NOTE: You may never use the dilution equation in place of stoichiometry for a reaction. 1) A 10.00 mL aliquot of 0.010 M CaCO3 is titrated with 18.22 mL of EDTA solution. What is the EDTA molarity? 2) A 100.0 mL water sample required 15.00 mL of EDTA solution during trial 1. What would be an appropriate volume to use during trial 2? (Note: You must read the full lab document to know how to answer this question, as it is always assumed that you answer these in the context of the lab being performed. This means you should have already read the whole lab document and written out your lab procedure before starting these prelab questions.) 3) A 250.0 mL water sample requires 30.85 mL of the EDTA solution from question 1 to reach the calmagite endpoint. What was the molarity of the hard metal ions in the water sample? 4) If the metal ions in the water sample of question 2 are assumed to be Ca²+ from CaCO3, express the concentration in ppm CaCO3. This is the same as the concentration in units of mg CaCO3 per liter of sample.

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Chapter4: Stoichiometry Of Chemical Reactions
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I need help with questions 1-4? Can you finish all of these questions please? 

NOTE: You may never use the dilution equation in place of stoichiometry for a reaction.
1) A 10.00 mL aliquot of 0.010 M CaCO3 is titrated with 18.22 mL of EDTA solution. What is the
EDTA molarity?
2) A 100.0 mL water sample required 15.00 mL of EDTA solution during trial 1. What would be an
appropriate volume to use during trial 2?
(Note: You must read the full lab document to know how to answer this question, as it is always
assumed that you answer these in the context of the lab being performed. This means you
should have already read the whole lab document and written out your lab procedure before
starting these prelab questions.)
3) A 250.0 mL water sample requires 30.85 mL of the EDTA solution from question 1 to reach the
calmagite endpoint. What was the molarity of the hard metal ions in the water sample?
4) If the metal ions in the water sample of question 2 are assumed to be Ca²+ from CaCO3, express
the concentration in ppm CaCO3. This is the same as the concentration in units of mg CaCO3 per
liter of sample.
Transcribed Image Text:NOTE: You may never use the dilution equation in place of stoichiometry for a reaction. 1) A 10.00 mL aliquot of 0.010 M CaCO3 is titrated with 18.22 mL of EDTA solution. What is the EDTA molarity? 2) A 100.0 mL water sample required 15.00 mL of EDTA solution during trial 1. What would be an appropriate volume to use during trial 2? (Note: You must read the full lab document to know how to answer this question, as it is always assumed that you answer these in the context of the lab being performed. This means you should have already read the whole lab document and written out your lab procedure before starting these prelab questions.) 3) A 250.0 mL water sample requires 30.85 mL of the EDTA solution from question 1 to reach the calmagite endpoint. What was the molarity of the hard metal ions in the water sample? 4) If the metal ions in the water sample of question 2 are assumed to be Ca²+ from CaCO3, express the concentration in ppm CaCO3. This is the same as the concentration in units of mg CaCO3 per liter of sample.
PROCEDURE
PART A-STANDARDIZATION
Obtain a buret and a buret clamp from the equipment cart. Treat the burets with great care, especially
the fragile tips. Rinse the buret with distilled water, then secure it to a vertical stand with the clamp.
Assign one of your beakers to collect rinsings. Use distilled water to verify that the stopcock functions
properly with no leaks or air bubbles.
Use a small beaker to transfer EDTA solution from the reservoir to the buret. Take EDTA only as you
need it to avoid wasting excess. Rinse the buret with very small portions of EDTA before filling. To find
the molarity of the EDTA it will be used to titrate a known concentration of CaCO3. Use a 50 mL beaker
to obtain about 40 mL of the CaCO3 standard solution from the cart. Use a transfer pipet to deliver 10.00
mL of the standard into a clean 125 mL or 250 mL Erlenmeyer flask. Use a graduated pipet to add 5 mL
of pH 10 buffer (The instructor may have set out a beaker and pipet for the entire class to use with the
buffer). Next add 3-5 drops of the calmagite indicator. The standard solution has been laced with Mg²+
so the solution should appear red-pink.
Record the initial liquid level in the buret. All readings should be recorded to the nearest 0.01 mL. Add
EDTA to the flask until the indicator changes from red-pink to "purple", slow down because you want to
stop just barely when it turns a more blue-purple. Some may find this endpoint difficult to see at first. On
the verge of the endpoint the color is a somewhat complex mixture. Focus on the elimination of traces of
redness in it. It may help to compare the color to an untitrated (next) sample, and to save previously
titrated samples. Record the final buret volume. Repeat the process for a second and third trial. Refill
the buret between trials. Each partner should do at least one standard titration.
Try to perform operations consistently to enhance precision but do not be overly concerned if it is not
high. Several factors including the low concentrations and interference from the buffer work against
obtaining a sharp endpoint.
PART BUNKNOWN ANALYSIS
In this experiment, you are usually given the option to use your own untreated water sample or to draw
from a reservoir of lab tap water. Indicate the source of your sample (e.g., what city or water district or
"lab water") in the report section. Due to the range of possible metal ion concentrations in the samples,
choosing a good sample size may require a trial-and-error approach. Ideally, a sample would require 20-
40 mL of EDTA to titrate. Start with a 50 or 100 mL sample for the first trial. As it should ideally require
between 20-40 mL of EDTA, if it does not, then you must adjust the sample size if necessary for the
remaining trials. There will be points allotted for this during lab, so be ready to determine how much of
your water sample to use for subsequent trials. Make sure to record the sample volume you use in each
case. Before taking a sample, be sure that the source is well-mixed by shaking or swirling.
Your instructor will indicate whether to use repeated transfers with a 50 mL pipet or with your 50 mL
graduated cylinder to deliver the sample volume into your 500 mL Erlenmeyer flask. Add buffer and
indicator as with the standard. If at this stage, the sample solution does not give the red-pink color,
consult your instructor. You will either be directed to choose an alternative sample source or be
instructed in a method to add an Mg²+ spike and perform a spike-plus-blank titration to correct for it.
Assuming your sample did become wine red, titrate with EDTA as with the standard recording the buret
levels. If your group has one sample source, perform at least three titrations with it. If two partners wish
to analyze samples from two different sources, perform two titrations on each. Then each partner should
determine the average Ca²+ molarity for their source only and record it the postlab calculations section of
the report.
When finished, dispose of all solutions in the sink and rinse all glassware. Carefully return the burets
and pipets to the cart along with the buret clamps.
Transcribed Image Text:PROCEDURE PART A-STANDARDIZATION Obtain a buret and a buret clamp from the equipment cart. Treat the burets with great care, especially the fragile tips. Rinse the buret with distilled water, then secure it to a vertical stand with the clamp. Assign one of your beakers to collect rinsings. Use distilled water to verify that the stopcock functions properly with no leaks or air bubbles. Use a small beaker to transfer EDTA solution from the reservoir to the buret. Take EDTA only as you need it to avoid wasting excess. Rinse the buret with very small portions of EDTA before filling. To find the molarity of the EDTA it will be used to titrate a known concentration of CaCO3. Use a 50 mL beaker to obtain about 40 mL of the CaCO3 standard solution from the cart. Use a transfer pipet to deliver 10.00 mL of the standard into a clean 125 mL or 250 mL Erlenmeyer flask. Use a graduated pipet to add 5 mL of pH 10 buffer (The instructor may have set out a beaker and pipet for the entire class to use with the buffer). Next add 3-5 drops of the calmagite indicator. The standard solution has been laced with Mg²+ so the solution should appear red-pink. Record the initial liquid level in the buret. All readings should be recorded to the nearest 0.01 mL. Add EDTA to the flask until the indicator changes from red-pink to "purple", slow down because you want to stop just barely when it turns a more blue-purple. Some may find this endpoint difficult to see at first. On the verge of the endpoint the color is a somewhat complex mixture. Focus on the elimination of traces of redness in it. It may help to compare the color to an untitrated (next) sample, and to save previously titrated samples. Record the final buret volume. Repeat the process for a second and third trial. Refill the buret between trials. Each partner should do at least one standard titration. Try to perform operations consistently to enhance precision but do not be overly concerned if it is not high. Several factors including the low concentrations and interference from the buffer work against obtaining a sharp endpoint. PART BUNKNOWN ANALYSIS In this experiment, you are usually given the option to use your own untreated water sample or to draw from a reservoir of lab tap water. Indicate the source of your sample (e.g., what city or water district or "lab water") in the report section. Due to the range of possible metal ion concentrations in the samples, choosing a good sample size may require a trial-and-error approach. Ideally, a sample would require 20- 40 mL of EDTA to titrate. Start with a 50 or 100 mL sample for the first trial. As it should ideally require between 20-40 mL of EDTA, if it does not, then you must adjust the sample size if necessary for the remaining trials. There will be points allotted for this during lab, so be ready to determine how much of your water sample to use for subsequent trials. Make sure to record the sample volume you use in each case. Before taking a sample, be sure that the source is well-mixed by shaking or swirling. Your instructor will indicate whether to use repeated transfers with a 50 mL pipet or with your 50 mL graduated cylinder to deliver the sample volume into your 500 mL Erlenmeyer flask. Add buffer and indicator as with the standard. If at this stage, the sample solution does not give the red-pink color, consult your instructor. You will either be directed to choose an alternative sample source or be instructed in a method to add an Mg²+ spike and perform a spike-plus-blank titration to correct for it. Assuming your sample did become wine red, titrate with EDTA as with the standard recording the buret levels. If your group has one sample source, perform at least three titrations with it. If two partners wish to analyze samples from two different sources, perform two titrations on each. Then each partner should determine the average Ca²+ molarity for their source only and record it the postlab calculations section of the report. When finished, dispose of all solutions in the sink and rinse all glassware. Carefully return the burets and pipets to the cart along with the buret clamps.
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