Therefore, one of the disadvantages of litmus papers is that they cannot be used to determine the pH value. The acid-base environment alters the pi conjugated system and causes a shift in absorbance, causing colour change. Dip the litmus paper in the solution, then remove it and place it down. A litmus test will be effective in this case. It does not give an idea about how acidic or basic is the medium but the intensity of color may slightly vary in low and high basic mediums. A litmus test originally meant a simple method to determine whether something was acidic or basic. Start by stating a hypothesis for each substance on whether it will be acidic, basic, or neutral.
But from pH papers, the pH range of the solution can be determined. If a substance is a base, it will turn the red litmus paper blue. If a litmus paper is wet, it can also test gases. At pH 7, the sample is maybe just a little red. Today, litmus is prepared mainly from the species Roccella montagnei from Mozambique and Dedographa leucophoea from California. It comes in red and blue. When exposed to acids below pH 4.
But what is actually the chemical reaction for that? The litmus test is quick and simple, but it suffers a few limitations. Hydrochloric acid is a strong acid and ethanoic acid is a weak acid. When we think of litmus paper, the colors red and blue come to mind. The dyes in a litmus paper react with acids and bases to produce specific colors; viz. It turns out there is also a gray area, or purple, to be more accurate. Often times, plant extracts will change color if exposed to acidic or basic conditions and can therefore be used to indicate if a substance is an acid or a base.
The litmus test is virtually always performed with a litmus paper a litmus solution can also be used, as has been explained further on in this article, but a paper is much more practical. Chlorine, for example, turns litmus paper very pale, by bleaching it. In general, litmus paper is red below a pH of 4. Whereas blue litmus papers turn red when encounter with an acidic solution. The more apparent the change in colour is, the stronger the alkali or acid. Litmus paper is formed by coating filter paper with litmus, a mixture of dyes obtained from various lichens, primarily of the Roccella genus. The salt, or its solution, so formed can be acidic, neutral or basic.
The pH scale was developed to measure how acidic or basic a substance is. The pH values more than 7 indicate basicity. Neutral litmus paper turns red under acidic conditions and blue under alkaline conditions. The process for blue litmus paper is similar, but no sulfuric or hydrochloric acid is added to the solution. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions.
Second, the paper can change colors for other reasons besides an acid-base reaction. There are all sorts of possibilities. Some indicators can take different colors to different pH values. Strong acids are fully ionised but weak acids are only partly ionised in solution. They are used as indicators.
Thanks for contributing an answer to Chemistry Stack Exchange! Acidic substances tend to taste sour, for example, citrus fruits like lemons, oranges and limes are all acidic and have a slightly sour taste. Try this with different liquids. They only have to know which color is relevant to acidic and basic pH value. Design and carry out an experiment to test the pH of Tums and its effect on the pH of a known acidic solution when they are mixed. Alkalies and acids are at opposite extremes chemically, and will cancel each other out to form a neutral substance when mixed together at equal strengths. Indicators like phenolphthalein only change its color to show that the medium is acidic or basic.
Therefore, one of the disadvantages of litmus papers is that they cannot be used to determine the pH value. If it turns Blue the solution is alkaline. Milk of magnesia is slightly less alkaline, with a pH level of around 10. Use MathJax to format equations. The Blue Litmus test paper does not come with a color chart as it cannot provide you with a defined pH value. Pure water is said to be having pH 7.
Litmus Test Initially, litmus paper is either red or blue. This means that if you mix a substance with a pH of 3 and a substance with a pH of 9, then the resulting solution will have a pH closer to 7. Red litmus paper is dipped into a solution to establish whether a substance is acidic or alkaline. You can use all of the materials listed above to carry out this additional experiment. The strength of the acidity or the basicity also cannot be determined using litmus papers. Most salt solutions are neutral and do not change the color of the blue paper strips and the red paper strips.
Image source: Wikipedia You can test this for yourself further with some of the liquids in the chart below. An acid with pH 1 is said to be very strong, and as the pH value increases, acidity is decreased. Or for gases, put the Litmus paper at the top of the glass tube containing the gas you wish to test. It is this solution that makes the paper pH active. Switch the color of the papers, repeat and observe the change.