Why lower meniscus of acid hematin is considered in sahli method of hemoglobin estimation?
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This is due to the reason that in case of coloured solutions lower meniscus is not visible clearly.
In the case of colourless liquid, it is easy to observe the phase boundary, whether it is convex or concave hence in the colourless liquid lower meniscus may be considered.
A meniscus is the curvature of the surface of the water. Water "sticks" to the walls of the graduated cylinder, but only on the sides and not the middle. When students look at the surface, the water level is not straight. Measurement should be therefore done at the lowest point.
However, in the case of coloured liquids observing this phase boundary (spatial interface, called a phase boundary) is not possible, hence only the upper meniscus is considered.
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Vivek Karma, Chemical Engineering, Mtech Scholar
Answered Nov 17, 2016 · Author has 109answers and 50.2k answer views
As Kuldeep Singh said, we always take readings with lower meniscus only but if lower meniscus is not visible then and only then we take readings with upper meniscus.
if you have read the instruction before doing titration it says
1 Never blow last drop out of pipette
2 never touch burette tip to titrating flask
3 Never add too much of indicator
4 carefully watch for end point
5 avoid any parallax while taking readings
so if you take look on 1 & 2 point they will make sense of reading lower meniscus. If not you can understand this as the meniscus is the last drop of solution that left in the burette or pipette which should not be blown out or used while calculation and if you are taking upper meniscus then you have to blow out the last drop out of burette or pipette which will violate the 1 point.
hum log lower meniscus isliye consider karte hai quki jab hum titration karte hai to humare instruments jaise ki burette aur pipette me last drop hoti hai wo meniscus ki hoti hai par humne liquid ki reading lower meniscus ke hisab se li thi matlab jo liquid humne read kiya wo pipette ki tip se lower meniscus ke level tak ka tha or agar hum upper meniscus ko padh kar reading lenge to burette or pipette me last drop bachegi wo humare calcutation me shamil nhi hogi or end point alag aajyga isliye hum lower meniscus or last remaining drop ke concept se titration karte hai
In the case of colourless liquid, it is easy to observe the phase boundary, whether it is convex or concave hence in the colourless liquid lower meniscus may be considered.
A meniscus is the curvature of the surface of the water. Water "sticks" to the walls of the graduated cylinder, but only on the sides and not the middle. When students look at the surface, the water level is not straight. Measurement should be therefore done at the lowest point.
However, in the case of coloured liquids observing this phase boundary (spatial interface, called a phase boundary) is not possible, hence only the upper meniscus is considered.
25.8k Views · View 42 Upvoters · Answer requested by Nitish Kumar
Your feedback is private.
Is this answer still relevant and up to date?
RELATED QUESTIONS (MORE ANSWERS BELOW)
How coloured and colourless liquid are read by their meniscus and why ?
3,038 Views
Why is the lower meniscus read when a burette is filled with HCl while the upper meniscus is read when the it is filled with potassium permanganate?
2,212 Views
Should I check the upper meniscus or lower while measuring the burette reading in permanganometric titration?
553 Views
How do I give color to a colourless solution?
429 Views
Can we observe the upper meniscus for colourless compounds?
906 Views
OTHER ANSWERS

Vivek Karma, Chemical Engineering, Mtech Scholar
Answered Nov 17, 2016 · Author has 109answers and 50.2k answer views
As Kuldeep Singh said, we always take readings with lower meniscus only but if lower meniscus is not visible then and only then we take readings with upper meniscus.
if you have read the instruction before doing titration it says
1 Never blow last drop out of pipette
2 never touch burette tip to titrating flask
3 Never add too much of indicator
4 carefully watch for end point
5 avoid any parallax while taking readings
so if you take look on 1 & 2 point they will make sense of reading lower meniscus. If not you can understand this as the meniscus is the last drop of solution that left in the burette or pipette which should not be blown out or used while calculation and if you are taking upper meniscus then you have to blow out the last drop out of burette or pipette which will violate the 1 point.
hum log lower meniscus isliye consider karte hai quki jab hum titration karte hai to humare instruments jaise ki burette aur pipette me last drop hoti hai wo meniscus ki hoti hai par humne liquid ki reading lower meniscus ke hisab se li thi matlab jo liquid humne read kiya wo pipette ki tip se lower meniscus ke level tak ka tha or agar hum upper meniscus ko padh kar reading lenge to burette or pipette me last drop bachegi wo humare calcutation me shamil nhi hogi or end point alag aajyga isliye hum lower meniscus or last remaining drop ke concept se titration karte hai
Answered by
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Hello Students,
◆ Answer -
- Lower meniscus of acid hematin describes the phase boundary between acid hematin and air.
- This is the approximate level of hemoglobin in the blood.
# Methods of Hb estimation -
- Sahli's acid hematin method (easiest)
- Cyanomethaemoglobin method (most accurate)
- Oxyhemoglobin method (visual method)
- Electronic hemoglobinometer (direct reading)
- Alkali hematin method (unusual)
- Coulter counter method (electronic)
Hope this helps you. Keep asking..
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