Describe the trend in oxidation states of the period 3 elements in their chlorides from sodium to phosphorus.

The oxidation state of the period 3 element increases from +1 in NaCl to +5 in PCl5.

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Why do all the period 3 elements exist in positive oxidation states in their chlorides?

Because chlorine has a higher electronegativity than any of the other period 3 elements.

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What is the oxidation number of silicon in silicon tetrachloride (SiCl4)?

+4

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Describe what happens when sodium chloride is added to water.

Sodium chloride dissolves in water to give a colourless solution.

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Which chlorides of period 3 elements dissolve in water?

Sodium chloride (NaCl) and magnesium chloride (MgCl2).

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Why does Al2Cl6 form an acidic solution when added to water? Explain your answer with an equation.

When Al2Cl6 is added to water the dimers are broken down. Each hydrated Al3+ ion is relatively small and highly charged - this causes a water molecule bonded to it to lose an H+ ion which turns the solution acidic.

[Al(H2O)6]3+(aq) ➔ [Al(H2O)5(OH)]2+(aq) + H+(aq)

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Describe the trend in pH of the solutions formed when the chlorides of period 3, from Na to P,  are added to water.

pH decreases from pH 7 (NaCl) to pH 2 (PCl5).

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Decribe what happens when the chlorides of period 3, from Al to P, are added to water.

They react rapidly with water, giving off white fumes of hydrogen chloride gas and leaving an acidic solution.

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What is the equation, including state symbols, for the reaction that occurs when phosphorus(V) chloride is added to water?

PCl5(s) + 4H2O(l) ➔ H3PO4(aq) + 5HCl(g)

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What is the equation, including state symbols, for the reaction that occurs when silicon(IV) chloride is added to water?

SiCl4(l) + 2H2O(l) ➔ SiO2(s) + 4HCl(g)

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What type of reaction occurs when the chlorides of period 3 elements, from Al to S, are added to water?

Hydrolysis

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What is the oxidation number of chlorine in any period 3 chloride?

-1

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Describe what happens when magnesium chloride is added to water.

It dissolves to form a colourless solution.

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What is the equation, including state symbols, for the reaction of sodium with chlorine?

2Na(s) + Cl2(g) ➔ 2NaCl(s)

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What is the equation, including state symbols, for the reaction of magnesium with chlorine?

Mg(s) + Cl2(g) ➔ MgCl2(s)

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What is the equation, including state symbols, for the reaction of aluminium with chlorine?

2Al(s) + 3Cl2(g) ➔ Al2Cl6(s)

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What is the equation, including state symbols, for the reaction of silicon with chlorine?

Si(s) + 2Cl2(g) ➔ SiCl4(l)

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What is the equation, including state symbols, for the reaction of phosphorus with chlorine?

2P(s) + 5Cl2(g) ➔ 2PCl5(l)

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