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. ?

Chem Talk #13

In our lab, we heated a substance inside a crucible but left the lid tilted so the water molecules could be released. We started with a substance that had water as a part of its crystal structure. These are called a hydrates. After heating it the water was released leaving a anhydrate. An anhydrate is whats left when the water is removed from the hydrate.

Many compounds are formed as a result of reactions that happen in water solutions. When we heat these compounds the water is released. The water molecules apart of the crystalline structure are weakly bonded to the ions and molecules that make up the compound.

A way chemists measure the number of atoms in a substance is with a unit of measurement called a mole. One mole is equal to the number of carbon atoms in 12 g of pure carbon-12. The exact number a mole represents is 6.022 * 10^23 and this is known as Avogadro’s number. To calculate the molar mass which is the mass of one mole of a pure substance, you add up the masses of all the elements present in the compound.

Chemists use percent composition to calculate a formula for an unknown compound. Percent composition is the mass of each element in a compound expressed as a percent. To calculate it you add up the total mass of each element and then the total mass of the compound. Two formulas chemists use is the empirical formula and the molecular formula. The empirical formula is the formula for the smallest possible ratio of the elements in the compound. The molecular formula is a description of the number and types of atoms in a molecule.

Chem Talk #12

In this investigation we used bobby pins to observe the different properties of three types of steels. Each time we heated the bobby pin we altered the arrangement of iron atoms as carbon atoms were introduced into the crystal structure. We made annealed steel, hardened steel, and tempered steel. When we made the annealed steel, we heated it then let it cool. As the iron cooled the crystalline structure rearranged and excess carbon was squeezed out. Annealed steel has fewer carbon atoms between the iron atoms which makes it a more malleable steel. To make hardened steel, after heating it we quickly cooled it in water. We locked the carbon atoms into the crystalline structure which made it hard and brittle. To make tempered steel we heated it lightly but not red hot then let it cool. This relieved some of the bonds between the carbon atoms and electrons. The tempered steel was hard but malleable.

Metals have metallic bonding. These bonds are formed by the sharing of valence electrons among all atoms in the metal. Metals do not hold on tightly to their valence electrons. We can look at the bonding of metals with an electron sea model. Metals have a crystal structure with a sea of valence electrons surrounding metal cations (cations are positively charged metal ions). The electrons are free to move about therefore the atoms in most metals can move past each other when hammered which is the property; malleability.

An alloy is a substance that has the properties of a metal but consists of two or more metals. For example steel is an alloy of iron and carbon. 

Chem to Go #11

  1. a) 1 valence electron b) 7 valence electrons c) 2 valence electrons d) 8 valence electrons e) 5 valence electrons f) 3 valence electrons
  2. Na: lose 1 electron, positive charge of 1
  3. F: gain 1 electron, negative charge of 1
  4. Mg: lose 2 electrons, positive charge of 2
  5. Ne: stays the same
  6. P: gain 3 electrons, negative charge 3
  7. Al: lose 3 electrons, positive charge 3
  8. The octet rule is that the outer shell of an atom has to have 8 electrons. The atom must lose or gain electrons in order to have a full outer shell or an empty outer shell. 
  9. To zinc-plate a piece of copper metal you would attach the zinc to the positive terminal  in the battery and change the copper sulfate solution to a zinc solution. 

10. Mg —> Mg^2+ + 2e^- 

2H^+ + 2e^- —>H2

= 2H^+ + Mg —> Mg^2+ + H2

11. ?

12. Some items are silver and gold plated because it is cheaper and has the same effect as solid silver and gold. 

13. An artist might chose to electroplate a sculpture to protect the sculpture from oxidizing and deterioration. 

Chem Talk #11

In our lab on Saturday we looked at the chemical reactivity of metals. This reactivity depends on the valence electrons. The valence electrons are also responsible for the reactivity of any element. The valence electrons are located in the outermost electron shell furthest away from the nucleus. Depending on the location of the element on the periodic table you can use that to determine the number of valence electrons it has. The metals that are in group 1A all have one valence electron, the metals that are in group 2A all have two valence electrons and so on and so forth all the way up to group 8A. In group 8A, the elements are called noble gases. Noble gases have eight valence electrons which gives a certain stability to the element. Elements in all the other groups tend to gain or lose electrons so that they will have eight valence electrons too. This is called the octet rule. 

For example, Flourine has seven valence electrons, therefore it would gain one electron to get a full outer shell. Since the element gained one electron it would now have a negative charge. Another example, Sodium has only one valence electron, therefore it would “give” or lose that electron rather than gain seven. “Giving” that electron away forms a sodium ion with a positive charge. 

In our lab, we were specifically looking at which metal lost these electrons easily and which ones did not. This is because some metals are better than other metals at losing their valence electrons. Metals tend to lose these electrons in chemical reactions with other substances. When a metal atom loses electrons it becomes an ion. An ion is a positively charged particle and is the name for a charged atom of charged group of atoms. When we compared zinc to all the other metals it would give either a positive reading or a negative reading, then when we switched the wires we got the opposite flow. Here is our list of metals from most active (easiest to oxidize) to least active (hardest to oxidize):

Magnesium (Mg), Aluminum (Al), Zinc (Zn), Iron (Fe), Tin (Sn), Copper (Cu)

Reactive metals lose electrons easily and form compounds readily. Sometimes the properties of these new compounds are very damaging to the metal. However, sometimes the new compounds can protect the underlying metal. For example, the Statue of Liberty is covered with a patina coating that is made of basic copper carbonate and basic copper sulfate. This coating protects the underlying copper from further corrosion by acting as a barrier between the atmospheric chemicals and the copper. 

Also during the lab, we put a copper strip and a zinc strip into a copper sulfate solution, the zinc strip turned black, it was coming from the copper and coating the zinc strip. This is called electroplating. The copper was released from the positive terminal as copper ions, into the solution, moved toward the negative terminal where it gained electrons, and then they adhered to the zinc strip. When we apply voltage to a metal ion in a solution it causes the metal connected to the positive terminal to oxidize and dissolve. The positive ions of this metal move through the solution and accept electrons from the second metal connected to the negative terminal therefore the atoms of the first metal will be plated on the second metal. 

 

Chem to Go #10

  1. An acid is a chemical substance that turns blue litmus paper red, has a sour taste, neutralizes bases, reacts with most metals and reacts with certain indicators to produce a colour change. A base turns red litmus paper blue, has a bitter taste, a slippery feel, is corrosive, neutralizes acids and causes certain indicators to produce a colour change. 
  2. pH measures the concentration of hydrogen ions. A higher concentration of H+ ions has a lower pH and vice versa. 
  3. a) 4 
  4. b) less than 7 
  5. SO2 + H2O = H2SO3

  6. The pH of a water sample will lower when SO2 is introduced because SO2 more acidic. 
  7. Sources of sulfur dioxide in the air are from the emission of fossil fuels. (motor vehicles, power plants)
  8. Old military gravestones are difficult to read because of acid rain. 

    H2SO4 + CaCO3 = CaSO4 + H2O + CO2

  9. Other materials used for artwork placed outside are limestone, marble and metals which will be affected by acid rain which will make the sculpture to deteriorate. 
  10. Other factors that could cause artwork to deteriorate are humans, the temperature and exposure to the sun. Depending on the artwork, to preserve it you need a temperature that is adjusted depending on the art, also have it covered away from where the sun cannot shine in also have a case around it so people cannot touch it.
  11. a) acidic 

Chem Talk #10

In this experiment we separately added SO2 and CO2 in a little bit of universal indicator to see what would happen. A universal indictor is a mixture of acid-base indicators used to show how acidic or basic a solution is. An acid-base indicator is a substance and when it is exposed to an acid or a base it changes colour. Acids and bases each have different properties. Acids usually have a sour taste, neutralize bases, react with most metals and react with certain indicators to make a colour change. While bases have a bitter taste, a slippery feel, are corrosive, neutralize acids and also cause certain indicators to make a colour change. 

To measure how acidic a solution is we use the measurement pH. The pH measures the concentration of hydrogen ions in the solution. An hydrogen ion is a hydrogen atom that has lots its only electron. Acidic solutions will have a low pH (below 7) whereas basic solutions will have a high pH (above 7). If the solution has a pH of 7 it is neutral. 

When we used a pipette to put SO2 gas into the universal indicator it changed to the colour red. Red on the pH means the it has a pH of 2 therefore it is very acidic. When we blew CO2 into the universal indicator with a straw it changed to the colour orange/yellow meaning it was also acidic with a pH of 5.

Chem Talk #9

In this lab, we held an orange peel and some red and green apple peels near a Bunsen burner flame to see what would happen. When we held the orange peel near the flame and squeezed there was a sharp yellow/whitish flame and when we did the same with the apple peels there was an orange and purple flame (sodium and potassium present). Ethene (ethylene) was also present in the lab. The compound ethene, is organic which means it is a molecular compound of carbon. The opposite of organic compounds are inorganic compounds which are not based on molecular compounds of carbon. Ethene is apart of a specific class of organic compounds called hydrocarbons. Like the name, hydrocarbons are largely made up of hydrogen and carbon. Hydrocarbons have intramolecular covalent bonds. When a hydrocarbon burns in the presence of oxygen, combustion happens (combustion basically means fire). 

The chemical formula from burning the fruit peels:

C2H4(g) + O2(g) —- CO2(g) + H2O(g)

The C2H4 + O2 are called the reactants and the CO2 +H2O are called the products. The reactants are turning into the products. The reactants have a total of 2 C atoms, 4 H atoms and 2 O atoms. The products have a total of 1 C atom, 2 H atoms and 3 O atoms. This is a violation of the law of conservation of mass. The law states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants entering into the reaction. In simpler terms, the reactants total mass must equal the products total mass. We cannot change who the product is but we can change how many/amount. If we add coefficients we are changing the number of that atom not the molecular formulas. In order to balance this equation, we must add a 2 in front of the CO2 and the H2O and we must add a 3 in front of the O2. 

C2H4(g) + 3O2(g) —- 2CO2(g) + 2H2O(g)

Now the reactants have a total of 2 C atoms, 4 H atoms and 3 O atoms and the products now have a total of 2 C atoms, 4 H atoms and 3 O atoms. Both sides are now equal.