The maximum amounts of lead and copper allowed in drinking water are 0.015 mg/kg for lead and 1.3 mg/kg for copper. Express these values in parts per million, and tell the maximum amount of each (in grams) allowed in 100 g of water.

Question

Accepted Answer

Welcome back everyone. Water Standards said that the maximum contaminant levels, MC L of mercury and cadmium in water are 0. mg per kilogram and 0.5 mg per kilogram respectively. What are these values in parts per million P PM and indicate the maximum level of each contaminant in milligrams in 200 g of water. Let's begin by recalling the conversion factor where one mg per kilogram has an equivalence of one part per million or one P PM. In this case, we can take the maximum contaminant level of our two metals beginning with mercury represented by its chemical symbol H G in which we would say we have 0.2 mg per kilogram, which is also equivalent to just 0.2 parts per million. Next, we can take the maximum contaminant level of our second metal being cadmium represented by its chemical symbol CD equal to the given MC L of 0. mg per kilogram, which we can interpret as equivalent to 0.5 parts per million. Now with our maximum contaminant levels in parts per million, we have our first two answers and we're going to need to get our last two answers by converting our given MC L values to now milligrams. And so beginning with our milligrams of mercury allowed in our water. We would find this by taking our given MC L of 0.2 mg per kilogram and multiply by a conversion factor to go from kilograms in the numerator two g in our denominator where we would recall that our prefix kilo tells us that we have an equivalent of 10 to the third power of our base unit gram in the denominator. So canceling out kilograms, we're left with units of milligrams And this is milligrams per gram rather. And now we want to just multiply by our volume of water being 200 g of water. And this will next allow us to cancel our unit of grams leaving us with milligrams as our final unit. And in our calculators, this is going to simplify to four times 10 to the negative fourth power milligrams of mercury allowed and 200 g of water. So this would be our third answer. And next, we want to calculate our maximum contaminant level in milligrams for cadmium in 200 g of water. So beginning with our given MCL of 0. mg per kilogram. Again, we're going to utilize sto geometry and multiply it by our conversion factor to go from kilograms in the numerator to grams in denominator where as we stated before, one kg has an equivalence of 10 to the third power grams, canceling out grams and introducing our volume of water, which we multiply by as 200 g, we would then be able to cancel out our unit of grams. And we're left with milligrams as our final unit. And in our calculators, this is going to simplify so that we have one times 10 to the negative third power milligrams as our fourth final answer for the maximum contaminant level of cadmium allowed in our 200 g of water. And all of our answer choices are going to correspond to choice B which states that the MC L of Mercury is 0.2 parts per million and four times 10 to the negative fourth power milligrams. Whereas for Cadmium, we have 0.5 parts per million and one times 10 to the negative third power milligrams as it's MC L. So I hope that this makes sense and let us know if you have any questions.

The maximum amounts of lead and copper allowed in drinking water are 0.015 mg/kg for lead and 1.3 mg/kg for copper. Express these values in parts per million, and tell the maximum amount of each (in grams) allowed in 100 g of water.

Verified video answer for a similar problem:

Key Concepts

Parts Per Million (PPM)

Conversion from mg/kg to PPM

Calculating Maximum Allowable Amounts