quality Analysis
Theoretical preparation:
Complete the analysis of solute quality, and then complete the analysis of solution quality. The basic idea is:
(1) solution mass = solute mass+solvent mass
(2) Total solution mass = original solution mass+added substance mass-insoluble substance mass.
Students practice "Example 3" and exchange experiences.
Summary: the change of solution and its quality
Students practice Example 4 and exchange experiences.
Summary: the relationship between solution quality and volume
Students practice Example 5 and exchange experiences.
Abstract: the influence of chemical changes on solutions.
Summary of this lesson: Students exchange learning experiences.
Attachment: Examination questions for senior high school entrance examination.
First, multiple choice questions
1, (Zhenjiang, 2007) is a mixture of Mg(OH)2 and MgO, in which the mass fraction of magnesium is 48%. Take this mixture 10g, put it into a proper amount of dilute sulfuric acid for full reaction, and the mass of solute in the obtained solution is ().
A. 12g B.24g C.36g D.48g
2. (Yancheng, 2007) The right figure shows the solubility curve of hydrated lime. At 20℃, a small amount of calcium oxide (CaO) powder was added into saturated clear limewater (solution A) for full reaction. The following statement about the solution after the reaction is incorrect.
A. When the temperature of the solution does not return to 20℃, the solution must be saturated.
B when the temperature of the solution does not return to 20℃, the mass fraction of solute is greater than that of solution a.
C when the temperature of the solution returns to 20℃, the mass of solute is less than that of solution a.
D When the solution temperature returns to 20℃, the mass fraction of solute is equal to that of solution A..
3. (Taizhou, 2007) gave the solubility curves of A, B and C. When the saturated solution of A, B and C was cooled to t 1℃, the solute mass fraction relationship of the obtained solution was correct.
A.A > B > C。
C.A = B > C D。
4. (Nantong, 2006) It is known that the solubility of potassium chloride is 40 g at t℃. At this temperature, 25 g of potassium chloride solid was added into 50 g of water and fully dissolved, and the mass fraction of solute in the formed solution was
25% 28.6% 33.3% d . 50%
5. (Suzhou, 2006) Take 70g saturated solution of potassium chloride at a certain temperature, evaporate 10g water at constant temperature, and precipitate 4g solid potassium chloride, then the solute mass in the remaining solution is
A. 16g B.20g C.40g D.56g
6. (Taizhou, 2006) The following substances are exposed to the air for a long time, and the quality of the solution is reduced due to chemical changes.
A, concentrated sulfuric acid b, caustic soda solution c, concentrated hydrochloric acid d and limewater
7.(Yancheng, 2006) When preparing a certain mass fraction of sodium chloride solution, the following operational errors will lead to the decrease of solute mass fraction in the prepared solution.
A. When weighing sodium chloride with the tray balance, put the weight on the left board, but do not use the moving code. B. When reading distilled water with a measuring cylinder, look down at the lowest point of concave liquid level. When the water in the measuring cylinder is poured into the beaker, it overflows. D. When the prepared sodium chloride solution is transferred to the narrow-mouthed bottle, part of the solution overflows unexpectedly.
8.(Yancheng, 2006) When electrolyzing water, adding a small amount of sodium hydroxide can enhance the conductivity of water. After 0. 1% sodium hydroxide solution is electrified for a period of time, the following statements are correct: a. The mass fraction of hydrogen and oxygen elements in the solution decreases; B, the mass fraction of sodium hydroxide in the solution is reduced; C. the number of ions in the solution increases; The reduced volume of the solution is the volume of the generated gas.