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17

The existence of $\ce{H4O^{2+}}$ has been inferred from hydrogen/deuterium isotopic exchange monitored through $\ce{^{17}O}$ NMR spectroscopy in the most extremely acidic condensed phase superacid we can make, fluoroantimonic acid ($\ce{HF:SbF5}$ or $\ce{HSbF6}$). It seems that even the slightly weaker but still very much superacidic magic acid $\ce{HSO3F:...


6

No, it is not correct because it happens with other liquids (solvents) also. Taking Wikipedia's definition: Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. Only as extra ...


5

I think, first I should clarify what causes the osmotic pressure: Osmosis occurs when two solutions of different concentrations are separated by a membrane which will selectively allow some species, e.g. the solvent, through it but not others, e.g. the solute. So, there is a concentration gradient between the two solutions which would lead to a diffusion ...


4

According to this document (https://arxiv.org/pdf/physics/0305011v1.pdf) "Water molecules can pass through the membranes in either direction, and they do. But because the concentration of water molecules is greater in the pure water than in the solution, there is a net flow from the pure water into the solution." Hydraulic equilibrium is achieved when ...


4

Your example with the no-polar substance wouldn't qualify in a discussion of osmosis. There needs to be a solution on at least one side of the membrane. Since a typical non-polar substance would be insoluble in water, osmosis would not apply. However, in your diagram, water would move from left to right due to a concept called pressure potential. You will ...


4

It has to do with the fact, that osmotic pressure of any solution is dependent only on the relative number of particles in the solution (in case of dilute solutions), irrespective of the nature(called colligative property). Therefore, you take certain known weight of the substance you want to calculate the molecular mass of, prepare a solution and measure ...


4

IIRC, the solubility of virtually all gases in water decreases with temperature. This is the reason why heating water will result in bubble nucleation, and this can be exploited to produce very clear ice by boiling water, perhaps several times, before putting it into the trays.


4

Your concept of a cell is a little vague. Although the cell wall is made from a diglyceride bilayer, it is not impregnable. In fact, there are many proteins that pass through the cell wall where dissolved material can pass. One of the proteins is called the sodium potassium pump. In a living cell, the protein uses ATP to move sodium out of the cell and drag ...


3

Yes, I think so. Based on our comments above, I believe you want to prepare two solutions that are isotonic with each other (have the same concentrations of different solutes) and allow them to communicate across a membrane that is selectively-permeable to water only. Tonicity is described here as: Tonicity is a measure of the effective osmotic pressure ...


3

You are correct in thinking that urea and sucrose would have van't hoff factor (i) = 1, since they are non-electrolytes and don't undergo disassociation(or ion pairing). What you are left with are the following: $\ce{NaCl}$ , $\ce{BaCl_2}$ and $\ce{[Cr(NH_3)_4Cl_2]Cl}$. Let us begin with the the two chloride salts: $\ce{NaCl}$ , $\ce{BaCl_2}$. we assume ...


3

To minimize the air bubbles in ice, either 1) hold the water under a vacuum or 2) 'degas' the water with an ultrasonic cleaner before freezing. 1) Holding the water under a vacuum will pull the dissolved gases out of solution. The will diffuse to the air-water surface, and then be vacuumed away. 2) An ultrasonic cleaner will vibrate the liquid at ...


3

There are way more sensitive ways to measure dextrose (glucose) concentration than polarimetry. For example, there are reducing sugar tests like the Dinitrosalicylic Acid test or (better) the 2,2'-Biconchoninic acid test. Just measure the dextrose concentrations inside and outside of the bag. I have protocols for these tests if you want; it involves getting ...


3

Benedict's reagent detects reducing sugars (free aldehyde group) by reducing soluble blue Cu(II) to insoluble red Cu(I) oxide. Sucrose aquoous solution is inert unless it is pre-hydrolyzed by heating with strong acid catalyst. That certainly is a poser. One possibility (SWAG, not fact) is regenerated crosslinked cellulose is overall not permeable to ...


3

Let the subscript A refer to the solvent and B refer to the solute, and let the subscript 1 refer to the pure solvent container and 2 refer to the mixture container. Then the free energy of the combined system is given by: $$G=n_{A1}\mu_A^0+n_{A2}\left(\mu_A^0+RT\ln{\left[\frac{n_{A2}}{n_{A2}+n_{B_2}}\right]}\right)+n_{B2}\left(\mu_B^0+RT\ln{\left[\frac{n_{...


2

There exist many types of semi-permeable membranes (the ones used for dialysis tubing), with various pore sizes. One of the very common lab experiment on the topic of osmosis is using a sucrose solution (sucrose is cheap) and small-pores membrane, such that water and small ions (typically Na+ and Cl–) can pass, but not sucrose. The one which you link to ...


2

I did it in this step: First I use ΔTb=kbm And substitute following Tb=101.45 and kb=0.512 I get m=198.144 mol/kg This should be the first clue that something went wrong. 198 mol of sucrose is about 67 kilograms of sucrose, so your implied molality means that for every kg of water, there are 67 kg of sucrose. That can't be right. (It would be about the ...


2

You are not wrong in your understanding of a water softener, nor are you wrong in your understanding of a reverse osmosis filtration system. Does the RO filter care whether the supply water is salty or hard? I would like to make the point that your RO filter is incapable of caring about the hardness of the water. This is more about carefully choosing ...


2

Most of the time what you say about semi-permeable membranes is correct. a semi-permeable membrane is a membrane that allows only solvent molecules to pass between the membrane; solute molecules are blocked. Solvent molecules flow from the membrane side that has from low solute concentration (i.e. high solvent concentration) to high solute concentration (...


2

If I understand correctly if the concentration of water is greater on the outside of a bacterial cell the water will go inside the bacteria allowing it to multiply or grow faster. Does glycerin have the same effect? Usually the point of adding salt to water is to lower its activity, in order to make the water concentration outside the cell lower than on the ...


2

If you dribble a basketball, the force of your hand on the ball, that keeps it bouncing, is not (1) gravity; (2) the weak force; or (3) the strong force. It must be electromagnetic force--the electrons in the molecules of your skin repelling the electrons in the molecules on the surface of the ball. Also, your skin and the ball remain (largely) intact ...


2

I am afraid you are stuck because you considered glucose as osmotically active. But you assumed that glucose can freely move across the membrane, which is the opposite of osmotic activity. So, short-short answer : ignore the glucose, it is an osmolyte, but it is not osmotically active on the membrane you are thinking of; its concentration is going to ...


2

To evaluate whether the process is spontaneous you have to take the difference of the chemical potentials $\mu$. Solvent molecules go from the pure solvent (reactant) to the solution (product): $$\Delta_r G = \mu_\text{product} - \mu_\text{reactant} =$$ $$ = (\mu_\text{solvent}^\circ + R T \ln x_A) - \mu_\text{solvent}^\circ < 0$$ Throughout the process, ...


1

Polyethylene oxide, AKA polyethylene glycol or PEG has MW > 100,000. You can find higher-MW PEG in disposable diapers and similar absorbent products. You could also use agar, pectin or gelatin, available in groceries and from lab supply companies. One of my favorite demos was to make an agar solution with a bit of phenolphthalein added and put it in ...


1

To first order the solute doesn't matter, though it probably has a small influence. The driving force for osmosis is entropic. The osmotic pressure then is not due to the forces between the solute and solvent, but mostly from the fact that you can mix the two together. Indeed, osmosis works even when there's less interaction between the solvent and solute, ...


1

$\ce{MgCl2}$ has the highest osmotic pressure because it breaks up into three ions in water, as opposed to all the others, which only break up into two.


1

A semi-permeable membrane is not ‘smart’. If you wish, it is actually rather dumb. All it can do is perform a simple selection of ‘I’m letting you through’ versus ‘I’m not letting you through.’ Most membranes will work along the lines of size, polarisability or both. Size is easily explained: The membrane’s pores have a certain size and what is larger than ...


1

The short answer is pressure. What you've described above is basically just osmosis, and without applied pressure to overcome the osmotic pressure of the system, reverse osmosis doesn't happen. This Wikipedia article gives a good description of the concept, and the difference between filtration, osmosis and reverse osmosis: Osmosis is a natural ...


1

The expression you need is $$\Pi = i\mathrm{MRT}$$ where $i$, the van't Hoff factor, describes the degree of ionization of the solute (for sucrose, it's 1; for $\ce{NaCl}$, it's 2, since we get 2 moles of ions for each mole of salt we dissolve). The other variables are as you describe. Thus, the osmotic pressure for your salt solution is twice that of your ...


1

The water molecules move across the membrane due to thermal energy. If concentration of solute on both sides of the membranes is the same, the amount of water crossing the membrane in either direction is same but when the concentration is unequal, the side with more solute particles (higher concentration, that is) attracts the water molecules and thus ...


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