A small crystal of the slightly soluble salt, CaSO4, dissolves in a solution of calcium sulfate. The original solution must have
2 answers:
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<u>Answer:</u> The molecular formula for the compound is
<u>Explanation:</u>
We are given:
Percentage of C = 92.26 %
Percentage of H = 7.74 %
Let the mass of compound be 100 g. So, percentages given are taken as mass.
Mass of C = 92.26 g
Mass of H = 7.74 g
To formulate the empirical formula, we need to follow some steps:
- <u>Step 1:</u> Converting the given masses into moles.
Moles of Carbon =
Moles of Hydrogen =
- <u>Step 2:</u> Calculating the mole ratio of the given elements.
For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 7.68 moles.
For Carbon =
For Hydrogen =
- <u>Step 3:</u> Taking the mole ratio as their subscripts.
The ratio of C : H = 1 : 1
The empirical formula for the given compound is
- <u>Calculating the molar mass of the compound:</u>
To calculate the molecular mass, we use the equation given by ideal gas equation:
PV = nRT
Or,
where,
P = pressure of the gas = 820 torr
V = Volume of gas = 250 mL = 0.250 L (Conversion factor: 1 L = 1000 mL )
m = mass of gas = 0.6883 g
M = Molar mass of gas = ?
R = Gas constant =
T = temperature of the gas =
Putting values in above equation, we get:
For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.
The equation used to calculate the valency is:
We are given:
Mass of molecular formula = 78.10 g/mol
Mass of empirical formula = 13 g/mol
Putting values in above equation, we get:
Multiplying this valency by the subscript of every element of empirical formula, we get:
Hence, the molecular formula for the compound is
The mass of HCHO2 and NaCHO2 to be added to the buffer solution are 0.23g and 0.44g respectively
Data;
- Volume of solution = 260mL
- conc. of HCHO2 = 2.5*10^-2M
- conc. of NaCHO2 = 2.5*10^-2M
To calculate the mass of reagent added, let's start with HCHO2
The mass of HCHO2 to be added is the number of moles of HCHO2 multiplied by it's molar mass.
The mass of NaCHO2 to be added in the buffer solution is
The mass of HCHO2 and NaCHO2 to be added to the buffer solution are 0.23g and 0.44g respectively
Learn more about buffer solution here;