chemistry F4 (urgent) 10pts

1). A student added 300.0 cm^3 of water to 700 cm^3 of 5.50 M hydrochloric acid solution. What is the molarity of the diluted acid solution?
Using the equation of mole = conc x vol/1000, u can find the number of moles of HCL in this solution:
mole = 5.5 x 700/1000
mole = 3.85
When u add more water into this solution, the number of moles in the solution would not change, only increase in volume such that the new concentration will be:
mole = conc x vol/1000
3.85 = conc x 1000/1000
conc = 3.85M.
Note that the volume used is the combined volume. This make sense as the concentration should decrease as u are adding more water into the solution.
2) What volume of water must be added to 50.0cm^3 of 2.0M nitric acid solution to make it exactly 0.40M?
Firstly, u have to find the number of mole of nitric acid in the solution using the above formula:
mole = conc x vol/1000
mole = 2 x 50/1000
mole = 0.1
as the number of mole should not be changed, by applying the above formula:
mole = conc x vol/1000
0.1 = 0.4 x vol/1000
vol = 250 cm^3
Note that u are adding water into the solution. The volume of water added sould be 250-50 = 200cm^3
3). Calculate the concentration of the resulting solution when 25.0 cm^3 of 1.00M sulphuric acid is mixed with 25.0 cm^3 of 2.00M sulphuric acid.
The concentration should be half way between 1M to 2M as equal amount of solution is added (i.e 1.5M). To prove this, we use this calculation:
the number of mole of sulphuric acid in 1M solution.
mole = conc x vol/1000
mole = 1 x 25/1000
mole = 0.025
the number of mole of sulphuric acid in 2M solution.
mole = conc x vol/1000
mole = 2 x 25/1000
mole = 0.05
When mixing this two solution together, the total number of moles of sulphuric will be 0.025+0.05 = 0.075mole. The total volume of solution will be 50cm^3. Using the same formula:
mole = conc x vol/1000
0.075 = conc x 50/1000
conc = 1.5M
hope you can understand these calculation la ^^"