Question

Calculate the molar mass of NaCl.
How many moles of O2 are in 32 grams of O2?
What is the empirical formula for a compound that contains 52.14% C, 13.13% H and 34.73% O by mass?
How many grams of NaOH are needed to neutralize 100 mL of 0.5 M HCl?
Calculate the pH of a solution with [H+] = 1 x 10^-8 M.
What is the concentration of a solution made by dissolving 10 g of NaCl in enough water to make a final volume of 250 mL?

Answer 1

Ответ:

The molar mass of NaCl is 58.44 g/mol.

To calculate the number of moles of O2 in 32 grams of O2, we need to divide the given mass by the molar mass of O2: 32 g / 32 g/mol = 1 mole of O2.

To find the empirical formula for a compound, we need to convert the percentages to mole ratios. Assuming a 100 g sample, we have 52.14 g C, 13.13 g H, and 34.73 g O. Converting these masses to moles gives us 4.343 moles C, 13.01 moles H, and 2.171 moles O. Dividing these by the smallest value (2.171) gives us the empirical formula, which is C2H6O.

To find the number of grams of NaOH needed to neutralize 100 mL of 0.5 M HCl, we can use the equation: moles of HCl = moles of NaOH. The number of moles of HCl in 100 mL of 0.5 M HCl is 0.1 moles (0.5 moles/L * 0.1 L), so we need 0.1 moles of NaOH. Using the molarity of NaOH, we can find the volume needed: 0.1 moles / 1 M = 0.1 L = 100 mL. Therefore, we need 4.0 grams of NaOH (0.1 moles * 40 g/mol).

The pH of a solution with [H+] = 1 x 10^-8 M can be calculated using the equation pH = -log[H+], so pH = -log(1 x 10^-8) = 8.

The concentration of a solution made by dissolving 10 g of NaCl in enough water to make a final volume of 250 mL is 0.4 M. This can be calculated by dividing the moles of NaCl by the volume in liters: 10 g / 58.44 g/mol = 0.171 moles NaCl, and 0.171 moles / 0.25 L = 0.4 M