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в 200 г воды растворили 4,6 г натрия. Какова массовая доля гидроксида натрия в получившимя растворе?
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Дано:m (H₂O) = 200 г ;m (NaOH) = 4,6 г.Найти:ω (NaOH в р-ре) – ?Решение:200 г + 4,6 г = 204,6 (г).204,6 г – 100 %4,6 г – х %х = 4,6 · 100 : 204,6 = 2,24 (%) – ω NaOH в р-ре.Ответ: 2,24 %.
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Автор:
elsaknox - 5 лет назад
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The banks of Sacramento (by J. London)
"Young" Jerry was a fourteen-year-old boy with red hair, blue eyes and freckled skin. Together with his father "old" Jerry, he lived on the bank of the Sacramento in California. "Old" Jerry was an old sailor who had been given a job at the Yellow Dream mine and was in charge of the ore cables that ran across the river. On the bank one could see a steel drum round which the endless cable passed. An ore car, when loaded, crossed the river, carried down by its own weight and dragging back, at the same time, an empty car travelling in the opposite direction along the same cable. The Yellow Dream mine had been abandoned and the cars were no longer used for carrying ore, but "old" Jerry still remained watchman over the cables. That morning "young" Jerry was alone in the cabin. His f ather had gone to San Francisco and was not to be back till next day. It was raining heavily all the morning, and Jerry decided not to go out, when, at one o'clock, there came a knock at the door. A man and a woman came in. They were Mr. and Mrs. Spillane, ranchers who lived a dozen miles back from the river.
"Where is your father?" Spillane asked, and Jer- ry noticed that both he and his wife were excited."San Francisco," Jerry answered briefly.
"We've got to get across, Jerry," Spillane continued, taking his wife by the hand, "her father's been badly wounded in an explosion; he's dying. We've just been told. Will you run the cable for us?"
Jerry hesitated. Of course, he had worked t'he cable many times, but only with the help of his father.
I'll stand for the risk," Spillane added, "don't you see, kid, we've simply got to cross."
Jerry nodded his head. They all came out into the raging storm, and the man and the woman got into the ore car.
"Let's get started!" Spillane shouted to make himself heard above the roar of the wind. Jerry slowly and carefully let the car go, and the drum began to go round and round. Jerry carefully watched the cable passing round the drum.
"Three hundred feet" he was saying to himself, "three hundred and fifty, four hundred –" The cable stopped. Something had gone wrong.
The boy examined the drum closely and found nothing the matter with it. Probably it was the drum on the other side that had been damaged ...
He was afraid at the thought of the man and woman hanging out there over the river in the driving rain. Nothing remained but to cross over to the other side by the Yellow Dragon cable some distance up the river. He was already wet to the skin as he ran along the path to the Yellow Dragon. Safely across, he found his way up the other bank to the Yellow Dream cable. To his surprise, he found the drum in perfect working order. From this side the car with the Spillanes was only two hundred and fifty feet away. So he shouted to the man to examine the trolley of his car. The answering cry came in a few moments.
"She's all right, kid!"
Nothing remained but the other car which hung somewhere beyond Spillane's car.
The boy's mind had been made up. In the toolbox by the drum he found an old monkey-wrench, a short iron bar and a few feet of rope. With the rope he made a large loop round the cable on which the empty car was hanging. Then he swung out over the river, sitting in the rope loop and began pulling himself along the cable by his hands. And in the midst of the storm which half blinded him he arrived at the empty car in his swinging loop. A single glance was enough to show him what was wrong. The front trolley wheel had jumped off the cable, and the cable had been jammed between the wheel and the fork. It was clear that the wheel must be removed from the fork. He began hammering on the key that held the wheel on its axle. He hammered at it with one hand and tried to hold himself steady with the other. The wind kept on swinging his body and often made his blows miss. At the end of half an hour the key had been hammered clear but still he could not draw it out. A dozen times it seemed to him that he must give up in despair. Then an idea came to him – he searched his pockets and found a nail. Putting the nail through the looped head of the key he easily pulled it out. With the help of the iron bar Jerry got the wheel free, replaced the wheel, and by means of the rope pulled up the car till the trolley once more rested properly on the cable.
He dropped out of his loop and down into the car which began moving at once. Soon he saw the bank rising before him and the old familiar drum going round and round.
Jerry climbed out and made the car fast. Then he sank down by the drum and burst out crying. He cried because he was tired out, because his hands were all cut and cold and because he was so excited. But above all that was the feeling that he had done well, that the man and woman had been saved.
Yes, Jerry was proud of himself and at the same time sorry that his father had not been there to see!
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