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HCl solution is a strong acid and NaOH solution is a strong base
Typology: Lab Reports
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Cautions: Hydrochloric acid solution is a strong acid. Sodium hydroxide solution is a strong base. Both are harmful to skin and eyes. Affected areas should be washed thoroughly with copious amounts of water.
Purpose: The purpose of this lab is to determine the concentration of a hydrochloric acid solution using acid‐base titration.
Background: Titration is a technique that chemists use to determine the unknown concentration of a known solution (we know what chemical is dissolved, but not how much in a solution). Because we know what the chemical is, we know how it will react with other chemicals and we can use that reaction to determine the concentration of the solution by measuring the formation of product(s). In the case of an unknown concentration of acid, we can use a known concentration of hydroxide base. This type of reaction is a neutralization reaction, where salt and water are products of the reaction:
Acid + Base Salt + H 2 O
We can use a pH indicator, a chemical that changes color depending on the pH, to show us when the reaction has completely neutralized. This point, where all acid was consumed and there is no excess of base, is called the equivalence point. We can use this equivalence point to determine the initial concentration of acid using a series of calculations. The goal of the titration is to get as close as possible to the equivalence point by careful addition of the base; this will ensure the calculated acid concentration is as close to the true value as possible. You will do three titrations and average the trials.
The terms below will help you understand the terminology used throughout the experiment:
Titrant—the solution of known concentration is also called the standardized solution. In this lab, the titrant is sodium hydroxide solution. Buret—a long, cylindrical piece of glass that can be used to determine small, accurate quantities of a solution. A buret is controlled by a stopcock, a white Teflon piece that can be turned to deliver the solution. The markings on the buret are such that you must subtract the initial reading (where the titrant level is initially) from the final reading to determine the volume of base delivered. The buret measures 2 digits after the decimal point accurately. Volumetric pipette/pipette bulb—a thin glass tube with only one marking used to measure a very specific volume of liquid. You will use a pipette bulb to draw the liquid into the pipette.
Phenolphthalein—a pH indicator. In acidic and neutral solutions, the indicator is colorless, but in a basic solution, the color is a vibrant pink. The higher the pH is, the stronger the pink color is. The equivalence point will be when the color is a very faint pink color. Keep your flask with acid and indicator over a white piece of paper to ensure you can see the color change.
Materials: 50 ‐mL Buret with clamp Phenolphthalein indicator 125 mL or 250 ‐mL Erlenmeyer flasks Buret funnel 250 ‐mL beaker 25 ‐mL volumetric pipette Pipette bulb
Also of importance in titrations are the calculations you need to determine the unknown concentration of the acid. These calculations are outlined below. You may want to refer to your notes from lecture for additional examples. Determination of moles of base delivered: After each titration, you will need to determine the number of moles of sodium hydroxide used. First, you will need to know the molarity of the solution (the solution has been previously standardized , meaning it has a very accurate molarity that has been experimentally determined). Write this down when you start the titration. Next, you must^ determine^ the^ volume^ of^ the solution delivered to reach the equivalence point. Next, you will find the moles of base used in the titration: ܸ ݁ݏ ܾܽ ݁݉ݑ݈ ݁ݏ ܾܽ ݂ ݕݐ݅ݎ݈ܽܯ ൈ ሻܮሺ ݉൬
*Note that the volume of base is in L, not in mL Determine number of moles of HCl in flask: If you write the balanced reaction for the neutralization of sodium hydroxide and hydrochloric acid, you will see that the reaction proceeds in a 1:1 fashion. That is, for every hydroxide (OH‐) ion added, it can neutralize exactly one hydronium (H +) ion. This is not always the case for neutralization reactions, and is thus not always the case for acid‐base titrations. The general formula is below, where the determined moles of base from the equation above are multiplied by the stoichiometric ratio found by looking at the balanced equation: ݉ ሻ݁ݏܾܽሺ ݈ 1 ൈ
*Attach all of your calculations for full credit
Name:____________________________ Lab Partner:________________________________
Concentration of sodium hydroxide: __________________M
Balanced Chemical Equation of the titration reaction:
Trial 1 Trial 2 Trial 3 Trial 4
Initial buret volume (mL)
Final buret volume (mL)
Volume of base (mL)
Volume of base (L)
Moles of base (mol)
Acid to Base Mole Ratio
Moles of acid (mol)
Volume of acid (L)
Acid concentration (M)
Average concentration (M)
Percent Difference
*Show all of your work for full credit
Name:_____________________________________