Question

What mass of solute must be used to prepare 500ml of 0.100M aqueous sodium borate Na2B4O7 from solid hydrated sodium borate Na2B4O7.10H2O?
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Answer 1

0.000132 g of hydrated sodium borate (Na₂B₄O₇ · 10 H₂O)

Explanation:

First we need to find the number of moles of sodium borate (Na₂B₄O₇) in the solution:

molar concentration = number of moles / volume (L)

number of moles = molar concentration × volume (L)

number of moles of Na₂B₄O₇ = 0.1 × 0.5 = 0.05 moles

We know now that we need 0.05 moles of hydrated sodium borate (Na₂B₄O₇ · 10 H₂O) to make the solution.

Now to find the mass of hydrated sodium borate we use the following formula:

number of moles = mass / molar weight

mass =  number of moles × molar weight

mass of hydrated sodium borate = 0.05 / 381 = 0.000132 g

Learn more about:

molar concentration

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