Chem Talk – Dyes

In our lab we placed 4 strings that were soaking in 4 different mordants then put them in a beaker of carrot greens and heated it for 15 minutes. 

A dye is typically defined as an organic molecule that bonds directly to a textile to produce a colour. Humans have been making dyes for a very, very long time; they were made from animal, vegetable and mineral materials. What chemical features make dyes useful? The chromophore is an important chemical feature. It is the part of the dye molecule that is responsible for the colour we see. The groups of atoms within an organic molecule absorbs only certain colours of visible light. The light of the colours that is not absorbed is reflected to our eyes. Another important chemical feature is an auxochrome. An auxochrome will sometimes be present. This modifies the chromophore’s ability to absorb light energy. It can also alter the wavelength, intensity or both. 

A dye must also be water soluble so that it can interact with the textile to be coloured. The mordant (metallic salts added to dye to make it less likely to wash out) helps in the binding of the dye to the textile. The mordant helps because natural dyes normally fade after you wash it multiple times. When a dye is introduced with a metal ion it forms an insoluble complex salt called a lake. A lake is a pigment formed by precipitation of colouring matter with a metal ion. 

Dyes used to be made from natural resources but now they are made synthetically because it provides more colours. 


Chem Talk #14

In our lab we tested nine different solutions with each other and observed to see if it stayed a solution, turned into a precipitate or both. We were also supposed to be making paint but did not get to it in time. When the two solutions turned into a solid precipitate we were observing insoluble compounds (insoluble means a substance that will not dissolve in a liquid and soluble means a substance that will dissolve in a liquid). They can be used as pigments for paints. When making paint, the pigments is made into a powder then mixed with a liquid. If the pigment is insoluble in the liquid, it will become a suspension of particles in the liquid. 

Most reactions that occur in the world take place in water. When certain cations (ion with a positive charge) and anions (ion with a negative charge) are combined, water-insoluble ionic compounds may form. A precipitate forms when these ions that are in separate water solutions are mixed together. The precipitate is an ionic compound (often called a salt) that forms because certain ions attract each other so strongly that they are removed from the water solution as the product of a chemical reaction.   One type of precipitation reaction is a double replacement reaction. This reaction is when two ions in two different compounds exchange places to form new compounds. 

Ions that do not participate in the reaction and stay in solution before and after the reaction are called spectator ions. There is a chemical equation that lists only those compounds that participate in the reaction called the net ionic equation.

Chemists have a list of rules that predict whether of not a precipitate will form in a double-replacement reaction:

  1. Most nitrate, acetate and perchlorate compounds are soluble.
  2. Group 1A metal and ammonium compounds are soluble. 
  3. Most chloride, bromide and iodide compounds are soluble. The most notable exceptions are when these anions are combined with Cu^+, Ag^+, Pb^2+, Hg^2+ and Hg2^2+. 
  4. Most sulfate compounds are soluble, except when they are combined with Ba^2+, Hg2^2+, Sr^2+ and Pb^2+. Ca^2+ compounds are slightly soluble. 
  5. Carbonate and phosphate compounds are only slightly soluble. 
  6. Most hydroxide compounds are insoluble except when combined with group 1A cations. Ca(OH)2 is slightly soluble. 

Chem to Go #13

  1. Knowing the percentage by mass of water is different than knowing the mole ratio of water to the hydrate because ?
  2. Chemists use the unit moles because it is a set measurement that can easily be converted to mass and back again. 
  • The molar mass of NaN3(s) is 65g. 
  • 52 NaN3(s) * 1 mole/65g –> 0.8 moles
  • 64.5 Zn * 1 mole/65g –> 1.006 moles    
  • 12.0 C * 1 mole/12g –> 1 mole
  • 48.0 O * 1 mole/16g –> 3 moles 
  • 1.006:1:3
  • Mg = 25.5% = 48.5g 
  • Cl = 74.5% 
  • Al2Si2O5(OH)4 –> 259g/ 1 mole
  • 250 Al2Si2O5(OH)4 * 1 mole/259g –> 0.097 moles
  • Desiccants in electronic equipment might be made of copper sulfate or some sort of gel. They are placed in electronic equipment to protect and absorb the product during the manufacturing process incase something spills or liquid manages to get inside. 
  • If the crucible was not heated long enough the percentage of water would be larger because all of the water molecules have not had enough time to be released therefore they stay in the crucible. 
  • Determining the percent composition of water might be useful to a potter because they need to know figure how malleable they need the clay to be in order to shape it.  
  • 11. Na2SO4 * (10H20) ?
  • 3.22 Na2SO4         * 1 mole/ 142g
  • 12. ?
  • 13. ?