Answer:
What is chl? For this answer I will assume chl is something simple: NaCl. The process for answering the question for NaCl can be used for chl, once it is more clearly defined.
35.1 g of NaCl to make 200 ml of a 3.0M NaCl solution.
Step-by-step explanation:
The question asks us to prepare a 3.0M solution. M stands for Molar. Molar is a concentration that is defined as moles/liter. A 3.0 M solution has 3 moles of solute (chi) per 1 liter of solvent.
Assuming the solute is NaCl, we first find the molar mass of NaCl by adding the atomic masses of the individual atoms making up the compound. In his case we add 23 g/mole for sodium (Na) and 35.5 g/mole for the chlorine (Cl). This adds to 58.5 grams/mole for NaCl.
To make 1 liter of a 3.0M solution of NaCl, we would need 3 moles of NaCl. (3 moles)*(58.5 g/mole) = 175.5 grams of NaCl would be placed in a flask into which 1 liter of solvent (often water) would be added. But we are only asked to make 200.0 ml, or 0.2 liters. This is 1/5 the amount calculated above, so (1/5)*(175.5 g) or 35.1 grams is all that is needed to make 200.0 ml of a 3.0M solution. 200 ml of water is added to the 35.1 grams of NaCl.
Another way to approach this is to calculate the moles of NaCl required to make the 200.0ml of 3M NaCl solution.
Use the units to help understand the math:
Understand that the concentration(in M) times the volume(in L) will give us moles:
(M)*(L) = moles
(3.0 moles/liter NaCl)*(0.200 liters) = 0.6 moles NaCl
We need 0.6 moles of NaCl to make 200 ml of 3.0M solution of NaCl.
To find the mass: (0.6 moles)*(58.5 grams/mole) = 35.1 grams, the same answer as before. 200 ml of solvent is added to 35.1 g of NaCl to make 200 ml of a 3.0M NaCl solution.