Calculate the weight in grams of the primary standard solid oxalic acid needed to prepare 250 ml of a 0.200 n solution to be used in this laboratory exercise.

2.25 g.

Explanation:

N = (mass / equivalent mass) of the solute x (1000 / V of the solution)

The solute is oxalic acid.

N is the normality of the solution (N = 0.2 N),

mass of the solute (oxalic acid) (??? needed to be calculated),

equivalent mass of the oxalic acid = molar mass / n (the no. of reproducible H) = (90.03 g/mol) / (2) = 45.015.

V is the volume of the solution (V = 250 ml).

∴ The mass of the oxalic acid in g = (N x equivalent mass x V) / 1000 = (0.2 N) (45.015) (250.0 ml) / 1000 = 2.25 g.

Very important note:

If the solute source is oxalic acid dihydrate:

The molar mass = 126.07 g/mol.

The equivalent mass = 63.035 g.equ./mol.

∴ The mass of the oxalic acid in g = (N x equivalent mass x V) / 1000 = (0.2 N) (63.035) (250.0 ml) / 1000 = 3.15 g.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.