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(a) A sample of cesium metal reacted completely with water, evolving 48.7 mL of dry H2 at 24°C and 774 mmHg. What is the equation for the reaction? Include states-of-matter under SATP conditions in your answer. Use the lowest possible coefficients. (b) What was the mass of cesium in the sample? I figure out part A but not part B can someone help me?

Use PV = nRT and solve for n = number of moles. Use moles H2 and the equation to solve for the mass of Cs. Here is a worked example of a stoichiometry problem such as this.

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

thanks

Sure, I can help you with part B of the question.

To determine the mass of cesium in the sample, we need to use the stoichiometry of the reaction and the volume of hydrogen gas evolved.

First, let's determine the number of moles of hydrogen gas produced using the ideal gas law equation:

PV = nRT

Where:
P = pressure of the gas (774 mmHg)
V = volume of the gas (48.7 mL or 0.0487 L)
n = number of moles of gas (to be calculated)
R = ideal gas constant (0.0821 L·atm/(mol·K))
T = temperature in Kelvin (24°C or 24 + 273.15 = 297.15 K)

Using the ideal gas law equation, we can rearrange it to solve for n:

n = PV / RT

Substituting the given values into the equation:

n = (774 mmHg * 0.0487 L) / (0.0821 L·atm/(mol·K) * 297.15 K)

Next, we need to determine the mole ratio between cesium and hydrogen. From the equation for the reaction, we know that:

2 Cs + 2 H2O -> 2 CsOH + H2

From the balanced equation, we can see that 2 moles of cesium react to produce 1 mole of hydrogen gas. Therefore, the number of moles of cesium is half of the number of moles of hydrogen gas produced.

Once we have the number of moles of hydrogen gas, we can divide it by 2 to get the number of moles of cesium. Finally, we can multiply the number of moles of cesium by its molar mass to obtain the mass of cesium in the sample.

The molar mass of cesium is approximately 132.9 g/mol.

So, the equation for part B can be summarized as follows:

Mass of cesium = (n H2 / 2) * molar mass of cesium

Now you can substitute the value of n H2 (number of moles of hydrogen gas determined in part A) into the equation and calculate the mass of cesium in grams.