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.
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.
- a) 1 valence electron b) 7 valence electrons c) 2 valence electrons d) 8 valence electrons e) 5 valence electrons f) 3 valence electrons
- Na: lose 1 electron, positive charge of 1
- F: gain 1 electron, negative charge of 1
- Mg: lose 2 electrons, positive charge of 2
- Ne: stays the same
- P: gain 3 electrons, negative charge 3
- Al: lose 3 electrons, positive charge 3
- 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.
- 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
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.
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.
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.