Question

Relationship between wavelength and concentration measurements in colorimetry.

Dilutions, and proper method of making diluted solutions

Beer's law (Concentration vs Absorbance) and the general process of colorimetry

Rate of Reaction and what affects the rate

The initial rates method

Le Chatalier's principle

Titrations (be able to thoroughly analyze titration curves and calculate important values from said curves)

Measurement of precision

Study the pH indicators

Buffers and how to make buffer solutions of a given ratio

Solubility of certain compounds (experiment 8)

Understand whether or not two ionic compounds would react.

explain each

Answer 1

The law measures the absorbance of a substance in a medium by determining how well light passes through it. The more heavily concentrated the substance, the less visible light passes through. The law also states that when judging the penetration of light using a spectrometer, fewer wavelengths of light, both visible and invisible, can pass through as the concentration of the substance increased. There is a direct relationship between absorbance and concentration is the higher the absorbance of a substance, the more concentrated its solution will be in water or another medium.

LE CHATELIER'S PRINCIPLE:

According to Le Chatelier’s principle, adding additional reactant to a system will shift the equilibrium to the right, towards the side of the products. By the same logic, reducing the concentration of any product will also shift equilibrium to the right.

The converse is also true. If we add additional product to a system, the equilibrium will shift to the left, in order to produce more reactants. Or, if we remove reactants from the system, equilibrium will also be shifted to the left.

Thus, according to Le Chatelier’s principle, reversible reactions are self-correcting; when they are thrown out of balance by a change in concentration, temperature, or pressure, the system will naturally shift in such a way as to “re-balance” itself after the change.

BEER'S LAW: Beer’s law governs the amount of radiation absorbed and indicates that absorbance is directly proportional to concentration. Thus, as the concentration of a compound dissolved in a given solvent increases, the absorbance of the solution should also increase proportionally. Chemists take advantage of this relationship to determine the concentration of unknown solutions. This first requires absorbance data on a series of solutions of known concentration called standard solutions. The absorbance and concentration data is then plotted in a calibration curve to establish their mathematical relationship. The concentration of the unknown sample can be determined by measuring its absorbance.

RATE OF REACTION: The rate of reaction or reaction rate is the speed at which reactants are converted into products.

Factors That Affect Rate

There are four main factors that can affect the reaction rate of a chemical reaction:

1. Reactant concentration. Increasing the concentration of one or more reactants will often increase the rate of reaction. This occurs because a higher concentration of a reactant will lead to more collisions of that reactant in a specific time period.

2. Physical state of the reactants and surface area. If reactant molecules exist in different phases, as in a heterogeneous mixture, the rate of reaction will be limited by the surface area of the phases that are in contact. For example, if a solid metal reactant and gas reactant are mixed, only the molecules present on the surface of the metal are able to collide with the gas molecules. Therefore, increasing the surface area of the metal by pounding it flat or cutting it into many pieces will increase its reaction rate.

3. Temperature. An increase in temperature typically increases the rate of reaction. An increase in temperature will raise the average kinetic energy of the reactant molecules. Therefore, a greater proportion of molecules will have the minimum energy necessary for an effective collision (Figure. 17.5 “Temperature and Reaction Rate”).

4. Presence of a catalyst. A catalyst is a substance that accelerates a reaction by participating in it without being consumed. Catalysts provide an alternate reaction pathway to obtain products. They are critical to many biochemical reactions. They will be examined further in the section “Catalysis.”