Grade Level/Subject
Chemistry grades 10 -12
Unit
This is a culminating activity that should be attempted after
demonstrating/teaching acid base titrations
I. Matter is classified by its chemical and physical properties
II.
Molarity = moles of solute/L of solution
III.
[] refers to molar concentration
IV. Two important classes of compounds are acids and bases
V. Indicators show color changes at certain pH levels
VI. Titrations measure [H+] and [OH-]
VII. Repeated trials during experimentation ensures verifiable data
VIII.
Techniques for experimentation involve the identification and
proper use of chemicals and the description of equipment
Enduring Understanding
SOL Standards
CH.1, CH. 4
Title
Solutions Inquiry Lab
Lesson Objective
Inquiry Level
Materials Required
I.
II.
III.
IV.
2
Students will identify unknown solutions through inquiry
Students will perform titrations in the laboratory setting using
indicators
Relate the hydronium ion concentration to the pH scale
Perform calculations for % error and unknown molar concentration
1 M NaOH and 1M HCl solutions prepared by teacher as accurately as
possible, multiple acidic solutions for students to test at varying molarities
Acid base indicators, Burettes, beakers, funnels
Acid Base Titration Inquiry Lab
Refer to your notes and the Titration of Vinegar with Sodium Hydroxide lab before
beginning this investigation.
An acid-base titration is a neutralization reaction that is performed in the lab in order to determine an unknown
concentration of acid or base. The moles of acid will equal the moles of base at the equivalence point. Here's how to
perform the calculation to find your unknown.
For example, if you are titrating hydrochloric acid with sodium hydroxide:
HCl + NaOH → NaCl + H2O
You can see from the equation there is a 1:1 molar ratio between HCl and
NaOH. If you know that titrating 50.00 ml of an HCl solution requires 25.00 ml
of 1.00 M NaOH, you can calculate the concentration of hydrochloric acid,
[HCl]. Based on the molar ratio between HCl and NaOH you know that at the
equivalence point:
moles HCl = moles NaOH
MHCl x volumeHCl = MNaOH x volumeNaOH
MHCl = MNaOH x volumeNaOH / volumeHCl
MHCl = 25.00 ml x 1.00 M / 50.00 ml
MHCl = 0.50 M HCl
For this investigation you will be given three solutions of “unknown” pH. You and
your partner(s) are to plan and preform a titration using 1M NaOH and/or 1 M
HCl(provided by teacher) to determine the pH of the three unknown solutions.
Sketch and label a titration apparatus in you lab books. Create a procedure and
record in your lab book, and preform the investigation; record calculations to
determine pH of each sample in your lab book. Finally, check on blackboard tonight
to discover the actual pH of the unknown solutions, and answer the following
questions for homework.
Remember you are working with acids and bases. Follow all safety protoco ls.
Questions:
I.
II.
How would you go about checking the accuracy of your data?
Calculate your % error and explain possible sources of error.
Error is a measure of the accuracy of the values in your
experiment. It is important to be able to calculate
experimental error, but there is more than one way to
calculate and express it. Here are the most common
ways to calculate experimental error:
Error
Relative Error
Percent Error
Error = Experimental Value - Known Value
Relative Error = Error / Known Value
% Error = Relative Error x 100%
Let's say a researcher measures the mass of a sample to be
5.51 g. The actual mass of the sample is known to be 5.80 g.
Calculate the error of the measurement.
Experimental Value = 5.51 g
Known
Value = 5.80 g
Error = Experimental Value - Known Value
Error =
5.51 g - 5.80 g = - 0.29 g
Relative Error = Error / Known Value
Relative
Error = - 0.29 g / 5.80 g = - 0.050
% Error = Relative Error x 100%
% Error = - 0.050
x 100% = - 5.0%
Although oxygen gas is colorless,
the liquid and solid forms of oxygen are blue