Viscosity is affected by NaCl , why?

Question

I work in a lab testing carboxymethyl ether (wallpaper paste) When I add salt to a fixed quantitiy of flake and water, the viscosity collapses as the salt level increases. any takers?

by the way the water is NOT saturated with salt so it could absorb more!

Answer 1

This is a good question, and there is not a simple answer!
There is a similar effect with a number of surfactants.
I believe the effect is caused by the salt, due to it's strong ionic effect, affecting the position of the various atoms within the longer chain molecule, so that they become easier, or conversely more difficult, to "get past" other molecules in the solution. You will notice a similar effect with other salts (sodium sulphate etc.), but sodium chloride is often used as a viscosity modifier as it is cheap and highly ionic. Sometimes, in some materials, it appears to have little or no effect, whereas other chemicals do have an effect, or have a better effect at low concentrations. Also sodium chloride is highly corrosive, so in certain applications, it is preferrable to avoid it.
Somebody with an expertise in organic chemistry, especially one with experience of surfactants, may be able to give a better answer on a molecular level, but that's as much as I know.

Answer 2

Hey:
Sodium chloride crystals are cubic in form. Table salt consists of tiny cubes tightly bound together through ionic bonding of the sodium and chloride ions. The salt crystal is often used as an example of crystalline structure. It can be modified by temperature.

It varies in color from colorless, when pure, to white, gray or brownish, typical of rock salt (halite). Chemically, it is 60.663% elemental chlorine (Cl) and 39.337% sodium (Na). The atomic weight of elemental chlorine is 35.4527 and that of sodium is 22.989768. Since it is made up of more chlorine and chlorine is a halogen and halogens are reactive then sodium chloide will be reactive!

Properties of Pure Sodium Chloride

Molecular weight - NaCl 58.4428

Atomic weight - Na 22.989768 (39.337%)

Atomic weight - Cl 35.4527 (60.663%)

Eutectic composition 23.31% NaCl

Freezing point of eutectic mixture -21.12° C (-6.016°F)

Crystal form isometric, cubic

Color clear to white

Index of refraction 1.5442

Density or specific gravity 2.165 (135 lb/ft3)

Bulk density, approximate (dry, ASTM D 632 gradation) 1.154 (72 lb/ft3)

Angle of repose (dry, ASTM D 632 gradation) 32°

Melting point 800.8° C (1,473.4° F)

Boiling point 1,465°C (2,669° F)

Hardness (Moh's Scale) 2.5

Critical humidity at 20 °C, (68° F) 75.3%

pH of aqueous solution neutral

Because of these chemical properties salt (NaCl) can raise the viscosity of any fluid or solution without changing the chemical property of the soultion it is immeresed in!
It is well know that if u want your water to boil faster u add a pinch of salt! Salt actually increases the boiling point hence incresing viscosity!
Good luck and i hope that answers your question!
Love SANAM

Answer 3

Firstly the carboxymethyl ether and water mix, not dissolving but becomeing a suspention. So it becomes a mixture of the two. When your adding the salt, its binding and breaking up the suspention of carboxymethyl ether and water making it less viscos, there fore the more salt you add the more the viscosity collapases

Answer 4

It must be to do with altered polarity. I assume magnesium sulphate (sorry about the 'ph' - I am English) would do the same.
The paste is certainly a colloid with, initially, the individual groups of molecues having a charged layer at the surface (helmholz). Adding ionic material changes the whole environment, possibly by neutralizing this charge and causing the colloid to coagulate.

Answer 5

Viscosity decreases with temperature, including water. See attached table for viscosity of water at varying temperatures.

Answer 6

Duh.

Adding salt to a liquid is likely to increase its salt content. I wonder why that happens? The water has absorbed all the salt and cant liquify the paste.

Answer 7

It's a colligative effect...am surprised you are working in a science lab without any knowledge of fundamental physical chemistry, frankly.

Answer 8

It increases density

Answer 9

of course!