Serial dilution / calibration curve

What is the first step?

Label a series of tubes for each dilution (e.g. 10⁻¹, 10⁻², 10⁻³) and add a fixed volume of distilled water (e.g. 9 cm³) to each.

What is the second step?

Using a pipette, add a measured volume of the original solution (e.g. 1 cm³) to the first tube and mix thoroughly to ensure an even distribution.

What is the third step?

Then transfer the same volume (1 cm³) from this tube into the next tube and mix again. Repeat this process down the series, ensuring the solution is mixed at each stage and a fresh pipette tip is used to avoid contamination.

What is the last step?

Each step reduces the concentration by the same factor (e.g. tenfold), producing a range of known concentrations suitable for further investigation

How do you use a calibration curve to find the concentration?

Prepare a range of known concentration and absorbance using a colorimeter. Plot a graph of concentration on the x-axis against the measured value on the y-axis and draw a line of best fit to create the calibration curve. Then measure the same variable for the unknown sample, locate this value on the y-axis, and draw a line across to the curve and then down to the x-axis to find the corresponding concentration.

How do colorimeters improve conclusions?

Quantitative, no bias

How to use a colorimeter to determine the concentration of something in an unknown sample?

Zero the colorimeter, use red filter (for sugars test), use known concs, produce serial dilutions, construct calibration curve, read from the graph to determine conc