Professionals in a scientific laboratory and in the healthcare field need to acc

Question

Professionals in a scientific laboratory and in the healthcare field need to accurately prepare solutions for a number of reasons. If you wear contacts, you probably use a saline solution to rinse your contacts. What solutions do you use at work?

How would you calculate the amount of solute to the solvent to prepare this solution?

If you do not wear contacts but you use or make cleaning solutions for your housework, how would you accurately prepare solutions to clean? What solutions do you use that use percent concentration?

Demonstrate how to convert the number of atoms into mass or mols.

Explain how the mol ratio is derived from the chemical equation and its fundamental importance in solving for amounts in chemical reactions.

Demonstrate the use of the mol ratio in problem solving through dimensional analysis. Any ideas on where to start on this one?

Explanation / Answer

I'm answering based on my experience in a professional laboratory.

1. What solutions do you use at work?

I used all kinds of acid solutions to digest samples, the most common being HCl, H2SO4 and HNO3.

I also used some basic solutions when doing titrations, being NaOH the most common one.

I used metal solutions (stocks) with 1000ppm concentrations when performing analysis of atomic absorption spectroscopy, being the most common metals Fe, Pb, Cr, Ni and Zn.

2. How would you calculate the amount of solute to the solvent to prepare this solution?

For any given solution, if we know its concentration, we can calculate how much grams of the solute to add to the solvent to get our solution. The volume of solvent is our choice. For example if we chose 1L to be the volume of solution, we would use that as the total volume (only if the solute is not another liquid). Typical concentration units involve %w/w, %v/v, %w/v and M. When we know how much of solute to add, we need to be as precise and accurate as possible and use an analytical balance, and when measuring volumes we should use volumetric flasks or volumetric pippetes.

3. If you do not wear contacts but you use or make cleaning solutions for your housework, how would you accurately prepare solutions to clean?

Cleaning solutions are usually made by liquids, and clearly we don't have volumetric flasks or pippetes to use in the house, a way to prepare accurate solutions would be by using a measuring cup from our kitchen to measure the liquid amounts as accurately as possible.

4. What solutions do you use that use percent concentration?

In the house we can find muriatic acid for cleaning (that is around 30% HCl) or we can also use hydrogen peroxide (which is around 3% H2O2).

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