experiment 8: determination of calcium by complexometric titrations
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
卡片预览 (24 张)
a titration which involves the complexation of a chelating agent with a metal
complexometric titration
chelating agent
a compound which provides more than one pair of electrons for complexation
example of chelating agent
ethylene diamine tetraacetic acid EDTA
6 covalent bonds to a metal - 4 covalent bonds to a metal -
6 covalent bonds to a metal - tetrabasic form (EDTA^-4) 4 covalent bonds to a metal - dibasic form (H2EDTA^-2)
define water hardness
amt of calcium ad magnesium ions in the water sample
water hardness is usually reported as
ppm CaCO3
true or false: analysis does distinguish between Ca2+ and Mg2+
false - does not
why does the high concentrations of Ca +2 and Mg +2 are undesirable
due to the formation of insoluble carbonate deposits and formation of soap scum
CaCO3 ppm 0-60: 61-120: 121-180: above 180:
0-60: soft 61-120: moderately hard 121-180: hard above 180: very hard
how can water hardness be determined
titration with a standard EDTA solution using EBT indicator
at what pH is titration conducted and why
at pH 10 so that EDTA will maintain its dibasic form and also to prevent precipitation of Mg(H)
what happens when all of the Ca+2 and Mg+2 have already reacted with EDTA (dibasic form)
the excess EDTA will interact with the Mg-EBT indicator complex producing a color change from wine red to blue.
titration with EDTA can also used to determine …
the percentage of Ca in an unknown solid
reagents
MgCl2.6H2O distilled water 6.0 M HCl 6.0 M NaOH pre-dried standard calcium carbonate ethylene diaminetetraacetic acid disodium (EDTA) eriochrome black T (EBT) indicator pH 10 Buffer methyl red indicator
disposal of waste
down the sink in running water
weigh how many grams of EDTA disodium dihydrate
0.93 to 0.95g
preparation of EDTA solution
weigh EDTA transfer it into 250ml volumetric flask clean beaker, weigh 0.052g MgCl2 6H2O and dissolved into 50mL distilled water transfer to volumetric flask invert the flask thrice transfer content to clean colored glass
weigh how many grams of standard calcium carbonate
weigh 0.012 to 0.015g
EDTA ethylene diaminetetraacetic acid chemical formula - structure -
chemical formula - C10H16N2O8 structure - nil
how many mL of 6.0 M HCI then add how many ml of water
2 mL using a 5mL serological pipette 80ml
how many mL of 6.0 M NaOH
Until first appearance of a yellow color
why do we need to boil the solution for 2 minutes in the standardization of EDTA solution
to remove the carbon dioxide
add how many drops of methyl red indicator then what is the next step
3 drops add 6.0 M NaOH dropwise until the first appearance of a yellow color
add how many drops of EBT indicator and ml of pH 10 buffer solution then what is the next step
2mL of pH 10 buffer 3 drops EBT indicator then titrate usingthe standard EDTA solution till color changes from wine red to blue