Calculate the concentration of 4 mg of hydrochloric acid dissolved in 25 cm³ of water.

To calculate the concentration of hydrochloric acid, we need to convert the volume of water from cm³ to liters and then use the formula:

Concentration (mol/L) = amount of solute (mol) / volume of solvent (L)

First, we convert the volume of water from cm³ to liters:
25 cm³ = 25/1000 = 0.025 L

Next, we need to convert the amount of hydrochloric acid from mg to g and then to mol:
4 mg = 0.004 g
Molar mass of HCl = 1 g/mol (hydrogen) + 35.5 g/mol (chlorine) = 36.5 g/mol

Now, we can calculate the amount of hydrochloric acid in mol:
0.004 g / 36.5 g/mol = 0.000109 mol

Finally, we can calculate the concentration of hydrochloric acid:
Concentration = 0.000109 mol / 0.025 L = 0.00436 mol/L

Therefore, the concentration of 4 mg of hydrochloric acid dissolved in 25 cm³ of water is 0.00436 mol/L.

Step 1: Convert the mass of HCl to moles.

mass of HCl = 4 mg = 0.004 g

molar mass of HCl = 36.46 g/mol

moles of HCl = 0.004 g / 36.46 g/mol = 0.00011 mol

Step 2: Calculate the volume of the solution in liters.

volume = 25 cm³ = 0.025 L

Step 3: Calculate the concentration of HCl in molarity.

concentration = moles of HCl / volume of solution

concentration = 0.00011 mol / 0.025 L = 0.0044 M

Therefore, the concentration of 4 mg of hydrochloric acid dissolved in 25 cm³ of water is 0.0044 M.