Question

Use the data table to answer the questions below Mass of

evaporating dish.......... ..................12.07g Mass of
evaporating dish plus hydrate.....................15.12 g Mass of
evaporating dish and anhydrous crystals ......13.58g
If the hydrate used in the lab for the above data table is
MgSO4.7H20, then calculate the theoretical % water in the hydrate
15%
51%
73%
95%
100%

Answer 1

Option B is correct : 51%

Step-by-step explanation:

Data Given:

Hydrates used in lab = MgSO₄ .7H₂O

% water in hydrate = ?

Solution:

As we look for the the theoretical % water in hydrates

So

• First of all find the atomic masses of each component in a molecule

For H₂O atomic masses are given below

H = 1 g/mol

O = 16 g/mol

Then find the total mass of H₂O in hydrated salt

7H₂O = 7 (2x1 +1x16) g/mol

7H₂O = 7 (2+16) g/mol

7H₂O = 7 (18) g/mol

• 7H₂O = 126 g/mol

Now,

> find total Molar Mass of Molecule:

Molar Mass of MgSO₄ • 7H₂O = [24 + 32 + 16x4] + 7(2+16)

Molar Mass of MgSO₄ • 7H₂O = [24+ 32 + 64] + 126

Molar Mass of MgSO₄ • 7H₂O = [120] + 126

• Molar Mass of MgSO₄ • 7H₂O = 246 g/mol

Now to find the mass by percent of (water) H₂O

Formula used to find the mass by percent of a component

Percent composition of H₂O = mass of H₂O in Molecule / molar mass of MgSO₄•7H₂O x 100%

Put the values in above formula

Percent by mass of H₂O = 126 (g/mol) / 246 (g/mol) x 100%

Percent by mass of H₂O = 0.51 x 100%

Percent by mass of H₂O = 51%

So,

Option B is correct : 51%