please I need help with this. what is the difference between molality, normality and molarity?
and adhesive forces and cohesive forces? I am very confused. please help thanks
molality = # moles/kg solvent = m.
molarity = # mols/L of solution = M.
normality = # equivalents/L of solution = N.
Adhesive forces are those between different atoms. Cohesive forces are those forces between the same kind of atom. For example, if you notice water in a capillary tube tends to curve upward on the glass surface. Those are adhesive forces between the glass and the water molecules. Water wets the glass. If you have used a buret the meniscus is the U shaped water line and adhesive forces are responsible. If you placed liquid mercury in a capillary tube, the curvature is the opposite. That is, the mercury forms an upside down U (I can't type one like that) and that is because the cohesive forces between the mercury atoms is strong and mercury does NOT wet the glass (the adhesive forces are weak). Look up cohesive and adhesive in a dictionary. It may give a better definition. Do you know how I remember them? I think of adhesive tape that I put on my son when he was a baby and had a cut or a scrape. Adhesive tape sticks to the skin and that is a bond between two different kinds of atoms/molecules. Then, of course, cohesive must be the opposite. I hope this helps.
thanks
Sure! I can help you understand the differences between molality, normality, and molarity, as well as the differences between adhesive forces and cohesive forces.
1. Molality, Normality, and Molarity:
- Molality (symbolized as "m") is a measure of concentration that relates the mass of the solute to the mass of the solvent in a solution. It is expressed in moles of solute per kilogram of solvent.
- Molarity (symbolized as "M") is another measure of concentration that relates the moles of solute to the volume of the solution. It is expressed in moles of solute per liter of solution.
- Normality (symbolized as "N") is a measure of concentration that considers the number of equivalents of a solute in a liter of solution. It is often used for acid-base reactions or reactions involving ions with multiple charges.
To calculate molality, you need to know the mass of the solute and the mass of the solvent. Divide the number of moles of solute by the mass of the solvent in kg.
To calculate molarity, you need to know the number of moles of solute and the volume of the solution in liters. Divide the number of moles of solute by the volume of the solution in liters.
To calculate normality, you need to know the number of equivalents of the solute and the volume of the solution in liters. Divide the number of equivalents of the solute by the volume of the solution in liters.
2. Adhesive Forces and Cohesive Forces:
- Adhesive forces are the attractive forces between molecules of different substances. They cause the substances to stick together. For example, when water is poured onto a glass surface, the adhesive forces between water molecules and the glass surface cause water to spread out and wet the surface.
- Cohesive forces are the attractive forces between molecules of the same substance. They cause the molecules to stick together. Water molecules, for example, exhibit cohesive forces between each other, forming drops or creating surface tension.
In summary, molality, molarity, and normality are different measures of concentration in a solution. Molality relates the mass of the solute to the mass of the solvent, molarity relates the moles of solute to the volume of the solution, and normality relates the number of equivalents to the volume of the solution. Adhesive forces are the attractive forces between molecules of different substances, while cohesive forces are the attractive forces between molecules of the same substance.