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Example 2. How much mole is contained in 29.25 kg NaCl?

Given: Solution:

m (NaCl) = 29,25 kg The quantity of substance is determined by the

to determine: m
formula:   ;
ν (NaCl) – ? M

The molar mass of NaCl is: M (NaCl) = 23 + 35,5 = 58.5 g/molе. Then

the amount of mole of NaCl:

Answer: ν (NaCl) = 500 molе.

Example 3 Calculate the mass of one atom of magnesium in grams.

Given: Solution:

N (Mg) = 1 Molar mass of magnesium: M (Mg) = 24 g/mol.

to determine: Using formulas

m 0 (Mg) – ? m N
  ;   ;
M N A

N M
m    M  .
N
we write: A

Since N = 1, then the mass of 1 atom is determined by

the formula

Hence

-23
M (Mg) = = 4·10 g

0

–23
Answer:m 0 (Mg) ≈ 4·10 g

Example 4 . Determine the equivalent masses of sulfuric acid H 2SO 4, aluminum

hydroxide Al (OH) 3 and aluminum sulfate Al 2(SO 4) 3.

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