问题 问答题

溶液与人类的生活息息相关,溶液的配制是日常生活和化学实验中的常见操作.下表是硫酸溶液和氨水的密度与其溶质的质量分数对照表(20℃).

溶液中溶质的质量分数/%412162428
硫酸溶液的密度/g/mL1.021.081.111.171.20
氨水的密度/g/mL0.980.950.940.910.90
请仔细分析后回答下列问题:

(1)20℃时,随着溶液中溶质的质量分数逐渐增大,硫酸溶液的密度逐渐______(填增大、减不或不变);氨水的密度逐渐______(填增大、减小或不变)

(2)取12%的硫酸溶液100%配制成6%的溶液,向100g12%的硫酸溶液中加水的质量应______100g(填大于、小于或等于).

(3)向100g24%的氨水中加入100g水,摇匀,溶液体积是______mL(保留到0.1).

答案

(1)根据表格中的数据表可以得出硫酸的密度随溶液浓度的增加而增加,氨水的密度随溶液浓度的增大而减小;

(2)将12%的溶液加水稀释后溶质的质量不变,所以根据溶质的质量分数的计算公式可以知道,要使12%的溶液变为6%只要使溶液的质量增加一倍即可,所以加入水的质量应该为100g;

(3)向氨水中加入100g水后,氨水的质量变为200g,则根据(2)的分析可知此时溶质的质量分数为12%,从表格中可以查得此时氨水的密度为0.95g/mL,根据密度公式ρ=

m
v
可知:v=
m
ρ
=
200g
0.95g/mL
=210.5mL.

故答案为:(1)增大;减小;

(2)等于;

(3)210.5mL.

名词解释
问答题

Our daily existence is divided into two phases, as distinct as day and night. We call them work and play. We work many hours a day and we allow the necessary minimum for such activities as eating and shopping. 46) The rest we spend in various activities which are known as recreations, an elegant word which disguises the fact that we usually do not even play in our hours of leisure, but spend them in various forms of passive enjoyment or entertainment.

We need to make, therefore, a hard-and-fast distinction not only between work and play but, equally, between active play and passive entertainment. 47) It is, I suppose, the decline of active play — of amateur sport — and the enormous growth of purely receptive entertainment which have given rise to a sociological interest in the problem. If the greater part of the population, instead of indulging in sport, spend their hours of leisure "viewing" television programs, there will inevitably be a decline in health and physique. In addition, we have yet to trace the mental and moral consequences of prolonged diet of sentimental or sensational spectacles on the screen. 48) There is, if we are optimistic, the possibility that the diet is too thin and unnourishing to have much permanent effect on anybody. Nine films out of ten seem to leave absolutely no impression on the mind or imagination of those who have seen them.

49) It is only when entertainment is active, participated in, practiced, that it can properly be called play, and as such it is a natural use of leisure. In that sense play stands in contrast to work, and is usually regarded as an activity that alternates with work.

Work itself is not a single concept. We say quite generally that we work in order to make a living. Some of us work physically, tilling the land, minding the machines, digging the coal; others work mentally, keeping accounts, inventing machines, teaching and preaching, managing and governing. 50) There does not seem to be any factor common to all these diverse occupations, except that they consume our time, and leave us little leisure.

46) The rest we spend in various activities which are known as recreations, an elegant word which disguises the fact that we usually do not even play in our hours of leisure, but spend them in various forms of passive enjoyment or entertainment.