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373. Equal quantities of water at 79° C. and of ice are mixed together. What is the temperature of the mixture? Instead of ice, water at o° C. is used, what is the temperature in this case?

374. Explain the term thermal unit.

375. Describe an experiment to show how the latent heat of steam may be ascertained.

376. What is meant by the term "tension of aqueous vapour," and how may it be measured?

377. In measuring a moist gas in a eudiometer, how would you ascertain the correction to be made for the tension of aqueous vapour?

378. Describe any experiment which proves that during the evaporation of water heat is absorbed.

379. What methods have been suggested for obtaining large quantities of ice artificially?

380. On what physical conditions does the amount of a gas capable of being dissolved by water, depend?

381. When water is decomposed by the galvanic current the oxygen measures rather less than half the hydrogen. How do you account for this?

382. Aqueous solutions of carbon dioxide, ammonia,

and oxygen are frozen. Is the gas expelled or retained at the moment of solidification?

383. On what physical conditions does the amount of a solid capable of being dissolved in water usually depend?

384. Describe the construction and use of an oxyhydrogen blowpipe. What is the temperature of the flame of an oxyhydrogen blowpipe, and how may it be used to fuse platinum?

385. If the water produced by burning hydrogen in oxygen be collected, is it pure or impure?

386. Classify the various kinds of impurities found in natural waters. Which impurities may be removed by filtration?

387. What do you understand by the terms "hard" and "soft," as applied to water?

388. How may the degree of hardness of a water be ascertained?

389. What produces the incrustation on the sides of a vessel in which large quantities of water have been boiled?

390. How may water be freed from all impurities and obtained chemically pure?

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.

395. How

are 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?

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

399. Air usually contains 20°924 volumes oxygen and 70076 volumes nitrogen. Air dissolved in pure water

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, (b) 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, (5) 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, (f) finely divided platinum.

411. Represent by equations the action of hydrogen dioxide on (a) sulphur dioxide, (b) 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?

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