Lab Manual- Chapter 9

Calculate the mass of the KHCHO that reacts with 15 mL of the 15 M NaOH solution.

1HCHO: 1 NaOH 15 mL--> .015 L .015 L (.15M)= .00225 mol NaOH .00225 NaOH x (1 mol KHCHO/1 mol NaOH)= .00225 KHCHO .00225 HCHO x (204.23g/1 mol) =.4595 g.

Volumetric Analysis

A chemical analysis that is performed primarily with the aid of volumetric glassware. A known quantity or a carefully measured amount of one substance reacts with a to be determined amount of anotehr substance.

Standard Solution

A measured number of moles of a substance is present in a measrued volume of a solution, generally expressed as the molar concentration of the substance. A measured volume of the standard solution than reaction with the substance being analyzed.

Stoichiometric Amounts

A reaction is complete when the stoichiometric amounts of the reacting substances are combined. These are the mounts corresponding to the mole ratio of the balanced equation.

Acid-Base Indicator

A substance with an acidic structure with a different color than its basic structure. In this experiment, phenolphthalein is colorless in an acidic solution but pink in a basic solution. Indicators are selected so that the stoichiometric point coincides with the endpoint of the indicator.

Hygoscopic

Able to absorb water vapor readily In this experiment, sodium hydroxide is very hygroscopic, therefore, its mass cannot be measured to prepare a solution with an accurately known molar concentration.

Primary Standard

An accurate mess of a solid substance is measured, dissolved in water and then reacted with the substance being measured. Relatively large molar mass, is nonhygroscopic an reacts in a predictable way.

Pure potassium hydrogen phthalate is used for he standardization of the sodium hydroxide solution. Suppose PHP is not completely dry, will the reported molar concentration of the sodium hydroxide solution be too high, too low, or unaffected because of the moistness?

If the pure PHP is not completely dry than the reported molar concentration will be too high. This is because the added weight from the moisture makes the solution appear to have more PHP than it really does.

The student forgot to prepare any boiled, deionized water for the preparation of the NaOH solution and then forgot to cap the bottle. Will the concentration for the NaOH solution be greater, less than or unaffected?

If the student forgets to do the part A.2, than the reported molar concentration will be too high, as leaving the mixture uncapped means that contaminants from the air can get mixed in, thus making the mass larger. Without being boiled, the water may also be contaminated and thus effecting the outcome of the experiment.

Primary Acid Standard

Is an accurate mass measurement of a solid substance that is dissolved in water and then reacted. The primary acid standard in this experiment is potassium hydrogen phthalate. Has a high purity, relatively high molar mass and it only very slightly hygroscopic. It will determine the molar concentration of a sodium hydroxide solution.

Secondary Standard Solution

Once the molar concentration of the sodium hydroxide is calculated, the solution is said to be standardized.

What is the primary standard used in this experiment? Define a primary standard. What is the secondary standard used in this experiment. Define.

Primary Standard: accurate mass of a solid substance which is measured, dissolved in water and then reacted. The primary standard is PHP KHC₈H₄O₄ Secondary Standard: Once the molar concetration of the titrant is measured, the remaining solution is standardized and thus considered a secondary standard. The secondary will be the sodium hydroxide solution.

Distinguish between a stochiometric point and an endpoint in an acid-base titration.

Stoichiometric Point- when a reaction is complete because the stoichiometric amounts of reactants have combined. Endpoint- when the indicator changes colors due to the change in pH. Indicators are selected so that the stoichiometric endpoint and the other endpoint coincide.

A drop of the NaOH titrant adheres to the side of the buret (because of a dirty buret) between the initial and final recordings for the titration. As a result, will the molar concentration of the NaOH solution be reported as too high or too low?

That drop would not have reacted w/the acid solution but the recordings would have mistakenly indicated that it did. thus the volume of NaOH used that was measured would be higher than it should be, making the calculated molarity lower than the actual value. aka since molarity=mass/moles and moles=concentration x volume and volume is too high, which causes moles to be too high since they are directly proportional, meaning molarity would be too low since molarity and moles are directly unproportional.

Titrant Analyte

The liquid being dispensed in the buret. The liquid present in the flask.

pH

The negative logarithm of the molar concentration of H30+ pH=-log[h30+]

Endpoint

The point in the titration where the phenolp changes color.

What is the titrant for this experiment? Is the indicator generally added to the titrant or analyte in a titration.

The titrant is a standard solution of sodium hydroxide. The indicator is phenolphtalein, and it is added to the acid, or in this case, the analyte. This is because it is colorless in an acid, but pink in basic solutions.

The wall of the flask is occasionally rinsed with water from the wash bottle during the analysis of the acid solution. Will this technique error result in the molar concentration of the acid solution being too high, too low or unaffected.

This will lower the molar concentration of the acid. Molarity is determined by dividing the mols of the solute (in this case the acid) by the Liters of solution (Adding water increases the volume of the solution, thus decreasing the Molarity)

Purpose

To prepare and standardize a sodium hydroxide solution. To determine the molar concentration of a strong acid.

When rinsing a buret after cleaning it with soap and water, should the rinse be dispersed through the tip or the opening on the top? In preparing the buret for titration, the final rinse is with the NaOH titrant rather than the deionized water. Why?

When rinsing a buret, the water and rinse should go through the tip. The reason you rinse with sodium hydroxide is because whenever you clean, a small amount of water remains in the buret and it must be cleansed before the experiment begins, or it may alter the values-- especially since NaOH is very hygroscopic.

Stoichiometric Point

When the above definition occurs.