What type of reaction is calcium water calcium hydroxide hydrogen?

Subjects: Introduction to chemistry, elements - behavior of alkaline earth metals, periodic trends, chemical reactions

Description: A piece of granular calcium metal is added to water. After a few moments a vigorous reaction takes place producing hydrogen gas and calcium hydroxide.

Materials:

• Calcium metal, granular†
• Water
• 400 mL beaker (watch glass or petri dish for smaller scale or use larger 2 or 4 L beaker above prep shelf for larger scale)
• Phenolphthalein† (optional)

  †Located in the general chemical storage cabinets. Phenolphthalein is located in the flammables cabinet.

Procedure:

1. Fill the beaker with water.
2. Add several drops of indicator (optional).
3. Add a granule (pea size) of calcium metal to the water.
4. Observe the evolution of H2 gas (and the color change of the solution to indicate that the reaction produces basic calcium hydroxide.)

Discussion: The reaction of calcium and water is given below:

Ca(s) + 2H2O(l) → H2(g) + Ca(OH)2(s)

Calcium metal is an alkaline earth metal found in Group 2A and reacts with water to form calcium hydroxide and hydrogen gas. Group 2A metals don’t have as high a solubility in water as Group 1A, which is why the reaction of calcium (or magnesium) in water goes faster in warm water and also explains why calcium is found in various minerals. The reaction is not as vigorous or dangerous as the highly reactive alkali metals Na, K, or Li found in Group 1A, but gives an indication of the reactivity of these metals.

Because calcium hydroxide is basic, adding an indicator will show the solution changing from neutral to basic.

Safety: Hydrogen gas is produced during the reaction. If not collecting the gas, perform well-ventilated area.

Disposal: Add a small amount of HCl to clear up the hydroxide in solution and flush down the drain with plenty of water.

Calcium is a silvery white metal. The surface of calcium metal is covered with a thin layer of oxide that helps protect the metal from attack by air, but to a lesser extent than the corresponding layer in magnesium. Once ignited, calcium metal burns in air to give a mixture of white calcium oxide, CaO, and calcium nitride, Ca3N2. Calcium oxide is more normally made by heating calcium carbonate. Calcium, immediately below magnesium in the periodic table is more reactive with air than magnesium.

2Ca(s) + O2(g) → 2CaO(s)

3Ca(s) + N2(g) → Ca3N2(s)

Reaction of calcium with water

Calcium reacts slowly with water. This is in contrast with magnesium, immediately above calcium in the periodic table, which is virtually unreactive with cold water. The reaction forms calcium hydroxide, Ca(OH)2 and hydrogen gas (H2). The calcium metal sinks in water and after an hour or so bubbles of hydrogen are evident, stuck to the surface of the metal.

Ca(s) + 2H2O(g) → Ca(OH)2(aq) + H2(g)

Reaction of calcium with the halogens

Calcium is very reactive towards the halogens fluorine, F2, chlorine, Cl2 bromine, Br2, or iodine, I2, and burns to form the dihalides calcium(II) fluoride, CaF2 , calcium(II) chloride, CaCl2, calcium(II) bromide, CaBr2, and calcium(II) iodide, CaI2 respectively. The reactions with bromine and iodine require heat to enable the formation of the products.

Ca(s) + F2(g) → CaF2(s)

Ca(s) + Cl2(g) → CaCl2(s)

Ca(s) + Br2(g) → CaBr2(s)

Ca(s) + I2(g) → CaI2(s)

Reaction of calcium with acids

Calcium metal dissolves readily in dilute or concentrated hydrochloric acid to form solutions containing the aquated Ca(II) ion together with hydrogen gas, H2.

Chemistry Equation Stoichiometry

1 Answer

Ernest Z. · Denise Granger

Apr 1, 2016

You need#"87.69 g of CaH"_2#to form#"8.400 g of H"_2#.

Explanation:

There are four steps to answering this type of stoichiometry problem.

1. Write the balanced equation for the reaction.
2. Use the molar mass of#"H"_2#to convert grams of#"H"_2#to moles of#"H"_2#.
3. Use the molar ratio from the balanced equation to convert moles of#"H"_2#to moles of#"CaH"_2#.
4. Use the molar mass of#"CaH"_2#to convert moles of#"CaH"_2#to grams of#"CaH"_2#.

Step 1. Write the balanced equation.

#"CaH"_2 + "2H"_2"O" → "Ca(OH)"_2 + "2H"_2#

Step 2. Convert grams of#"H"_2#to moles of#"H"_2#.

The molar mass of#"H"_2#is 2.016 g/mol.

#8.400 cancel("g H"_2) × ("1 mol H"2)/(2.016 cancel("g H"2)) = "4.1667 mol H"_2#

Step 3. Use the molar ratio to calculate the moles of#"CaH"_2#.

From the balanced equation, the molar ratio is#"1 mol CaH"_2:"2 mol H"_2#.

#4.1667 cancel("mol H"_2) × ("1 mol CaH"_2)/(2 cancel("mol H"_2)) = "2.0833 mol CaH"_2#

Step 4. Convert moles of#"CaH"_2#to grams of#"CaH"_2#.

The molar mass of#"CaH"_2#is 42.09 g/mol.

#2.0833 cancel("mol CaH"_2) × ("42.09 g CaH"_2)/(1 cancel("mol CaH"_2)) = "87.69 g CaH"2#

The reaction requires#"87.69 g CaH"_2#.

This video link allows you to furthur practice similar problems.

Answer link

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