Answer:
2.40 M
Explanation:
The molarity of a solution tells you how many moles of solute you get per liter of solution.
Notice that the problem provides you with the volume of the solution expressed in milliliters,
mL
. Right from the start, you should remember that you must convert this volume to liters by using the conversion factor
1 L
=
10
3
mL
Now, in order to get the number of moles of solute, you must use its molar mass. Now, molar masses are listed in grams per mol,
g mol
−
1
, which means that you're going to have to convert the mass of the sample from milligrams to grams
1 g
=
10
3
mg
Sodium chloride,
NaCl
, has a molar mass of
58.44 g mol
−
1
, which means that your sample will contain
unit conversion
280.0
mg
⋅
1
g
10
3
mg
⋅
molar mass
1 mole NaCl
58.44
g
=
0.004791 moles NaCl
This means that the molarity of the solution will be
c
=
n
solute
V
solution
c
=
0.004791 moles
2.00
⋅
10
−
3
L
=
2.40 M
The answer is rounded to three sig figs, the number of sig figs you have for the volume of the solution.
Answer is: mass <span>of 4,30 moles of sodium</span> is 98800 mg.
n(Na) = 4,30 mol.
m(Na) = ?
m(Na) = n(Na) · M(Na).
m(Na) = 4,30 mol · 23 g/mol.
m(Na) = 98,90 g.
m(Na) = 98,90 g · 1000 mg/1g.
m(Na) = 98900 mg.
n - amount of substance.
m - mass of substance.
M - molar mass of substance.
-20.16 KJ of heat are released by the reaction of 25.0 g of Na2O2.
Explanation:
Given:
mass of Na2O2 = 25 grams
atomic mass of Na2O2 = 78 gram/mole
number of mole = 
= 
=0. 32 moles
The balanced equation for the reaction:
2 Na2O2(s) + 2 H2O(l) → 4 NaOH(aq) + O2(g) ∆Hο = −126 kJ
It can be seen that 126 KJ of energy is released when 2 moles of Na2O2 undergoes reaction.
similarly 0.3 moles of Na2O2 on reaction would give:
= 
x = 
= -20.16 KJ
Thus, - 20.16 KJ of energy will be released.
Answer:
0.5 M
Explanation:
From the question given above, the following data were obtained:
Mass of NaOH = 80 g
Volume of solution = 4 L
Molarity =?
Next, we shall determine the number of mole in 80 g of NaOH. This can be obtained as follow:
Mass of NaOH = 80 g
Molar mass of NaOH = 23 + 16 + 1
= 40 g/mol
Mole of NaOH =?
Mole = mass / molar mass
Mole of NaOH = 80 / 40
Mole of NaOH = 2 moles
Finally, we shall determine the molarity of the solution. This can be obtained as follow:
Mole of NaOH = 2 moles
Volume of solution = 4 L
Molarity =?
Molarity = mole / Volume
Molarity = 2/4
Molarity = 0.5 M
Therefore, the molarity of the solution is 0.5 M.
