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Marina86 [1]
3 years ago
12

Hard water often contains dissolved Mg2+and Ca2+ions. Water softeners often use sodium carbonate to soften the water. Sodium car

bonate is soluble in water, but the carbonate ions form insoluble precipitates with the calcium and magnesium ions, removing them from solution. Suppose a 2.91L solution is 0.0396 M in calcium nitrate and 0.0661 M in magnesium chloride. What mass of sodium carbonate would have to be added to this solution to completely eliminate the hard water ions?
Chemistry
1 answer:
Dvinal [7]3 years ago
3 0

Answer:

32.5g of sodium carbonate

Explanation:

Reaction of sodium carbonate (Na₂CO₃) with Mg²⁺ and Ca²⁺ as follows:

Na₂CO₃(aq) + Ca²⁺(aq) → CaCO₃(s)

Na₂CO₃(aq) + Mg²⁺(aq) → MgCO₃(s)

<em>1 mole of carbonate reacts per mole of the cations.</em>

<em />

To know the mass of sodium carbonate we must know the moles of carbonate we need to add based on the moles of the cations:

<em>Moles Mg²⁺:</em>

2.91L * (0.0661 moles MgCl₂ / 1L) = 0.192 moles MgCl₂ = Moles Mg²⁺

<em>Moles Ca²⁺:</em>

2.91L * (0.0396mol Ca(NO₃)₂ / 1L) = 0.115 moles Ca(NO₃)₂ = Moles Ca²⁺

That means moles of sodium carbonate you must add are:

0.192 moles + 0.115 moles = 0.307 moles sodium carbonate.

In grams (Using molar mass Na₂CO₃ = 105.99g/mol):

0.307 moles Na₂CO₃ * (105.99g / mol) =

<h3>32.5g of sodium carbonate</h3>
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  • Question 19: the three are molecular compounds.
  • Question 20: CuSO₄.5H₂O

Explanation:

<em>Question 19.</em>

  • C₂H₄
  • HF
  • H₂O₂

All of them are the combination of two kinds of different atoms in fixed proportions.

  • C₂H₄: two carbon atoms per four hydrogen atoms
  • HF: one hydrogen atom per one fluorine atom
  • H₂O₂: two hydrogen atoms per two oxygent atoms

Thus, they all meet the definition of compund: a pure substance formed by  two or more different elements with a definite composition.

Molecular compounds are formed by covalent bonds and ionic compounds are formed by ionic bonds.

Two non-metal elements, like H-F, C - C, C - H, H-O, H - H, and O - O will share electrons forming covalent bonds to complete their valence shell. Thus, the three compounds are molecular and not ionic.

<em>Question 20. </em>Formula of copper(II) sulfate hydrate with 36.0% water.

Copper(II) sulfate is CuSO₄. Its molar mass is 159.609g/mol

Water is H₂O. Its molar mass is 18.015g/mol

Calling x the number of water molecules in the hydrate, the percentage of water is:

       \dfrac{18.015x}{18.015x+159.609}=36\%\\ \\ \\ \dfrac{18.015x}{18.015x+159.609}=0.36

From which we can solve for x:

      18.015x=6.4854x+57.45924\\ \\ 11.5296x=57.45924\\ \\ x\approx4.98\approx5

Thus, there are 5 molecules of water per each unit of CuSO₄, and the formula is:

  • CuSO₄.5H₂O
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