Chemistry的问题~~

×寂寞°心

longman作业簿的问题
In an experiment ,100 cm^3 of 2.0 mol dm^-3 hydrochloric acid reacts with a magnesium ribbon of length 10 cm. The time taken for the reaction is recorded in Table 2.The experiment is then repeated using different concentrations of hydrochloric acid,as shown in Table 2.


Volume of hydrochloric acid/cm^3                               100 80 60 40 20                                                                         Volume of water/cm^3                                                       0 20 40 60 80
Concentration of hydrochloric acid/mol dm^-3            2.0
Time taken/s                                                                   15 35 65 110 200


Complete Table 2 by calculating the concentration of hydrochloric acid used.

“插入表格”不知道为什么用不了＝＝

×寂寞°心

为啥我算到的是:
Concentration of hydrochloric acid/mol dm^-3            2.0 2.5 3.3 5.0 10.0

可，答案是
Concentration of hydrochloric acid/mol dm^-3            2.0 1.6 1.2 0.8 0.4

我错？还是答案错？

yh_tan

答案是 2.0 , 1.6, 1.2, 0.8,0.4
这是用FORM 5 CHAPTER 1的 CALCULATION 来算的
HCL : vol=100cm^3   molarity=2.0
So calculate the concentration of HCL , we have to use the orginal molarity and volume
the formula is ( vol HCL x molarity / 100 )
ans : 80x2 /100 = 1.6 mol
         60x2 /100= 1.2 mol
         40x2 /100= 0.8 mol
         20x2 /100= 0.4 mol

yh_tan

为啥我算到的是:
Concentration of hydrochloric acid/mol dm^-3            2.0 2.5 3.3 5.0 10.0

可， ...
×寂寞°心 发表于 25-3-2012 08:02 PM

bear in mind that the concentration decrease with time.
therefore the concentration of HCI should be decreasing

the time taken of the reaction increase, the concentration of HCL decrease

×寂寞°心

bear in mind that the concentration decrease with time.
therefore the concentration of HCI shou ...
yh_tan 发表于 26-3-2012 12:42 PM

   喔喔～懂了～谢谢你我还以为全部的mol是全部constant的
我就用n=mv/1000...- -"