Hi everyone,

 

I basically want to know how you can determine an unknown from a calibration curve?

 

this is not my homework or anything but i want to know for my own knowledge, i have tried researching on the internet but no good explanation, does anyone have a link to a site which explains this in a easy way ?

 

Thanks

The calibration curve, also called a standard curve, is typically represented with a mathematical expression showing the relationship between the independent and dependent variables. By plugging in the independent variable of the unknown into the expression, you calculate the dependent variable. For example:

 

• Various substances (that is, standards) with known characteristics (for example, salt concentration in water) are measured for a particular characteristic dependent upon this characteristic (for example, electrical resistance between two electrodes set a fixed distance apart).
  
• The electrical resistance of each standard is measured, and a mathematical expression is generated that best matches the relationship between the salt concentrations (independent variable) and resistances (dependent variable).
  
• Then the sample of unknown salinity is measured for electrical resistance. The measured value is plugged into the expression, which then gives the salinity of the unknown sample.
  

Almost nothing is measured directly. Even a bathroom scale does not measure mass, but the force of gravity due to the mass. And even then, the old-fashioned spring scales measure the deflection of a spring with a known spring constant subjected to the gravitational force due to the mass.