Alkali metals react with water to form hydrogen gas and the hydroxide of the metal. When 3.55 grams of an alkali metal reacts with excess water, 1020ml of hydrogen gas, measured at STP, are evolved. What is the alkali metal?
2X + 2H20 = 2XOH + H2
So two moles of X reacts with water to produce 1 mole of hydrogen.
Let R = relative atomic weight of the alkali metal.
1.020 l /22.4 l = 3.5 g /2R
R=(3.55/2)*22.4/1.02
=39.0
The alkali metal with a RAM closest to 39.0 is.....
To determine the alkali metal in this reaction, we need to use the given information about the amount of hydrogen gas produced. We can then calculate the molar mass of the alkali metal using stoichiometry and compare it to the known values of alkali metals.
Let's break down the steps to find the alkali metal:
Step 1: Convert the given volume of hydrogen gas to moles.
According to the ideal gas law at STP (Standard Temperature and Pressure), one mole of any ideal gas occupies 22.4 liters. Since we have 1020 mL of hydrogen gas, we can convert it to liters:
1020 mL * (1 L/1000 mL) = 1.02 liters
Thus, we have 1.02 liters of hydrogen gas.
Next, we can use the ideal gas law to find the number of moles of hydrogen gas (H2) produced:
PV = nRT
Where:
P = pressure (at STP, it is 1 atm)
V = volume in liters
n = number of moles
R = ideal gas constant (0.0821 L*atm/mol*K)
T = temperature in Kelvin (at STP, it is 273 K)
Solving for n:
n = PV/RT
n = (1 atm * 1.02 L) / (0.0821 L*atm/mol*K * 273 K)
n = 0.0434 moles
Therefore, we have 0.0434 moles of hydrogen gas.
Step 2: Determine the molar ratio between alkali metal and hydrogen gas.
From the balanced chemical equation, we know that the molar ratio between the alkali metal and hydrogen gas is 2:1 (2 moles of alkali metal react with 1 mole of hydrogen gas).
So, if we have 0.0434 moles of hydrogen gas, we can multiply it by 2 to find the number of moles of alkali metal:
0.0434 moles H2 * (2 moles alkali metal/1 mole H2) = 0.0868 moles alkali metal
Step 3: Calculate the molar mass of the alkali metal.
To find the molar mass of the alkali metal, we need to divide the mass of the alkali metal by the number of moles:
Molar mass = Mass (g) / Moles
Given that the mass of the alkali metal is 3.55 grams and the number of moles is 0.0868 moles:
Molar mass = 3.55 g / 0.0868 mol
Molar mass ≈ 40.9 g/mol
By comparing the molar mass of 40.9 g/mol with the known molar masses of alkali metals, we find that it closely matches the molar mass of potassium (K), which is approximately 39.1 g/mol.
Therefore, the alkali metal in this reaction is most likely potassium (K).