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391. Name the impurities most commonly found in river-water, distinguishing the suspended, saline, and gaseous impurities.

392. How would you test a sample of water for chlorides and for sulphates ?

393. How is the presence of lead in many waters accounted for, and how may its presence be detected ?

394. Why is it of importance to determine the amount of organic matter present in water ? Describe fully the processes of Frankland and of Wanklyn for this purpose.

the inorganic impurities in water detected and their amount estimated ?

396. State briefly the considerations which would guide a chemist in determining whether or not a sample of water was suitable for domestic use.

397. Describe a process in use on the large scale for softening hard water ?

338. What is the colour of perfectly pure water, and how may this be best seen?

399. Air usually contains 20'924 volumes oxygen and 7)*076 volumes nitrogen. Air dissolved in pure water

395. How

are

consists of 34:91 volumes oxygen and 65'09 volumes nitrogen. How is this difference explained, and what is the action of air dissolved in impure water on the organic matter present ?

400. Why is water called a neutral body ?

401. Certain bodies when added to water cause a lowering of the temperature, others raise it. Give examples of each and explain the cause.

402. What is the action of each of the following bodies on water, (a) lime, (6) sulphuric acid, (c) phosphorus trichloride, (d) soda, (e) phosphorus pentoxide ?

403. What occurs when anhydrides are added to water? Give examples.

HYDROGEN DIOXIDE.

404. By whom and when was hydrogen dioxide first prepared ? Does it occur in nature? if so, how? By what other names is the substance known?

405. How is hydrogen dioxide prepared? Give two methods. Can it be obtained in the pure state?

406. What are the properties of hydrogen dioxide, and what occurs when it is heated ?

407. Give examples of reactions in which hydrogen dioxide (a) oxidizes, (6) deoxidizes (reduces).

408. Give various reactions for the detection of hydrogen dioxide. Which test would you apply to detect extremely small quantities?

409. Explain the action of hydrogen dioxide on (a? silver oxide, (6) manganese dioxide, (c) ozone.

410. What is the action of hydrogen dioxide on each of the following bodies ? (a) potassium iodide, (b) lead sulphide, (c) potassium permanganate, (d) potassium chromate, (e) charcoal, (S) finely divided platinum.

411. Represent by equations the action of hydrogen dioxide on (a) sulphur dioxide, (6) nitrogen tetroxide, (c) barium monoxide.

412. How may hydrogen dioxide and ozone be detected as products of the combustion of hydrogen in air ?

413. Hydrogen dioxide is sometimes used for cleaning old oil paintings. What is its action when used for this purpose ?

COMPOUNDS OF CHLORINE.

414. How does hydrochloric acid occur in nature, and by what other names is it known?

415. How may hydrochloric acid be prepared from its elements ? Describe different ways of effecting the union.

416. Starting with common salt, how could you prepare hydrochloric acid ?

417. A burning jet of hydrogen is plunged into a jar of chlorine ; what occurs, and what property does the product possess which distinguishes it from both hydrogen and chlorine ?

418. Using only chlorine and water, how may hydrochloric acid be prepared ?

419. What occurs when a galvanic current passes through a strong solution of hydrochloric acid, previously saturated with chlorine ?

420. In what proportions by volume and weight do hydrogen and chlorine unite?

421. What volume of hydrogen at N.T.P. is needed to unite with i gramme of chlorine?

422. A cylinder contains a mixture of equal volumes of hydrogen and chlorine, it is opened under a solution of potassium iodide. State what occurs, and express the reaction by an equation.

423. Describe various methods which may be used to ascertain the proportion of hydrogen and chlorine contained in hydrochloric acid gas.

424. Give several reactions to show the tendency of chlorine to unite with combined hydrogen.

425. How much hydrochloric acid must be decomposed to yield enough chlorine to liberate 2*34 grammes of iodine from potassium iodide ?

426. A solution of hydrochloric acid required 1067 grammes of silver nitrate to precipitate it completely. Find the volume of hydrochloric acid (at N.T.P.) in solution,

427. Sketch the apparatus required for preparing small quantities of pure hydrochloric acid, and calculate the quantities of common salt and sulphuric acid required to

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