Answer and Explanation: In paper chromatography, the starting line must be drawn with the help of pencil because the pencil lead does not dissolve in solvent, thus it will not affect the separation. The spots of the compounds are separated correctly.
Why do we use pencil to draw the line in chromatography?
In paper chromatography, a starting line in drawn on the paper in pencil (pencil so that it does not dissolve in the solvent and affect the results). Small spots of each sample are placed on the starting line. If a substance is more strongly attracted to the paper than the solvent then it will move a short distance.
What is the pencil line called in chromatography?
solvent front line
Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line. Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent.
What would happen if the solvent level is above the start line?
The start line above the solvent level allows the solvent to move past the start line, carrying the dissolved samples along with it.
Why do you have to make sure the paper line is above the water?
Because you want the products to be carried by the front of solvent but do not want to dilute your spot with your solvent. Filling above the spotting point would result in a huge dissolution without chromatography. Typically the solvent (or solvent mixture) used for the chromatography is rather volatile.
Why is water not used in chromatography?
The stationary phase of paper chromatography is cellulose paper which polar and water are also quite polar, therefore there is no distinction by which to separate the molecules. The water is not used in the paper chromatography, due to the water the paper swells up and ultimately dissolves.
Why do the colors separate in paper chromatography?
The reason why the colors separate has to do with the chemicals that make up the color, the water, and the paper. The chemicals that make up the color are called pigments. Some pigments attach to water better than others so they move further through the paper before sticking.
Why are Rf values less than 1?
Rf is a fraction. It is the ratio of how far a substance travels up the chromatography paper compared to the distance the solvent has travelled. This means that it must be less than 1.
What happens if the ink line or mark touches the water in the paper chromatography?
When the water reaches the ink, it dissolves some of the dyes in the ink, and the dyes travel up the paper towel with the water. That’s how you can see all the different colors that make up the ink. Try it out with different types of pens.
Why is water not used in paper chromatography?
Why do you use a pencil for chromatography?
Pencil is always used to mark chromatography paper or TLC plates because ink may run and interfere with the chromatogram. Ensure the spot is dry before running the chromatogram. Why would you cover your chromatography chamber?
Why do we use pencils instead of inks?
The reason why people use pencils instead of inks it’s just because pencils are made of carbon. Inks in pens contains dyes that might affect the chromatogram as inks has dyes that can potentially separate while doing chromatography. Carbon is less likely to seperate during chromatography.
Why is ball point pen used for chromatogram?
A ball-point pen’s ink, on the other hand, is made of a mixture of liquid components that may interact with the mobile phase and separate into its constituent components, which will interfere with the analysis of the sample mixture (s). The ink may also interact chemically with the samples changing their nature and give inaccurate results.
Why do you use pencil instead of graphite?
It is quick and easy with a more polar solvent. Because pen ink will undergo the chromatography process and mess up your results. Pencil contains only graphite, while pen ink contains a variety of compounds, which would become separated by the process.
