Chapter 6, Problem 1MCP

(a)

Interpretation Introduction

Interpretation:

The reason why water is a good solvent for magnesium chloride has to be explained.

Explanation of Solution

Magnesium chloride is an ionic compound containing positively charged magnesium ions and negatively charged chloride ions bonded through electro static interaction.  Water is also a polar compound due to the difference in electro negativities of oxygen and hydrogen.  So according to the rule “like dissolves like” polar magnesium chloride dissolves in polar water.

(b)

Interpretation Introduction

Interpretation:

The $\%\left(m/V\right)$ of $1L$ solution containing $5gMgC{l}_2$ has to be calculated.

Concept Introduction:

The $\%\left(m/V\right)$ can be calculated as follows,

    $\%\left(m/V\right)=\frac{massofsolute}{volumeofsolution}\times 100\%$

Answer to Problem 1MCP

The $\%\left(m/V\right)$ of $1L$ solution containing $5gMgC{l}_2$ is $0.5\%.$

Explanation of Solution

The $\%\left(m/V\right)$ of $1L\left(1000mL\right)$ solution containing $5gMgC{l}_2$ can be calculated as follows,

    $\begin{array}{c}\%\left(m/V\right)=\frac{massofsolute}{volumeofsolution}\times 100\%\\ \\ =\frac{5g}{1000mL}\times 100\%\\ \\ =0.5\%.\end{array}$

Percent mass/volume is $0.5\%.$

(c)

Interpretation Introduction

The $\%\left(m/m\right)$ of $1L$ solution containing $5gMgC{l}_2$ has to be calculated.

Concept Introduction:

The $\%\left(m/m\right)$ can be calculated as follows,

    $\%\left(m/m\right)=\frac{massofsolute}{massofsolution}\times 100\%$

Answer to Problem 1MCP

The $\%\left(m/m\right)$ of $1L$ solution containing $5gMgC{l}_2$ is $0.47\%.$

Explanation of Solution

The mass of solution can be calculated using the given volume of solution $\left(1000mL\right)$ and given density $\left(1.06g/mL\right)$ as below.

    $\begin{array}{c}mass=volume\times density\\ \\ =1000mL\times 1.06g/mL\\ \\ =1060g\end{array}$

The $\%\left(m/m\right)$ of $1060g$ solution containing $5gMgC{l}_2$ can be calculated as follows,

    $\begin{array}{c}\%\left(m/V\right)=\frac{massofsolute}{volumeofsolution}\times 100\%\\ \\ =\frac{5g}{1060mL}\times 100\%\\ \\ =0.47\%.\end{array}$

Percent mass/mass is $0.47\%.$

(d)

Interpretation Introduction

Interpretation:

Number of moles of magnesium chloride in the solution has to be calculated.

Concept introduction:

Number of moles can be calculated as follows,

    $numberofmoles=\frac{givenmass}{molarmass}$

Answer to Problem 1MCP

Number of moles of $5gMgC{l}_2$ is $0.05mole.$

Explanation of Solution

Molar mass of $MgC{l}_2$ is $95.211g/mol.$

Number of moles of $5gMgC{l}_2$ can be calculated as follows,

    $\begin{array}{c}numberofmoles=\frac{givenmass}{molarmass}\\ \\ =\frac{5g}{95.211g/mole}\\ \\ =0.05mole.\end{array}$

Number of mole is $0.05mole.$

(e)

Interpretation Introduction

Interpretation:

The molarity of $1L$ solution containing $5gMgC{l}_2$ has to be calculated.

Concept Introduction:

Molarity can be calculated using following equation.

    $Molarity=\frac{molesofsolute}{Volumeofsolution\left(L\right)}$

Answer to Problem 1MCP

The molarity of $1L$ solution containing $5gMgC{l}_2$ is $0.05M.$

Explanation of Solution

Number of moles of $5gMgC{l}_2$ can be calculated as follows,

    $\begin{array}{c}numberofmoles=\frac{givenmass}{molarmass}\\ \\ =\frac{5g}{95.211g/mole}\\ \\ =0.05mole.\end{array}$

The molarity of $1L$ solution containing $5gMgC{l}_2$ can be calculated as follows,

    $\begin{array}{c}Molarity=\frac{molesofsolute}{Volumeofsolution\left(L\right)}\\ \\ =\frac{0.05mole}{1L}\\ \\ =0.05M.\end{array}$

Molarity is $0.05M.$

(f)

Interpretation Introduction

Interpretation:

The given magnesium chloride solution is an electrolyte or not has to be predicted.

Explanation of Solution

The given magnesium chloride solution is an electrolyte, because when dissolved in water it dissociates to form positive charged magnesium ion and negatively charged chloride ions.

(g)

Interpretation Introduction

Interpretation:

The boiling point of the given magnesium chloride solution has to be compared with the boiling point of water.

Explanation of Solution

The boiling point of the given magnesium chloride solution will be greater than that of pure water, because boiling point is the temperature at which vapor pressure becomes equal to atmospheric pressure.  If a non volatile solute (magnesium chloride) is added then the vapor pressure get lowered.  So, more temperature has to be provided for vaporizing.  Hence the boiling point increases.

(h)

Interpretation Introduction

Interpretation:

The melting point of the given magnesium chloride solution has to be compared with the melting point of water.

Concept Introduction:

Explanation of Solution

The melting point of the given magnesium chloride solution is lower than that of pure water, because at freezing point solid phase of the solvent will be in equilibrium with liquid phase.  When solute molecule (magnesium chloride) is added, it will interfere with the rate at which the liquid molecules associate to form solid state, hence lower the freezing point of the solution.