Some Strong acids to handle with care
Apart from their obvious use in laboratories, we use acids for household cleaning too. Here are some strong acids that you should be extra careful of while handling them.How strong are strong acids? Brush up a little on your chemistry while we explain (Once you get to know the chemistry of acids, you will understand why strong acids are different from so-called weak acids) What is one of the prerequisites for working in a chemistry lab? Laboratory coats, notebook and yes, a minimum knowledge in chemistry! Well, we are not talking about chemical biologists here! We are talking to you all would be lab technicians and chemists. One of the first things you need to learn before working safely in a chemistry lab is knowing your acids. This knowledge is essential to avoid accidents. Today, let's take a look at strong acids and their chemical constitution. What are strong acids? Strong acids are acids that ionize entirely or nearly 100% in aqueous solutions. In other words, they completely dissociate into their ions when added to water as their molecules break up completely, releasing at least one hydrogen ion (H+) per molecule. Strong acids, therefore, are suitable proton donors. A strong acid loses a proton in aqueous solutions and transfers it to H2O molecules, thereby forming a hydronium ion. (H3O+). How strong acids react: HA + H2O → H3O+(aq) + A–(aq) where, A represents the anion of an acid, like a nitrate or chloride ion. Note, the reaction only proceeds in one direction. Once a strong acid completely ionizes, the change becomes irreversible. Example: HCl + H2O → H3O+(aq) + Cl–(aq) Weak acids dissociate partially into their ions when added to an aqueous solution. Now here is how weak acids dissociate in the presence of water: HA + H2O ⇆ H3O+(aq) + A–(aq) where, A represents the anion of an acid, like an acetate or phosphate ion. Note, the reaction proceeds in both directions. As the dissociation is only partial in the case of weak acids, the hydrogen ions continue to move between being part of the weak acid and part of the water. Therefore, these reactions are reversible. Example: CH3COOH + H2O ⇆ H3O+ + CH3COO– https://image.freepik.com/free-photo/warning-sign-caution-icon-word_53876-132177.jpg (Always add acid to water drop by drop while continuously stirring the solution. Doing the other way round may lead to disastrous blasts.) How is the strength of a strong acid determined? The 'strength' of an acid refers to its ability to release hydrogen ions into a solution and not on how corrosive it is. The standard measure of the strength of an acid is its Ka or acid dissociation constant. It is determined experimentally through titration methods. Strong acids have a more considerable Ka value and a smaller pKa value (logarithmic constant) than weak acids. In simple words, the pKa value measures the tendency of an acidic solute to transfer protons to a standard solvent. Therefore, any acid with a pKa value less than -2 is a strong acid. Note, there are only seven acids with a pKa value less than -2. https://as1.ftcdn.net/v2/jpg/03/14/34/38/500_F_314343809_EGag6K3j9oQXUrRQ2rlvcv51GXHpzGS4.jpg (Titration that helps determine the Ka values of acids is a term derived from the French word 'tiltre', which means a measure of the purity of gold and silver coins.) Seven strong acids and their pKa value: Strong Acids Formula pKa value (in water) Hydrochloric acid HCl -5.9 ± 0.4 Hydrobromic acid HBr -8.8 ± 0.8 Hydroiodic acid HI -9.5 ± 1 Nitric acid HNO3 -1.6 Sulphuric acid H2SO4 -3 Triflic acid H[CF3SO3] -14 ± 2 Perchloric acid H[ClO4] -15 ± 2 https://image.freepik.com/free-photo/happy-young-woman-blue-rubber-using-mop-while-cleaning-floor-home_28283-1482.jpg (Muriatic acid, an aqueous solution of hydrochloric acid, is used to clean bathroom tiles.) Strong Acids Vs weak acids: Difference There's a chart on the main differences between strong and weak acids. Strong Acids Weak Acids Strong acids ionize almost completely in aqueous solutions Weak acids dissociate partially into their ions when added to an aqueous solution. Once a strong acid completely ionizes, the change becomes irreversible. Weak acids ionize partially when added to an aqueous solution and hence, the reaction is reversible. pKa value generally less than -2 pKa value always greater than -2 There are only 7 strong acids. All other acids are weak acids. https://image.flaticon.com/icons/png/512/971/971634.png (Strong acids like hydrochloric acid helps in digestion by breaking down food and eliminating the harmful bacteria and viruses in the stomach.) How is the pKa value different from the pH value? pKa value measures the tendency of an acidic solute to transfer a proton to a standard solvent. Strong acids have a pKa value less than -2. pH value measures the concentration of hydrogen ions in a solution. It is defined as the negative log of the hydrogen ion concentration in a solution. In simple words, the greater the concentration of hydrogen ions in a solution, the lesser is the pH value. Concentrated strong acids, therefore, have a meagre pH value. To learn more on pKa and pH value, click here https://image.freepik.com/free-vector/ph-value-scale-chart-acid-base-balance-infographic-education-poster_356415-1083.jpg (pH scale has values ranging from 0 to 14, with 0 to 5 representing the acidic nature of a solution, whereas values between 9 to 14 stand for the alkaline (basic) nature.) pH and pKa of Strong Acids Strong acids have a higher concentration of hydrogen ions in the solution. They, therefore, have a low pH value. pH = -log [H+] Ka is the measure of how completely an acid dissociates in an aqueous solution. Strong acids, therefore, have an enormous Ka value. pKa is the logarithmic acid dissociation constant (Ka) and has a direct relationship to Ka. Thus, the lower the pKa value, the stronger the acid. pKa = -log [Ka] Strong acids Vs Concentrated acids: Difference Strong acids are not the same as concentrated acids. There exists a misconception that strong acids are the same as focused acids, whereas weak acids are the same as diluted acids. This is because both concentrated acids and strong acids have a low pH value generally. Let us see why this happens. Ø The 'strength' of an acid refers to its ability to release hydrogen ions into a solution. In simple words, it is the measure of the degree of ionization that occurs when an acidic solute is added to an aqueous solution. Therefore, the greater the number of cations and anions released in a solution, the stronger the acid. Ø The concentration of an acid is the measure of the number of available acid ions dissolved in a solvent. In simple words, it refers to how much water or solvent is there in an acid. It is measured in moles, parts per million, or percentage. A concentrated acid has a small amount of solvent in it. This increases the concentration of acid ions in the solvent. Therefore, concentrated acids have a low pH value (generally around 3). On the other hand, diluted acids have a lesser amount of acid ions dissolved in them, and hence, they have a lower concentration of acid ions in the solvent. Their pH value, therefore, is higher than concentrated acids (around 7). To learn more on this, click here. It is essential to note that we can have a strong acid that is diluted and a weak acid that is concentrated, and in such cases, their pH value varies accordingly. https://www.freepik.com/premium-vector/human-blood-ph-range-medical-illustration-chart-scale-acidic-normal-akaline-diagram_18760607.htm#page=1&query=blood%20ph&position=0 (A blood pH value below 7.35 is called acidosis, which means an increased concentration of acid in the bloodstream that may eventually lead to death.) Difference between strong acids and corrosive acids It is essential to note that strong acids are not synonymous with corrosive acids. Corrosiveness refers to the potential of a substance to damage the surface that it touches. The substance can be acidic, basic, or even oxidizers. Just like strong acids that are non-corrosive, weak acids like hydrofluoric acid can be highly corrosive as they can damage our bones. On the contrary, the superacids (carboranes) can be safely held in hands. The strength of an acid, therefore, doesn't determine its corrosiveness. Hence, even certain weak acids should be handled with care. https://image.freepik.com/free-vector/diagram-showing-acid-rain-pathway-white-background_1308-51596.jpg (Caption: Sulphuric acid, a highly corrosive acid, is known to cause acid rains.) Strong Acids: Final words There are only seven strong acids known presently. However, just because acid is strong doesn't mean it is damaging. Similarly, even weak acids like hydrofluoric acid can prove disastrous if not handled with care. It is, therefore, essential that we take proper precautions while dealing with acids, irrespective of whether they are weak or strong.
