Question

Solute concentration is defined as the amount of the solute present in a given volume of solution. The concentrations of solutes in a solution are key to their ability to produce physiological actions. One measure of the amount of a substance is its mass expressed in grams. The unit of volume in the metric system is a liter (L). The concentration of a solute in a solution can then be expressed as the number of grams of a substance present in any one liter of solution (g/L). A comparison of the concentrations of two different substances on the basis of the number of grams per liter of solution does not directly indicate how many molecules of each substance are present. Thus, concentrations are expressed based upon the number of solute molecules in solution, using a measure called the molecular weight. One mole (mol) of a compound is the amount of the compound in grams equal to its molecular weight. One mole of solute dissolved in a liter of water is known as a 1 molar solution (1 mol/L).

To practice calculating molecular weight and examining the relationship between volume and solute variations, complete the following exercises.

First, calculate the molarity of a 2 L solution with five different amounts of solute (20, 40, 60, 80, and 100 g). The solute for this activity is glucose with a molecular weight of 180 daltons. Round all of your calculations to the nearest hundredth for credit.

Then plot each of these data points by clicking to select the amount of solute from the "Tools" section at right and then clicking on the exact location on the graph corresponding to your calculations. If you wish to change your data point on the graph after first placement, you can double click the data point and adjust the values.

Second, calculate the molarity for five different solution volumes (0.5, 1.0, 1.5, 2.0, and 2.5 L) each with 80 grams of solute. The solute for this activity is glucose with a molecular weight of 180 daltons. Round all of your calculations to the nearest hundredth for credit.

Then plot each of these data points by clicking to select the final total volume from the "Tools" section at right and then clicking on the exact location on the graph corresponding to your calculations. If you wish to change your data point on the graph after first placement, you can double click the data point and adjust the values.

Answer 1

Molarity is defined as number of moles of solutes in 1 litre of solution.

Molarity =no. of moles of solute / Volume of solution in L

In the 1st case given in the question, denominator( volume of solution) is same for all solution.On plotting this in a graph, we will get an inference that molarity increases with increase in mass of solute in solution.

In the second case, numerator of the equation ( mass of solute) is same for all solutions. But denominator changes.

On plotting this in a graph, we will get an inference that molarity decreases with increase in volume of solution when mass of solute is same.