Acid Base Titration

This week, we revisited the subject of acids and bases. As defined by the Bronsted-Lowry duo, an acid is a substance that donates protons, and a base is a substance thats acceptors protons. These “protons” are, in other words, hydrogen ions. All acid-equations have hydrogen present, due to the acid in the equation. In the case of strong acid base reactions, water is always produced, and it is the driving force of the reaction.

Titration is an analytical technique in which one can calculate the concentration of a solute in a solution. This concentration is determined by using a known solvent and an indicator. Frequently, it is utilized for performing acid/base neutralizations. During this process, a known substance, or titrant, is slowly added to an unknown solution until neutralization occurs. An color indicator is used to exhibit at what moment the solutions neutralize.

In our lab, we were tasked with empirically determining the concentration of a sample of hydrochloric acid. To do this, we created 1M NaOH, and then used a bulb and a pipette to transfer 20 mL of the hydroxide to an Erlenmeyer flask. Then, indicator drops were added, followed by the addition of unknown molarity HCl via a buret until neutralization occurred. The change of the indicator color from hot to light pink meant that the solutions had been neutralized. Using the amount of HCl needed to neutralize the reaction, molarity of HCl can be calculated. If multiple trials are performed, as was our case, the molarities can be averaged for a more accurate number.

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Three Questions 9/12/14

1. What tasks have you completed recently? 

Recently, I have completed tons of tasks in relation to homecoming. Poster decorating, spirit week planning, dress shopping, you name it! In terms of school, I have completed multiple chemistry labs, along with daily calculus assignments.
2. What have you learned recently?

Recently, I have learned that dropping AP psychology was a reallllllllllly good idea. It has taken a lot of stress off of my plate, and for that I am very grateful. In relation to school  and classes, I have learned about differentiability and derivatives in calculus, and reviewed precipitate reactions and electrolytes in chemistry.
3. What are you planning on doing next?

Next, I plan to review past chemistry concepts, particularly redox reactions, considering I was not successful with them the first time around, and prepare for a calculus test. Regarding sports and my social life, I plan to cut my cross country race time down to 27 minutes, and travel to El Paso for the One Direction concert with my best friend for her birthday.

Precipitate Reactions

In chemistry, precipitate reactions cannot be used to determine solubility rules. These reactions prove that one of the substances created in the double replacement reaction is soluble and one is solid, but not which is which, meaning that without knowing the solubility rules, the soluble substance cannot be determined. This relates to our latest chemistry experiment, which involved numerous chemical reactions, some of which produced a precipitate.

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This lab consisted of a laminated reaction sheet, on which we performed the experiments using different chemicals. Repeating our processes a total of sixty six times, we were able to produce consistent results and confirm previous observations. In addition, our data allowed us to ensure presence of certain substances. Some reactions produced a precipitate, while others did not. After our experiment, we practiced converting between molecular and ionic reactions, and, where applicable, net ionic reactions. In reactions where a precipitate was not produced, the net ionic equation was the same as the ionic equation because all substances were aqueous, meaning none cancelled in the reaction to create a more simple equation. An example of  conversion between molecular, ionic, and net ionic equations is shown below.

Molecular:    Na2CO3 (aq) + CaCl2 (aq) = 2 NaCl (aq) + CaCO3 (s)

Ionic: Na(1+)aq + CO3(2-)aq + Ca(2+)aq + Cl(2-)aq = 2Na(1+)aq + 2Cl(1-)aq + Ca(2+)aq + CO3(2-)aq

Net Ionic: CO3(2-)aq + Ca(2+)aq = CaCO3 (s)

The presence or absence of particular cations and anions determined what level of reaction occurred. If a cation or anion was the same in both substances, then no precipitate was created because the substances produced were similar in chemical composition to the reactants. In other words, the solubility of all substances involved was aqueous, because of the combination of chemicals via double replacement. Substances in a sample could be qualitatively identified by the production of a precipitate. In our case, a precipitate presented as a darker section of coloring, or cloudiness in the substance produced. The solubility rules allowed us to predicted what reactions would produce precipitates, making them incredibly useful.

Resources:

Small Scale Precipitate Reactions Lab

Electrolytes and Dihydrogen Monoxide

In our most recent exploration lab, we played with solutions of table salt, or sodium chloride, and water. The sodium chloride component is termed an electrolyte, due to the fact that sodium chloride is a salt, and, therefore, an ionic compound. An electrolyte is an ionic compound that dissociates into both cations and anions in a solvent. Due to the positive and negative charges, said solution conducts electricity. A solution is a solute dissolved in a solvent, or in other words, particles of a surrounded by water molecules (or another solvent, water is simply the most common). Below are our varying concentrations of salt solutions.

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Supersaturated concentration.

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Saturated towards unsaturated concentration.

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Deionized water only.

A particle diagram of a salt solution such as the one we made can be easily created. The image would be based off of the polarity of water. In the diagram, the hydrogen would face the chlorine because of the slight opposing charges, and the oxygen would face the sodium for the same reasons. An example is shown below.

Mathematically, we can show the difference in concentration by comparing the grams of salt per milliliter of water. On our first two tries, we kept track of the amount of salt used per 100 mL water, but were later instructed to not worry about the mass of salt, so we were unable to calculate our g/mL ratios for the solutions that were ultimately tested and deemed acceptable.We identified the solutions qualitatively by the level of brightness produced by the light bulb when it was placed in solution. This is based off of the characteristic of conductibility. The level of dissociated ions in the water impacted the amount of glow. In other words, the more salt present per constant amount of water, the brighter glow produced by the bulb. Molarity and molality can also be used to track difference in concentration, with the formulas appearing as M= mols solute/ L solution and m= mols solute/ kg solvent, where M is molarity and m is molality.

Baking Soda and Vinegar Stoichiometry

Another day, another lab! Most recently, we observed a small scale reaction that involved baking soda and vinegar. This combination of acetic acid and sodium bicarbonate resulted in the production of sodium acetate, water, and carbon dioxide, as explained by the balanced equation below.

HC2H3O2(aq) + NaHCO3 (s) –> NaC2H3O2(aq) + CO2(g) + H2O(l)

We performed multiple repetitions of the experiment, using two fingers of vinegar with varying amounts of baking soda, ranging from .25 to 4.00 grams. Using this technique, we discovered that the limiting reactant changed from vinegar to baking soda as the amount of baking soda used increased. With lighter masses, there was not enough baking soda to react with all of the vinegar, and with heavier masses, there was not enough vinegar to dissolve the baking soda. This corresponds to our graph, which exhibits the plateau in CO2 production due to lack of vinegar. The section prior to the constant amount of CO2 production shows the masses at which all baking soda reacted. This change in limiting reactant is due to the molar ratio from the balanced equation. The mole to mole ratio is what determines the possible amount of substances produced, or in this case, carbon dioxide production.

 

The point of this lab was to review limiting reactants and stoichiometry. Using the mass of the substances prior to reaction, it is possible to calculate the theoretical number of grams produced by utilizing stoich, therefore verifying the results of the experiment.

Three Questions 8/29/14

Recently, I have analyzed complex complex texts in English, reviewed stoichiometry in chemistry, and observed function limits in calculus. I have learned about the scientific side of psychology, and how to calculate limiting reactant problems, among other things. Next, I plan on acing my chemistry and calculus tests. In addition, to improve my cross country pace and focus on better eating habits in order to keep up with the tougher practices that will be starting this coming week.