Chem Talk LED lab

Metals have a lot of important properties:

  • They are shiny (or can be polished to shine)
  • They conduct electricity
  • They conduct heat
  • They can withstand high temperatures
  • They can be pounded into different shapes 

Most of the periodic table is made up of metals. The majority of metals are more reactive than hydrogen and are normally found in their ionic forms (as positively charged ions involved in solid crystals or dissolved in water).

The activity series was created by alchemists who found that some metals react more easily with most metal ion solutions than other metals do. 

The reactions that can occur between neutral metal atoms and metal ions are part of a special class of reactions called oxidation-reduction reactions (redox). Oxidation is the loss or one or more electrons and reduction is a gain of one or more electrons. Oxidation and reduction changes are typically called half reactions because you need both halves for a reaction to occur. To balance redox equations you need to make sure that the number of electrons lost is equal to the number of electrons gained. 

The activity series is useful because you can use it to predict which equation represents a reaction that will occur. Even though hydrogen is not a gas it is included in the activity series. This is because hydrogen takes a positive nature of a metal in its role in strong acids. The main reason it is included is because these acids are simple and convenient reagents that can quickly establish where an unknown metal stands in the series. For example is a metals reacts with dilute HCl, it is above hydrogen however if a metal does not react with dilute HCl, it is below hydrogen in the series. 

 

Chem Talk Chp 4 Section 3

Chemists use moles to count very large quantities of very small objects. One mole is always the same quantity. A mole is similar to the word “dozen”, we use these words to count groups of things. Moles are usually used to count atoms and molecules. The exact number a mole represents is 6.022 * 10^23 units.

There is also the molar mass. The molar mass is the mass of one mole of a pure substance. For example, oxygen’s atomic mass 16.00 amu therefore one mole of oxygen atoms has a mass of 16.00 grams (16.00 grams is the molar mass of oxygen atoms).

To find the mass of a compound, you have to add the masses of each atom in the compound together. For example H2O, H has an atomic mass of 1.01 and oxygen has an atomic mass of 16. When you add all of those together (1.01 + 1.01 + 16.00), you get the mass of one mole of water which is 18.02 grams. (Also you add two hydrogen masses because there are 2 H atoms in H2O) 

One mole of almost any gas at standard temperature and pressure (STP) will occupy the same volume (22.4L) — (Standard pressure = 760 mm Hg)–(Standard temperature = 273.15 kelvins). Standard pressure is close to the pressure under which we live. When the temperature of a gas increases, the volume occupied by the gas increases. One mole of a gas is normally (at standard conditions) occupying 22.4L however one mole of a gas at room temperature will be larger. 

There is the study of the relationships between mass-mole-volume among substances in chemical reactions that is called stoichiometry. When you are calculating the volume you need to calculate the number of moles of one chemical based on the number of moles of one of the other chemicals in the reaction. The coefficients in the balanced equation relate the number of moles of any reactant or product to the other reactant or product. 

To solve a stoichiometry problem you need to know what measurement you want to start and end with. You set the problem up using dominoes. There are three kinds of dominoes:

  1. You can use the molar mass of a substance. One mole of the substance and its molar mass.
  2. You can use the coefficients from a balanced chemical equation. (both units in moles)
  3. You can use the volume that one mole of gas occupies. This will always be the same domino: 1 mol of gas at STP is = to 22.4 L of gas. 

To actually solve these problems you use dimensional analysis. This method involves canceling units. You convert from on the bottom of the ratio so that it will cancel the chemical and measure on the top of the preceding ratio. Chemists also use something called percent yield. When a reaction takes place the product recovered is normally less than 100 percent of the expected product. Percent yield is a ratio of the product recovered and the product expected. To find the percent yield you put the volume found over the volume expected and multiply it by 100. 

 

 

Chem to Go Chp 4 Section 1

  1. a) Exothermic because it is releasing energy when it dissolves and the water is absorbing that energy. b) Exothermic because when it goes from a gas to a liquid it is releasing energy. c) Endothermic because the copper is absorbing the oxygen energy.
  2. a) Disorder increases because the tablet is dissolving in the water which makes it aqueous. b) Disorder decreases because when it goes from a gas to a liquid, liquid particles are more orderly and compacted. c) Not possible to tell. 
  3. a) Reactants: 4Fe(s) + 3O2(g)   Products: 2FeO3(s)                                        a) Reactants: 2KClO3(s)   Products: 2KCl(s) + 3O2(g)                                            b) Disorder decreases because the product is a solid and the solid particles are very compact and orderly.                                                                            b) Disorder increases because the products are a solid and a gas and gas particles are more disorderly. 
  4. c)
  5. d)
  6. d)

Chem Talk Chp 4 Section 1

In our lab, my group had to execute Method 2 to produce CO2. We mixed calcium carbonate and HCl to make CO2 gas. 

When matter goes through a change, there is most likely a change in energy involved. The energy will move from being stored in one form or placed to another form or place. If the matter involved loses energy in a change it has to go somewhere. Likewise, if the matter involved gains energy, the energy must come from somewhere. For example, heat energy. Is heat energy gained or lost when a change happens? If heat energy goes in, the chemicals gain energy and if heat energy is released the chemicals lose energy. A good way to understand energy change is with water. When you go from ice to vapor it is gaining energy and as you go from vapor to water it is losing energy. 

There are bonds holding a molecule together (bonds are within the molecule) and attractive forces holding molecules together. Bonds hold the atoms in a molecule together. Attractive forces are between molecules in a solid and liquid and they hold together the molecules so the solid and liquid do not separate. It takes heat energy input to break bonds between ions in materials and to break apart the forces. It does not matter if you are breaking chemical bonds or intermolecular forces of attraction, they both need an input of energy. 

There are “positive” and “negative” energy changes. To determine this we look from perspective of the reactants. There are endothermic changes and exothermic changes. Endothermic changes absorb heat energy whereas exothermic changes release heat energy. The method my group used to create CO2 gas was an exothermic reaction. 

When a change occurs there is a change in how the particles are made up in the matter. Chemists choose to measure the disorganization. The more spread out the particles are the more disorder there is. Therefore when a substance goes from a solid to liquid to a gas it increases in disorder. Chemists call this entropy. Entropy uses the symbol, S, and it shows tells us the disorder of particles in a substance.