Alkali metals are so reactive that they react directly with water in the absence of acid. For Example...

2 K(s) + 2 H2O(l) �¨ 2 K+(aq) + 2 OH− (aq) + H2(g).

How many milliliters of hydrogen will be evolved over water when 4.52 g K reacts with an excess of. H2O (l)?

Just follow the steps in this example.

http://www.jiskha.com/science/chemistry/stoichiometry.html

To determine the number of milliliters of hydrogen gas evolved in the given reaction, we need to use stoichiometry and the given mass of potassium (K).

Here's how you can calculate it step by step:

Step 1: Write down the balanced chemical equation:
2 K(s) + 2 H2O(l) → 2 K+(aq) + 2 OH− (aq) + H2(g)

Step 2: Calculate the molar mass of potassium (K):
Molar mass of K = 39.10 g/mol

Step 3: Convert the given mass of potassium (4.52 g) to moles:
Number of moles of K = Mass of K / Molar mass of K
= 4.52 g / 39.10 g/mol

Step 4: Determine the mole ratio between potassium (K) and hydrogen (H2):
From the balanced equation, we see that 2 moles of K react to produce 1 mole of H2.

Step 5: Calculate the number of moles of hydrogen (H2) produced:
Number of moles of H2 = Number of moles of K × (1 mole of H2 / 2 moles of K)

Step 6: Convert moles of hydrogen to volume (in milliliters):
1 mole of any gas occupies 22.4 liters at STP (standard temperature and pressure). This is equivalent to 22.4 × 1000 = 22,400 milliliters.

Number of milliliters of H2 = Number of moles of H2 × 22,400 milliliters/mol

By following these steps, you can calculate the number of milliliters of hydrogen gas evolved when 4.52 g of potassium reacts with an excess of water (H2O).

Note: It's important to ensure that the units are consistent throughout the calculations and to use appropriate conversion factors when necessary.