GROUPS 1&2: REACTIONS WITH WATER

Write the equation for the reaction between potassium and water.

• 2K(s) + 2H₂O(l) -> 2KOH(aq) + H₂(g)

• K(s) + H₂O(l) -> KOH(aq) + H₂(g)

• 2K(s) + 2H₂O(aq) -> 2KOH(s) + H₂(g)

• 4K(s) + 2H₂O(aq) -> 2K₂O(aq) + 2H₂(g)

If you drop a small piece of sodium onto some water, it turns into a silvery ball which rushes around the surface, leaving a white trail in the water which dissolves to give a colourless solution. If the sodium becomes trapped on the side of the glass container there may be a flash of orange flame. Why does the sodium turn into a small ball?

• Sodium is less dense.

• Sodium dissolves.

• The heat given out by the reaction melts the low-melting point sodium.

• sodium is very reactive.

If you drop a small piece of sodium onto some water, it turns into a silvery ball which rushes around the surface, leaving a white trail in the water which dissolves to give a colourless solution. If the sodium becomes trapped on the side of the glass container there may be a flash of orange flame. Why does the ball rush around the surface of the water?

• Hydrogen gas is evolved and the sodium is pushed around the surface by that.

• The heat given out by the reaction melts the low-melting point sodium.

• Sodium is less dense than water.

• Sodium is very reactive

If you drop a small piece of sodium onto some water, it turns into a silvery ball which rushes around the surface, leaving a white trail in the water which dissolves to give a colourless solution. If the sodium becomes trapped on the side of the glass container there may be a flash of orange flame. What is the white trail in the water?

• sodium hydroxide

• hydrogen gas

• sodium

• a mix of sodium and hydrogen

If you drop a small piece of sodium onto some water, it turns into a silvery ball which rushes around the surface, leaving a white trail in the water which dissolves to give a colourless solution. If the sodium becomes trapped on the side of the glass container there may be a flash of orange flame. What causes the orange flame if the sodium becomes trapped?

• because it is contaminated by sodium ion

• The heat released by the reaction

• by the

  movement of the sodium

• The heat released no longer being spread around the water

• is enough to ignite the hydrogen.

• It burns with an orange flame rather

  than a blue one

How does the reactivity of the Group 1 metals with water change as you go down the group?

• Reactivity decreases down the group

• Reactivity increases down the group

• Reactivity increases then decreases down the group

• Reactivity decreases then increases down the group

How does the reactivity of group 2 metal with cold water vary from beryllium to barium? 3 answers

• Beryllium doesn't react with water.

• Magnesium reacts with water very very slowly.

• Reactivity increases as you go down the group.

• Barium doesn't react with water.

Write the equation for the reaction of strontium with cold water.

• Sr (s) + 2H₂O (l)-->

  Sr(OH)₂ (aq)+ H₂ (g)

• Sr (s) + 2H₂O (l)-->

  Sr(OH)₂ (s)+ H₂ (g)

• Sr (s) + H₂O (l)-->

  SrO (s)+ H₂ (g)

• Sr (s) + H₂O (l)-->

  SrO (aq)+ H₂ (g)

Write the equation for the reaction of calcium with cold water and its' observation. (two answers)

• Ca (s) + 2H₂O (l)-->

  Ca(OH)₂ (aq)+ H₂ (g)

• Ca (s) + 2H₂O (l)-->

  Ca(OH)₂ (s)+ H₂ (g)

• Ca (s) + H₂O (l)-->

  CaO (s)+ H₂ (g)

• Effervescence. The calcium would

  disappear to leave a white precipitate in a colourless solution.

• Effervescence. The calcium would

  disappear to leave a colourless solution.

Answer explanation

calcium hydroxide is only slightly soluble in water

Write the equation for the reaction of magnesium with hot water (steam).

• Mg (s) + H₂O (g) --> MgO (s) + H₂ (g)

• Mg (s) + H₂O (g) --> MgO (aq) + H₂ (g)

• Mg (s) + 2H₂O (g) --> Mg(OH)₂ (s) + H₂ (g)

• Mg (s) + 2H₂O (g) --> Mg(OH)₂ (aq) + H₂ (g)

Answer explanation

Magnesium + cold water --> magnesium hydroxide + hydrogen

Magnesium + hot water --> magnesium oxide + hydrogen