Reactions of Elements (Water & Oxygen)

Equation and Observation: Sodium + Cold Water.

• 2Na + 2H_2O \rightarrow 2NaOH + H_2

• Obs: Vigorous reaction, fizzing, floats, melts into ball. pH 13–14.

Equation and Observation: Magnesium + Cold Water

• Mg + 2H_2O \rightarrow Mg(OH)_2 + H_2

• Obs: Very slow reaction. pH 9 (sparingly soluble hydroxide).

Equation and Observation: Magnesium + Steam.

• Mg + H_2O(g) \rightarrow MgO + H_2

• Obs: Burns with bright white flame, forms white powder (MgO).

Write the equations for the reaction of Na, Mg, Al, Si, P, S with Oxygen.

1. 4Na + O_2 \rightarrow 2Na_2O

2. 2Mg + O_2 \rightarrow 2MgO

3. 4Al + 3O_2 \rightarrow 2Al_2O_3

4. Si + O_2 \rightarrow SiO_2

5. P_4 + 5O_2 \rightarrow P_4O_{10}

6. S + O_2 \rightarrow SO_2

• *This doesn’t generally need to be remembered, but can be solved when considering the Oxidation Numbers of these elements.

What are the flame colours for Na, Mg, P, and S?

• Na: Yellow.

• Mg: Bright White.

• P: Very Bright White.

• S: Blue.