凝固點降低法測定相對分子高質(zhì)量

1、交通大學(xué)實驗報告課程：物理化學(xué)實驗系別：專業(yè)班號：組別：第二大組實驗日期：2015年4月3日:學(xué)號：交報告日期：2015年4月10日同組者：實驗名稱：凝固點降低法測定相對分子質(zhì)量一、實驗?zāi)康?. 用凝固點降低法測定萘的相對分子量。2. 掌握步冷曲線法測定液體凝固點的方法。3. 掌握數(shù)字貝克曼溫度計的使用方法。二、實驗原理稀溶液中溶劑的蒸氣壓下降、凝固點降低（析出固態(tài)純?nèi)軇⒎悬c升高（溶質(zhì)不揮發(fā)）和滲透壓的數(shù)值，僅與一定量溶液中溶質(zhì)的質(zhì)點數(shù)有關(guān)，而與溶質(zhì)的本性無關(guān)，故稱 這些性質(zhì)為稀溶液的依數(shù)性。固體物質(zhì)和它的液體成平衡時的溫度稱為凝固點。加一溶質(zhì)于純?nèi)軇┲?，其溶液的?固點必然較純?nèi)軇┑哪?/p>

2、點低，其降低的數(shù)值與溶液中溶質(zhì)的質(zhì)量摩爾濃度成正比。對于在溶液中不離解、不締合的溶質(zhì)的稀溶液有如下關(guān)系式：T To T kc式中：To 純?nèi)軇┑哪厅c;T 濃度為C的溶液的凝固點;k 比例常數(shù)。如果C以質(zhì)量摩爾濃度miB :每千克溶劑所含溶質(zhì)的物質(zhì)的量)來表示,k則為溶劑的摩爾凝固點降低常數(shù)，今以Kf表示這個常數(shù)，于是示可改寫為:TTo T KfmB若取一定量的溶質(zhì)(Wb)和溶劑(Wa)配制成稀溶液，則此溶液的質(zhì)量摩爾濃度mB為:mBWb / MBWa1000式中：mB為溶質(zhì)的相對分子質(zhì)量。如果已知溶劑的 Kf值，則測定此溶液的凝固點降低值即可按下式計算溶質(zhì)的相對分子質(zhì)量。Mb 4 1000W

3、BTo TWa純?nèi)軇┑哪厅c是它的液相和固相共存的平衡溫度。若將純?nèi)軇┲鸩嚼鋮s，其冷卻曲 線如圖1中I的曲線圖形。但實際過程中往往發(fā)生過冷現(xiàn)象，即在過冷時開始析出固體后,溫度才回升到穩(wěn)定的平衡溫度，當(dāng)液體全部凝固后，溫度再逐漸下降，其冷卻曲線呈現(xiàn)如 圖1中n的形狀。溶液的凝固點是該溶液的液相與溶劑的固相共存的平衡溫度。若將溶液逐步冷卻，其 冷卻曲線與純?nèi)軇┎煌?，見圖9中川、W。由于部分溶劑凝固而析出，使剩余溶液的濃度逐漸增大，因而剩余溶液與溶劑固相的平衡溫度也逐漸下降。本實驗所要測定的是濃度已 知的溶液的凝固點。因此，所析出的溶劑固相的量不能太多，否則要影響原溶液的濃度。如稍有過冷現(xiàn)象如圖 9

4、中W所示，對相對分子質(zhì)量的測定，無顯著影響；如過冷嚴(yán)重，則 冷卻曲線如圖9中V所示，測得之凝固點將偏低，影響相對分子質(zhì)量的測定結(jié)果。因此在 測定過程中必須設(shè)法控制適當(dāng)?shù)倪^冷程度，一般可控制寒劑的溫度、攪拌速度等方法來達(dá) 到。由于稀溶液的凝固點降低值不大，因此溫度的測量需要用較精密的儀器，在本實驗中 采用精密溫差測量儀。做好本實驗的關(guān)鍵：一個是控制攪拌速度，每次測量時的攪拌條件和速度盡量一致。 二是寒劑的溫度，過高則冷卻太慢，過低則測不準(zhǔn)凝固點，一般要求較溶劑的凝固點低 4C,因此本實驗中采用冰一水混合物作冰浴。圖1冷卻曲線三、儀器和藥品凝固點測定儀、水銀溫度計、SWC-II型數(shù)字貝克曼溫度計、

5、壓片機(jī)、秒表、環(huán)己烷(Kf 20.2K mol 1 kg, 0.774g mL1 )、萘(分析純)四、實驗步驟1. 調(diào)節(jié)寒劑的溫度調(diào)節(jié)冰的量使寒劑 F的溫度處于3C左右。在實驗過程中用攪拌器D經(jīng)常攪拌并根據(jù)寒劑的溫度要經(jīng)常補(bǔ)充少量的冰，使寒劑保持此溫度。2. 環(huán)己烷的凝固點測定用移液管吸取30mL環(huán)己烷，把它加入凝固點管 A。然后 塞上橡皮塞，并調(diào)整貝克曼溫度計的探頭B使其浸入環(huán)己烷的液面之下。先將盛放環(huán)己烷液體的凝固點管A直接插入寒劑F中，當(dāng)剛有固體析出時迅速將其外壁擦干，當(dāng)其析出的固體完全融化后迅速將其插入空氣套管E中。打開秒表，每15秒記錄一次待測系統(tǒng)的溫度。重復(fù)試驗。取出凝固點管 A,

6、用手溫?zé)嶂?。待管中的固體剛完全熔化后，將它直接插 入空氣套管E中冷卻。后續(xù)的操作同上，重復(fù)測量兩次。純?nèi)軇┑谝淮渭內(nèi)軇┑诙稳芤旱谝淮稳芤旱诙稳芤旱谌?. 溶液凝固點的測定取出凝固點管 A,使管中的環(huán)己烷熔化。把壓成片狀并已精準(zhǔn)測量的的萘加入到環(huán)己 烷中。然后測定該溶液的凝固點，測定方法與上述相同。五、數(shù)據(jù)記錄與處理1.數(shù)據(jù)記錄時間t/s溫度T/ C時間t/s溫度T/ C時間t/s溫度T/ C時間t/s溫度T/ C時間t/s溫度T/ C06.97506.98106.90807.04107.073156.819156.862156.728156.849156.889306.779306.81

7、7306.554306.669306.709456.770456.793456.381456.502456.545606.764606.777606.220606.324606.382756.761756.767756.060756.174756.229906.758906.761905.927906.018906.0911056.7561056.7591055.8071055.8931055.9621206.7531206.7541205.7121205.7911205.8521356.7501356.7481355.7201355.8051355.7641506.7451506.74415

8、05.7751505.8241505.7791656.7391656.7401655.7941655.8271655.8041806.7341806.7351805.7961805.8221805.8101956.7291956.7311955.7901955.8171955.8082106.7252106.7252105.7832105.8112105.8012256.7192256.7232255.7792255.8062255.7912406.7122406.7172405.7792405.8032405.7902556.7002556.7122555.7742555.7932555.7

9、812706.6972706.7052705.7652705.7842705.7742856.6922856.7002855.7532855.7802855.7723006.6873006.6953005.7423005.7733005.7673156.6843156.6903155.7323155.7643155.7543306.6793306.6863305.7233305.7573305.7443456.6753456.6813455.7173455.7493455.7373606.6733606.6773605.7103605.7463605.7283756.6693756.67137

10、55.7003755.7433755.7213906.6633906.6673905.6913905.7383905.7134056.6584056.6624055.6824055.7334055.7084206.6534206.6564205.6744205.7254205.7044356.6514356.6524355.6654355.7184355.6984506.6474506.6504505.6564505.7124505.6924656.6424656.6474655.6474655.7044655.6844806.6394806.6434805.6404805.6964805.6

11、734956.6364956.6404955.6304955.6884955.6675106.6325106.6375105.6215105.6805105.6575256.6315256.6365255.6125255.6735255.6485406.6325406.6335405.6015405.6635405.6405556.6345556.6315555.5925555.6565555.6325706.6345706.6295705.5825705.6475705.6245856.6345856.6275855.5735855.6365855.6166006.6356006.62560

12、05.5636005.6226005.6086156.6356156.6256155.5506155.6116155.6026306.6366306.6236305.5386305.6046305.5936456.6366456.6206455.5276455.5976455.5836606.6366606.6206605.5166605.5886605.5756756.6396756.6196755.5046755.5796755.5656906.6376906.6186905.4946905.5746905.5567056.6337056.6167055.4827055.5627055.5

13、457206.6337206.6157205.4687205.5527205.5347356.6317356.6157355.4557355.5387355.5247506.6307506.6127505.4427505.5287505.5147656.6287656.6117655.4297655.5187655.5057806.6227806.6117805.4187805.5107805.4947956.6267956.6087955.4057955.5047955.4868106.6298106.6108105.3918105.4958105.4808256.6308256.61182

14、55.3768255.4878255.4728406.6308406.6048405.3618405.4788405.4648556.6298556.6028555.3488555.4688555.4538706.6268706.6038705.3358705.4608705.4408856.6208856.6038855.3218855.4518855.4299006.6289006.6029005.3059005.4449005.4189156.6159156.5999155.2909155.4349155.4049306.6129306.5979305.2769305.4239305.3

15、949456.6099456.5949455.2609455.4109455.3859606.6079606.5929605.2429605.4019605.3769756.6069756.5899755.2259755.3909755.3509906.6059906.5869905.2109905.3779905.34310056.60310056.58510055.19410055.36510055.32610206.60010206.57910205.17610205.35410205.31010356.59810356.57610355.16210355.34310355.294105

16、06.59610506.57510505.14610505.33410505.27510656.59310656.57110655.13110655.32410655.25810806.59110806.56710805.11610805.31310805.23710956.59010956.56610955.10110955.30110955.21911106.58711106.56211105.08611105.29111105.19911256.58311256.55911255.06811255.27711255.17311406.58111406.55511405.05011405.

17、26211405.14811556.57711556.55311555.03211555.24811555.12311706.57411706.54911705.01411705.23711705.09811856.57011856.54611854.99711855.23111855.07412006.56712006.54112005.22912005.04912156.56312156.53612155.22212155.02512306.56012306.53212305.21212305.00112456.55712456.52912455.20212606.55412606.525

18、12605.18812756.55112756.51912755.17412906.54912906.51312905.15913056.54513056.50613055.14813206.54213206.49813205.13613356.53813356.49113355.12213506.53313506.48513505.11013656.52913656.47713655.09713806.52613806.46513805.08213956.52113956.45313955.06814106.51514106.44114105.05314256.51014256.428142

19、55.04014406.50314406.41414405.02614556.49514556.40214555.01214706.48514706.38814704.99814856.47414856.37615006.46415006.36315156.45215156.34815306.43715306.33115456.41715456.31415606.39515606.29315756.37515756.26915906.35315906.24216056.33316056.21516206.31416206.18216356.29416356.14316506.27316506.

20、10616656.25116656.06916806.23016806.03016956.20716955.98917106.18017256.15017406.11917556.08017706.04017855.9962. 根據(jù)環(huán)己烷的密度計算實驗中所用環(huán)己烷溶劑的質(zhì)量WA 。環(huán)己烷的體積30mL環(huán)己烷的密度0.774g mL環(huán)己烷的質(zhì)量23.22g萘片的質(zhì)量 0.1166g3. 根據(jù)環(huán)己烷溶劑和溶液的步冷曲線，確定溶劑和溶液的凝固點。由1中的數(shù)據(jù)可繪制如下步冷曲線：溶劑第一次:Temperature.6.4.2.0& 5 亂e. (a )omroJIodEol-200020040

21、0600 BQQ 1000 1200 1400 1600 1800 2000Time (s)溶劑第二次:-Temperaturem 百.4 立 血7.6.& 各6.&(OJ電n話曲dEMl次 第 液 溶2004006008001000 1200 UDO 1600 1800Time (s) TemperatureT=5 899 aC0 5-0-507 6 B 5- 5OJ aJaalsdEal20040060030010001200Time (s)溶液第二次:O160O,008O60004UHo-5.0-5-0 r & 65-樂OJ aJHEJalduJHJ.溶液第三次:(0)nro9duuML由上面的步冷曲線可得:物質(zhì)凝固點/ c凝固點降低值/ c測量值平均值0.