Asolution of naoh has a concentration of 25.00% by mass. what mass of naoh is present in 0.250 g of this solution? use the periodic table in the toolbar if needed. 0.0625 g what mass of naoh must be added to the solution to increase the concentration to 30.00% by mass? g

1) 0.0625  g.

2) 0.0125 g.

Explanation:

1) A solution of NaOH has a concentration of 25.00% by mass. What mass of NaOH is present in 0.250 g of this solution?

mass% of NaOH = [(mass of NaOH)/(mass of solution)] x 100.

mass% of NaOH = 25.0%, mass of NaOH = ???  g, mass of solution = 0.250 g.

∴ mass of NaOH = (mass% of NaOH)(mass of solution)/100 = (25.0%)(0.250 g)/100 = 0.0625  g.

2) What mass of NaOH must be added to the solution to increase the concentration to 30.00% by mass?

We can use the relation:

mass% of NaOH = [(mass of NaOH)/(mass of solution)] x 100.

mass% of NaOH = 30.0%, mass of NaOH = ???  g, mass of solution = 0.250 g.

∴ mass of NaOH = (mass% of NaOH)(mass of solution)/100 = (30.0%)(0.250 g)/100 = 0.075  g.

∴ The mass of NaOH should be added = 0.075 - 0.0625 = 0.0125 g.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.