Explanation:
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Answer : The mass of sodium sulfate needed is 5.7085 grams.
Explanation : Given,
Concentration of sodium ion = 0.148 mol/L
Volume of solution = 2.29 L
Molar mass of sodium sulfate = 142 g/mole
First we have to determine the moles of sodium ion.


Now we have to calculate the moles of sodium sulfate.
The balanced chemical reaction will be,

As, 2 moles of sodium ion produced from 1 moles of 
So, 0.08035 moles of sodium ion produced from
moles of 
Now we have to calculate the mass of sodium sulfate.


Therefore, the mass of sodium sulfate needed is 5.7085 grams.
Formation of a precipitate
Answer:
79.9 amu
Explanation:
Given data:
Atomic mass of bromine = ?
Percent abundance of 1st isotope = 50.7%
Atomic mass of 1st isotope = 78.92 amu
Percent abundance of 2nd isotope = 49.3%
Atomic mass of 2nd isotope =80.92 amu
Solution:
Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) / 100
Average atomic mass = (50.7×78.92)+(49.3×80.92) /100
Average atomic mass = 4001.24 + 3989.36 / 100
Average atomic mass = 7990.6 / 100
Average atomic mass = 79.9 amu.