现有一瓶标签已破损的过氧化氢溶液，为测定瓶内溶液中溶质的质量分数，取该溶液34g于烧杯中，加入一定量的二氧化锰，完全反应后，称得烧杯内剩余物质的总质量是34.4g，将杯内剩余物质过滤、洗涤、干燥后得滤渣2g．计算：
（1）生成氧气的质量．
（2）瓶内过氧化氢溶液中溶质的质量分数．
（1）根据质量守恒定律可知，生成氧气质量即为反应前后烧杯中物质的质量之差，（34g+2g）-34.4g=1.6g
答：生成氧气的质量为1.6g．
（2）设反应前溶液中含溶质过氧化氢质量为x
2H2O2
O2↑+2H2O MnO2 .
68 32
x 1.6g
=68 x 32 1.6g
解之得：x=3.4g
过氧化氢溶液中溶质质量分数=
×100%=10%3.4g 34g
答：瓶内过氧化氢溶液中溶质的质量分数为10%．
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| Hearing is very important to all of us. We can 1 beautiful music, nice songs of birds, the laughter of people or other different kinds of 2 in the world with our ears. 3 we must try to protect our ears. The following will tell you 4 protect ears. Listening to 5 music a lot can be bad for ears, 6 when headphones (耳机) are used. So try not to wear headphones or 7 the volume (音量) when you're wearing headphones. You should give your ears a rest if you like wearing headphones. Before swimming, remember 8 earplugs (耳塞) into your ears or wear a swim hat to stop water 9 into your ears. If you are going to a concert, wear earplugs to protect your ears 10 the terrible music! 11 , special earplugs can be made for you if you go to concerts a lot or if you are a musician yourself. See a doctor if your ears 12 . 13 some medicine if the doctor asks you to do so. 14 the advice above now and you won't be saying "what?" when you are getting 15 . | ||||
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