Question 1: Why is it necessary to use water that is both distilled and at room temperature when doing dilutions?
Answer: It is necessary to use distilled water for dilutions in order to avoid any reactions or alterations caused by the minerals, or any other impurities, present in water that is not distilled. The water should be at room temperature, in combination with being distilled, so that it does not support any side reactions that may be caused by the increased or decreased temperature.
Question 2: Outline an experimental procedure (step by step) by which 25.00 mL of 1.00 M HCl can be made from a stock solution of 5.00 M HCl.
Answer: The steps for preparing a 1M HCl from 5M HCl are as follows.
The required solution is prepared by diluting the 5M solution as the concentration is higher than required.
Calculate the required amount of 5M HCl and water as follows.
Use the formula C1V1 = C2V2
1M x 25mL = 5M x V2
So, V2 = 25/5 = 5mL
Take 5 mL of 5M HCl in a beaker and add 20 mL water to get the required solution.
These are the steps that need to be taken in order to prepare 25.00 mL of 1.00 M HCl from a stock solution of 5.00 M HCl.
Question 3: Calculate the molarity of an H3PO4 solution prepared as follows: 5.00 mL of 10.0 M phosphoric acid is diluted to 250.0 mL in a volumetric flask, and from this flask 25.00 mL of this solution is diluted to 500.0 mL in another flask.
Answer: The molarity of the solution is calculated in the following steps.
First, calculate the molarity of the solution after first dilution as follows.
C1V1=C2V2
5mL×10M=C2×250mL
C2=50250=0.2M
Second, calculate the molarity of the solution after the second dilution.
C1V1=C2V2
25mL×0.2M=C2×500mL
C2=5500=0.01M
Hence, the molarity of the final solution is 0.01M.
Question 4: A 50.00 mL sample of Sulphuric acid required a total of 15.28 mL of Potassium Hydroxide solution (0.478 M) for complete neutralization. Determine the molarity of the Sulphuric acid solution.
Answer: The molarity of the Sulphuric acid solution is calculated as follows.
Write down the chemical equation for the reaction. The equation is:
H2SO4 + 2KOH --> K2SO4 + 2H2O
Find out the number of moles of Potassium Hydroxide required per mole of Sulphuric acid which is 2 moles KOH per mole H2SO4.
Find out the moles of Sulphuric acid per liter of solution by using the unitary method as follows.
?moles of H2SO41L of H2SO4=15.28mL KOH50mL H2SO4×1000mL1L×0.478mol KOH1000mL KOH×1mol H2SO42mol KOH
Molarity of H2SO4=0.073molL=0.073M
Hence the molarity of Sulphuric acid solution is 0.073 mol/dm3.
