No you should not just walk out of class.
The number of callers that did not consent to the survey is 40 callers.
<h3>Number of callers that did not consent to the survey</h3>
Using this formula
Number of caller=Callers×(1-Percentage of those that solicited)÷Callers at conclusion survey
Let plug in the formula
Number of caller=400 ×(1-20%)÷8
Number of caller=400 ×80%÷8
Number of caller=320÷8
Number of caller=40 callers
Therefore the The number of callers that did not consent to the survey is 40 callers.
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The pH where you might be able to precipitate as much Cu2 as possible will be any value that is less than 5.85.
<h3>How to illustrate the information?</h3>
The solubility product of salt is defined as the product of molar concentrations of ions in a saturated solution of it.
An ion will be precipitated if the ionic product exceeds the solubility product of the cation. In the case of Cu and Zn, the solubility product is greater for Zinc than Copper.
Also Cu will be precipitated in an acidic medium while Zn is precipitated in an alkaline medium. We have for CuS, K= S2 so S = 2.4495*10-8. For ZnS, S = 0.1414. So the lower the pH higher will be the amount of CuS precipitated.
If we are starting with 0.075M CuS and ZnS solution it will have 0.075 moles each of Cu2+, Zn2+, and S2. Since the anion concentration can be equated to POH, POH for Cus and Zns are 14.096 and 5.85.
The maximum precipitation will take place is any value which is less than 5.85.
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