AP Chemistry : Concentration and Units
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Example Questions
Example Question #8 :Titrations
How much solid NaOH must be dissolved to make 740mL of a 0.32M solution?
12.8g
9.47 * 102g
The sodium hydroxide will boil off with the water
9.47g
4.26g
9.47g
This problem can be solved by stoichiometry. Remember that 0.32M gives us the moles of NaOH per liter, and solve for the number of moles per 0.740L.
Example Question #9 :Titrations
Find the mass of
Molality is grams of solute per kilogram of solvent.
Water has a density of one gram per mililiter, so one liter of water equal to one kilogram. If we have a 2m solution, that means we have two moles of
This gives us
Example Question #2 :Identifying Unknown Volume
A chemist has a bottle containing a 2M aqueous solution of hydrochloric acid. He needs to create a 50mL solution of hydrochloric acid that has a concentration of 0.5M. What is the volume of 2M hydrochloric acid that he should dilute in order to achieve the desired concentration?
In order to dilute the concentrated acid, we need to find the amount of concentrated acid that will be diluted to 50mL of total solution. We can find the volume of concentrated acid necessary by setting the final volume and concentration equal to the initial concentration and unknown volume.
The initial concentration is 2M, the final concentration is 0.5M, and the final volume is 50mL
This means that 12.5mL of concentrated acid needs to be diluted to 50mL of solution. This will result in a solution with a concentration of 0.5M.
Example Question #21 :解决方案
A chemist wants to turn a 50.0mL solution of
To solve this problem, we may use the following equation relating the molarity and volume of two solutions:
Recall:
Plug in known values and solve.
However, this is not the final answer. The whole volume of the second, 0.4M solution is 85mL. Thus the chemist needs to add 25mL of water to the original solution to obtain the desired concentration.
Example Question #22 :解决方案
In order to dilute a 1mL solution that is 0.01M so that the solution is diluted to
Use the dilution formula:
Rearranging this equation gives:
Plugging in the values gives:
Example Question #31 :解决方案
What concentration would you have prepared if you diluted 30mL of a 0.350M salt solution to 50mL?
Use the dilution formula:
Rearranging this equation gives:
Plugging in the values gives:
Therefore, after diluting the solution to 50mL, the solution concentration would be lowered from 0.35M to 0.21M.
Example Question #32 :解决方案
How many moles are in a 0.010L solution with a concentration that is
By using the concentration as a conversion factor, the number of moles can calculated by multiplying the concentration by the number of liters.
Therefore, there are
Example Question #33 :解决方案
In order to prepare a needed solution for an experiment, 0.082 grams of
In order to calculate the concentration, we must use molarity formula:
We must use the molecular weight of sodium chloride to calculate the moles of solute:
Therefore, the concentration in molarity of this solution is 0.040M.
Example Question #34 :解决方案
How many moles are in 1000mL solution with a concentration that is
By simply using the concentration as a conversion factor, the number of moles can be calculated by multiplying the concentration by the number of liters. Before calculating the number of moles, the number of milliliters must be converted to liters using the fact that
Therefore, there are
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