Tag Archives: mixtures

Easy Emulsifier Chemistry Demonstration

Oil and Water Don't Mix - That's why you need an emulsifier.  (Joanne Goldby)

Oil and Water Don’t Mix – That’s why you need an emulsifier. (Joanne Goldby)

How an Emulsifier Works (Fvasconcellos)

How an Emulsifier Works (Fvasconcellos)

Soap is good at cleaning because it acts as an emulsifier, enabling one liquid to disperse into another immiscible liquid. While oil (which attracts dirt) doesn’t naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.

It’s easy to demonstrate the action of an emulsifer. All you need are two immiscible liquids and a little dishwashing detergent or soap.

Emulsifier Demo Materials

  • water
  • oil or kerosene
  • dishwashing detergent or soap
  • flask or clear glass

If you like, you can add food coloring to this demonstration. It will color the water and not the oil or kerosene. You don’t need to add coloring to tell the water and oil apart, though. Some oils are naturally colored. Or, if you use kerosene, it’s often tinted so people can identify it on sight.

Perform the Demonstration

  1. Add some oil or kerosene together with some water in a flask. Swirl the contents around to try to mix them. What happens?
  2. Add a squirt of dishwashing liquid. Swirl or shake the flask to mix the ingredients. How has the layer of kerosene or oil been changed?

What could be easier, right?

Pepper and Water Emulsifier Trick

This video shows another fun way to illustrate emulsification. If you sprinkle pepper on a dish of water and touch your finger to the surface of the liquid, you get a wet finger but no reaction from the pepper. Next, if you put a drop of liquid dishwashing soap on the tip of your finger and touch the surface of the water, the pepper seems to scatter away.

Homogeneous or Heterogeneous – Mixtures Practice Worksheet

Mixtures can be a confusing topic for new chemistry students. On the surface, mixtures do not seem all that complicated. A mixture is a collection of different materials. Take more than one thing, combine them and you have a mixture.

Mixtures can be further classified as either homogeneous or heterogeneous mixtures. A homogeneous mixture is a mixture where the combined components is uniformly distributed throughout the mixture in a single phase. A heterogeneous mixture is when the components are not uniformly distributed or contain more than one state of matter.

Sometimes, multiple components can be combined and not form mixtures. These combinations are called pure substances. These combinations can be separated as elements or compounds. Elements are combinations of atoms of the same element. Compounds are formed when atoms of different elements are combined.

This worksheet can help practice identifying heterogeneous and homogeneous mixtures or elements and compounds.

Mixtures WorksheetThis worksheet is available in PDF format here.

The answer key is also available in PDF format or if you’d prefer a quick look, an image of the completed sheet can be found here.

Concentration Units For Solutions

Beaker and FlaskChemistry is a science which deals a lot with solutions and mixtures. Knowing just how much of one thing is mixed in with a solution is an important thing to know. Chemists measure this by determining the concentration of the solution or mixture.

There are three terms that need to be defined in concentration discussions: solute, solvent and solution.

Solute: The dissolved substance added to the solution.
Solvent: The liquid that dissolves the solute.
Solution: The combination of solute and solvent.

The relationship between these three terms is expressed by many different concentration units. The unit you choose to use depends on how the solution is going to be used in your experiments. Common units include molarity, molality, and normality. Others are mass percent, mole fraction, formality and volume percent. Each unit is explained along with information about when to use them and the formulas needed to calculate the unit.

Molarity

Molarity is the most common concentration unit. It is a measure of the number of moles of solute in one liter of solution. Molarity measurements are denoted by the capital letter M with units of moles/Liter.

The formula for molarity (M) is

This shows the number of moles of solute dissolved in a liquid to make one liter of solution. Note the amount of solvent is unknown, just that you end up with a known volume of solution.

A 1 M solution will have one mole of solute per liter of solution.  100 mL will have 0.1 moles, 2L will have 2 moles, etc.

Molarity Example Problem

Molality

Molality is another commonly used concentration unit. Unlike molarity, molality is interested in the solvent used to make the solution.

Molality is a measure of the number of moles of solute dissolved per kilogram of solvent. This unit is denoted by the lower case letter m.

The formula for molality (m) is

molality formula

Molality is used when temperature is part of the reaction. The volume of a solution can change when temperature changes. These changes can be ignored if the concentration is based on mass of the solvent.

Molality Example Problem

Normality

Normality is a concentration unit seen more often in acid-base and electrochemistry solutions. It is denoted by the capital letter L with units of moles/L. Normality is more concerned with the chemically active part of the solution. For example, take two acid solutions, hydrochloric (HCl) acid and sulfuric (H2SO4) acid. A 1 M solution of HCl contains one mole of H+ ions and one mole of Cl ions where a 1 M solution of H2SO4 contains 2 moles of H+ ions and one mole of SO4 ions. The sulfuric acid produces twice the number of active H+ ions as the same concentration of HCl. Normality addresses this with the idea of chemical equivalent units. Equivalent units are the ratio of the number of moles of solute to the number of moles needed to produce 1 mole of the active ion. In our example, this ratio is 1:1 for HCl, both H+ and Cl ions so the equivalent unit for both ions is 1. For H2SO4, the ratio is 1:12 for H+ and 1:1 for SO4. The equivalent unit for H+ is 2 and 1 for SO4.

This number is used to calculate the normality of a solution using the formula

Note it is essentially the same as the molarity equation with the addition of equivalent units.
For our example, the 1 M solution of HCl would have a normality of 1 N for both H+ and Cl and the 1 M H2SO4 would have a normality of 2 N for H+ and 1 N for SO4.

Mass Percent, Parts per Million and Parts per Billion

Mass percent or mass percent composition is a measurement to show the percentage composition by mass of one part of a solution or mixture. It is most often represented by a % symbol.

The formula for mass percent is

where A is the part needed and the total is the total mass of the solution or mixture. If all the mass percent parts are added together, you should get 100%.

Mass Percent Example

If you think of mass percent as parts per hundred, you can make the leap to the units of parts per million (ppm) and parts per billion (ppb). These two units are used when the solute’s concentration is very small compared to the volume measured.

The formula for parts per million is

and parts per billion

Note the similarity between mass% and these two equations.

Volume Percent

Volume percent is a concentration unit used when mixing two liquids. When pouring two different liquids together, the new combined volume may not be equal to the sum of their initial volumes. Volume percent is used to show the ratio of the solute liquid to the total volume.

The formula is very similar to the mass percent, but uses volume in place of the mass. VolumeA is the volume of the solute liquid and the volumeTOTAL is the total volume of the mixture.

On a side note, v/v % measurements of alcohol and water are labelled commercially with the unit known as Proof. Proof is twice the v/v % measurement of ethanol in the beverage.

Mole Fraction

Mole fraction is the ratio of the number of moles of a single component of a solution to the total number of moles present in the solution.

Mole fractions are often used when discussing mixtures of gases or solids, but could be used in liquids. Mole fraction is denoted by the Greek letter chi, χ. The formula to calculate mole fraction is

Formality

Formality is a less common concentration unit. It appears to have the same definition as molarity with the formula:

Notice how the only difference between formality and molarity is the letters F and M. The difference is formality disregards what happens to the solute after it is added to the solution. For example, if you take 1 mole of NaCl and add it to 1 liter of water, most people would say you have a 1 M solution of NaCl. What you actually have is a 1 M solution of Na+ and Cl ions. Formality is used when it matters what happens to the solute in the solution. The above solution is a 1 F solution of NaCl.

In solutions where the solute does not dissociate, such as sugar in water, the molarity and formality are the same.

Smart Coatings Separate Oil And Water

Oil and Water Separation

This mesh is coated with an oleophobic-hydrophobic material to separate oil and water. Credit: American Chemical Society.

Oil and water don’t mix. That’s the old wisdom we’ve always been told. If it’s true, why are oil and water so difficult to separate?

When oil spills occur, absorbents like clay, straw, or wool are added to sop up the oil. The problem is, it also sops up a lot of water. The absorbent needs to be gathered up and the oil recovered using costly, inefficient methods.

Researchers have been working on a new class of coatings called “oleophobic-hydrophobic” materials. These materials let water through but repel oil. Early tests showed these materials would take minutes to separate oil and water and not really do a good job at all.

Chemists at Durham University have found a material that works faster and much better. They applied their coating to a metal screen and found the water ran through the mesh while the oil floated on top. Then to remove the oil, the screen was simply tipped to one side and poured into a collection tank. It also works much faster than previous films. Separation was achieved in seconds instead of minutes.

They also demonstrated these coatings have excellent anti-fogging and self-cleaning properties. This research appears online at the American Chemical Society’s Applied Materials & Interfaces journal.