Вычислить количество 60%-ной извести, необходимое для умягчения 500 м3 воды с исходной карбонатной жесткостью 3, 8 мг-экв/л

По закону эквивалентов, для снижения жесткости 3,8 мг-экв/л нужно добавить 3,8 мг-экв/л извести на каждый литр воды.
Мэ (Са(ОН)2)=M / z =74 / 2 = 37 г/моль
Следовательно, для понижения жесткости к 500 м3 воды надо добавить
m(Са(ОН)2)= 3,8 ∙10^-3 ∙ 37 ∙ 500∙10^3 = 70300 г = 70,3 кг
Если известь 60%-ная, то m(Са(ОН)2) = 70,3/0,6 = 117,17 кг

Неплохая  сказка, как и все сказки пушкина. извечная тема борьбы добра со злом  . добро олицетворяет царевна, зло - злая мачеха ( королева) . помню, читая сказку в детстве, испытала злость к короле. сейчас , читая, сие творение пушкина, понимаешь , что из сказки можно вынести важные уроки.    корень всех бед - обычная зависть , в этом случае, зависть  к красоте, молодости. кто не знаком с творчеством пушкина можно начать знакомство с этой сказки, думаю, что разочарования не будет.

My favourite season.there are four seasons in a year: winter, spring, summer and autumn. all seasons are good in their own way. winter, for example, is full of celebrations, presents and snow. spring is the time of nature awakening and flower blooming. autumn can be rainy and yet beautiful, full of multi-coloured leaves. however, my favourite season is summer. i choose summer not only because my birthday is in june, but also because it’s the time of holidays. summer is the season when the sun shines brightly, the sky is rarely cloudy and the water in the sea becomes warm enough to swim. even if it becomes too hot, you can always go for a walk in the shady woods. i also like summer because there are many berries, fruit and vegetables, not to mention numerous flowers on the fields. among them roses, dandelions, daisies, and other flowers. sometimes the air in summer becomes stuffy, but occasional thunderstorms bring relief. after the thunderstorms the air becomes remarkably fresh and very often we can see the rainbow in the sky. summer is also the time when i and my family go on holiday to the seaside. it’s a wonderful time, when we can have a rest from the intense academic year and relax. i think all children love summer because of long school holidays and i’m no exception. i also enjoy my free time, playing with my friends, watching tv, and doing other fun activities. nevertheless, i don’t forget to do some useful reading from time to time.